Microbial Interactions

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Microbial Interactions Microbe
Microbe Microbe Plant
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Cooperation (within population) Minimum
Dose for Infection (growth) Prepares growth
substrate Establish Redox conditions Release
growth substances Colony Formation more
efficient use of nutrients esp if
polymers and need exoenzymes examples
Myxobacteria needs gt 103 cells to grow on casein
Genetic exchange Plasmids (AB and heavy metal
resist) Enterococcus faecalis F- makes
Pheromones causes F to synthesis agglutinins
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Quorum Sensing (sufficient numbers) bacteria
respond to cells of their own kind e.g. release
toxin only if sufficient numbers Regulatory
molecule homoserine lactone (specific) SO if
lots made (diffusable) then sufficient to
induce transcription. Regulates bioluminescence
Vibrio fischeri (?) luciferin/luciferase lux
operon controlled by LuxR gene (inducible)
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Vibrio fischeri Quorum sensing first observed in
Vibrio fischeri Bioluminiscent mutualistic
symbiont in the photophore (or light-producing
organ) squid. When V. fischeri free-living the
autoinducer is at low concentration and not
luminescent. When they are highly concentrated
in the photophore (about 1011 cells/ml)
transcription of luciferase is induced, leading
to bioluminescence.
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Quorum Sensing (sufficient numbers) P.
aeruginosa at high density converts from free
living to biofilm growth. Natronococcus
occultus Archaea alk/halo (protease
synth) Detection of quorum sensing signals in the
haloalkaliphilic archaeon Natronococcus occultus
FEMS microbiology letters 2003, vol. 221
PAGGI Roberto A.
Pseodoalteromonas ??? Quorum sensing in
algicidal activity and association with
cyanobacterium Lyngbia
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Competition Substrate and/or niche (within
population) Food Toxin Production
antibiotics (bacitracin) acid H2S E.
coli killer genes (checked by antikiller on
plasmid) loose plasmid die plasmid
has antibiotic resistance
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Between Populations Neutralism No effect
(spores/resting) Commensalism One , One no
effect Desulfovibrio SO4 lactate ? H2S
H2 acetate Methanobacterium H2 CO2 ?
CH4 PSB H2S CO2 ? CH2O So
Cometabolism growing on one substrate,
oxidizes another that it is unable to use for
C or E Mycobacterium vaccae grows on
propane (ATP, CO2) cometabolizes
cyclohexane ? cyclohexanol which can be
metabolized by Pseudomonas ? ATP, CO2, H2O
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Protocooperation - both benefit (not obligatory)
(synergism) Auxotrophy S. faecalis ?
phenylalanine each needed by
other Lactobacillus ? folic acid PIX
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Syntrophism when supply each others
nutritional needs Anabaena heterocysts food vs
low DO
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Mutualism (Symbiosis) - both benefit
Obligatory Lichen BG alga (phycobiont)
fungus (mycobiont) Protozoa Paramecium
Chlorella (endosymbiont) alga ? O2, CH2O
(allows enter anoxic habitat) Parameciu
m ? Protect, motility,CO2
Rumen endosymbiotic archaeal methanogens
in the gut of anaerobic, ciliated protozoa
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This is important because rumen protozoa are
harmful in that they ingest and digest beneficial
bacteria in the rumen. Protozoa are also
associated with bacteria called methanogens that
rob energy available to the cow for milk
production. Protozoa also consume (and waste)
dietary protein, which lowers the protein
available to the animal for growth or milk
production. This is very important in a starting
calf and a fresh dairy cow.
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Competition - Negative Effect Both Chemostat
eventually only ONE species gtest growth rate
wins BUT environmental effect if gt nutrients
E. coli wins if lt nutrients Spirillum
wins Antagonism (Amensalism) - One inhibits
other Lactobacillus ? lactic acid inhibits E.
coli, Candida Thiobacillus ? H2SO4 Antibiotics
O2 consumption
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Parasitism One benefits BY harming
other bacteriphage Bdellovibrio on Gram
bacteria ectoparasite in
periplasm Predation One benefits by
engulfing other Protozoans on bacteria
Cilliate engulfing algae