1
Q
what are biogeochemical cycles?
A
pathways by which chemical substances move through living and nonliving parts of Earth
2
Q
major reservoirs of elements:
terrestrial
A
lithosphere
3
Q
major reservoirs of elements:
aquatic
A
hydrosphere
4
Q
major reservoirs of elements:
atmospheric
A
atmosphere
5
Q
major reservoirs of elements:
living
A
biosphere
6
Q
flux =?
A
movement of elements between reservoirs
7
Q
sources vs sinks
A
sources: provide elements
(ex. atmosphere that trees breathe)
sinks: recipients of elements
(ex. trees for C)
8
Q
what are 3 human drivers that disturb natural balance
A
- land-use change
- fossil fuel burning
- industrial N2 fixation
increases biologically avail N, primary prod (C/N ratio), climate change
9
Q
biogeochemical cycle:
microbial contributions
A
- move elements b/w organic and inorganic forms
- metabolism for production and degradation of biomass
-> cycling involves change to oxidative state via redox rxn
- energy in metabolism often flows using e-
10
Q
“cycling involves change to _______ via _______”
A
cycling involves change to oxidative state via redox rxn
11
Q
what is the oxidative state?
A
charge that an atom would have if all its bonds were ionic!
12
Q
what is electronegativity? periodic table trend (directions)?
A
tendency to attract e-
- increases from bottom to top, left to right
(F is super electronegative!)
13
Q
what determines which atom gets the e-?
A
the one w higher electronegativity
14
Q
in CH4, which would get the e-?
A
C! (-4)
15
Q
Q: in CO2, which element “gets the electrons”? what is the oxidative state of C?
A
O would get the electrons
C = +4
- 2 double bonds = 4 e- shared w O
16
Q
what oxidative state does O always have (other than O2)?
A
-2!
17
Q
H will always be more/less electronegative? (not incl H2)
A
less!!!
18
Q
Q: Which 3 metabolisms do you think are most important to the C cycle?
A
- Chemoorganoheterotroph (organic → inorganic)
- Chemolithoautotroph (inorganic → organic)
- Photolithoautotroph (inorganic → organic)
19
Q
carbon cycle details (means, 3 processes)
A
- balance b/w organic and inorganic C reservoirs
- photosynthesis (inorganic -> organic), respiration (organic -> inorganic), decomposition (makes organic C avail to other org)
20
Q
C cycle: phytoplankton
A
- exist in open bodies of water, esp ocean
- take up CO2 from ocean, turns into organic C (support heterotrophic growth)
- photosynthetic aquatic microbes
- responsible for almost 50% photosynthesis overall
21
Q
carbon fixation means?
A
turning inorganic C into organic compounds
- mainly through photosynthesis
22
Q
oxygenic vs anoxygenic photosynthesis
- reaction
- C source & e- donor
- products
A
oxygenic:
light + CO2 + H2O -> sugar + O2
- makes oxygen!
- CO2 = C source
- H2O = e- donor
anoxygenic:
light + CO2 + H2S -> sugar + S
- does NOT make oxygen!
- CO2 = C source
- H2S = e- donor
e- donor = big difference!!!!!
23
Q
are oxygenic/anoxygenic and aerobic/anaerobic diff? how?
A
oxygenic/anoxygenic:
- make or don’t make O, e- donor is diff
aerobic/anaerobic:
- use/consume or don’t use O
24
Q
Q: Which of the following statements is/are true?
a) All C-fixing organisms are phototrophs.
b) Oxygenic photosynthesis is conducted by aerobic organisms exclusively.
c) Anoxygenic photosynthesis cannot occur in the presence of oxygen.
d) Carbon fixation always results in the production of organic carbon.
A
d)!!!
25
explain redox behind C fixation:
oxygenic photosynthesis
- light + CO2 + H2O -> sugar + O2
- what is oxidative state of O in H2O and O2?
- what happens to C?
oxidative state of O in H2O:
- -2
oxidative state of O in O2:
- 0
-> O gets oxidized
oxidative state of C goes down from CO2 to sugar!!!!
-> carbon fixation AKA carbon reduction!!!
26
carbon fixation aka? why?
carbon reduction
- reduction: gain of e- or a decrease in oxidation state
27
explain redox behind C fixation:
oxygenic photosynthesis
- what is oxidative state of C in CO2 vs sugars
C in CO2: +4
C in sugar: 0!!!
28
oxygenic photosynthesis:
light powers ___ of water; loss of ___
light powers oxidation of water; loss of e-
29
oxygenic photosynthesis:
e- from the light rxn drive?
"reducing power"
- stored in e- carriers like NADPH, drive reduction of inorganic C in second step of photosynthesis (light-independent rxn)
30
Biological C cycling: remineralization
carbon oxidation
- organic C -> CO2
- opposite net rxn of photosynthesis
mainly through respiration!
- sugar + O2 -> CO2 + H2O
(oxygen is optional, not just aerobic; sulphate, iron)
31
A cyanobacterium undergoes photosynthesis: H2O is oxidized to O2 and e- transferred to NADP+ during the light-dep rxn, and CO2 is reduced to glucose during the light-indep rxn.
- energy, electron, and carbon sources?
- Energy: light
- e-: H2O (whatever is being oxidized is e- donor)
- C: CO2
32
A cyanobacterium undergoes photosynthesis: H2O is oxidized to O2 and e- transferred to NADP+ during the light-dep rxn, and CO2 is reduced to glucose during the light-indep rxn.
- terminal e- acceptor?
- metabolic category?
terminal e- acceptor: NADP+
Photolithoautotroph
33
A heterotrophic bacterium uses glucose produced by the cyanobacterium, where it is ultimately broken down to CO2. During this process, electrons are transferred to electron carriers, which pass the electrons through an electron transport chain, at the end of which oxygen is reduced to water.
- Is the conversion of glucose to carbon dioxide an oxidation or reduction reaction?
- oxidation!!!
glucose (net 0) to carbon dioxide (C: +4)
34
A heterotrophic bacterium uses glucose produced by the cyanobacterium, where it is ultimately broken down to CO2. During this process, electrons are transferred to electron carriers, which pass the electrons through an electron transport chain, at the end of which oxygen is reduced to water.
- energy, e-, C sources?
- energy: glucose
- e-: glucose
- C: glucose
(common for heterotrophs that C sources also serve as energy and e- sources)
35
A heterotrophic bacterium uses glucose produced by the cyanobacterium, where it is ultimately broken down to CO2. During this process, electrons are transferred to electron carriers, which pass the electrons through an electron transport chain, at the end of which oxygen is reduced to water.
- terminal e- acceptor?
- metabolic category?
- oxygen (reduced to water)
- chemoorganoheterotroph
36
T/F methanogenesis and methanotrophy are like opposite rxns
T!
37
methanogenesis =?;
anoxic/oxic env?
production of CH4 (methane) as a byproduct of biodegradation of organic/inorganic C in an anoxic env
38
T/F all methanogens are archaea
True!
39
what are the 2 types of methanogens?
- Acetotrophic AKA acetoclastic methanogens
- hydrogenotrophic methanogens
40
hydrogenotrophic general meaning
any organism that uses H as an e- and energy source
41
Acetotrophic AKA acetoclastic methanogens
make CH4, CO2 from acetate
42
hydrogenotrophic methanogens
make CH4, CO2 from CO2, H2
43
acetate is a product of glucose (primary) ____?
how is it used by acetotrophic/acetoclastic methanogens?
glucose fermentation
C source!
44
CO2, H2 are products of _____ _____? how are they used by hydrogenotrophic methanogens?
secondary fermentation
H2 = e- and energy sources
CO2 = C source (autotrophs)
45
what is the common terminal e- acceptor for both acetotrophic and hydrogenotrophic methanogens?
CO2!
CO2 gets reduced and becomes CH4
- hence methanogenesis
46
explain methane bubbles
anoxic bottom: where methanogenesis occurs
- methanogens are anaerobes
(use CO2 as terminal e- acceptor, not O2)
47
syntrophic partners in methanogenesis
"interspecies hydrogen transfer"
- one species creates H, another uses it up
48
how do ethanol-fermenting syntroph and H2-utilizing methanogen work together?
- fermentation makes H2, can't continue indefinitely (becomes unfavourable)
- [H] is reduced to low level by hydrogenic methanogens!
49
cows cannot digest all the C in grass. what does this lead to?
microorganisms in rumen (fermentation -> CO2 and H2)
- H2 used by methanogens -> CH4
- greenhouse gas
50
Q: What type of symbiotic relationship do cows and methanogens have?
a) Mutualistic
b) Commensal
c) Parasitic
a)
51
methanogenesis means?
aerobic/anaerobic?
making methane
anaerobic process
52
methanotrophy means? details
uses methane as C source
- aerobic OR anaerobic
- most methanotrophs need some O2
- need to be close to CH4 source
53
T/F methanogens and methanotrophs are often found together. why or why not? where are they?
True
- methanogens near anoxic side, methanotrophs near oxic side
54
__% of atmosphere is N2?
can a lot of organisms use N2?
79% of atmosphere is N2
- most organisms cannot use it in this form
55
nitrogen fixation:
(__ ->__), enz
overall: N2 -> NH4+ (nitrogenase)
N2 + 8H+ + 8e- -> 2NH3 + H2
56
T/F nitrogen fixation is NOT done by any eukaryotes
true! only some bacteria and archaea
57
nitrogenase is irreversibly destroyed by?
O2!
organisms using it are often aerobes so they need an anoxic zone for the enzyme in cell
58
nitrogen fixation happens where?
terrestrial, aquatic; free-living, symbionts
- esp in root nodules!
59
root nodule: N-fixers explain
- turns N2 to ammonia
- plants give bacteria food
60
Q: What type of symbiotic relationship to plants and root nodule-inhabiting N fixers have?
a) mutualistic
b) commensal
c) parasitic
a) plants give them a protective habitat/food, bacteria give them source of N
61
commamox
group of bacteria that do complete ammonia oxidation (ammonia -> nitrate);
NH3 -> NO3-
62
anammox
converts both nitrite and ammonia into nitrogen
(anaerobic ammonia oxidation)
63
anammox:
e- donor, e- acceptor
e- donor: ammonia (oxidized)
e- acceptor: nitrite (reduced)
64
DNRA stands for? and?
dissimilatory nitrite reduction to ammonia
- reduces nitrite to ammonia
65
During nitrification by comammox bacteria, which are aerobic, ammonium is converted to nitrate. Comammox can be grown in a medium including carbon dioxide or bicarbonate (HCO3-) as the only carbon source. In this process, what is....
- ammonium
- nitrate
- CO2/bicarbonate
- ammonium = e- donor and energy source
(usu for chemotrophs, e- and energy sources are same)
- nitrate = waste/byproduct
- CO2/bicarbonate = C source
66
During nitrification by comammox bacteria, which are aerobic, ammonium is converted to nitrate. Comammox can be grown in a medium including carbon dioxide or bicarbonate (HCO3-) as the only carbon source. In this process, what is....
- terminal e- acceptor?
- metabolic category?
- terminal e- acceptor = O
- chemolithoautotrophs
67
non-biological contributions to N cycle
- lightning
- fertilizer
- synthetic N fixation
68
Haber-Bosch process
fixes nitrogen synthetically
69
Q: Which effect(s) would the introduction of synthetically-produced fixed N fertilizers to the N-cycle have?
a) Increase in agricultural yield.
b) Increase in the number of pigs a farm can sustain.
c) Increase in size/occurrence of marine dead zones.
d) Decrease in the abundance of weeds.
a)
c)
70
sulfur cycle: big sink?
rock! (deposition)
71
sulphur disproportionation?
sulphur being both e- donor and acceptor
- oxidized and reduced simultaneously
-> to (SO4)2- and H2S
(sulphate and sulfide)
72
When sulphur-containing compound is the terminal e- acceptor (reduced):
aerobic or anaerobic?
anaerobic!
73
When sulphur-containing compound is e- donor (oxidized):
anaerobic or aerobic?
what would be the terminal e- acceptor?
aerobic
O would be terminal e- acceptor
74
sulfate-reducing bacteria (SRB) convert sulfate to sulfide. some SRB can be grown in a medium with no organic carbon, but instead a supply of CO2 and H2
- What are the coupled redox reactions? Which is an oxidation and which a reduction reaction?
- Sulfate =?
- Sulfide =?
- H =?
- CO2 =?
- Sulfate is being reduced to make sulfide
- Sulfate = e- donor and energy source
- Sulfide = e- acceptor
- H = energy source
- CO2 = C source
75
sulfate-reducing bacteria (SRB) convert sulfate to sulfide. some SRB can be grown in a medium with no organic carbon, but instead a supply of CO2 and H2
- predict aerobic/anaerobic?
- metabolic category
anaerobic
chemolithoautotrophs
76
what can be a water pollutant?
- feces and urine
- microbes
-> viruses, bacteria, euk parasites
- other biological material (e.g., food)
- chemicals
-> industrial, agricultural runoff; chemicals excreted in urine
77
examples of harmful microbes in water: bacteria (4)
from feces:
- E. coli O157:H7
- cholera (Vibrio cholerae)
- typhoid fever (Salmonella enterica Typhi)
cyanobacterial blooms
- smtimes called algae, but usu only euk are considered algae
78
examples of harmful microbes in water: viruses (2)
from feces
- norovirus (cruise ships)
- polio
(also heptatis A, rotavirus, adenovirus...)
79
example of harmful microbes in water: eukaryotes
from feces
- Giardia
- Cyclospora
- Cryptosporidium
algal blooms (bacterial/euk)
80
wastewater treatment goals
- remove or kill/inactivate harmful microbes
- lower total organic carbon (TOC)
- lower inorganic nutrients
81
TOC =? represents?
total organic carbon
- amt of organic compounds
82
ex of inorganic nutrients that we want to lower in wastewater treatment?
- NH4+, NO2-, phosphates
83
why do C, N, P matter? (runoff)
N + P = phytoplankton grow faster (eutrophication)
(can make toxins that harm humans + wildlife)
dead phytoplankton (after algal boom)
- organic C feed heterotrophs, which use up O2
turbidity stops photosynthesis from seaweeds
- no O2 made
84
Q: Which of the following is true?
a) Water released from a wastewater treatment plant should contain sufficient C, N, and P to support microbial life in the natural waters it is released into.
b) As long as solid waste (e.g., feces) has been removed from wastewater, the remaining water is clean enough to be released.
c) Human waste-derived microorganisms pose a threat to human health.
d) Cyanobacterial blooms have positive effects in natural water systems.
c)
85
general wastewater treatment steps (4)
- pre-treatment
- primary treatment
- secondary treatment
- tertiary treatment
86
which wastewater treatment step is only included sometimes?
tertiary treatment!
87
purpose of pre-treatment
remove large objects (branches, stones)
88
purpose/process of primary treatment
- particles removed by *sedimentation and raking*
- oils and floating material skimmed
- several hours
89
purpose/process of secondary treatment, 2 types
microbes degrade organics!!!
- decrease BOD
lowers # of intestinal pathogens
- competition, predation, settling w/ floc
trickling filter or conventional activated sludge process (CAS)
90
what is BOD
biological oxygen demand
91
purpose of tertiary treatment
- pathogen treatment, nutrient removal (C, P, N), or additional treatments
- only incl sometimes!
92
which wastewater steps remove large debris?
pre-treatment and primary treatment!
93
secondary treatment: trickle filter
steps + design
1. water sprayed over surface of trickling filter
2. water moves down, feeding biofilm microbes that live in the filter
- O2 may be pumped into big filter beds (feed heterotrophs)
design: tank with solid substrate that microorganisms can grow on; "fixed" film bc substrate is fixed
94
secondary treatment: activated sludge reactor
design
- relies on flocs
- incl aeration tnak (5-10hr, variable) and settling tank (flocs settle to bottom)
95
what are flocs
- clumps of free-flowing material and biofilm microbes
96
why is some sludge in final sedimentation returned back to sludge tank?
activated sludge acts like an inoculant
97
Q: Main goals of secondary wastewater treatment include....
a) Removing large debris - focus of pretreatment and primary treatment, although secondary involves some sedimentation
b) Reducing the amount of organic carbon
c) Reducing the amount of nitrogen
d) Photosynthesis to produce oxygen
e) Sterilizing the water
b)
c)
98
anaerobic sludge digester
- anaerobic microbes remove waste from sludge
-- waste incl excess microbes from activated sludge reactor
- takes 2-4 weeks, makes less biomass
- produces methane
- leftover sludge is dehydrated then disposed
99
disinfection step
- chlorination, UV, ozonation
100
3 examples of problems in wastewater treatment (2 conditions, 1 bacteria)
- change in condition can promote growth of filamentous bacteria
- less dense flocs that don't settle
- Sphaerotilus natans (non-beneficial bacteria that clogs)
101
how to assess reduction in organic C in wastewater treatment? what is that?
reduction in biological oxygen demand (BOD)
- amt of O2 needed by microbes to decompose what is left in water
- indirect measurement of organic C in sys
- we should not release water w high BOD! (result: remove O2 from lake/river)
102
how to measure BOD? (general + 1 method)
- incubate water sample at 20C for 5 days
- measure diff in O2 pressure -> BOD
- in darkness
1 method:
- CO2 absorbed by NaOH pellets
- measure pressure change
- convert to O2 consumption
103
how to remove nitrogen from wastewater sys?
sys design?
- encourage nitrification and denitrification
- multiple reactors instead of 1
(aerobic for nitrification then anerobic for denitrification)
- needs input of organics ($$$)
104
why is nitrification necessary in wastewater treatment?
- ammonia and nitrite are toxic to aquatic life!
nitrification reduces them
105
what is an alternative method for treating nitrogen in wastewater?
anammox bacteria
- converts ammonium and nitrite to N2 directly!
106
anammox: convert ammonium and nitrite to N2 directly
ammonium =?
nitrite =?
metabolic category?
- ammonium = energy source, e- donor
- nitrite = e- acceptor for respiration
- chemolithoautotrophs (doesn't need organic C input, so it saves us $$$)
107
Q: Encouraging nitrification in wastewater treatment is important because…
a) Nitrate is toxic to aquatic life
b) Ammonia is toxic to aquatic life
c) Ammonia can lead to eutrophication
d) Nitrification helps reduce BOD
b)
c)
a) false - only nitrite and ammonia
d) chemolithoautotrophs so do not require organic C; doesn't change BOD
108
following disinfection, is the treated water safe to discharge and drink?
can be discharged, should not drink
109
diff gaols of treating wastewater and source water (drinking)
wastewater:
- domestic wastewater from toilets and sinks
- industrial wastewater
- storm water
source water:
- safe to use and consume water
110
Q: If wastewater treatment is adequate, drinking water treatment is not necessary.
a) True
b) False
b) False
111
water reservoirs =?
storage space to hold water; natural or artificial
112
natural water sources?
- mountain snowmelt
- streams, rivers, ponds, lakes
113
drinking water:
particle removal steps (3)
- coagulation
- flocculation
- sedimentation
114
drinking water: coagulation
chemical coagulant addition to aggregate aprticles
- +ve charged polymer binds to particles in H2O
- makes particles denser
115
drinking water: flocculation
mixing & aggregation of particles to form flocs
- increased contact
116
drinking water: sedimentation
- settling of flocs to bottom of tank
- top of water goes into filtration tank
117
drinking water:
pathogen removal steps (2)
- filtration
- disinfection
118
drinking water:
filtration
- size exclusion!
- remove any remaining particles by passing through filter beds
119
drinking water: disinfection
- chemical, UV, or ozone addition to kill/inactivate microorganisms
- ex. introduction of chlorin to disinfect water greatly contributed to reduction in waterborne disease
120
what is the most common chemical water disinfectant?
chlorine!
121
why might a disinfectant be ineffective?
how do we try to avoid this?
if particle removal is insufficient
- if there is too much organic material, chlorine will not affect microbes bc chlorine demand is taken up by particles
- disinfection is after particle removal!
122
ozone is also v effective like chlorone. why do we not use it?
pricey
123
chlorination - modes of action (4)
- change cell membrane permeability
- destroy enz activities
- destroy DNA structure
- disrupt balance of lipid peroxidation
124
Q: What is the purpose of adding disinfectants to water?
a) Increase the density of microorganisms
b) Physically remove microorganisms through filtration
c) Promote biofilm formation
d) Inactivate/kill microorganisms
e) Enhance nutrient availability for beneficial microbes
d)
125
what harmful waterborne bacteria causes legionnaires' disease?
Legionella pneumophila
126
Walkerton Water Catastrophe
- May 2000 - contaminated drinking H2O in Walkerton, ONtario
- 2300 sick, 7 dead
- E. coli O157:H7 & Campylobacter jejuni
- cattle farm contamination
- not enough Cl, staff negligence
127
what legislature did Walkerton Water Catastrophe result in?
Safe Drinking Water Act
- to provide for protection of human health and prevention of drinking H2O hazards through control and regulation of drinking H2O sys and testing
Clean Water Act
- to protect existing and future sources of drinking H2O
128
Q: If a drinking water treatment plant has high quality source water, do they still need to add disinfectants?
a) Yes
b) No
a) Yes
129
what harmful toxins do cyanobacteria make (2)
anatoxin (quick death)
- neurotoxin, acts in place of acetylcholine
- not regulated in Canada
microcystin
- hepatoxin (liver toxin)
- regulated in Canada
130
Q: How do cyanobacteria pose a threat to drinking water quality?
a) They cause food poisoning-like symptoms when ingested.
b) They can produce neurotoxins that can persist in source waters.
c) They can produce hepatotoxins that can persist in source waters.
d) They lead to green or blue colored drinking water, even after treatment.
e) They can cause infections within the human body.
b)
c)
131
2016 Horse River Wildfire
- higher water treatment costs in Fort McMurray
- increased cyanobacterial blooms in reservoir
(runoff of nutrients, less foliage)
132
Q: How do wildfires increase the frequency of cyanobacterial blooms?
a) The added heat promotes growth of cyanobacteria.
b) Wildfires lead to increased input of organic matter and nutrients into
watersheds.
c) The decreased tree cover allows more access to sunlight.
d) Wildfires kill all organisms other than cyanobacteria resulting in reduced
competition.
b)
c)
133
what toxin in source water cannot be removed with chlorine?
anatoxin cannot be removed; microcystin can be
- Fort McMurray cannot remove anatoxin (ozone)
134
why do we use indicator organisms for water analysis?
- can't test for all pathogens
- we use indicator organisms found in feces
-> indicate POSSIBLE presence of pathogens
135
coliforms: characteristics, metabolism, habitat, indicates?
- Enterobacteriaceae
- Gram -ve, rods
- ferment lactose & makes acid & gas, when incubated at 35-37C
- found in env but *always* in animal digestive tracts
- indicates fecal contamination
136
detection of coliforms: MPN
most probable number
- 5 replicate tubes w 10mL / 1mL / 0.1mL sample
- note down how many positive reactions (gas formation)
refer to table
137
You set up an assay to measure the number of coliforms in a water sample, using five replicates each with 10, 1, and 0.1 mL of water sample.
You observe the following:
- 5 of the 10 mL tubes, 4 of the 1 mL tubes, and 2 of the 0.1 mL tubes are turbid
- 5 of the 10 mL tubes, 4 of the 1 mL tubes, and 1 of the 0.1 mL tubes have a colour change indicative of acid production.
- Of these, 4 of the 10 mL tubes, 2 of the 1 mL tubes, and 0 of the 0.1 mL tubes have gas in the Durham tube
Which of these are the most representative for coliforms in your water sample?
The gas production!!!
138
what's another variation of MPN?
Quanti-Tray
- add sample, incubate, count +ve wells
- refer to MPN table!
139
detection of coliforms: confirmatory test
- why?
- how is it performed?
- other organisms can make acid and gas!
ex. eosin methylene blue (EMB) media; selective + differential
- streak from +ve MPN tubes, incubate @37C, observe at 24h
selective:
- inhibits Gram+
differential:
- lactose fermenters (pink/purple)
- E coli (metallic green)
140
explain how microbes in food can:
1) contaminate
2) spoil
3) modify
1) can contaminate food & water, causing disease
2) can spoil food
- unwanted changes, not always unsafe
3) can modify food to make new varieties
- ex. cheese, vinegar
141
define foodborne intoxication vs foodborne infection!
foodborne intoxication:
- ingestion of microbial exotoxins (e.g., Staphylococcus aureus exotoxins)
foodborne infection:
- ingestion of a harmful organism itself, which multiply typically in the intestines (where they might make toxins)
142
cell growth phases (5)
- lag phase
- exponential / log
- stationary
- deceleration/death
- long-term stationary
143
cell phase: lag
- no overall population growth
- cells adapting to a new env
144
cell phase: exponential / log
- population doubling
- nutrients in excess
145
cell phase: stationary
- rate of cell division = rate of cell death
- nutrients are limited
146
cell phase: deceleration/death
- lack of nutrients or buildup of toxic metabolites
147
cell phase: long-term stationary
- env continues to support a small population
148
Q: Which phase of the microbial growth curve should you aim to extend through appropriate food preservation methods?
a) Lag phase
b) Exponential phase
c) Stationary phase
d) Death phase
e) Long-term stationary phase
a)
149
broad food preservation strategies
- take away what is needed for growth
(water, nutrients, pH, temp, O2, etc)
- remove the microbes
(killing w heat, irradiation, chemicals)
- store under conditions that minimize microbial growth
150
distinguish b/w:
- perishable food
- semi perishable food
- non-perishable food
perishable:
- easily support microbe growth
- ex. salad greens, fresh meat
semi-perishable
- don't spoil as quickly
- nuts, potatoes
non-perishables
- edible for long periods
- flour, sugar, dried beans
151
likelihood and rate of food spoilage are rated to ___ properties of the food and ___ factors related to storage conditions
- intrinsic
- extrinsic
152
some intrinsic/extrinsic factors affecting food spoilage
intrinsic
- water avail
- osmolarity
- nutrient content
- pH
- antimicrobial constituents
- structures (rinds, shells)
extrinsic
- temp
- humidity
- presence & conc of gases
153
Q: An apple and a bag of sugar both contain energy sources microorganisms can use, but have very different spoilage rates. If you leave an apple on the counter, you could expect spoilage within weeks, whereas a bag of sugar might remain unchanged for years. Why?
water content
154
what is water activity (a_w)?
range? (gen, most spoilage bacteria, SA, mold)
amount of water AVAILABLE for microbes to use, NOT total water!
- excludes water bound by molecules
- reduced w drying, adding salt/sugar (solutes)
0-1 range (fresh foods near 1)
- most spoilage bacteria >0.91
- Staph aureus >= 0.86
- molds >= 0.80
155
reduction of water activity can be achieved by ___ food by adding ___ (ex.)
drying food by adding solutes (sugar/salt)
- sun-dried tomateos
- smoked salmon
- ham
- jelly/jam
- freeze dried
156
Q: Non-perishable foods are often non-perishable because they…
a) Have been sterilized
b) Are naturally sterile
c) Have very limited organic content
d) Have limited water availability
d)
157
natural antimicrobial preservatives (added or made in food) (3)
- mode of action?
- vinegar (lower pH)
- lactic acid (lower pH)
- bacteriocins (nisin) - antimicrobial peptide -> disrupts cell wall synthesis
158
artificial food preservatives (4)
- how?
- sodium benzoate (benzoic acid) -> pH
- propionate (propionic acid) -> pH
- sulfites (disulfide bonds) -> restrict growth
- nitrites (binds to iron-sulfur complexes) -> restrict growth
159
food preservation: temperature
- heating/cooling
- pasteurization
- extends which cell phase?
- heating to KILL microbes
- cooling to PREVENT growth
pasteurization
- reduces microbe # by killing SOME species
- flash heat 72C (15 min) or 63C (60 min) + cooling
extends lag phase before exponential growth
160
why does pasteurization work against human pathogens?
they like living at our body temp
161
food preservation: irradiation
effect
- kills microorganisms
- doesn't make food itself radioactive (Cs/Co in proximity, not touching food)
- no noticeable effects on food
- causes dmg to microbe DNA
162
types of irradiation
non-ionizing radiation (UV)
- surface lvl only, not strong
ionizing radiation (gamma/Xrays)
- stronger, more penetrating
163
why is irradiation less popular?
pricey, consumer misconception abt radiation
164
food preservation: modified atmosphere packaging
- vacuum packing removes O2 -> prevent aerobic spoilage
- flood packing with CO2 or N2 -> prevent aerobic spoilage
- red meat in high O env -> reduce anaerobes and maintain red colour
(makes sense given body tissue is usu less exposed to O)
165
food preservation: canning
- effect
- heat, pressure, acidity
- sterilizes food!
- heat + pressure = kills ALL microbes and eliminates endospores
- heat + acidity = kills SOME microbes and prevents further growth
166
when canning, what should you do if the food is higher in pJ
need both heat and pressure!
167
botulism
- toxin, organism
Botulinum toxin (botox)
- protein
- most toxin known substance
- easily inactivated by heat*
doesn't necessarily kill the organism!!!! just the toxin!!!*
- Clostridium botulinum
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Clostridium botulinum
- characteristics
- how do they grow w canning?
- anaerobic (ferments)
- spore-forming (resistant to pasteurization & boiling)
- grows in pH>4.6!
- canning removes oxygen -> anoxic env
- canning w/o pressure doesn't kill C botulinum
- if food has higher pH (low in acidity), can grow!
169
Q: The principle behind canning as an effective means of food preservation is...
a) It reduces available water content (aw).
b) Exposure to high temperatures under pressure for an extended period reduces the number of potential spoilage organisms.
c) Limiting exposure to the atmosphere by storage in a sealed container reduces the potential of contamination by spoilage organisms.
d) The chemical additives used during the canning process will significantly lower the pH and inhibit the growth of potential spoilage organisms
b)
170
hurdle technology
- using multiple types of antimicrobial control
- better overall protection than a single method alone
ex. temp, a_w, pH working together;
can be lower intensity to better preserve food taste/texture
171
what is an added benefit to desirable food spoilage like in cheese and yogurt?
also helps to preserve food!
172
fermentation/pickling
- low pH prevents growth/kills many microbes
pickling - allow fermentation to naturally drop pH over time
"quick pickling" - adding food to vinegar
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general info: food fermentation
- diff microorganisms are used in fermentation of diff foods
- a "starter culture" is often added to start
174
Q: An advantage of using starter cultures instead of relying on the microbes found naturally in the raw material is…
a) The starter cultures yield much more consistent products.
b) The naturally occurring microbes may not be present in sufficient numbers to be commercially viable.
c) The starter cultures can be maintained more cost effectively.
d) All of these choices.
d)!
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milk fermentation
- to make?
- what starter?
- gen steps
- lactic acid bacteria used to make cheese & yogurt
- start w pasteurized milk, inoculate w start culture, allow fermentation
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fermentation with mould
- gen steps
- esp common in Asian countries
- similar for miso, tempeh, sake
soysauce:
- moulds break down polymers better than bacteria (aerobic first) -> make simple sugars
- sugars are fermented by lactic acid bacteria & yeast (anaerobic)
- pasteurized!
177
do 2 step fermentations tend to involve mould?
not necessarily! like vinegar!
178
vinegar (acetic acid)
- gen steps
1) yeast: sugar -> ethanol
- facultative anaerobes
2) acetic acid bacteria: ethanol -> acetic acid
- obligate aerobes
179
soysauce and vinegar:
aerobic vs anaerobic order
soysauce: aerobic then anaerobic
vinegar: anaerobic then aerobic
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vinegar production
- how is it made?
- how to make diff vinegars?
- setup
- made by fermentation of ethanol by acetic acid bacteria
- source of ethanol can result in diff flavours and diff vinegars
- setup is like wastewater treatment
(biofilm, take out waste, vinegar drains out)
181
industrial microbiology:
products! (whole cells/from cells or enz)
whole cells:
- yeast
- probiotics
products from cells or enz
- alcohol from fermentation
- antibiotics
- enzymes
182
diff b/w primary and secondary metabolites?
- best harvest time?
primary metabolite
- directly involved in normal growth
- most in exponential phase
ex. enzymes, AAs, vit
secondary metabolite
- not essential for growth
- most in stationary phase
ex. antibiotics, pigments, toxins
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BIOL 241
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