Novel green sulfur bacteria phylotypes detected in saline environments: ecophysiological characters versus phylogenetic taxonomy.

The taxonomic significance of salt tolerance or requirements in green sulfur bacteria has been analyzed with environmental populations and enrichment cultures from several saline systems (inland and coastal water bodies) with different salinities (salt composition and concentration). Novel phylotypes of green sulfur bacteria have been found in hypersaline and brackish environments and 16S rRNA gene sequence analysis affiliated them into phylogenetic groups in which neither halotolerant nor halophilic species have been known to date. Therefore, salt tolerance does not seem to be restricted to members of any specific subgroup but is widespread among all the different phylogenetic branches of the green sulfur bacteria group, and closely-related phylotypes can have dissimilar salt tolerance capacities. Thus the phenotypic characteristics and phylogenetic structure of the green sulfur bacteria present some incongruities. Phenotypic traits should be studied further in order to determine the ecophysiological features of green sulfur bacteria phylotypes.