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Abstract

Microorganisms possess diverse mechanisms to regulate investment into
individual cellular processes according to their environment. How these
regulatory strategies reflect the inherent trade-off between the benefit
and cost of resource investment remains largely unknown, particularly
for many cellular functions that are not immediately related to growth.
Here, we investigate regulation of motility and chemotaxis, one of the
most complex and costly bacterial behaviors, as a function of bacterial
growth rate. We show with experiment and theory that in poor nutritional
conditions, Escherichia coli increases its investment in motility in
proportion to the reproductive fitness advantage provided by the ability
to follow nutrient gradients. Since this growth-rate dependent
regulation of motility genes occurs even when nutrient gradients are
absent, we hypothesize that it reflects an anticipatory preallocation of
cellular resources. Notably, relative fitness benefit of chemotaxis
could be observed not only in the presence of imposed gradients of
secondary nutrients but also in initially homogeneous bacterial
cultures, suggesting that bacteria can generate local gradients of
carbon sources and excreted metabolites, and subsequently use chemotaxis
to enhance the utilization of these compounds. This interplay between
metabolite excretion and their chemotaxis-dependent reutilization is
likely to play an important general role in microbial communities.