Kada Shigeki, Nanamiya Hideaki, Kawamura Fujio, Horinouchi Sueharu
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, 113-8657, Japan.
FEMS Microbiol Lett. 2004 Jul 1;236(1):13-20. doi: 10.1016/j.femsle.2004.05.028.
Poly-gamma-glutamate (gamma-PGA)-producing Bacillus subtilis contains two glutamate racemase genes, glr and yrpC, as does gamma-PGA-nonproducing B. subtilis strain 168. glr and yrpC on the chromosome of gamma-PGA-producing strain r22 were separately disrupted by means of gene replacement with an erythromycin resistance determinant. yrpC-disruption caused no effects on growth or gamma-PGA-production, whereas glr was disrupted only when an exogenous glr copy was present on a plasmid. In addition, the D-glutamate content of gamma-PGA produced by the yrpC-disruptant was the same as that produced by the parental strain r22. Glr in strain r22 is therefore responsible for the supply of D-glutamate to the synthesis of both peptidoglycan and gamma-PGA. Consistent with this idea, glr was transcribed actively during the exponential growth phase for peptidoglycan synthesis and continuously at a low, but distinct, level during the stationary phase for gamma-PGA production, whereas yrpC was transcribed at a very low level throughout growth. Phylogenetic analysis of glutamate racemases from eubacteria showed that YrpC is distinct from other glutamate racemases.
产聚γ-谷氨酸（γ-PGA）的枯草芽孢杆菌含有两个谷氨酸消旋酶基因，即glr和yrpC，不产γ-PGA的枯草芽孢杆菌168菌株也含有这两个基因。利用含红霉素抗性决定簇的基因置换法，分别破坏了产γ-PGA菌株r22染色体上的glr和yrpC。破坏yrpC对生长或γ-PGA的产生没有影响，而只有当质粒上存在外源glr拷贝时，glr才会被破坏。此外，yrpC破坏株产生的γ-PGA中D-谷氨酸含量与亲本菌株r22产生的相同。因此，菌株r22中的Glr负责为肽聚糖和γ-PGA的合成提供D-谷氨酸。与此观点一致的是，glr在肽聚糖合成的指数生长期活跃转录，而在γ-PGA产生的稳定期持续以低但明显的水平转录，而yrpC在整个生长过程中都以非常低的水平转录。对真细菌谷氨酸消旋酶的系统发育分析表明，YrpC与其他谷氨酸消旋酶不同。
