Salt Stress Induces Imbalanced ADI Pathway Gene Expressions in Pediococcus acidilactici Drives Citrulline Accumulation as an Ethyl Carbamate Precursor in Soy Sauce

Abstract

Citrulline is the main precursor of a carcinogen compound ethyl carbamate (EC) in soy sauce. Accumulation of citrulline is mainly related to metabolism of arginine by Pediococcus acidilactici via the arginine deiminase (ADI) pathway during soy sauce fermentation. Elucidating the metabolic mechanism of ADI pathway that regulated by arc operon in P. acidilactici is essential for reduction of EC and its precursor in soy sauce. In this work, influences of pH, salt, ethanol and glucose on conversion of citrulline from arginine by P. acidilactici were investigated. Salt stress was the factor that most significantly influenced citrulline accumulation via the ADI pathway. Under salt stress, the ADI pathway in P. acidilactici exhibited a metabolic imbalance characterized by stronger inhibition of ornithine carbamoyltransferase (OTC) relative to arginine deiminase (ADI), directing substrate preferentially toward citrulline accumulation. Furthermore, the addition of ADI pathway activators (2, 4-dinitrophenol (DNP) and cyclic adenosine monophosphate (cAMP)) significantly increased arginine flux and suppressed intracellular citrulline accumulation; however, this inhibitory effect was abolished in the presence of 18% NaCl (w/v). These findings elucidate the mechanisms underlying the response of P. acidilactici to salt stress, revealing a dysregulation of the arc operon genes and key metabolic enzymes under high salt conditions. This insight provides a foundation for developing novel strategies to mitigate ethyl carbamate (EC) accumulation in soy sauce production.

Keywords

arginine deiminase pathway / citrulline / ethyl carbamate / Pediococcus acidilactici / soy sauce

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