Patterns of microbial diversity along a salinity gradient in the Guerrero Negro solar saltern, Baja CA Sur, Mexico

Abstract

The goal of this study was to use environmental sequencing of 16S rRNA and bop genes to compare the diversity of planktonic bacteria and archaea across ponds with increasing salinity in the Exportadora de Sal (ESSA) evaporative saltern in Guerrero Negro, Baja CA S., Mexico. We hypothesized that diverse communities of heterotrophic bacteria and archaea would be found in the ESSA ponds, but that bacterial diversity would decrease relative to archaea at the highest salinities. Archaeal 16S rRNA diversity was higher in Ponds 11 and 12 (370 and 380 g l−1 total salts, respectively) compared to Pond 9 (180 g l−1 total salts). Both Pond 11 and 12 communities had high representation (47 and 45% of clones, respectively) by Haloquadratum walsbyi-like (99% similarity) lineages. The archaeal community in Pond 9 was dominated (79%) by a single uncultured phylotype with 99% similarity to sequences recovered from the Sfax saltern in Tunisia. This pattern was mirrored in bop gene diversity with greater numbers of highly supported phylotypes including many Haloquadratum-like sequences from the two highest salinity ponds. In Pond 9, most bop sequences, were not closely related to sequences in databases. Bacterial 16S rRNA diversity was higher than archaeal in both Pond 9 and Pond 12 samples, but not Pond 11, where a non-Salinibacter lineage within the Bacteroidetes >98% similar to environmental clones recovered from Lake Tuz in Turkey and a saltern in Chula Vista, CA was most abundant (69% of community). This OTU was also the most abundant in Pond 12, but only represented 14% of clones in the more diverse pond. The most abundant OTU in Pond 9 (33% of community) was 99% similar to an uncultured gammaproteobacterial clone from the Salton Sea. Results suggest that the communities of saltern bacteria and archaea vary even in ponds with similar salinity and further investigation into the ecology of diverse, uncultured halophile communities is warranted.

Phylogenetic analysis of the bacterial community in a crystallizer pond, Pomorie salterns, Bulgaria

“…The equal number of genera (15 each) represented in both archaeal [10] and bacterial communities from PS differs from the observations of other authors that members of the domain Archaea are dominant, whereas those of the domain Bacteria are slightly represented in hypersaline environments [4,[21][22][23][24]. Like our study, Dillon et al [22] have reported similar archaeal and bacterial 16S rRNA diversity (four genera each) in a hypersaline pond in evaporative Guerrero Negro salterns.…”

“…The unexpected high-number genera differed from the common opinion for low bacterial diversity in most of the hypersaline environments and domination of only one cluster [19,20] and determined this niche as belonging to saltern ecosystems with highest bacterial diversity. It was significantly higher than that observed by other authors in hypersaline salterns with higher than 30% salt content of the sampling site (Table 2): three bacterial genera have been established in Maras salterns, Peru [21]; five bacteral genera in a 32% salt pond, Santa Pola salterns, Spain [19]; four bacterial genera in 30% salt ponds, Guerrero Negro saltern, Mexico [22]; and five bacterial genera in the 31% salt pond S5 from a solar saltern in Tunisia [23]. The equal number of genera (15 each) represented in both archaeal [10] and bacterial communities from PS differs from the observations of other authors that members of the domain Archaea are dominant, whereas those of the domain Bacteria are slightly represented in hypersaline environments [4,[21][22][23][24].…”

“…Although sequences related to four cultured lineages from Gammaproteobacteria were retrieved in the PS clone library, representatives of the commonly cultivated genera Salicola and Halomonas [32] were not identified. Deltaproteobacterium OTU (PB-86) showed only modest similarity (96%) with an environmental clone found in the Guerrero Negro solar salterns [22] and was not closely related to cultured members of this subphylum (>15% similar to cultured Deltaproteobacterial species). Recovering of sulphate-reducing lineages from Deltaproteobacterium has been already reported for hypersaline environments [22,33].…”

“…The closest bacterial matches were recovered from 13 salt lakes or salterns without a clarified similarity to the community composition with clones from a certain niche. Among them, four bacterial OTUs showed the best match with clones from Guerrero Negro solar salterns, Baja CA Sur, Mexico [22]. Pomorie salterns and Guerrero Negro salterns have similar salinity (34%-38%); however, they differ in their very distant geographic locations and in the main cation present in the brine being Na C for PS and K C for Guerrero Negro salterns.…”

“…The uncultured Bacteroidetes lineage has been reported to comprise 69% of all bacterial 16S rRNA clones from Pond 11 in Guerrero Negro salterns [22] and 50% in the Chula Vista salterns [32]. Although Salinibacter has been found ubiquitously in numerous hypersaline environments [8,34], it was not identified in either PS or in Maras salterns [21].…”