Han Sung Ok, Yukawa Hideaki, Inui Masayuki, Doi Roy H
Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA.
J Bacteriol. 2003 Oct;185(20):6067-75. doi: 10.1128/JB.185.20.6067-6075.2003.
The regulation of expression of the genes encoding the cellulases and hemicellulases of Clostridium cellulovorans was studied at the mRNA level with cells grown under various culture conditions. A basic pattern of gene expression and of relative expression levels was obtained from cells grown in media containing poly-, di- or monomeric sugars. The cellulase (cbpA and engE) and hemicellulase (xynA) genes were coordinately expressed in medium containing cellobiose or cellulose. Growth in the presence of cellulose, xylan, and pectin gave rise to abundant expression of most genes (cbpA-exgS, engH, hbpA, manA, engM, engE, xynA, and/or pelA) studied. Moderate expression of cbpA, engH, manA, engE, and xynA was observed when cellobiose or fructose was used as the carbon source. Low levels of mRNA from cbpA, manA, engE, and xynA were observed with cells grown in lactose, mannose, and locust bean gum, and very little or no expression of cbpA, engH, manA, engE, and xynA was detected in glucose-, galactose-, maltose-, and sucrose-grown cells. The cbpA-exgS and engE genes were most frequently expressed under all conditions studied, whereas expression of xynA and pelA was more specifically induced at higher levels in xylan- or pectin-containing medium, respectively. Expression of the genes (cbpA, hbpA, manA, engM, and engE) was not observed in the presence of most soluble di- or monosaccharides such as glucose. These results support the hypotheses that there is coordinate expression of some cellulases and hemicellulases, that a catabolite repression type of mechanism regulates cellulase expression in rapidly growing cells, and that the presence of hemicelluloses has an effect on cellulose utilization by the cell.
在不同培养条件下培养的细胞中，在mRNA水平上研究了嗜纤维梭菌纤维素酶和半纤维素酶编码基因的表达调控。从在含有多糖、二糖或单糖的培养基中生长的细胞中获得了基因表达和相对表达水平的基本模式。纤维素酶（cbpA和engE）基因和半纤维素酶（xynA）基因在含有纤维二糖或纤维素的培养基中协同表达。在纤维素、木聚糖和果胶存在的情况下生长，会使所研究的大多数基因（cbpA-exgS、engH、hbpA、manA、engM、engE、xynA和/或pelA）大量表达。当以纤维二糖或果糖作为碳源时，观察到cbpA、engH、manA、engE和xynA的适度表达。在乳糖、甘露糖和刺槐豆胶中生长的细胞中，观察到cbpA、manA、engE和xynA的mRNA水平较低，而在葡萄糖、半乳糖、麦芽糖和蔗糖中生长的细胞中，未检测到cbpA、engH、manA、engE和xynA的表达或表达极少。在所有研究条件下，cbpA-exgS和engE基因最常表达，而xynA和pelA的表达分别在含木聚糖或果胶的培养基中更特异性地诱导至较高水平。在大多数可溶性二糖或单糖如葡萄糖存在的情况下，未观察到基因（cbpA、hbpA、manA、engM和engE）的表达。这些结果支持以下假设：一些纤维素酶和半纤维素酶存在协同表达；一种分解代谢物阻遏类型的机制调节快速生长细胞中纤维素酶的表达；半纤维素的存在对细胞利用纤维素有影响。
