Molecular phylogeny of the heterocystous cyanobacteria (subsections IV and V) based on nifD

Abstract

The heterocystous cyanobacteria are currently placed in subsections IV and V, which are distinguished by cellular division in one plane (false branching) and in more than one plane (true branching), respectively. Published phylogenies of 16S rRNA gene sequence data support the monophyly of the heterocystous cyanobacteria, with members of subsection V embedded within subsection IV. It has been postulated that members of subsection V arose from within subsection IV. Therefore, phylogenetic analysis of nucleotide sequences of the nitrogen-fixation gene nifD from representatives of subsections IV and V was performed by using maximum-likelihood criteria. The heterocystous cyanobacteria are supported as being monophyletic, with the non-heterocystous cyanobacteria as their closest relative. However, neither subsection IV nor subsection V is monophyletic, with representatives of both subsections intermixed in two sister clades. Analysis of nifD does not support recognition of two distinct subsections.Cyanobacteria are oxygenic, photosynthetic prokaryotes that can be found in almost every aquatic and terrestrial environment (Castenholz & Waterbury, 1989) and are ancient organisms that date back 3?5 billion years in the fossil record (Castenholz, 1992). It has been proposed that cyanobacteria were responsible for converting the ancient Earth's anaerobic atmosphere to an aerobic one (Hayes, 1983;Schopf et al., 1983). Many cyanobacteria fix nitrogen (diazotrophy) and they comprise one of the largest global suppliers of fixed nitrogen in the environment (Sprent & Sprent, 1990). In addition, some species of nitrogen-fixing cyanobacteria are involved in symbiotic relationships with many plant species and supply the host directly with a source of reduced nitrogen.The taxonomy of the cyanobacteria has been debated vigorously and revised many times (Golubic, 1976;Turner, 1997). The cyanobacteria have been reclassified by using bacteriological instead of botanical criteria, based on morphological and developmental features, but most species, including those used in this study, have not yet been given validly published names under the Bacteriological Code. Cyanobacteria are currently divided into five subsections (Rippka et al., 1979;Rippka, 1988;Castenholz & Waterbury, 1989;Castenholz, 1992Castenholz, , 2001Rippka & Herdman, 1992). Subsection I strains are unicellular and divide by binary fission or budding (Rippka et al., 1979). Subsection II strains are also unicellular but divide by multiple fission, resulting in the formation of baeocytes (Rippka et al., 1979;Rippka, 1988;Castenholz & Waterbury, 1989;Castenholz, 1992Castenholz, , 2001Rippka & Herdman, 1992). Subsection III strains are filamentous, non-heterocystous cyanobacteria that reproduce by trichome breakage (Rippka et al., 1979;Rippka, 1988;Castenholz & Waterbury, 1989;Castenholz, 1992Castenholz, , 2001Rippka & Herdman, 1992). Subsections IV and V are composed exclusively of heterocystous cyanobacteria, which are filamentous strains that reproduce by hormogonia formatio...

Phylogenetic and morphological evaluation of the genera Anabaena, Aphanizomenon, Trichormus and Nostoc (Nostocales, Cyanobacteria)

“…This monophyletic cluster contains the orders Nostocales and Stigonematales (Sections IV and V) (Rippka et al, 1979), which were found to be intermixed (Turner et al, 1997(Turner et al, , 1999Gugger & Hoffmann, 2004;Henson et al, 2004). However, the genera Anabaena Born.…”

“…Heterocytous cyanobacteria consistently form a monophyletic cluster among cyanobacteria on the basis of their 16S rRNA gene sequences (Wilmotte, 1994;Turner, 1997Turner, , 1999Wilmotte & Herdman, 2001;Lyra et al, 2001), RFLP and genomic fingerprinting (Lyra et al, 2001) and nifD sequences (Henson et al, 2004). This monophyletic cluster contains the orders Nostocales and Stigonematales (Sections IV and V) (Rippka et al, 1979), which were found to be intermixed (Turner et al, 1997(Turner et al, , 1999Gugger & Hoffmann, 2004;Henson et al, 2004).…”

Differential patterns of evolution and distribution of the symbiotic behaviour in nostocacean cyanobacteria

“…According to the International Code of Botanical Nomenclature, the genus Nostoc belongs to the order Nostocales and, in Bergey's Manual of Systematic Bacteriology, it is affiliated to subsection IV of Cyanobacteria (Rippka et al, 2001). In recent phylogenetic studies, using several molecular marker genes (small subunit rRNA, rpoB, rbcLX and nifD or nifH), the closest relatives to the genus Nostoc were shown to be the genera Anabaena, Aphanizomenon and Trichormus, also members of the family Nostocaceae (Rajaniemi et al, 2005;Svenning et al, 2005;Henson et al, 2002Henson et al, , 2004Lohtander et al, 2003). All members of the genus Nostoc are characterized by a complex life cycle that includes differentiation into heterocytes (nitrogen-fixing cells), akinetes (resting spores) and hormogonia (motile filaments), serving for dispersion and as infective units in symbiosis (Lazaroff, 1966;Lazaroff & Vishniac, 1961;Mollenhauer, 1970;Rippka et al, 1979).…”

Phylogenetic analysis of heterocystous cyanobacteria (Subsections IV and V) using highly iterated palindromes as molecular markers

“…Cyanobacteria, an ancient gram-negative photosynthetic group of prokaryotes, are one of the most ubiquitously found groups of microbial species on earth (Henson et al 2004). Evolutionary assessments of cyanobacteria have indicated towards a sluggish pace of evolution as indicated by the similarity of the present forms to the fossilized forms (Henson et al 2002).…”