Assessing Resource Partitioning in Marine Bacteria By Stable Isotope Probing

There is not much known about the mechanisms leading to microbial diversity in the ocean. In theory, all bacteria require similar constituents for biomass and there could be competition for resources. If this competition becomes extreme, competitive exclusion can occur where the “best” microbe wins. However, to compensate for this extreme competition, there also could be equalizing or stabilizing forces which will tend to minimize the fitness differences between species or increase intra-specific interactions relative to inter-specific interactions (Chesson ‘02). The purpose of this study is to examine whether equalizing mechanisms can be observed in samples of marine bacteria with respect to nitrogen, a macronutrient widely believed to be limiting in the oceanic environment. Specifically, we are testing if there is resource partitioning in coastal populations of microbes. That is, will marine bacteria utilize different nitrogen sources in the form of ammonia, nitrate, or urea when presented with all three in an incubation. In our experiments, stable isotope probing (SIP) methods are employed to determine which microbes(s) are actively using the various forms of nitrogen.