Abstract
Twelve strains of Leptolyngbya-like filaments were isolated from biological soil crust samples from two localities in the Central Region of Mexico. The strains were morphologically distinguished from most Synechococcalean species by the obligate presence of a blackish sheath. Phylogenetic analysis based on 16S rRNA gene sequence placed all strains into a strongly supported single clade sister to Scytolyngbya. The genetic identity between our strains and all other Synechococcales, including Scytolyngbya, was less than 95%, and the strains were further distinguished by morphology and terrestrial ecology. The conserved domains of the 16S-23S ITS region had secondary structures distinct from all other closely related genera, which included Scytolyngbya, Stenomitos, Chamaethrix, and Pantanalinema. Based on the combination of morphological, molecular, and ecological evidence, we here describe two species: Chroakolemma opaca gen. et sp. nov. and C. pellucida gen. et sp. nov. Based on the ability to form blackish sheaths, these two species are morphologically similar to Leptolyngbya edaphica, Chamaethrix vaginata and Trichocoleus badius. The latter two species have been sequenced and are phylogenetically distant from Chroakolemma. Leptolyngbya edaphica is a soil species described from Russia and shares other morphological similarities with Chroakolemma, including wide sheaths, coiled filaments, pale blue-green trichomes, and constricted cross-walls. We consider these characteristics diagnostic of Chroakolemma, and accordingly propose Chroakolemma edaphica comb. nov.
Highlights
Cyanobacterial classification has undergone rapid revision based upon use of a polyphasic approach to define new taxa and molecular characterization of classical taxa (Komárek et al 2014, Mareš 2017)
The first locality was near to Actopan, Hidalgo state within the Mezquital Valley with mean annual precipitation (MAP) of 436 mm, mean annual temperature (MAT) of 16.4°C, with soil type being a Feozem (Mollisol), and a xeric savanna-like scrub vegetation dominated by Prosopsis Linnaeus (1767: 68) spp. (Mesquite shrubs and trees) with crassiculate plants
The second site was around the crater lake of San Luis Atexcac (L.A), Puebla state, with MAP of 372 mmm, MAT of 13.9°C, soil type Feozem, and xeric vegetation dominated by Yucca Linnaeus (1753: 47) and other Agavoideae
Summary
Cyanobacterial classification has undergone rapid revision based upon use of a polyphasic approach to define new taxa and molecular characterization of classical taxa (Komárek et al 2014, Mareš 2017). Numerous new genera have been recognized based primarily on molecular phylogenetic evidence with supporting ecological and morphological characterization. The type genus of the Leptolyngbyaceae, Leptolyngbya Anagnostidis & Komárek (1988: 390), has been very problematic as it has been broadly circumscribed both morphologically and ecologically, and has few synapomorphies that define it. After molecular data showed that they were phylogenetically distinct from the clade containing the generitype were they placed in other genera, resulting in taxonomy that more accurately reflects evolutionary history. This group is difficult and revisionary work as well as α-level taxonomy still remains to be conducted
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