Muddy rain transports large numbers of diverse microbes -

Abstract

Muddy rain is frequently observed in Lebanon, yet its biological roles are unexamined, and there are no reports describing its microbial biodiversity. It is known that rain and snow can be nucleated by bacteria, that desert dust is transported globally, that human and crop pathogens are transported by dust, and that microbial exchange between distant habitats is rapid relative to climate changes and evolution. Muddy rain may be an important means by which microbial biodiversity is exchanged, because microbes in muddy rain are exposed to less inactivating solar radiation and are deposited directly into soils and other rich ecologies. One can imagine that microbes have not only adapted to dispersal in dust and rain, but that they may facilitate the formation of dust and rain. This study investigates the microbial biodiversity in Beirut muddy rains. During 2011 and 2012, 23 rainfalls were collected, of which, 18 were distinctly muddy and contained observable DNA. Rainfalls were backtracked by HYSPLIT model (NOAA), indicating 14 North African sources and 4 Arabian Peninsular sources. DGGE revealed microbial diversity of the samples. Plasmid libraries of bacterial 16S and fungal 18S rDNA were constructed using PCR amplification. Sequences of isolated plasmids were analyzed by database comparison and yielded a total of 168 bacterial sequences; comprising, in decreasing order of relative abundance, Betaproteobacteria, Alphaproteobacteria, Firmicutes, Actinobacteria, Gammaproteobacteria-Bacteroidetes, Cyanobacteria, Epsilonproteobacteria, and Deltaproteobacteria. Thirty-five fungal sequences were found; 20 of which were Basidiomycota, 11 were Ascomycota, and 4 were uncultured eukaryotic clones. These results show that diverse active microbial communities are carried and dispersed via muddy rain.