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Abstract

Quorum sensing is usually thought of as a collective behavior in which
all members of a population partake. However, over the last decade,
several reports of phenotypic heterogeneity in quorum sensing-related
gene expression have been put forward, thus challenging this view. In
the respective systems, cells of isogenic populations did not contribute
equally to autoinducer production or target gene activation, and in some
cases, the fraction of contributing cells was modulated by environmental
factors. Here, we look into potential origins of these incidences and
into how initial cell-to-cell variations might be amplified to establish
distinct phenotypic heterogeneity. We furthermore discuss potential
functions heterogeneity in bacterial quorum sensing systems could serve:
as a preparation for environmental fluctuations (bet hedging), as a more
cost-effective way of producing public goods (division of labor), as a
loophole for genotypic cooperators when faced with noncontributing
mutants (cheat protection), or simply as a means to fine-tune the output
of the population as a whole (output modulation). We illustrate certain
aspects of these recent developments with the model organisms
Sinorhizobium meliloti, Sinorhizobium fredii and Bacillus subtilis,
which possess quorum sensing systems of different complexity, but all
show phenotypic heterogeneity therein. (C) 2019 Elsevier Ltd. All rights
reserved.