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The moderately halophilic bacterium Halomonas sp. QHL1 was identified as a member of the genus Halomonas by 16S rRNA gene sequencing. HPLC analysis showed that strain QHL1 synthesizes ectoine in its cytoplasm. The genes involved in the ectoine biosynthesis pathway were identified on the chromosome in the order ectABC. Subsequently, the ectB gene from this strain was amplified by PCR, and the entire ectABC gene cluster (3,580 bp) was cloned using genome walking. Analysis showed that the ectA (579 bp), ectB (1269 bp), and ectC (390 bp) genes were organized in a single transcriptional unit and were predicted to encode three peptides of 21.2 kDa, 46.4 kDa, and 14.7 kDa, respectively. Two putative promoters, a δ(70)-dependent promoter and a δ(38)-controlled promoter, as well as several conserved motifs with unknown function were identified. Individual ectA, ectB, and ectC genes, and the entire ectABC gene cluster were inserted into the expression plasmid pET-28a(+) to generate the recombinant plasmids pET-28a(+)-ectA, pET-28a(+)-ectB, pET-28a(+)-ectC and pET-28a(+)-ectABC, respectively. Heterologous expression of these proteins in Escherichia coli BL21 (DE3) was confirmed by SDS-PAGE. The recombinant E. coli strain BL21 (pET-28a (+)-ectABC) displayed a higher salt tolerance than native E. coli cells but produced far less ectoine than the wild-type QHL1 strain.

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Langaco Lake (LGL) is a strong Na2CO3-type lake that sits at an altitude of 4,548 m in the Qinghai-Tibet Plateau of China. LGL exhibits unique hydrochemical characteristics among Na2CO3-type lakes, but little is known about the microbial diversity of LGL and their interactions with environmental factors. Here, high-throughput sequencing of 16S rRNA genes revealed that LGL bacterial diversity comprised 327 genera in 24 phyla (4,871 operational taxonomic units [OTUs]; Shannon index values of 5.20–6.07) that represented significantly higher diversity than that of Archaea (eight phyla and 29 genera comprising 1,008 OTUs; Shannon index values of 2.98–3.30). The bacterial communities were dominated by Proteobacteria (42.79–53.70% relative abundances), followed by Bacteroidetes (11.13–15.18%), Planctomycetes (4.20–12.82%), Acidobacteria (5.91–9.50%), Actinobacteria (2.60–5.80%), and Verrucomicrobia (2.11–4.08%). Further, archaeal communities were dominated by Crenarchaeota (35.97–58.29%), Euryarchaeota (33.02–39.89%), and Woesearchaeota (6.50–21.57%). The dominant bacterial genus was Thiobacillus (8.92–16.78%), whose abundances were most correlated with total phosphorus (TP), pH, CO32− concentrations, and temperature. The most abundant archaeal genus was Methanoregula (21.40–28.29%), whose abundances were most highly correlated with TOC and TS in addition to the concentrations of K+, and Na+. Taken together, these results provide valuable insights towards a more comprehensive understanding of microbial diversity in these unique carbonate alkaline environments, in addition to a better understanding of microbial resources in the Qinghai-Tibet Plateau.