Concluding remarks
The efficiency of bacterial adaptation depends on the regulatory pathways that enable the cell to sense and respond to the external environment, that encompasses both abiotic and biotic factors. Biotic factors include the bacterial population itself and its density.Bacilli evolved to integrate population density using the Rap-Phr quorum sensing pathways that eventually diverged to modulate distinct, but partly overlapping, regulatory systems in the bacteria. Systemic dissection of the Rap-Phr systems (i.e. single- and multiple-deletions of the casettes) in different Bacillus species under diverse conditions, including their natural environments, will reveal their impact on the ecology of this group of microorganisms.