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Ornithine decarboxylation (ODC) system of Shewanella baltica regulates putrescine production and acid resistance.

Shewanella baltica , as one of the dominant spoilers in seafoods where they encounter acidic environments during spoilage, can synthesize putrescine from ornithine and cause food spoilage as well as health problems. Here, the ornithine decarboxylation (ODC) pathway composed of ornithine decarboxylases SpeC and SpeF and an ornithine-putrescine transporter PotE were identified in S. baltica by database searches and further by molecular biology operations, and SpeC functioned as an auxiliary adjusting component of ODC system. Ornithine and putrescine were found to promote putrescine accumulation through up-regulating the expression of speF and potE rather than speC . In addition, increased putrescine biosynthesis and alkalization of cytoplasm was detected at acidic pH especially at pH 6.0 compared to neutral pH. Particularly, the maximum up-regulation of ODC genes and the optimum decarboxylation activity of SpeF were detected at acidic pH around 6.0. It's concluded that the ODC pathway plays dual roles in cytoplasmic acid counteraction and putrescine production of S. baltica . This study contributes to our understanding of the spoilage mechanism of spoilers in the food system, and provides a novel target for seafoods preservation.