We present data from a phylogenetic and molecular clock analysis of heterocystous cyanobacteria within the family Rivulariaceae, including the genera Calothrix, Rivularia, Gloeotrichia and Tolypothrix. APO866 research buy The strains were isolated from distant geographic regions including fresh and brackish water bodies, microbial mats from beach rock, microbialites, pebble beaches, plus PCC strains 7103 and 7504. Phylogenetic inferences (distance, likelihood and Bayesian) suggested the monophyly of genera

Calothrix and Rivularia. Molecular clock estimates indicate that Calothrix and Rivularia originated ∼1500 million years ago (MYA) ago and species date back to 400–300 MYA while Tolypothrix and Gloeotrichia are younger genera (600–400 MYA).

Cyanobacteria have evolved to become one of the most diverse groups of bacteria (Waterbury, 1991; Whitton & Potts, 2000; Castenholz, 2001). They contribute significantly to global primary production via photosynthesis and some contribute considerably to the nitrogen cycle via dinitrogen (N2) fixation. Genome-scale analyses suggest that oxygenic photosynthesis evolved early in the cyanobacterial radiation (Swingley et al., 2008). The capacity to use water as an electron donor in oxygenic photosynthesis, with its consequent generation of molecular oxygen, most likely appeared by 2700 million years ago (MYA) or earlier (Falcón et al., 2010). Nitrogen GSI-IX research buy fixation is restricted to Bacteria and Archaea, and is present throughout the cyanobacteria (albeit not in all species), that are among the ecologically most important nitrogen most fixers (Capone et al., 1997; Raymond et al., 2004). In contrast to photosynthesis, the capacity to fix nitrogen is a paraphyletic event within the cyanobacterial radiation (Swingley et al., 2008). The ‘patchy’ distribution of nitrogen fixation

in cyanobacteria has been inferred to be a result of lateral gene transfer and/or gene duplication (Swingley et al., 2008). The origin of nitrogen fixation among cyanobacteria is dated at 3000–2500 MYA (Shi & Falkowski, 2008; Falcón et al., 2010), and probably appeared three times independently (Swingley et al., 2008). Taxonomic classification has divided Cyanobacteria in five subsections/groups: (1) Order Chroococcales includes unicellular cells with binary reproduction; (2) Order Pleurocapsales includes unicellular cells with reproduction by multiple bipartition; (3) Order Oscillatoriales includes filamentous colonies without heterocysts and cell division in one plane; (4) Order Nostocales includes filamentous colonies that divide in one plane and include heterocysts; (5) Order Stigonematales includes filamentous colonies with heterocysts that divide in more than one plane (Rippka et al., 1979; Waterbury, 1991; Castenholz, 2001).