Taxonomic resolution of the genus Cyanothece (Chroococcales, Cyanobacteria), with a treatment on Gloeothece and three new genera, Crocosphaera, Rippkaea, and Zehria

Abstract

The systematics of single‐celled cyanobacteria represents a major challenge due to morphological convergence and application of various taxonomic concepts. The genus Cyanothece is one of the most problematic cases, as the name has been applied to oval‐shaped coccoid cyanobacteria lacking sheaths with little regard to their phylogenetic position and details of morphology and ultrastructure. Hereby we analyze an extensive set of complementary genetic and phenotypic evidence to disentangle the relationships among these cyanobacteria. We provide diagnostic characters to separate the known genera Cyanothece, Gloeothece, and Aphanothece, and provide a valid description for Crocosphaera gen. nov. We describe two new genera, Rippkaea and Zehria, to characterize two distinct phylogenetic lineages outside the previously known genera. We further describe 13 new species in total including Cyanothece svehlovae, Gloeothece aequatorialis, G. aurea, G. bryophila, G. citriformis, G. reniformis, Gloeothece tonkinensis, G. verrucosa, Crocosphaera watsonii, C. subtropica, C. chwakensis, Rippkaea orientalis, and Zehria floridana to recognize the intrageneric diversity as rendered by polyphasic analysis. We discuss the close relationship of free‐living cyanobacteria from the Crocosphaera lineage to nitrogen‐fixing endosymbionts of marine algae. The current study includes several experimental strains (Crocosphaera and “Cyanothece”) important for the study of diazotrophy and the global oceanic nitrogen cycle, and provides evidence suggesting ancestral N2‐fixing capability in the chroococcalean lineage.

Two new Oculatella (Oculatellaceae, Cyanobacteria) species in soil crusts from tropical semi-arid uplands of México

“…Since that time, several authors have used the percent dissimilarity criterion to assist in defining species (Pietrasiak et al 2014;Bohunická et al 2015;Johansen et al 2017;Shalygin et al 2017;Vazquez-Martínez et al 2018;Mai et al 2018;Becerra-Absalón et al 2018;González-Resendiz et al 2018a, 2018bMareš et al 2019;Pietrasiak et al 2019). These authors all found a clear discontinuity between interspecies dissimilarity and intraspecies dissimilarity consistent with both Erwin & Thacker (2008) and Osorio-Santos et al (2014).…”

A bridge too far in naming species: a total evidence approach does not support recognition of four species in Desertifilum (Cyanobacteria)

“…Differences in secondary structure of conserved domains of the 16S-23S ITS region can be used as autapomorphies, but differences should be supported by other evidence, such as minor morphological differences, major ecological differences, or demonstrated differences in other genes. The most recent pragmatic criterion that has not yet failed to clearly separate species when intraspecies variation is known is the percent dissimilarity of aligned ITS regions in orthologous ribosomal operons (Erwin and Thacker 2008, Osorio-Santos et al 2014, Bohunick a et al 2015, Shalygin et al 2017, V azquez-Mart ınez et al 2018, Becerra-Absal on et al 2018, Gonz alez-Resendiz et al 2018b, Mai et al 2018, Mare s et al 2019. Phylogenetic analyses of aligned orthologous ITS regions can also be useful in demonstrating reciprocal monophyly within species (Perkerson et al 2011, V azquez-Mart ınez et al 2018).…”

The structure of the Moco carrier protein fromRippkaea orientalis

“…Thus, we selected a target gene from a cyanobacterium for further study, increasing the likelihood of selecting a genuine MCP. We chose the MCP homolog from the organism R. orientalis, a cyanobacterium belonging to the genus Rippkaea, a recently established phylogenetic lineage formerly assigned to the genus Cyanothece (Mareš et al, 2019). This putative MCP, referred to in the following as RoMCP, consists of 163 amino acids corresponding to a molecular weight of 17.1 kDa and shares 52.5% sequence identity with CrMCP.…”