Revision of the pantropical genus Brasilonema (Nostocales, Cyanobacteria), with the description of 24 species new to science

Abstract

<i>Brasilonema</i> was separated from <i>Scytonema</i> only in 2007 (Fiore et al. 2007). It possesses diagnostic morphological characteristics such as vacuole-like structures in older cells, frequent purple pigmentation of cells, rare false branching and fasciculate growth of filaments. Prior to this study, <i>Brasilonema</i> was always found attached to the substrate in subaerophytic habitats, exclusively in tropical-subtropical biomes (Brazil, Guadeloupe, Hawaii, Mexico). We have gathered 76 new <i>Brasilonema</i> strains from North, Central and South America, central Africa, South and East Asia and Europe, including specialized subaerophytic habitats in temperate climates, and applied a polyphasic approach to their species delineation. All taxa were first examined morphologically and subsequently their relationships were tested using the traditionally applied 16S rRNA gene sequence together with three additional markers (nifD, rpoC1, rbcLX). The results revealed close relationships between specimens obtained from very distant localities (different continents) as well as phylogenetic distance between single <i>Brasilonema</i> strains collected from the same biotope. Our results provide evidence that <i>Brasilonema</i>, although previously overlooked (or misidentified), is a morphologically easy genus to distinguish that is common over the world in tropical and subtropical regions with humid climate. It can be also found in tropical greenhouses, power-plant cooling towers and other microhabitats that mimic subtropical to tropical conditions in other climatic regions. We conclude that <i>Brasilonema</i> is a pantropical genus, there are few geographical constraints in <i>Brasilonema</i> dispersal, and its absence in natural habitats in temperate and polar climatic zones may be due to intolerance to desiccation or winter freezing.

Topics & Concepts