Reassessment of the cyanobacterial family Microchaetaceae and establishment of new families Tolypothrichaceae and Godleyaceae

Abstract

The family Microchaetaceae is a large group of heterocytous cyanobacteria, whose members bear typical morphological features of uniseriate heteropolar filaments never terminated by thin hairs and with simple false branching. However, phylogenetic analyses of the gene for 16S rRNA showed that members of this traditionally morphologically delimited family form several distant groups and therefore the current concept is hereafter indefensible. In this study, we provide reassessment of the status of the family Microchaetaceae based on morphology, ecology, biogeography, and phylogeny of 16S rRNA gene. Thorough examination of strains of the nominate genus Microchaete revealed their affiliation to two groups, Nostocaceae and Rivulariaceae, and their distant position to other traditional members of Microchaetaceae such as Tolypothrix, Hassallia, and Coleodesmium.To reflect the phylogenetic relationships and to accommodate members of the traditional family Microchaetaceae that are clearly not related to any of the Microchaete representatives, we propose establishment of two new families, Tolypothrichaceae and Godleyaceae. Based on both molecular and morphological evidence, we also provide a description of three new species of the genus Fortiea.

Roholtiella, gen. nov. (Nostocales, Cyanobacteria)—a tapering and branching cyanobacteria of the family Nostocaceae

“…The Nostocaceae has in the past been considered to lack forms that possess either tapering or false-branching and this historical morphological assumption is likely what has led to the misidentification of several of the strains in this subcluster. As recently shown by Hauer et al (2014) and also following from our phylogenetic analyses, the family Tolypothrichaceae and the typical genus Tolypothrix as well as the family Rivulariaceae and the genus Calothrix are genetically quite distant. Also M. diplosiphon CCALA 811 was recently found to not belong to Microchaete sensu stricto (Hauer et al 2014), although it was not placed in a different genus.…”

“…As recently shown by Hauer et al (2014) and also following from our phylogenetic analyses, the family Tolypothrichaceae and the typical genus Tolypothrix as well as the family Rivulariaceae and the genus Calothrix are genetically quite distant. Also M. diplosiphon CCALA 811 was recently found to not belong to Microchaete sensu stricto (Hauer et al 2014), although it was not placed in a different genus. One of the "Tolypothrix" strains, strain PCC 7415, which was deposited into the Pasteur Culture Collection as "Calothrix" was according to our results a species within Roholtiella.…”

“…In a broader study of the cyanobacterial types morphologically belonging to the traditional family Microchaetaceae (Hauer et al 2014), we encountered a group of genetically closely related strains characterized by morphological features not fully corresponding with any genus described thus far. The morphology of these strains varied throughout their life cycle.…”

“…Over the past century, characteristics such as tapering and false branching were thought to have evolved very seldom, and so most filaments that tapered were identified as Calothrix Agardh ex Bornet & Flahault (1886: 345) or Rivularia Agardh ex Bornet & Flahault (1887: 345), and false branching forms were commonly placed in either Tolypothrix Kützing ex Bornet & Flahault (1888a: 118) or Scytonema Agardh ex Bornet & Flahault (1888a: 85). When strains that were incorrectly assigned to these genera began to be sequenced (Rajaniemi et al 2005), it created a good deal of taxonomic confusion, some of which persists to the present (Hauer et al 2014).…”

Phylogenetic position reevaluation of Kyrtuthrix and description of a new species K. huatulcensis from Mexico´s Pacific coast

“…Not only are new species and genera being described, but new taxa are also being created as existing species are being transferred to different genera, families or orders with the advent of the polyphasic approach which incorporates morphological, ecological, and molecular data into our understanding of what constitutes cyanobacterial taxa (Komárek et al 2014). Molecular markers such as the 16S rRNA gene have been proven to give valuable information for comparing and helping to solve phylogenetic relationships at generic and family levels (Fiore et al 2007, Hauer et al 2014, Mareš et al 2015, and the characterization of the secondary structure of the 16S-23S (ITS) region has been useful in separation of morphologically similar species (Perkerson et al 2011, Osorio-Santos et al 2014, Bohunická et al 2015.…”