Moderately Halophilic Bacterial Diversity in Hypersaline Environments
Antonio VENTOSA*
Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Sevilla, 41012 Sevilla, Spain
Moderately halophilic bacteria are microorganisms which grow optimally in media containing 3 to 15% (wt/vol) salt. They are represented by a heterogeneous group of microorganisms included in many different genera. Although the first moderately halophilic species were isolated and characterized from salted foods, studies carried out during the last decades have permitted to determine their distribution in natural habitats, such as saline lakes and soils as well as marine or inland salterns.
While Gram-negative moderately halophilic bacteria have been studied in more detail, studies on Gram-positive species are more scarce. Recent studies carried out by our research group on Gram-positive moderate halophiles have permitted to clarify their taxonomic and phylogenetic position and to describe new species. Thus, the moderately halophilic Gram-positive coccus Nesterenkonia halobia (formerly Micrococcus halobius) was described on the basis of a single strain isolated from unrefined solar salt of unknown origin obtained from Noda, Japan. We have isolated six strains from ponds of salterns which show phenotypic and genotypic characteristics similar to those of N. halobia. Our data demonstrate quite clearly that they are members of this species and contribute to a better description of this moderately halophilic coccus. Similarly, a study of a large number of Gram-positive moderately halophilic rods which were able to produce endospores led us to describe a new species, designated Bacillus salexigens. Besides, other three phenons, obtained by numerical taxonomy analysis, with phenotypic features quite similar to those of this species, represent different genomovars, with very low DNA-DNA homology. Although they might represent new species, it should by necessary to determine new phenotypic features that permit to differentiate them from previously described Bacillus species.
