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BookmarkScienceDaily (Jan. 7, 2008) — Ecologists generally observe a positive relationship between sizes of predators and their prey, mainly because predators need to be large to eat a larger prey.
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But does this positive relationship hold for sizes of bacteria and their food molecules? Using a mathematical model, scientists at Michigan State University predict the opposite, an inverse relationship between sizes of bacteria and their resource molecules.
Theoretical biologists Kohei Yoshyama and Chris Klausmeier tweaked a model of bacterial growth in an aqueous medium to account for resource transport from medium to the cell surface by molecular diffusion together with biological uptake processes, and derived a negative relationship between sizes of resource molecule and bacterial cell that is most efficient in the resource competition.
They also showed that two bacterial consumers can coexist on two resources that are identical except for their sizes. This result implies that size differences of resource molecules, regardless of the quality, can promote microbial diversity.
"Theoretically, smaller cells are more favored under transport limitation for resource uptake than under limitations by biological processes, such as membrane uptake or catalysis within cells. As resource molecules become smaller, the molecular diffusion speeds up. And then the transport limitation for resource uptake is relaxed, and the optimal cell size becomes larger," states Kohei Yoshiyama, the study's leading author.
He adds, "Species diversity, at least at stable environments, is constrained by number of resources, which previously considered to be finite. Our results add a new dimension to the concept of 'resource', making the number of resources infinite."
The study "Optimal cell size for resource uptake in fluids: a new facet of resource competition" authored by Kohei Yoshiyama and Christopher A. Klausmeier (Michigan State University) was published in the January issue of the American Naturalist.
