The glutamate decarboxylase (Gad) system is an important amino acid-dependent acid resistance system commonly found in microorganisms. Actinobacillus succinogenes is one of the best natural producers of succinic acid (SA) but lacks glutamate decarboxylase. This study assessed the effects of Gad system introduction into A. succinogenes. The recombinant strains gadB-SW and gadBC-SW were constructed by heterologous expression of gadB alone, or gadB together with gadC, respectively. After 1.0 and 1.5 h of acid stress at pH 4.6, cell survival of gadBC-SW was greater than gadB-SW. The growth of gadB-SW and gadBC-SW was both affected by the expression of heterologous proteins and by γ-aminobutyric acid, with gadBC-SW growth reduced at a neutral pH. SA production in acidic conditions was evaluated by a shake flask and by 3-L bioreactor fermentation. The results showed gadBC-SW to increase SA production by 8.4% in shake flask compared to the parent strain, SW. For a 3-L bioreactor batch fermentation under acidic environment, the highest conversion rate of sugar to SA was observed for gadBC-SW, reaching 96%. However, SA concentration by gadBC-SW was only 47 g/L and 31 g/L at pH 6.5 and pH 6.0, respectively. In summary, the introduction of heterologous gadB and gadC into A. succinogenes not only improved acid tolerance but also influenced the synthesis of SA and added a metabolic burden.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.