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

Abstract

The heterocytous cyanobacteria form a monophyletic group according to 16S rRNA gene sequence data. Within this group, phylogenetic and morphological studies have shown that genera such as Anabaena and Aphanizomenon are intermixed. Moreover, the phylogeny of the genus Trichormus, which was recently separated from Anabaena, has not been investigated. The aim was to study the taxonomy of the genera Anabaena, Aphanizomenon, Nostoc and Trichormus belonging to the family Nostocaceae (subsection IV.I) by morphological and phylogenetic analyses of 16S rRNA gene, rpoB and rbcLX sequences. New strains were isolated to avoid identification problems caused by morphological changes of strains during cultivation. Morphological and phylogenetic data showed that benthic and planktic Anabaena strains were intermixed. In addition, the present study confirmed that Anabaena and Aphanizomenon strains were not monophyletic, as previously demonstrated. The evolutionary distances between the strains indicated that the planktic Anabaena and Aphanizomenon strains as well as five benthic Anabaena strains in cluster 1 could be assigned to a single genus. On the basis of the 16S rRNA, rpoB and rbcLX gene sequences, the Anabaena/Aphanizomenon strains (cluster 1) were divided into nine supported subclusters which could also be separated morphologically, and which therefore might represent different species. Trichormus strains were morphologically and phylogenetically heterogeneous and did not form a monophyletic cluster. These Trichormus strains, which were representatives of three distinct species, might actually belong to three genera according to the evolutionary distances. Nostoc strains were also heterogeneous and seemed to form a monophyletic cluster, which may contain more than one genus. It was found that certain morphological features were stable and could be used to separate different phylogenetic clusters. For example, the width and the length of akinetes were useful features for classification of the Anabaena/Aphanizomenon strains in cluster 1. This morphological and phylogenetic study with fresh isolates showed that the current classification of these anabaenoid genera needs to be revised.

Benthic cyanobacteria of the genus Nodularia are non-toxic, without gas vacuoles, able to glide and genetically more diverse than planktonic Nodularia

“…1E) in comparison to the oval, less numerous akinetes in N. spumigena. This result is in agreement with a recent morphological and phylogenetic study of various heterocytous filamentous cyanobacteria, such as Anabaena and Aphanizomenon, showing that shape, width and length of the akinetes were coherent with phylogenetic clustering (Rajaniemi et al, 2005). Strains of N. harveyana formed a separate group, which was more diverse (Figs 2, 3 and 4, Table 3).…”

“…The greater than 97 % similarity value does not necessarily guarantee that strains share a high degree of DNA-DNA reassociation and thus are closely related (Stackebrandt & Goebel, 1994). A recent study on the 16S rRNA gene of planktonic and benthic Anabaena showed that the two forms were intermixed and shared similarities as high as 99?2 % (Rajaniemi et al, 2005). However, the strains formed several distinct clades, possibly representing different species.…”

“…(Edwards et al, 1989) and B23S with PCR cycling as described by Lepère et al (2000). For amplification of over 500 bp of rpoB, primers (rpobF, rpoBR, rpoBF2 and rpoBR2) and PCR cycling conditions described by Rajaniemi et al (2005) were used. Region rbcLX (about 900 bp) was amplified with primers CW and DW and the PCR cycling conditions of Rudi et al (1998).…”

Phylogenetic evaluation of cyanobacteria preserved as historic herbarium exsiccata

“…The 16S rRNA gene sequence of Nostoc muscorum HUW 888 showed very high similarity (98?6 %) to the sequences published by Rajaniemi et al (2005) for Nostoc muscorum II and I. The 16S rRNA gene sequence of a strain affiliated to Nostoc muscorum CENA61 (GenBank accession no.…”

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

“…In the present study that focused on 12 heterocystous cyanobacterial genera and 41 cyanobacterial strains in total, the HIP primers and their resolution were found to be sufficient for estimating the phylogenetic relationships amongst heterocystous cyanobacteria. The dendrograms constructed using HIP fingerprints (HIP-AT, HIP-CA, HIP-GC, and HIP-TG) showed that the genus Nostoc was most genetically heterogeneous and advanced amongst all the 12 genera (Rajaniemi et al 2005;Svenning et al 2005;Willame et al 2006). One of the interesting features was the differential alignment of the strains Nostoc sp.…”