Highly efficient conversion of lignin-derived aromatic compounds into polyhydroxyalkanoate using Halomonas hydrothermalis LL1

The efficient utilization of lignin-derived aromatic compounds (LDACs) remains one of the major challenges in lignin valorization and urgently requires attention. Most microorganisms are susceptible to the toxicity of LDACs, leading to insufficient conversion into the high-value-added product polyhydroxyalkanoate (PHA). In this study, an alkali-halophilic lignolytic bacterium, Halomonas hydrothermalis LL1, was isolated for its ability to efficiently convert LDACs into PHA. This strain exhibits strong robustness when grown in media containing various LDACs. It demonstrates optimal cell growth at LDAC concentrations as high as 15 mM, indicating a significantly higher tolerance compared to previously reported strains. Moreover, strain LL1 reduced the total organic carbon content of most tested LDACs by over 50 %. Different LDACs resulted in PHAs with varying characteristics and titers, with the highest titer of 945.33 mg/L obtained from vanillic acid. A non-aseptic fermentation process was further developed to enhance PHA production, achieving a maximum titer of 1044 mg/L. Furthermore, H. hydrothermalis LL1 efficiently converted laccase-pretreated lignin and alkaline-pretreated lignin into PHA, yielding 1.95 g/L (63.91 %) and 1.20 g/L (55.69 %), respectively. These results collectively demonstrate that H. hydrothermalis LL1 possesses high LDAC tolerance and efficient PHA-producing capability, highlighting its great potential for lignin valorization. • H. hydrothermalis LL1 displayed high tolerance and efficient degradation of LDACs. • Different LDACs were efficiently produced PHA of varying characteristics and titers. • Genome of H. hydrothermalis LL1 revealed the molecular mechanism of LDAC conversion. • Unsterile fermentation promoted PHA synthesis with the highest titer of 1044 mg/L. • H. hydrothermalis LL1 converted LPL and APL efficiently into PHA.