Isolation of Halophilic and Halotolerant Bacterial Strains, Screening for Bioactive Compounds and Characterisation of Metabolites Produced by Pseudoalteromonas sp. ASV78.

Halophilic and halotolerant microorganisms are an important source of natural products. In this study, a collection of 150 bacterial isolates from a continental saltern (Añana Salt Valley, Spain) was obtained, identified and screened for the production of antimicrobial and/or surface-active compounds. The identification of the isolates showed the predominance of the Pseudomonadota phylum with 106 isolates (70.7%) classified under this taxon. Subsequent bioassays identified 20 antimicrobial producers and 14 isolates with the ability to both reduce surface tension and emulsify. One of them, namely, ASV78 was characterised in detail. Pseudoalteromonas sp. ASV78 showed simultaneous production of pentabromopseudilin and bromophene, with antibacterial activity, as well as glycolipids with the ability to reduce surface tension and glycoproteins with effective emulsifying properties. The low concentration of pentabromopseudilin (MIC values ranging from 0.02 to 0.04 μg/mL) at which it is effective against S. aureus ATCC 29213 was noteworthy, as was the compound's activity against other clinically relevant Gram-negative and Gram-positive bacteria. The presence of biosynthetic gene clusters (BGCs) in the genome of strain ASV78 that are not included among the known BGCs suggests the possibility that they encode unknown molecules. The applicability of the compounds synthesised by Pseudoalteromonas sp. ASV78 and the potential of the isolate collection require further investigation.