Production of polyhydroxybutyrate from wheat straw hydrolysate using a low-salt requiring and alkaliphilic Halomonas nigrificans X339 under non-sterile open condition

• A new isolate H. nigrificans X339 thrives in low salinity and high pH conditions. • X339 can utilize various carbon sources including lignocellulosic sugars. • X339 produced 5.11 g/L PHB from WSH under non-sterile open condition. • Genome sequencing of X339 reveals its key pathways for carbon source utilization. Utilizing agricultural waste is a sustainable approach to reduce the production cost of bio-based products. Here, we report a novel haloalkaliphilic strain, Halomonas nigrificans X339, which exhibits an exceptional ability to utilize various low-cost carbon sources. Compared to other halophiles, X339 could be cultivated at an optimal salinity as low as 2 % (w/v). X339 accumulated extraordinarily large granules of polyhydroxybutyrate (PHB). In open batch fermentation, X339 produced 5.11 g/L of PHB from wheat straw hydrolysate (WSH) at 3 % salinity and pH 9, with a PHB/carbon source conversion rate of 0.30 g/g. This represents the highest PHB yield reported from straw hydrolysates in shake-flask fermentation by halophiles. Additionally, whole genome of X339 was sequenced to identify candidate genes related to carbon source utilization. Our findings will benefit researchers in developing a suitable chassis for Next Generation Industrial Biotechnology, and offer a sustainable and eco-friendly solution for bio-based products.

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