%0 Journal Article
%T Comparative Assessment of Factors Involved in Acetoin Synthesis by Bacillus subtilis 168
%A Pratibha Sharma
%A Santosh Noronha
%J ISRN Microbiology
%D 2014
%R 10.1155/2014/578682
%X Acetoin is widely used as flavor agent and serves as a precursor for chemical synthesis. Here we focused on identifying the best physiological conditions (initial substrate concentrations, pH, temperature, and agitation) for enhanced acetoin accumulation by Bacillus subtilis 168. The optimal physiological conditions support maximum acetoin accumulation by minimizing byproduct (acetate and butanediol) synthesis and a maximum of 75% enhancement in acetoin yield could be achieved. Additionally, the effect of change in ALS (acetolactate synthase) and ALDC (acetolactate decarboxylase) activities was evaluated on acetoin accumulation. Increasing ALS and ALDC enzyme activities led to efficient utilization of pyruvate towards acetoin accumulation and about 80% enhancement in acetoin accumulation was observed. 1. Introduction Acetoin is a four-carbon hydroxy-keto compound that is secreted by various microorganisms when grown on glycolytic substrates. It is widely used in the food and dairy industry as a preservative [1]. Acetoin has two biological analogues, diacetyl and 2,3-butanediol. The ratio of these metabolites present depends on the culture redox potential [2]. Acetoin is a secondary carbon source synthesized during sporulation in various organisms such as Bacillus subtilis [3, 4], Klebsiella terrigena [5], and Pelobacter carbinolicus [6]. In Bacillus subtilis, acetoin synthesis involves alsSD operon that consists of alsS and alsD genes encoding for acetolactate synthase (ALS; E.C. 2.2.1.6) and acetolactate decarboxylase (ALDC; E.C. 4.1.1.5), respectively [3]. However, in Klebsiella and Pelobacter sp., a butanediol dehydrogenase (bdh) is integrated with alsSD operon that leads to production of 2,3-butanediol as major product instead of acetoin. Therefore, Bacillus subtilis is used as a model organism for study of acetoin synthesis. A number of factors can affect the fate of metabolites by diverse alternative metabolic pathways [7]. Among them, initial substrate concentration [8, 9], temperature [10], pH [11], and oxygen levels [12] are known to affect secondary metabolites production in Klebsiella and Pelobacter sp. To our knowledge, no report exists on the assessment of these physiological factors and activities of acetoin synthesis enzymes (ALS and ALDC) for acetoin accumulation by B. subtilis. Our current interest focuses on identification of important variables to enhance acetoin accumulation and minimizing byproduct formation. For this purpose, we focused on two effects. First, we focus on the systematic evaluation of physiological factors (initial
%U http://www.hindawi.com/journals/isrn.microbiology/2014/578682/