Isolation and Preliminary Characterization of Salt-Tolerant Polyhydroxyalkanoate-Producing Bacteria from the Hon Khoi Saltern, Khanh Hoa, Vietnam

Polyhydroxyalkanoates (PHAs) are biodegradable microbial polyesters that represent a promising sustainable alternative to petroleum-based plastics. Salterns, hypersaline environments, are recognized as significant sources of halotolerant microorganisms that can produce PHAs in high-salinity conditions; however, Vietnamese saltern ecosystems have not been extensively investigated. This research aimed to isolate and initially characterize salt-tolerant bacteria capable of synthesizing PHAs from the Hon Khoi saltern in Khanh Hoa province, Vietnam. A total of 37 halotolerant bacterial isolates were obtained, and potential PHA-producing strains were initially screened using Sudan Black B and Nile Blue A. TEM microscopy was then employed to confirm the existence of PHA granules. Furthermore, FTIR spectroscopy and GC–MS/MS spectrometry were utilized to analyze the chemical structure and monomer composition of the extracted polymers. Six isolates were identified as PHA-producing bacteria, including Salinivibrio sp. HK101 and HK116, Halomonas sp. HK105, Priestia sp. HK125 and HK142, and Bacillus sp. HK130. These strains exhibited growth across 3–10% NaCl and temperatures from 25 to 45 °C. Priestia sp. HK142 and Salinivibrio sp. HK101 exhibited the most substantial PHA accumulation, achieving 50.72 ± 1.83% and 42.07 ± 1.8% of DCW, respectively. These results indicate that the Hon Khoi saltern represents a promising source of halotolerant PHA-producing bacteria with potential relevance for future biopolymer production studies.