Microbes and Biofuels Flashcards
What are biofuels?
Renewable liquid or gaseous fuels made by and/or from living organisms or the waste they produce
-Microbes play a crucial role in production of sustainable biofuels
Purpose of sustainable and advanced biofuels?
-Are essential to ensure a constant secure supply of energy
-Will reducxe dependency on fossil fuels
-Limit impact on environment
What are 2 types of biofuels commercially produced?
Bioethanol and biodiesel
What is bioethanol produced from?
Sugar beet, sugar cane and corn by fermentation of soluble sugars (largely sucrose and glucose derived from starch) by the yeast Saccharomyces cerevisiae
What is biodiesel produced from?
Currently produced by the extraction of oil from crops such as soybean, oilseed rape ad oil palm followed by chemicak esterification
What enzymes are used in the bioethanol production and what happens?
-The yeast enzyme invertase converts sucrose to glucose and fructose which can both enter glycolysis - sucrose can be added directly to the fermentation vessel
-Starch is enzymatically degraded by amylases to produce glucose and other simple sugars in a separate process - the hydrolysis products are added to the fermentation vessel
What microorganisms are used in bioethanol production?
Zymomonas mobilis
Saccharomyces cerevisiae
What does saccharomyces cerevisiae do in bioethanol production?
-Can convert glucose to ethanol via glycolysis - look at diagram
Yeast in glycolysis
-Glycolysis in yeast produces 2 ATP for each glucose molecule and an increase in biomass
-Increase in biomass represents wasted carbon and energy resources which could have gone into ethanol production
-Bioengineering of yeast may allow reduction of ATP yield
-Alternative ethanol producing organisms may also be useful
Zymomonas mobilis in the bioethanol production?
-Zymomonas mobilis is an anaerobic Gram-neg bacterium that breaks down glucose via the Entner–Duodoroff pathway
-Glycolysis in Z-mobilis produces 2 pyruvates but only 1 ATP for each glucose molecule
-Z.mobilis can withstand higher ethanol levels than S.cerevisiae
-Z.mobilis can only use a few simple sugars (including glucose, fructose and sucrose) for ethanol production - may limit its broader usefulness
What is biodiesel composed of?
Fatty acid methyl and ethyl esters
-Yeasts like Saccharomyces cerevisiae and some algae can accumulate fatty acids as triglycerides but these cannot be used directly as fuels
What bacteria does not naturally produce triglycerides?
Escherichia coli
Microorganisms genetically engineered in productiom of biodiesel?
-Saccharomyces cerevisiae has been genetically engineered to divert lipid synthesis away from triglycerides and into fatty acid ethyl esters
-Escherichia coli has been egentically engineered to produce fatty acid ethyl esters
What is ‘first generation’ biofuels?
Biofuels rpoduced from edible crops are traditional or first generation biofuels
Whta are second or third generation biofuels?
-Produced from non-food crops or plant waste
-Microbes play a key role in the development of these biofuels
-Sources do not compete with crops grown for food
-Much of plant biomass is mixture of cellulose, hemicellulose and lignin known as lignocellulose
Lignocellulose?
-Lignocellulose biomass makes up about half of the total biomass in the world
-Approx 430 million tons of plant waste is produced from farmland each year
-Lignocellulose is very resistant to degradation - research is aimed at identification of microbial enzymes that can efficiently degrade cellulose and perhaps hemicellulose leaving lignin that can be burned to produce energy.
-solar energy is collected by plants via photosynthesis and stored as lignocellulose
How is decomposition of cellulosic material achieved?
Decomposition of the cellulosic material into simple 5 and 6 carbon sugars is achieved by physical and chemical pre treatment, followed by exposure to enzymes from biomass-degrading organisms
-The simple sugars can be subsequently converted into fuels by mo
Where are microbes that naturally produce cellulases (to degrade celluloses) found?
In diverse environments such as volcanic soil, termite guts and the stomachs of cows
Ligincellulose structure?
Cellulose, hemicelluloses (mainly xylan), lignin
Lignocellulose conversion to bioethanol
-Pretreatment of biomass - solubilisation of hemicellulose
-Simultaneous saccharification and fermentation (SSF) - enzyme hydrolysis (conversion of cellulose to sugar) - fermentation (coversion of sugars to ethanol)
-Distillation and evaporation - produces ethanol
-Filter wash - lignin produced
-Waste management - residue-to-power production - recirculation of porcess streams
Current research?
-Scaling up production of microbial cellulases for cellulose conversion into fermentable sugars - discovery of new enzymes
-Engineering yeast for higher tolerance to ethanol to increase bioethanol production
-Genetically modifying micro organisms to utilize a wider range of sugars and ferment these more efficiently
-Optimization of microbial strains to produce alternative products such as biobutanol
- Finding algae that produce high yields of oils or that are otherwise suitable for biodiesel production
Where does production of biofuels start?
-Begins with the conversion of lignocellulosic biomass into simple sugars
-Engineered microbes then convert these sugars to advanced biofuel compounds which can be used as automotive gasoline, diesel and jet fuels
What simple sugars are made?
Cellulose -> glucose
Hemicellulose -> xylose and arabinose
Screening tolerance and increasing titre?
-First transcriptomics of E.coli DH1 expressing an inactive mevalonate pathway (MevT*) in the presence of exogenous isopentenol was used to determine what genes are upregulated in response to isopentenol stress
-A library of those genes was overexpressed in the presence of exogenous isopentenol. Growth curves were used to measure enhanced tolerance.
-Finally, genes that conferred tolerance were tested for their ability to increase the isopentenol titer in a production strain.
