Lecture 18

Question 1

superphylum bacillota

Answer 1

• low GC content (28-35%)
• industrially and medically important
• divided into 9 phyla

Question 2

3 classes of bacillota

Answer 2

• class clostridia
• class bacilli
• class negativicutes

Question 3

class clostridia

Answer 3

• strict anaerobes, fermentative or respiratory metabolism
• spore forming
• industrially relevant - production of biohydrogen, biobutanol, and other chemical
• environmentally relevant - important fermenters and syntrophs in anaerobic environments
• medically relevant - many pathogens produce diverse disease causing exotoxins
  -> c. botulinum, c tetani, c. perfringens

Question 4

genus clostridium

Answer 4

• over 100 species in distinct phylogenetic clusters
• obligate anaerobes that form spores
• fermentative metabolism
  -> ferment amino acids using stickland reaction
  -> oxidation of one amino acid using another as electron acceptor
• fermentation products, sulfide and nitrogenous compounds and VFAs produced as a result cause the odors associated with putrefaction

Question 5

stickland fermentation

Answer 5

• Performed by many Clostridium species
• A paired amino acid fermentation:
• One amino acid is oxidized
• Another amino acid is reduced (electron acceptor)

Question 6

clostridium tetani

Answer 6

• strictly anaerobic spore forming bacteria
• ferments amino acids to butyrate, lactate, H2
• found in soil, intestines, and feces of livestock
• tetanus
  -> infection of wound with spores
  -> under anoxic conditions spores germinate and release neurotoxin
• toxin
  -> tetanospasmin - neurotoxin cleaves synaptobrevin in motor neurons
  -> inhibits release of GABA and glycine
• prolonged contraction of skeletal muscle
• lock jaw
• fatal in 30-90%
• vaccination - tetanus toxoid

Question 7

clostridium botulinum

Answer 7

• found in soil and aquatic sediments
• causes botulism
  -> home canned food in most common source of infection
• spores are present on the surface of many fresh foods
• require anoxic conditions to germinate and grow
• during canning if heating is insufficient to kill spores and pH is higher than 4.6 spores will germinate in canned foods
• germinated spores grow under anerobic conditions and produce exotoxin
  -> neurotoxin cleaves synaptobrevin and inhibits acetylcholine release in motor neurons
  -> flacid paralysis, respiratory/cardiac failure can result in death
• > can be treated with antitoxins
• boil for 10 mins to kill exotoxin
• botox is botulism toxin
  -> prevent muscle contraction (cosmetic, tremors, strabismus)

Question 8

clostridium perfringens

Answer 8

• normal intestinal microflora, spores are common in soil
• causes food poisoning
  -> relatively minor infection lasts around 24h
• gas gangrene
  -> infection of skeletal muscle tissue
  -> replicates quickly in human host (g=8-10mins)
  -> alpha-toxin (exotoxin) breaks down muscle tissue
  -> collagenase breaks down tissue as well
• H2 is a fermentation product, CO2 production
  -> causes unusual swelling

Question 9

class bacilli

Answer 9

• aerobic, facultative, fermentative chemoorganoheterotrophs
• spore forming and non spore forming monoderms
• live in diverse environments
• industrially relevant - lactobacillus, leuconostoc, bacillus
• medically relevant - staphylococcus, steptococcus, listeria, bacillus

Question 10

bacillus - industrially and medically relevant

Answer 10

• antibiotic producers, bacitracin, gramicidin, polymyxin
• B. anthracis = causative agent of anthrax
• B. thuringiensis, B. sphaericus - insecticides
  -> spore protein parasporal crystal turns into a toxin when exposed to insect alkaline hindgut -> cell lysis
  -> B. cereus - fungal control [food poisoning]
• B.subtilis - type strain, important model organism
  -> gene regulation, cell division, quorum sensing, sporulation, biofilms

Question 11

order lactobacillales

Answer 11

• no endospore formation
• non motile
• ferment sugars using homolactic or heterolactic fermentation
• acid tolerant/ acidophilic
• produce lactate acid

Question 12

lactobacillus spp.

Answer 12

• homo and heterolactic fermentation
• normal human gut and vaginal microbiome
• important in the food industry
  -> fermented milk products, vegetables, meat, beer
• can also result in food spoilage due to their metabolic capabilities

Question 13

leuconostoc spp.

Answer 13

• heterolactic fermenters
• buttermilk and sour cream production
• used in wine and distilled alcohol production
• causes food spoilage often due to being osmophilic
• some produce bacteriocins that precent listeria growth

Question 14

staphylococcus spp.

Answer 14

• facultative anaerobes
• normal members of microflora in upper respiratory tract, gut, skin, vagina
• pathogenic and non pathogenic can be distinguished by the ability to produce coagulase
• S. aureus is an important pathogen causing many infections - skin infections, toxic shock syndrome, endocarditis, infections related to medial implants, food poisoning
• many are resistant to antibiotics
  ->penicillin resistance is common due to presence of beta-lactamase
• MRSA
  -VMRSA

Question 15

hemolysis (strep and staph)

Answer 15

• ability to lyse red blood cells
• hemolysin - compound that lyses red blood cells
• grown on blood agar - contains 5% sheep/horse blood
• a hemolysis = partial results in greenish zone around colony -due to hemoglobin oxidation to methemoglobin by hydrogen peroxide
• b hemolysis - complete, results in clear zone around colony - associated with steptolysin
• y hemolysis = no affect, not hemolytic, less likely to be pathogenic

Question 15

streptococcus spp.

Answer 15

• aerobic, anerobic respiration, fermentation of organic compounds
• normal inhabitants of skin, mucous membranes
• many have evolved into pathogens/opportunistic pathogens
• many different species characterized by their hemolysis patterns
• oral streptococci - normal inhabitants of upper respiratory tract (y-hemolytic)
• s. pneumoniae - bacterial pneumonia (a-hemolytic)
• GAS - strep throat, skin infections (beta hemolytic)
• GBS - can cause serious infection in newborns leading to meningitis and death
  -> may often be transmitted from skin/vaginal canal or mother (beta hemolytic)
• recent global increase in invasive GAS infections following COVID-19 pandemic

Question 16

class negativicutes

Answer 16

• have inner and outer membrane with LPS
  -> stain gram negative
• received their own class due to the morphological differences from clostridia
• metabolically similar to clostridia
• ## live in or on many animals, some are parasitic

Question 17

how did the gram positive cell wall arise

Answer 17

• members of the firmicutes have always been considered gram positive
  -> negativicutes and halanerobiales made clear that this is not the case
• two phylogenetically distant groups with OMs
• gram negative cell wall was likely the ancestral trait
• loss of OM and expansion of PG led to Gram + wall
  -> loss of OM occurred several times - convergent evolution of cell wall structure
  -> sporulation process was easier in the absence of an OM and spore formers were evolutionarily success which made this adaptation to persist