Microbio 303 Exam questions and
answers graded A+
Methanogens process and habitats - ANS✅✅found in many places - obligate anaerobes make
methane like in anoxic sediments like marsh swamp, lake sediments and moist landfills, animal
digestive tract, rumen of cattle, large intestine and in mouth on teeth found in geothermal sources
of H2 and Co2 and sewage systems
-endosymbionts with protozoa
Methanogenesis - ANS✅✅type of anaerobic respiration - CO2 is terminal electron acceptor - gets
reduced to CH4 (H2 is a common electron donor but isn't always) - other electron acceptors can be
used like formate, alcohols, methyl amines, methanol, acetate all can get reduced
*uses F420 as an electron carrier- may make a sodium proton force to make ATP
What is the electron reduction potential of CO2? - ANS✅✅it has a -244 electron potential of being
reduced so in order for it to accept electrons favorable the electron donor must have a more
negative potential like H2S or H2
Methanogenesis proton gradient - ANS✅✅has the F420 non reducing hydrogenase (that oxidizes
H2 and removes the electrons) and a quinone pool like system and a sulfide reductase
Acetogens - ANS✅✅anaerobic bacteria - most are firmicutes, use CO2 as electron acceptor and
reduce to acetate instead of methane
Acetogenesis pathway - ANS✅✅-uses 2CO2 (very similar to acetyl CoA pathway) and reduces it to
acetate from CH3 and CO using a CO dehydrogenase which has Ni and Fe on it as cofactors and
creates a sodium motive force
*needs B12!!!
NET: 4H2 + 2HCO3- +H+ --> acetate + 4H2O
Methanogens vs. Acetogens - ANS✅✅both compete for CO2 and H2
-methanogens will win when CO2 or Co is low (Co needed for B12 which is needed for acetogens)
-acetogens win in higher nutrient situations
*methanogens are more efficient (have a more negative delta G)
,Microbial partnerships - ANS✅✅producers and consumers can take and share metabolites which
actually increases the speed and efficiency of the process
-an anaerobe can take lactate or alkanes and make acetate or formate and then a methanogen can
take these products and use them
Syntrophy - ANS✅✅some bacteria live together and supply each other with essential nutrients 0
producer consumer relationship is mandatory - they coorporate to degrade subtrate
Syntrophomonas - ANS✅✅can ferment butyrate to acetate for energy if a methanogen is present
to use the H2 generated
-protons are electron accepto generating hydrogen gas - this would be unfavorable unless the
methanogens were there to remove the H2 and use it
S - takes butyrate to acetate and makes H2 which is used by methanogens to make CH4
aerobic degradation - ANS✅✅aerobic respiration predominates - oxidized products like CO2,
nitrate, sulfate are made and oxygen is quickly consumed leading to anaerobic environments
anaerobic degradation - ANS✅✅nitrate and sulfate are used as electron acceptors using ETC
-when this is not possible fermentation happens which produces partially oxidized products these
can be used by acetogens and methanogens
-when environment is high in sulfate the SRB will dominate over methanogens and acetogens so H2S
and H2O and CO2 will be made
What type of hydrogen utilizers are in the human colon? - ANS✅✅there is likely methanogens and
acetogens
Symbiosis - ANS✅✅intimate association between two different types of organisms
Mutualism - ANS✅✅both organisms benefit
commensalism - ANS✅✅A relationship between two organisms in which one organism benefits
and the other is unaffected
,Amensalism - ANS✅✅a relationship in which one organism is harmed and the other is benefited
(pathogenesis)
Commensal microbiota - ANS✅✅Normal microbiota, commensal: host benefits, bacteria is
unaffected
helps us resist pathogens
we have a community of microbes on mucosal surface and in body cavity and in specefic organs
Holobiont/hologenome - ANS✅✅hologenome is hte host genome and the microbiome
How do we study symbiotic microbes? - ANS✅✅-can manipulate the genome with CRISPR and
make germ free animals and get rid of the microbiota and notice how the microbe survives
-can use model organisms
-analyze the microbiome by sequencing it and look for important functions and proteins within the
gut microbiome
Important functions of symbiotic microbes - ANS✅✅-assimilate major nutrients
-provision of minor but essential nutrients like AAs and vitamins
protection from predators or parasite (virbrio fischeri)
-role in reproduction
-role in normal physiology
-role in development - development of immune system
Assimilation of major nutrients with help from symbionts - ANS✅✅organisms that fix carbon can
incorporate carbon into the cells of other organisms
- methane oxidation and sulfur oxidation can create energy and metabolites for symbiotic organisms
Assimilating minor but essential nutrients - ANS✅✅many animals have an incomplete food source
(if blood consuming this lacks vitamins, grains and plants lack amino acids and a mainly xylem and
phloem (sap sucking)diet lacks amino acids
-bacterial symbionts that provide essential nutrients are commonly observed in insects
, Insects and their primary endosymbionts - ANS✅✅generally the symbiont is intracellular to the
insect and may associate with a specefic organ or tissue (bacterionome) or to a specefic cell
(bacteriocyte) they give amino acids or vitamins to host when the host provides food for the
symbiont
*the symbiont is usually passed on by the insect to their offspring - meaning they grow up with this
ability and don't acquire it
Symbiont-mediated protection - ANS✅✅microbes may provide protection for their host examples
of this defense include antibiotic production, protein toxins and pigments that provide protection for
the microbe
Actinomycetes as mutualists - ANS✅✅beewolf wasps lay eggs in underground burrows
streptomyces produces antibiotics that coat the egg/cocoon and protect it from predators in the
ground
Does the host always help the microbe and does the microbe have only one role within the host? -
ANS✅✅usually the microbe has many roles (protect, help fight off pathogens, make essential
nutrients) in the host but the microbe may not benefit from the relationship (may get food and
shelter)
Zebra fish experiment - ANS✅✅fish raised germ free developed normally until day 5 when they
started to show abnormalities that could be fixed if the microbiota was reintroduced
the microbiota was found to be involved in immune response, nutrient digestion mucus expression
and skin cell renewal and defense mechanisms
How do herbivores digest foods like cellulose? - ANS✅✅they enlist of the help of anaerobic
microbes
-some ferment in the foregut (like sheep and cows) which is higher before the stomach
-others ferment in the hindgut like primates
The rumen - ANS✅✅stomach chamber in cows and related animals in which symbiotic bacteria
digest cellulose - 100L anaerobic fermentation vessel, complex community of microbes(bacteria,
archaea and eukarya) that make FA which are used by the animal for food
-significant methanogen community make it from formate
-produce acetate, propionate and butyrate for the ruminant - gets taken up after the cellulose is
broken down
answers graded A+
Methanogens process and habitats - ANS✅✅found in many places - obligate anaerobes make
methane like in anoxic sediments like marsh swamp, lake sediments and moist landfills, animal
digestive tract, rumen of cattle, large intestine and in mouth on teeth found in geothermal sources
of H2 and Co2 and sewage systems
-endosymbionts with protozoa
Methanogenesis - ANS✅✅type of anaerobic respiration - CO2 is terminal electron acceptor - gets
reduced to CH4 (H2 is a common electron donor but isn't always) - other electron acceptors can be
used like formate, alcohols, methyl amines, methanol, acetate all can get reduced
*uses F420 as an electron carrier- may make a sodium proton force to make ATP
What is the electron reduction potential of CO2? - ANS✅✅it has a -244 electron potential of being
reduced so in order for it to accept electrons favorable the electron donor must have a more
negative potential like H2S or H2
Methanogenesis proton gradient - ANS✅✅has the F420 non reducing hydrogenase (that oxidizes
H2 and removes the electrons) and a quinone pool like system and a sulfide reductase
Acetogens - ANS✅✅anaerobic bacteria - most are firmicutes, use CO2 as electron acceptor and
reduce to acetate instead of methane
Acetogenesis pathway - ANS✅✅-uses 2CO2 (very similar to acetyl CoA pathway) and reduces it to
acetate from CH3 and CO using a CO dehydrogenase which has Ni and Fe on it as cofactors and
creates a sodium motive force
*needs B12!!!
NET: 4H2 + 2HCO3- +H+ --> acetate + 4H2O
Methanogens vs. Acetogens - ANS✅✅both compete for CO2 and H2
-methanogens will win when CO2 or Co is low (Co needed for B12 which is needed for acetogens)
-acetogens win in higher nutrient situations
*methanogens are more efficient (have a more negative delta G)
,Microbial partnerships - ANS✅✅producers and consumers can take and share metabolites which
actually increases the speed and efficiency of the process
-an anaerobe can take lactate or alkanes and make acetate or formate and then a methanogen can
take these products and use them
Syntrophy - ANS✅✅some bacteria live together and supply each other with essential nutrients 0
producer consumer relationship is mandatory - they coorporate to degrade subtrate
Syntrophomonas - ANS✅✅can ferment butyrate to acetate for energy if a methanogen is present
to use the H2 generated
-protons are electron accepto generating hydrogen gas - this would be unfavorable unless the
methanogens were there to remove the H2 and use it
S - takes butyrate to acetate and makes H2 which is used by methanogens to make CH4
aerobic degradation - ANS✅✅aerobic respiration predominates - oxidized products like CO2,
nitrate, sulfate are made and oxygen is quickly consumed leading to anaerobic environments
anaerobic degradation - ANS✅✅nitrate and sulfate are used as electron acceptors using ETC
-when this is not possible fermentation happens which produces partially oxidized products these
can be used by acetogens and methanogens
-when environment is high in sulfate the SRB will dominate over methanogens and acetogens so H2S
and H2O and CO2 will be made
What type of hydrogen utilizers are in the human colon? - ANS✅✅there is likely methanogens and
acetogens
Symbiosis - ANS✅✅intimate association between two different types of organisms
Mutualism - ANS✅✅both organisms benefit
commensalism - ANS✅✅A relationship between two organisms in which one organism benefits
and the other is unaffected
,Amensalism - ANS✅✅a relationship in which one organism is harmed and the other is benefited
(pathogenesis)
Commensal microbiota - ANS✅✅Normal microbiota, commensal: host benefits, bacteria is
unaffected
helps us resist pathogens
we have a community of microbes on mucosal surface and in body cavity and in specefic organs
Holobiont/hologenome - ANS✅✅hologenome is hte host genome and the microbiome
How do we study symbiotic microbes? - ANS✅✅-can manipulate the genome with CRISPR and
make germ free animals and get rid of the microbiota and notice how the microbe survives
-can use model organisms
-analyze the microbiome by sequencing it and look for important functions and proteins within the
gut microbiome
Important functions of symbiotic microbes - ANS✅✅-assimilate major nutrients
-provision of minor but essential nutrients like AAs and vitamins
protection from predators or parasite (virbrio fischeri)
-role in reproduction
-role in normal physiology
-role in development - development of immune system
Assimilation of major nutrients with help from symbionts - ANS✅✅organisms that fix carbon can
incorporate carbon into the cells of other organisms
- methane oxidation and sulfur oxidation can create energy and metabolites for symbiotic organisms
Assimilating minor but essential nutrients - ANS✅✅many animals have an incomplete food source
(if blood consuming this lacks vitamins, grains and plants lack amino acids and a mainly xylem and
phloem (sap sucking)diet lacks amino acids
-bacterial symbionts that provide essential nutrients are commonly observed in insects
, Insects and their primary endosymbionts - ANS✅✅generally the symbiont is intracellular to the
insect and may associate with a specefic organ or tissue (bacterionome) or to a specefic cell
(bacteriocyte) they give amino acids or vitamins to host when the host provides food for the
symbiont
*the symbiont is usually passed on by the insect to their offspring - meaning they grow up with this
ability and don't acquire it
Symbiont-mediated protection - ANS✅✅microbes may provide protection for their host examples
of this defense include antibiotic production, protein toxins and pigments that provide protection for
the microbe
Actinomycetes as mutualists - ANS✅✅beewolf wasps lay eggs in underground burrows
streptomyces produces antibiotics that coat the egg/cocoon and protect it from predators in the
ground
Does the host always help the microbe and does the microbe have only one role within the host? -
ANS✅✅usually the microbe has many roles (protect, help fight off pathogens, make essential
nutrients) in the host but the microbe may not benefit from the relationship (may get food and
shelter)
Zebra fish experiment - ANS✅✅fish raised germ free developed normally until day 5 when they
started to show abnormalities that could be fixed if the microbiota was reintroduced
the microbiota was found to be involved in immune response, nutrient digestion mucus expression
and skin cell renewal and defense mechanisms
How do herbivores digest foods like cellulose? - ANS✅✅they enlist of the help of anaerobic
microbes
-some ferment in the foregut (like sheep and cows) which is higher before the stomach
-others ferment in the hindgut like primates
The rumen - ANS✅✅stomach chamber in cows and related animals in which symbiotic bacteria
digest cellulose - 100L anaerobic fermentation vessel, complex community of microbes(bacteria,
archaea and eukarya) that make FA which are used by the animal for food
-significant methanogen community make it from formate
-produce acetate, propionate and butyrate for the ruminant - gets taken up after the cellulose is
broken down
