Tal­mu­dic Ques­tion #32

It seems to me that it has to be the ob­lig­ate anaer­o­bic respir­ers, no? If you ac­count for all the sub­sur­face ge­omi­cro­bi­ol­ogy (that peo­ple are just now ac­cess­ing), and the deep sea vent/deep sea sed­i­ment bugs, there is just a heck­uva lot of res­pi­ra­tion go­ing on based on in­or­ganic re­dox cy­cles. In spite of the gut mi­cro­bial den­sity, I think the sheer vol­ume of the more sparsely pop­u­lated biome out­weighs it. I won­der if we know enough about their bi­ol­ogy to be sure that they are all ob­lig­ate anaer­obes, though — we may just be imag­i­na­tion im­pov­er­ished when it comes to meth­ods for cul­tur­ing them, and we just blame on oxy­gen (an easy tar­get). I'm sure that many are true anaer­obes, but I think the over­all meta­bolic ca­pac­ity of en­vi­ron­men­tal mi­crobes is of­ten un­der­es­ti­mated, be­cause we of­ten study them based on en­rich­ment for in­ter­est­ing me­tab­o­lism. Be­cause of this, our as­sess­ment of meta­bolic ca­pac­ity is pos­si­bly too nar­row? I has­ten to add that I have a slight inkling of how hard it is to fig­ure out the meta­bolic path­ways even in rel­a­tively cul­ture-friendly bac­te­ria, so I know that tak­ing any bac­terium, even with a se­quenced genome, and fig­ur­ing out all it's meta­bolic tricks is a life­time of work! It's worth do­ing, though, be­cause you never know what you might find! (Of course get­ting a grant­ing agency to agree with my as­sess­ment may be a tougher sell)

I'd vote for the ob­lig­ate anaer­obes — oxy­gen is a lousy gas in terms of sol­u­bil­ity — so I sus­pect most niches will be lim­it­ing to some de­gree for oxy­gen. To spin Paul's com­ments a slightly dif­fer­ent way, per­haps given the fact that most of the di­ver­sity is (cur­rently) un­cul­tur­able, and that our meth­ods for de­tec­tion con­tinue to im­prove, per­haps the bugs we have yet to find are in the ma­jor­ity on Earth, mak­ing a novel meta­bolic liv­ing.