Lecture 6- metabolic processes in microbes Flashcards
what are chemolithotrophs?
-Bacteria and Archaea
-Obtain energy from the oxidation of inorganic compounds such as sulphide/ammonia, and use CO2 as carbon source
-eg deep sea vents-oxidation of hydrogen sulphide
-Biogeochemical cycles/global nitrogen cycle
what are phototrophs?
-exist in fresh water and soil
-plant-like photosynthesis
eg cyanobacteria
Produces and releases oxygen
what are Chemoorganotrophs-Heterotrophs?
Energy from organic compounds (eg glucose)
Also called ‘chemoheterotrophs’
Many sources of carbon (sugars, fats, proteins), making these microorganisms extremely versatile, able to live in many environments
Decomposers, feeding on dead
plants and animals
Metabolic processes:
-respiration
-fermentation
what is bacterial metabolism?
Bacteria are distinct as hugely diverse metabolic properties
Aerobic respiration
Anaerobic respiration
(terminal electron acceptor are compounds other than oxygen)
-Facultative anaerobes & obligate anaerobes
Fermentation
what is respiration?
Most respiration involves use of an electron transport chain
Aerobic respiration
final electron acceptor is oxygen
Anaerobic respiration
final electron acceptor is different exogenous acceptor such as nitrate & sulphate (NO3-, SO42-, CO2 or Fe3+ )
As electrons pass through the electron transport chain to the final electron acceptor, a proton motive force (PMF) is generated and used to synthesize ATP
what is the fermentation-anaerobic processes?
Uses an endogenous electron acceptor
usually an intermediate of the pathway e.g., pyruvate
Does not involve the use of an electron transport chain nor the generation of a proton motive force
Yields very little energy compared to aerobic/anaerobic resp
Lactobacilluslactic acid (intestine/milk/sourdough bread)
what is the Real-world application of bacterial metabolism eg Bioremediation?
Biotechnology using microbes to remove environmental contaminants
Bacterial metabolic processes are flexible and highly diverse
Anthropogenic substances and bacteria couple, facilitating terminal electron transfer
Bacteria degrade toxic pollutants such as petroleum hydrocarbons found in oil
Links to bioremediation to clean up contaminated sites eg. Exxon Valdez(1989)/Deepwater Horizon 2010 spill
what is the Microbial degradation of plastics?
Plastics are non-biodegradable-long carbon backbone, high molecular weight & hydrophobic
>300 million tons of plastic per year made, predicted to double in next 20 years (Urbanek et al, 2018)
Each year ~20 million tons of plastic leaks into oceans
Microbes struggle to degrade plastic due to high MW; can’t pass through cell membrane
Biodegradable plastics & microplastics can be degraded by microbial enzymatic activity
what is the microbial plastic degradation process?
1 - Adherence to plastic via biofilm
2 - Microbial extracellular enzymes such as hydrolases/lipases fragment polymers
3 - Small oligomers can then cross cell membranes and enter central metabolic pathways, producing energy through catabolism
4 - Conversion of biomass to gas, water, salts and minerals via aerobic or anaerobic degradation processes
what is the research into plastic degradation?
Pseudomonas spp are metabolically diverse & can degrade and metabolise plastics
Research focussing on:
Adherence to plastic surface-creation of biofilms
Using synthetic biology to improve extracellular polymer oxidation/hydrolytic enzyme activity
Investigating metabolic pathways mediating polymer uptake and degradation via catabolism
Enhancing factors e.g. pre-treatments, microbial communities and nutrients
what is the Hugh and leifson media?
Differentiating glucose metabolism
Looking for colour change, based on pH, acid production
Oxidative-Fermentative (OF) test
Tubes contain a liquid with glucose , peptone and bromophenol blue.
Pic 1: One tube has oil, therefore anaerobic conditions, one no oil, therefore aerobic conditions
Pic 2: A colour change in the aerobic tube, so oxidation of the glucose has occurred eg. Pseudomonas
Pic 3: Colour change in both indicates fermenting in anaerobic conditions eg. Enterobacteria such as E.coli. Facultative anaerobe so uses oxygen if present.
what is the biochemical analysis in a diagnostics lab?
Catalase Test
Most aerobic & facultative aerobic bacteria (not Streptococcus/Enterococcus) are catalase positive
Protection against toxic by-products of O2 metabolism
Diagnose Staphylococcus vs Streptococcus
how do we rapidly ID clinical isolates?
In labs a large panel of biochemical assays can be used for one patient sample to diagnose bacterial infection
how do you Exploit metabolic differences for drug developmentMalaria parasite?
Malaria is caused by the parasite Plasmodium and transmitted by a mosquito
200 million NEW cases a year
Can cause severe illness and death
Every 2 minutes a child dies of malaria
Mosquito nets, pesticides, chemoprophylaxis for prevention
how do we Exploit metabolic differences for drug development - Pyrimethamine
1960s, enzymatic studies showed that pyrimethamine inhibited malaria metabolic pathway for folate biosynthesis
Folate is used to make thymine, one of the four nucleotides, essential for DNA synthesis
Folate synthesis also in mammalian host
1,000-fold greater potency in Plasmodium vs mouse pathway
For the first time, a ‘magic bullet’ could selectively target an enzyme in a pathogen, even although an ortholog existed in the host
Differences between host and parasite DHFR* active sites create opportunities for the selective binding of pyrimethamine
who is Gertrude lion?
Nobel Prize winning scientist developed Pyrimethamine to combat malaria
This drug also treats Toxoplasmosis
Rational drug design leader, understanding drug target
Led to creation of AZT (AIDS treatment) and azathioprine (immunosuppressive drug)
Pathway a target for cancer and bladder infections
how do we target metabolic differences for diagnostics?
Aerobic cellular respiration-CO2 produced + low level of acids (e.g. citric acid, through Krebs cycle)
Anaerobic fermentation-acid produced (e.g. lactic acid) (glycolysis only)
what must micoorganisms be able to do to grow and replicate?
produce energy and use energy to synthasize molecules and structures (biomass production)
