Module 6: Section 2A

Question 1

Microbial Biofuels

Answer 1

• Yeast (e.g., Saccharomyces cerevisiae) can ferment glucose to produce ethanol through glycolysis
• Ethanol can be used for fuel or alcoholic beverages
• Downside: glycolysis also produces ATP, which yeast uses to grow more biomass instead of maximizing ethanol production
• In biofuel reactors, yeast uses the energy made in glycolysis to grow more cells, which takes resources away from making ethanol

Question 2

S. cerevisiae versus Z. mobilis

Answer 2

• Zymomonas mobilis can make ethanol using the Entner–Doudoroff pathway, which makes only half as much ATP as yeast does
• Therefore less energy goes into cell growth and more goes into ethanol production
• Z. mobilis can also survive higher ethanol levels than yeast

Question 3

Drawback of Z. mobilis

Answer 3

• It cannot use a wide variety of sugar substrates
• Means that source materials must be pretreated to optimize the bacterium’s ability to produce ethanol

Question 4

Radioactive waste

Answer 4

• Radioactive waste has accumulated due to use of radioactive materials in medicine, research and nuclear power generation
• The Fukushima Daiichi nuclear disaster in 2011 creates major radioactive contamination problems

Question 5

Microbial mediated elimination of radionuclides - 1

Answer 5

• Direct enzymatic reduction
• Indirect enzymatic reduction

Question 6

Microbial mediated elimination of radionuclides - 2

Answer 6

• Biosorption and bioaccumulation
• Biomineralization
• Biostimulation

Question 7

Microbial mediated elimination of radionuclides - 3

Answer 7

• Genetically modified microorganisms
• “Omics” integrated bioremediation

Question 8

Microbial Decontamination

Answer 8

• Microbes can help clean up radioactive contamination by turning radionuclides into insoluble, more stable forms (through biosorption or biomineralization
• Both natural and engineered microbes are used for this decontamination

Question 9

Discovering Genes for Detoxification

Answer 9

Scientists sequence organisms that live in radioactive waste to find genes that help with detoxification, and then engineer those genes to be highly expressed

Question 10

Microbial biosensors

Answer 10

• TCS can activate a response regulator that up regulates expression of cloned genes whose products assist with the clearance of environmental contaminant
• A reporter molecule could be expressed that is easily detected and serves as a signal of contamination

Question 11

Using Microbes to Make Better Animal Feed

Answer 11

• India produces a large amount of wheat straw, but it is hard for livestock to digest because of high tannins and lignin in the cell walls
• This makes wheat straw a low-protein, low-energy feed source
• Scientists are testing microbes to break down straw so it becomes more nutritious for cattle to eat

Question 12

Using Microbes to Make Better Animal Feed - The experiment

Answer 12

• wheat straw was first treated with a microbial enzyme to remove tannins
• then inoculated with a Ganoderma fungus (“white rot”) that breaks down lignin in the straw’s cell walls, making it easier to digest

Question 13

Fermented Foods

Answer 13

• Microbes preserve food and create new products (ex. milk into yogurt, grapes into wine)
• health benefits have only been recognized more recently

Question 14

Transforming Foods by Fermentation

Answer 14

• Microbes (naturally present or added) start fermentation
• They use enzymes to change fresh food into something that lasts longer or has a different taste/texture
• Fermentation adds helpful compounds and can remove harmful ones to improve health