Introduction
Bacteria in natural settings are constantly exposed to changing environmental conditions, and they must adapt to those changes in order to survive. Developing a phenotypically heterogeneous population is a strategy that bacteria utilize to increase their environmental fitness, and as a survival mechanism . This is due to the benefit for the population as a whole driven by cell-level phenotypic differences. Phenotypic heterogeneity can allow specific cells to survive sudden environmental changes that kill other members of the population. It can also lead to division of labour between individuals, which can increase the population’s growth rate and facilitate the development of new biological functions . In the last decade, the study of phenotypic heterogeneity among microbial populations and communities has become a major research focus, and new techniques and models are being generated to explore this facet of microbiology .
Bacillus subtilis is a Gram-positive non-pathogenic bacterium that has been studied for over a century in a wide range of topics , and has become a model organism for the study of bacterial differentiation, including community movement on semi-solid agar surfaces, swarming and sliding , sporulation , and biofilm formation . An interesting characteristic of B. subtilis, both under planktonic and biofilm conditions, is that its cells divide into discrete subpopulations, each with a different phenotype although all still possessing the same genotype . This phenotypic differentiation leads to division of labor or bet hedging, providing an important ecological advantage to this bacterium . In the following sections we address the role that the family of Rap phosphatases and their Phr peptides play in the regulation of B. subtilis phenotypic differentiation among Bacilli , their mechanism of action and structural functionality, as well as the ecological and genetic reasons that may explain their wide distribution in this genus.