Abstract
Fructooligosaccharides (FOSs) metabolism in Lactobacillus plantarum is controlled by two gene clusters, and the global regulator catabolite control protein A (CcpA) may be involved in the regulation. To understand the mechanism, this study focused on the regulation relationships of CcpA toward target genes and the binding effects on the catabolite responsive element (cre). First, reverse transcription-PCR analysis of the transcriptional organization of the FOS-related gene clusters showed that they were organized in three independent polycistronic units. Diauxic growth, hierarchical utilization of carbohydrates and repression of FOS-related genes were observed in cultures containing FOS and glucose, suggesting carbon catabolite repression (CCR) control in FOS utilization. Knockout of ccpA gene eliminated these phenomena, indicating the principal role of this gene in CCR of FOS metabolism. Furthermore, six potential cre sites for CcpA binding were predicted in the regions of putative promoters of the two clusters. Direct binding was confirmed by electrophoretic mobility shift assays in vitro and chromatin immunoprecipitation in vivo. The results of the above studies suggest that CcpA is a vital regulator of FOS metabolism in L. plantarum and that CcpA-dependent CCR regulates FOS metabolism through the direct binding of CcpA toward the cre sites in the promoter regions of FOS-related clusters.
Highlights
Lactobacilli have complex nutritional requirements for fermentable carbohydrates and derive metabolic energy from homofermentative or heterofermentative carbohydrate fermentation (Gänzle and Follador, 2012)
To determine whether FOS metabolism in L. plantarum is regulated by catabolite control protein A (CcpA)-dependent carbon catabolite repression (CCR), the present study investigated the growth of L. plantarum and its mutant strains in chemically defined medium (CDM) medium containing FOS and limited glucose
Previous sequence analysis suggested that the FOS-related gene clusters of L. plantarum ST-III might be organized in polycistronic units (Chen et al, 2015)
Summary
Lactobacilli have complex nutritional requirements for fermentable carbohydrates and derive metabolic energy from homofermentative or heterofermentative carbohydrate fermentation (Gänzle and Follador, 2012). Lactobacilli seldom use different carbon sources simultaneously. Rather, they organize their carbohydrate utilization in a hierarchical manner to achieve maximal growth (Zeng et al, 2017). The presence of a preferred carbon source prevents the utilization of the secondary substrate until the more favorable carbon source is exhausted. This hierarchical phenomenon, which was first described in relation to glucose-lactose diauxie in Escherichia coli, has been termed carbon catabolite repression (CCR) (Jankovic and Brückner, 2007; Görke and Stülke, 2008).
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