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Lecture 15

BIOLOGY 2EE3 Lecture Notes - Lecture 15: Sewage Treatment, Operational Taxonomic Unit, Archaea

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Turlough Finan

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Microbial Ecosystems
Microbes in the environment
Communities described as functional groups, interacting with each other and the environment
Microbes (very small) exist in microenvironments (conditions can change over short distances)
Success of bacteria in niches depends on their ability to obtain nutrients to produce biomass & energy
Groups/layers of microbes on a surface that interact and support each other
Found in nature and have a lot of resistance
Biofilm – Begins with attached bacteria forming the primary layer on a surface. Secondary colonizers then
join and together the microbes secrete exopolysaccharide (EPS). EPS helps protect the biofilm and form
water-filled channels for transport of nutrients and wastes
Enrichment Cultures
Method used to isolate particular groups of microorganisms.
oDesired microbes may grow slow and be rare but growth is promoted by enrichment methods
Isolate nitrogen-fixing bacteria:
oSoil can be added to liquid medium that lacks any biologically available nitrogen sources like NH4
oIncubate in the presence of air, which contains O2 and N2
oNitrogen-fixing bacteria will become dominant in the culture. An aliquot of this enriched culture can
then be plated on solid medium that lacks biologically available nitrogen. Again, only nitrogen fixers
will grow.
oNote – this requires a lot of energy thus must supply within the liquid media – carbon sources
oNote – if looking for anaerobic, do not allow air to enter
How would you enrich for nitrifying bacteria? These convert NH4+  NO2-  NO3-
oSame method but grow in liquid that has ammonia present and lacks nitrates
oAnaerobes – eliminate oxygen but if they are aerobic – allow O2
How would you enrich for anoxygenic photosynthetic bacteria that use H2S as a e- donor?
oThese fix CO2 using H2S as an energy
Encrichment for microorganisms that degrade proteins
oGrow them in media that only has petroleum as the energy source. But have a low level of the
petroleum but replenish often
oStarting sample -- get a soil sample near a garage area. This is actually a big issue, go to some site
that may have been contaminated with whaterver you are looking for ??????
A Winogradsky column illustrates enchainment in action; different microbes flourish in different areas of
the column that correspond to different nutritional microenvironments. Generally, photosynthetic and
aerobic at top and then anaerobic at bottom
Cultivation-Independent Techniques
Techniques used to analyze microbial communities.
These techniques rely on the analysis of SSU rRNA genes.
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