Apparently, not much known about the genetic diversity of bacterial populations — or so I’ve heard. As a eukaryotic geneticist, I can say that we know a whole bunch about multicellular organisms — mostly because they’re a lot easier to see and catch, and they’re more like us than are prokaryotic relatives. A paper in the PNAS pipeline provides a meta-analysis (I think that’s the first time I’ve ever used that word) of bacterial diversity in different environments (see here for a short review).
More after the jump . . .
The authors found that the usual predictors of plant and animal diversity (temperature, latitude, etc) are not correlated with bacterial diversity. Instead, soil pH is a better predictor of the genetic diversity of bacteria in, well, the soil. As you go from neutral soils to more acidic soils, the number of different bacterial phylotypes decreases. This means that highly acidic soils — like those found in the Amazonian rainforest — have less species diversity than soils taken from a deciduous forest or desert (which have more neutral pH).
This is in contrast to the animal and plant diversity in these different habitats. The Amazon is known for its multicellular species richness; if you examine two adjacent square meters you are likely to find different species in each (both plant and animal). I have heard this is due to the high turnover of soil and nutrients, and the effects of rainfall leeching nutrients from the soil . . . or something like that. Anyway, drier habitats tend to be more homogeneous at the multicellular level. A grassland will have a lot of the same species spread out over vast distances, but, upon closer inspection, the microbial diversity is actually quite high in the soil (seemingly due to the more neutral pH).
Whereas in multicellular communities, similar species richness may be found in adjacent environments, the only good predictor of species diversity in soil ecosystems is the pH. It appears that there is something about the pH that influences the diversity of the bacterial communities within the soil.