Isolation and Identification of PHA-Producing Haloalkaliphilic Bacteria from Bledug Kesongo Mud Volcano

Bledug Kesongo, a geothermal mud volcano in Indonesia, provides an extreme hypersaline and hyperalkaline environment that supports diverse haloalkaliphilic bacteria with potential for biopolymer production. This study explored the diversity of haloalkaliphilic bacteria inhabiting this site and evaluated their ability to synthesize polyhydroxyalcanoates (PHAs), intracellular polymers that serve as compatible solutes for osmotic balance. A total of 35 bacterial isolates were obtained, predominantly Gram-positive cocci exhibiting moderate halophicity and alkaliphicity. PHA screening revealed that 14 isolates were capable of accumulating PHAs, with isolates BK25 and BK30 showing the highest productivity, yielding 12.91±2.48% and 18.66±1.43% PHA content, respectively. Molecular identification based on 16S rRNA gene sequencing identified the isolates as Priestia flexa (BK25) and Bacillus flexus (BK30). These findings highlight Bledug Kesongo as a promising source of haloalkaliphilic bacteria with potential application in sustainable bioplastic production.