Finally, biology Ways of classifying lake organisms: phylogenetic functional autotrophs heterotrophs (herbivores, carnivores, omnivores, detritovores, mixotrophs) chemotrophs (methane, sulfur) mixotrophs habitat benthic vs. pelagic

Bacteria (prokaryotes) Can fill any functional roles in lakes Play a number of roles in food web Defy species concept Key questions about bacteria: How many are there? How do we measure their diversity? Other prokaryotes- cyanobacteria, purple sulphur bacteria, Nitrosomas

Ways of counting bacteria- culturing prehistoric Limitation- not all bacteria grow in the lab, some can’t use organic medium supplied, others are dormant Culturing typically finds 100s-1000s of cells/ml

Ways of counting bacteria- staining, e. g. DAPi, FISH Azam et al Ways of counting bacteria- staining, e.g. DAPi, FISH Azam et al. 1983 Marine Ecology Progress Series 10:257 Typically finds 1,000,000- 100,000,000cells/ml Two possibilities: 1. All those glowing cells are dead or dormant (culturing is correct) 2. Most bacteria can’t be cultured in the lab (staining is correct)

How much do bacteria contribute to biomass. Gasol et al How much do bacteria contribute to biomass? Gasol et al. 1997 Limnology and Oceanography 42:1353

Ways of measuring bacterial diversity- Ancient (1970s): culturing and morphological diversity

Ways of measuring bacterial diversity- 1980’s: use of different organic resources, Biolog plates Functional diversity

Measuring bacterial diversity- Modern: PCR to amplify, gels to separate (DGGE) and sequencing

What determines bacterial diversity in BC lakes What determines bacterial diversity in BC lakes? Longmuir, Shurin and Clasen 2007 Ecology 88:1663 Light Dissolved O2 How is bacterial richness related to zooplankton and phytoplankton richness?

What determines bacterial diversity in BC lakes What determines bacterial diversity in BC lakes? Longmuir, Shurin and Clasen 2007 Ecology 88:1663

Bacteria, zooplankton and algae biomass are positively related slope <1, heterotrophs don’t keep up with autotrophs diversity unrelated determined by different processes

What ecological roles to bacteria play? Interactions with phytoplankton predators (pathogens) compete for nutrients (autotrophs) recycle nutrients (heterotrophs) Interactions with zooplankton pathogens prey Recycling detritus (POM -> DOM)

Bacteria and nutrient cycles- the microbial loop

Biology 302 revisited- the food chain classical food chain

The brown world- death and decay classical food chain everything dies, becomes detritus

The central role of bacteria classical food chain but wait, there is recycling everything dies, becomes detritus

Closing the loop 1- Ecology is about recycling classical food chain but wait, there is recycling inorganic nutrients (N,P,DIC) everything dies, becomes detritus

Closing the loop 2- Feeding the beast classical food chain but wait, there is recycling inorganic nutrients (N,P,DIC) everything dies, becomes detritus

How much zooplankton carbon comes from bacteria vs. phytoplankton? Using stable isotopes of Carbon (13C and 12C) to measure bactivory consumer prey 1 prey 2 Percent 13C in tissues

How much zooplankton carbon comes from bacteria vs. phytoplankton? If Daphnia eats 50% algae, 50% bacteria, it will have 13C concentration half way between the two Daphnia 5% bacteria 2% phytoplankton 8% Percent 13C in tissues

How much zooplankton carbon comes from bacteria vs. phytoplankton? If Daphnia eats 90% algae, 10% bacteria, it will have 13C concentration that is 0.9*[algae]+0.1*[bacteria] = .074 Daphnia 7.4% bacteria 2% phytoplankton 8% Percent 13C in tissues

How much zooplankton carbon comes from bacteria vs. phytoplankton? Grey et al. 2001 Limnology and Oceanography 46:505 50% averaged over the year, 80-90% in winter, 10-20% in summer

How much zooplankton carbon comes from bacteria vs. phytoplankton? Pace et al. 2001 Nature 427:240 added NaH13CO3 (radio labeled DIC) DIC can be used by phytoplankton but not bacteria Measured 13C in POM and Daphnia Accumulation of 13C in Daphnia indicates amount of bacteria eaten 20-50% in summer

How do infectious diseases influence Daphnia reproduction How do infectious diseases influence Daphnia reproduction? Decaestecker et al. 2005 Oecologia 144: 382 4 fungi 1 amoeba 2 bacteria 1 nematode

How does zooplankton diversity influence disease transmission How does zooplankton diversity influence disease transmission? Hall et al. Ecology 2009 Daphnia species

How does zooplankton diversity influence disease transmission How does zooplankton diversity influence disease transmission? Hall et al. Ecology 2009 more susceptible hosts less susceptible hosts

How does zooplankton diversity influence disease transmission How does zooplankton diversity influence disease transmission? Hall et al. Ecology 2009 high zooplankton diversity lowers transmission- less susceptible competitors can benefit one another

Bacteria and disease- cholera Pascual et al. 2000 Science 289: 1766

Vibrio cholerae (cause of cholera) has zooplankton as intermediate host attached to Daphnia in gut of Daphnia Do high plankton populations in El Niňo years cause cholera outbreaks?

How do bacteria get energy? Autotrohs (cyanobacteria) Heterotrophs (DOC) Inorganic chemotrophs (purple sulfur bacteria, methanotrophs)

What do parasites do in ecosystems? Kuris et al. Nature 2008

What do parasites do in ecosystems? Kuris et al. Nature 2008

Chemical communication in bacteria allelopathy (chemical warfare) quorum sensing (switch between dormant and active stages)

Mutualism between bacteria and phytoplankton

What about viruses? (Suttle 2005 Nature 437:356)

Viruses and you (Suttle 2005 Nature 437:356)

Viruses rule the world Suttle et al. 1990 Nature 347:467 no viruses 106-109 per ml Reduce algal production by up to 78% (in cultures) viruses viruses are in the 0.002-0.2 micron size class

What determines viral abundance. Jessie Clasen et al What determines viral abundance? Jessie Clasen et al. 2008 Freshwater Biology 53: 1090 Same things that determine algal and bacterial abundance, but things work differently in lakes and the ocean