RT-qPCR analysis of dexB and galE gene expression of Streptococcus alactolyticus in Astragalus membranaceus fermentation

Abstract

Streptococcus alactolyticus strain FGM, isolated from chicken cecum, was used to increase the extract yield of polysaccharides during Astragalus membranaceus fermentation. It was previously demonstrated that polysaccharides from fermented A. membranaceus by S. alactolyticus had some similar properties to those from A. membranaceus in terms of its ability to help heal hepatic fibrosis in rats and modulate immunopotentiation of broiler chicken. However, methods to increase the yield of the polysaccharides during fermentation of A. membranaceus are not well understood. In this paper, we investigated the involvement of uridine diphosphate (UDP)-glucose 4-epimerase (galE) and glucan-1,6-α-glucosidase (dexB) during A. membranaceus fermentation through real-time reverse transcription quantitative PCR. The galE and dexB genes of S. alactolyticus were cloned by homology-based cloning and the genome walking method for the first time, and the 3D structure of dexB was analyzed by Swiss-PdbViewer 4.0.1 software. The expression of both the galE and dexB genes in A. membranaceus fermentation was studied using the determined ideal reference gene ldh for transcript normalization. The results showed that these two genes were both highly induced and peaked after 12 h of fermentation. The expression level of galE was stepwise increased from 48 to 72 h, while dexB transcripts were markedly increased at 60 h and decreased by 72 h. These data suggested that dexB and galE of S. alactolyticus strain FGM were involved in the regulation of A. membranaceus fermentation and they might play some roles in the increase of polysaccharides.