On the evolution of bacterial multicellularity

Abstract

Multicellularity is one of the most prevalent evolutionary innovations and nowhere is this more apparent than in the bacterial world, which contains many examples of multicellular organisms in a surprising array of forms. Due to their experimental accessibility and the large and diverse genomic data available, bacteria enable us to probe fundamental aspects of the origins of multicellularity. Here we discuss examples of multicellular behaviors in bacteria, the selective pressures that may have led to their evolution, possible origins and intermediate stages, and whether the ubiquity of apparently convergent multicellular forms argues for its inevitability.

Figure 1

Hypothetical evolutionary paths from unicellular to multicellular lifestyles. A) Elaboration of a pre-existing sporulation pathway by insertion of aggregation and aerial structure formation between the stress sensing and spore development. B) Attachment to regions of high nutrients may have spurred the development of a protective matrix, forcing a communal existence. C) The SOS response pathway can induce filamentation independent of DNA damage, for example by the presence of a predator; co-option of the SOS pathway may have lead to a permanent filamentous lifestyle.