Gluconate metabolism and gas production by Paucilactobacillus wasatchensis WDC04

Abstract

Paucilactobacillus wasatchensis, a nonstarter lactic acid bacteria, can cause late gas production and splits and cracks in aging cheese when it metabolizes 6-carbon substrates, particularly galactose, to a 5-carbon sugar, resulting in the release of CO2. Previous studies have not explained late gas production in aging cheese when no galactose is present. Based on the genome sequence of Pa. wasatchensis WDC04, genes for potential metabolic pathways were mapped using knowledgebase predictive biology software. This metabolic modeling predicted Pa. wasatchensis WDC04 could metabolize gluconate. Gluconate contains 6 carbons, and Pa. wasatchensis WDC04 contains genes to convert it to 6-P-gluconate and then to ribulose-5-P by using 6-phosphogluconate dehydrogenase in a decarboxylating step, producing CO2 during its metabolism. The goal of this study was to determine if sodium gluconate, often added to cheese to reduce calcium lactate crystal formation, could be metabolized by Pa. wasatchensis WDC04, resulting in gas production. Carbohydrate-restricted DeMan, Rogosa, and Sharpe broth was mixed with varying ratios of ribose, sodium gluconate, or d-galactose (total added substrate content of 1% wt/vol). Oxyrase (Oxyrase Inc.; 1.8% vol/vol) was also used to mimic the anaerobic environment of cheese aging in selected tubes. Tubes were inoculated with a 4-d culture of Pa. wasatchensis WDCO4, and results were recorded over 8 d. When inoculated into carbohydrate-restricted DeMan, Rogosa, and Sharpe broth containing only sodium gluconate as the added substrate, Pa. wasatchensis WDC04 grew, confirming gluconate utilization. Of the 10 ratios used, Pa. wasatchensis WDC04 produced gas in 6 scenarios, with the most gas production resulting from the ratio of 100% sodium gluconate with no added ribose or galactose. It was confirmed that obligately heterofermentative nonstarter lactobacilli such as Pa. wasatchensis WDC04 can utilize sodium gluconate to produce CO2 gas. Addition of sodium gluconate to cheese thus becomes another risk factor for unwanted gas production and formation of slits and cracks.