Journal Article

Transcriptome profile of carbon catabolite repression in an efficient l-(+)-lactic acid-producing bacterium Enterococcus mundtii QU25 grown in media with combinations of cellobiose, xylose, and glucose

Fujiwara, Haruko, Shiwa, Yuh, Zendo, Takeshi, Shimizu-Kadota, Mariko, Numaguchi, Mao, Tanaka, Naoto, Fujita, Nobuyuki, Sonomoto, Kenji, Abdel-Rahman, Mohamed Ali, Tashiro, Yukihiro, Nabeta, Keisuke, Kanesaki, Yu, Yoshikawa, Hirofumi

2020

Overview

Enterococcus mundtii QU25, a non-dairy lactic acid bacterium of the phylum Firmicutes, is capable of simultaneously fermenting cellobiose and xylose, and is described as a promising strain for the industrial production of optically pure l -lactic acid (≥ 99.9%) via homo-fermentation of lignocellulosic hydrolysates. Generally, Firmicutes bacteria show preferential consumption of sugar (usually glucose), termed carbon catabolite repression (CCR), while hampering the catabolism of other sugars. In our previous study, QU25 exhibited apparent CCR in a glucose-xylose mixture phenotypically, and transcriptional repression of the xylose operon encoding initial xylose metabolism genes, likely occurred in a CcpA-dependent manner. QU25 did not exhibit CCR phenotypically in a cellobiose-xylose mixture. The aim of the current study is to elucidate the transcriptional change associated with the simultaneous utilization of cellobiose and xylose. To this end, we performed RNA-seq analysis in the exponential growth phase of E . mundtii QU25 cells grown in glucose, cellobiose, and/or xylose as either sole or co-carbon sources. Our transcriptomic data showed that the xylose operon was weakly repressed in cells grown in a cellobiose-xylose mixture compared with that in cells grown in a glucose-xylose mixture. Furthermore, the gene expression of talC , the sole gene encoding transaldolase, is expected to be repressed by CcpA-mediated CCR. QU25 metabolized xylose without using transaldolase, which is necessary for homolactic fermentation from pentoses using the pentose-phosphate pathway. Hence, the metabolism of xylose in the presence of cellobiose by QU25 may have been due to 1) sufficient amounts of proteins encoded by the xylose operon genes for xylose metabolism despite of the slight repression of the operon, and 2) bypassing of the pentose-phosphate pathway without the TalC activity. Accordingly, we have determined the targets of genetic modification in QU25 to metabolize cellobiose, xylose and glucose simultaneously for application of the lactic fermentation from lignocellulosic hydrolysates.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Acids / Bacteria / Bacterial cultures / Bacterial Proteins - genetics / Bioengineering / Biology and Life Sciences / Biomass / Biotechnology / Carbohydrate metabolism / Carbon / Carbon sources / Catabolism / Catabolite Repression / Cellobiose / Cellobiose - metabolism / Chemical properties / Composition / Culture media / Culture Media - chemistry / Enterococcus / Enterococcus - genetics / Enterococcus - growth & development / Enterococcus - metabolism / Enterococcus mundtii / Fermentation / Firmicutes / Gene expression / Gene Expression Profiling - methods / Gene Expression Regulation, Bacterial / Gene silencing / Genes / Genetic aspects / Genetic modification / Genomes / Genomics / Glucose / Glucose - metabolism / Glucose-Xylose / Gram-positive bacteria / Hydrolysates / Industrial production / Kinases / Lactic acid / Lignocellulose / Metabolism / Methods / Microbial enzymes / Microbiological research / Milk free / Operon / Pentose / Phosphatase / Physical Sciences / Physiological aspects / Ribonucleic acid / RNA / Sequence Analysis, RNA / Sugar / Talc / Transaldolase / Transcription (Genetics) / Transcriptomics / Xylose / Xylose - metabolism