If you were to try thinking of a model ‘lake’ bacterium you may consider using a Polynucleobacter spp.
Some taxonomy (if you are into that type of thing):
Phylum – Proteobacteria
Order – Burkholderiales
Family – Burkholderiaceae
Genus – Polynucleobacter
Members of the genus Polynucleobacter are considered ‘cosmopolitan’, at least in freshwater ecosystems. Common species in this genus are P. necessarius and P. cosmopolitanu. These organisms are globally widely distributed and chances are that next time you jump into your favorite lake or wade across your local stream you will cross paths with a member of this group. Along with their distribution, these organisms are also temporally variable and one study showed that their relative abundance can fluctuate from 4 – >50% of the total microbial community (Hahn et al., 2005 AEM). However, in some Michigan lakes the abundance of this group is <1% showing that there is large spatial variability too (unpublished). Despite this, none would disagree that this group of organisms is fascinating.
In my opinion, the species P. necessariusmay be one of the more interesting in this group (see image below from Bergey’s Manual® of Systematic Bacteriology: Volume Two The Proteobacteria Part C The Alpha-, Beta-, Delta-, and Epsilonproteobacteria). For some time we have known that P. necessarius is an endosymbiont of ciliates (specifically Euplotes spp.). In addition, this interaction is known to be an obligate symbiosis and ciliates that are cleared of their endosymbiont die soon there after. Furthermore, P. necessarius has been implicated as the agent responsible for mate killing among these ciliates. Why does this interaction exist? How did it come to be? If you weren’t captivated by the spatial and temporally variability, I bet you are now.
Feel free to share your thoughts or do a little research of your own (via the web of course).