Gloeobacter violaceus: primitive reproductive scheme and its significance

Gloeobacter violaceus is a simple unicellular cyanobacterium believed to be basal to all cyanobacteria. It is unique among the cyanobacteria in various features, but most significantly in the absence of thylakoids and a circadian clock. We found additional features which support the basal status of the clade of G. violaceus in samples from a wet wall in a waterfall cave in central Mexico. We encountered a high morphological and morphometric variability in the populations studied. In trying to explain the reasons for this, we discovered that it can be attributed basically to two phenomena: a lack of synchronicity, circadian or other, in the cell cycles of the organisms; and the presence of a scheme with three simultaneous reproductive options. These two characteristics interfere with the development of a life cycle comparable to that found in other organisms. We coined the term reproductive routes for the alternative to a life cycle and discuss the consequences of having several routes instead of a cycle. Our results open avenues for studies to understand how the rest of the cyanobacteria acquired circadian clocks, organized life cycles and evolved complex regulating mechanisms.