Title: Isolation and identification of halophilic archaea with polysaccharide-converting enzyme potential from a Vietnamese solar saltern
Authors: Phan Thi Thuy Trang, Cao Thi Thuy Hang, Tran Ha Anh
Volume: 10
Issue: 9
Pages: 111-121
Publication Date: 2026/09/28
Abstract:
Solar salterns are the most accessible hypersaline habitats for the recovery of extremely halophilic archaea (haloarchaea), yet the culturable fraction of Vietnamese saltern communities has never been assigned taxonomically. Here the culturable haloarchaeal component of the Hon Khoi solar saltern (Khanh Hoa, Vietnam) was characterised and the previously reported polysaccharide-degrading isolate VS7M5.3 was placed phylogenetically. Four brine, microbial-mat and sediment samples spanning 165-340 g L?¹ total salts, pH 6.8-7.6, redox potential ?50 to +243 mV and in-situ temperatures of 36.5-60.2 °C were plated on modified growth medium containing 23% (w/v) salts and incubated at 40 °C for up to 30 days. Twenty-seven isolates were purified. Colonies were scored for pigmentation: 13 (48%) were unpigmented and 14 (52%) were yellow (9), orange (2), pink (2) or red-brown (1), a distribution consistent with the coexistence of moderately halophilic bacteria and carotenogenic haloarchaea. No isolate grew after transfer to media containing less than 20% (w/v) salts, identifying the collection as obligately halophilic. Five isolates were susceptible to anisomycin, and genomic DNA of adequate purity (A???/A??? 1.8-2.0) was recovered from four of them. Near-complete amplification of the 16S rRNA gene succeeded for VS7M5.3, whose 1,453-nucleotide sequence and neighbour-joining phylogeny placed it robustly within the genus Halorubrum but did not resolve it to species level, the closest relatives being Halorubrum luteum and Halorubrum aethiopicum. The strain is therefore designated Halorubrum sp. VS7M5.3. These results provide the first taxonomic anchor for a culturable, enzymatically active haloarchaeon from a Vietnamese saltern and delimit what single-gene data can establish in this recombination-prone genus.