447 - hydrocarbon degradation

Hydrocarbon degradation role in nutrient cycling

microbes convert hydrocarbons into metabolites that feed carbon cycling and respiration pathways

Why hydrocarbons can be degraded by microbes

hydrocarbons occur naturally in insects plants cyanobacteria so microbes evolved pathways to use them as carbon and energy sources

Difference between short cycle and long cycle hydrocarbons

short cycle hydrocarbons are produced and degraded rapidly while long cycle hydrocarbons form over millions of years and persist until released by spills

What hydrocarbons are in petroleum

petroleum contains diverse aliphatics alkanes alkenes cyclics and aromatics so no single degradation pathway exists

Why petroleum cannot be degraded with one pathway

crude oil is a mixture of hundreds of hydrocarbons requiring different enzymes and microbial groups for degradation

Natural hydrocarbon sources

insects produce wax and signaling molecules plants produce cuticular wax cyanobacteria produce hydrocarbon chains in thylakoid membranes

What determines hydrocarbon biodegradation

hydrocarbon properties microbial traits and environmental conditions as shown in the diagram on slide three

How hydrocarbons move in the environment

oil can evaporate dissolve in water spread on surface form droplets photo oxidize or be consumed by microbes

Why hydrocarbons spread on water

oil has lower density and hydrophobic structure causing surface spreading and formation of slicks

What photo oxidation does to hydrocarbons

sunlight introduces oxygen groups making hydrocarbons more polar and sometimes easier for microbes to degrade

Why aromatic hydrocarbons are more recalcitrant

aromatic rings are stable require oxygenase enzymes and need ring cleavage to enter metabolism

Why alkanes are easier to degrade than aromatics

alkanes require initial hydroxylation but have no ring structure making them more accessible for oxidation

Role of oxygen in aerobic hydrocarbon degradation

oxygen acts as reactant to oxidize substrate and as electron acceptor for respiration and is required for ring cleavage

Why oxidation is rate limiting in aerobic hydrocarbon degradation

the first hydroxylation step requires specialized oxygenase enzymes and slows overall degradation

Example of aerobic alkane degradation enzyme

alkane hydroxylase converts alkanes into primary alcohols enabling entry into beta oxidation pathways

How chain length affects alkane degradation

different alkane hydroxylases specialize in short medium or long chain substrates

How microbes degrade aromatics aerobically

oxygenases add oxygen to ring to produce catechol then ring cleavage enzymes open the ring allowing entry into central metabolism

Why catechol pathway is important

catechol is a key intermediate for many aromatic degradation pathways and indicates ring oxidation has occurred

What happens to hydrocarbons after oxidation

products are converted to acetyl coa and other TCA intermediates then oxidized for energy

Why anaerobic hydrocarbon degradation is harder

initial oxidation cannot use oxygen and requires addition of functional groups like fumarate which is slow and energetically costly

Electron acceptors for anaerobic hydrocarbon degradation

microbes use nitrate sulfate carbon dioxide or oxidized metals instead of oxygen

Initial step of anaerobic alkane degradation

fumarate addition to hydrocarbon produces alkyl succinate enabling further metabolic conversion

Why anaerobic hydrocarbon degradation is slower

reactions release less energy and rely on less efficient electron acceptors

What syntrophy means in hydrocarbon degradation

anaerobic bacteria degrade substrate only if partner methanogenic archaea consume hydrogen or acetate making reactions thermodynamically favorable

Why syntrophy is required for deep hydrocarbon degradation

oxidation becomes energetically impossible unless methanogens remove inhibitory intermediates

What methanogens produce in syntrophic degradation

methane and carbon dioxide which complete anaerobic mineralization of hydrocarbons

Why crude oil requires microbial communities not single species

no microbe has pathways to degrade all hydrocarbons and some microbes only perform specific steps of pathways

Why microbial competition matters in bioremediation

added microbes may fail if native microbes outcompete them or if they cannot survive site conditions

Why microbial consortia may be beneficial

different species degrade different hydrocarbons or provide metabolites like oxygen to each other

Why you cannot just mix microbes for bioremediation

interactions can cause competition inhibition or incompatibility so communities must be tested experimentally

How pH affects hydrocarbon degradation

extreme pH inhibits enzymes and membrane function slowing microbial metabolism

How salinity affects hydrocarbon degradation

high salt requires halotolerant microbes and affects solubility and diffusion of hydrocarbons

How temperature affects hydrocarbon degradation

low temperature reduces enzyme activity and increases viscosity of oil while high temperature accelerates microbial metabolism

What pressure does to hydrocarbon degradation

deep sea pressure influences membrane fluidity and requires barotolerant microbes

Why oxygen availability determines degradation pathway

presence of oxygen allows fast aerobic oxidation while absence forces slow anaerobic pathways

Environmental condition prediction example

oil spill in cold anoxic deep sea will degrade slowly due to low temperature poor mixing and anaerobic metabolism

Environmental condition prediction example two

oil spill in warm oxygenated coastal water will degrade faster due to active aerobic microbes and mixing

Bioremediation strategy oxygen addition

injecting air peroxide or ozone accelerates aerobic oxidation which is rate limiting step

Bioremediation strategy electron acceptor addition

adding nitrate or sulfate enhances anaerobic degradation when oxygen is limited

Bioremediation strategy nutrient addition

low nitrogen or phosphorus limit microbial growth so adding nutrients increases metabolic rate

Bioremediation strategy microbial addition

adding degraders can help but only if environment supports their growth and competition does not eliminate them

How to choose a bioremediation strategy

consider hydrocarbon type oxygen levels nutrients microbial community and environmental constraints

Why isolation of hydrocarbon degraders is difficult

some microbes depend on partners syntrophy or specific conditions making solo growth impossible

What marker enzyme indicates aerobic aromatic degradation

catechol dioxygenase produces yellow product allowing detection of pathway activity

How experimental methods detect hydrocarbon degradation

measure carbon dioxide formation oxygen consumption substrate loss intermediate formation or enzyme activity

What experiments cannot tell you

they cannot determine which species in a consortium did each metabolic step without genomic or expression data

How to evaluate hydrocarbon degradation experimental design

check for proper controls realistic environmental conditions replication and evidence of actual metabolic activity

How microbes and environment interact in hydrocarbon degradation

microbes respond to oxygen nutrients pH temperature and hydrocarbons change by oxidation diffusion and microbial consumption

How environmental changes affect hydrocarbon degradation

shifts in oxygen mixing temperature and nutrient levels alter microbial pathways and degradation rates