Phenotypic and genomic characterization provide new insights into adaptation to environmental stressors and biotechnological relevance of mangrove Alcaligenes faecalis D334.

Alcaligenes faecalis D334 was determined in this study as a salt-tolerant bacterium isolated from mangrove sediment. In response to 6% (w/v) NaCl, strain D334 produced the highest ectoines of 14.14 wt%. To understand adaptive features to mangrove environment, strain D334 was sequenced using Pacific BioScience platform, resulting in a circular chromosome of 4.23 Mb. Of note, D334 genome harbored 81 salt-responsive genes, among which two membrane-associated genes ompc and eric were absent in 3 selected A. faecalis genomes. Apart from that, a complete pathway for ectoine and 5-hydroxyectoine synthesis was predicted. To resist 40 mM HO, 46 genetic determinants contributing to oxidative stress response were employed. Moreover, two operons involved in polyhydroxyalkanoate (PHA) production were identified in the D334 genome, resulting in maximum PHA content of 5.03 ± 0.04 wt% and PHA concentration of 0.13 ± 0.001 g/L. A large flagellar biosynthesis operon contributing to swimming motility was found to be conserved in D334 and 8 other A. faecalis genomes. These findings shed light for the first time on the high versatility of A. faecalis D334 genome to adapt to mangrove lifestyle and the possibility to develop D334 as an industrial platform for PHA and 5-hydroxyectoine production.