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MBIO- Microbial interactions- in a single population (done)

Terms in this set (21)

give an example of incomplete separation
heterocyst
Give an example of a temporary association between microbes in a single population and explain why it is temporary
production of fimbriae and pili, they are temporary because they briefly use them to communication
how do cells glue together and why does this happen
through polysaccharides

the glue after cell division to aggregate
list three examples of ways cells from association between individuals in a population
incomplete separation
fimbriae and pili
cells glue together to aggregate
what are three benefits to aggregation between individuals in a population
-cells adhere to solid surfaces, so they are less susceptible to shearing forces in water (biofilms)
-helps them trap organic particles
-very large aggregates can inhibit larger predators
what is a major thing that influences a process between microbes in a population
population density
define positive and negative density dependence in a microbial population
+ = process increases as population density increases
- = process decreases as population density increases
what are the four types of positive density dependence
shared resources
quorum sensing
complex life cycles
genetic exchange
define the positive density dependence of shared resources
low molecular weight metabolites that diffuse across membrane can be shared among cells. If population density increases the concentration of the metabolites increases as well
give an example of shared resources, for who and where is it important
species such as Ectothiorhodospira spp accumulate or release compatible solutes like glycine, betaine in hypersaline environments
give an example of shared resources. For who and where is it important?
extracellular enzymes like cellulases release products that can be used by all members of a population, as population density increases, the concentration of extracellular enzymes increases and therefore the release product concentration increases.important for myxobacteria, clostridium, actinomycetes and ruminococcus and is important in forest floor, anoxic sediments and animal guts
define quorum sensing
when species are able to sense when a critical population density exists, as cell density increases, the amount of autoinducer reaches critical levels which causes gene expression
give an example of quorum sensing (order of chemicals: NBKHL, lux operon, luciferase, FMNH2, O2
Vibrio Fischeri in fish:

when N-B-ketocaproyl homoserine lactone reaches critical concentration it reacts with activator protein which causes the expression of lux operon. Lux operon encodes enzyme luciferase and passes electrons from FMNH2 to O2 and light becomes emitted

This chemical process happens in special light organs in certain fish and squid

quorum sensing is also important for Myxococcus xanthus, agrobacterium tumefaciens
give an example the positive density-dependent complex life cycles
Myxococcus xanthus feed on cellulose of dead bacteria. They do this to gain necessary substrates for gliding motility and formation of fruiting bodies and myxospores
Describe positive density dependence for genetic exchange, give three examples of lateral gene transfer
lateral gene transfer: if population is dense enough, cells will be close enough to exchange DNA laterally

transformation: uptake of free DNA
conjugation: transfer of DNA through pili and fimbriae
transduction: transfer via bacteriophage
what are the two types of genetic exchange in microbial populations
lateral gene transfer and gene transfer through plasmids
describe how plasmids are a part of genetic exchange in positive density dependence
antibiotic resistance is possible through plasmids
what are two types of negative density dependence
competition for nutrients
end product accumulation
describe competition for nutrients (- density dependence)
at high population density, microbes have greater competition for substrates

microbes can adapt to starvation however ultimately they need some substrates for energy
define the Dr. Liebig principle
growth will be limited by the substrate that expires first
describe and give two examples of end product accumulation (- density dependence)
some products of metabolism are detrimental to the original cell and other cells in a population:

ex: organic acids release from fermentation such as lactic acid which lowers pH and can inhibit growth
ex: sulfide produced by sulfate-reducing bacteria inhibits even sulfate reducers if reaches high concnetrations
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