Kornacker M G, Boyd A, Pugsley A P, Plastow G S
Leicester Biocentre, University of Leicester, UK.
J Gen Microbiol. 1989 Feb;135(Pt 2):397-408. doi: 10.1099/00221287-135-2-397.
This study has shown that Klebsiella pneumoniae strain K21 differs from the previously characterized and closely related K. pneumoniae strain PAP996 in that expression of the pullulanase gene (pulA) and other genes of the maltose regulon is partially independent of exogenous inducer (maltose/maltotriose). Mutants of strain K21 which are defective in pullulanase synthesis and/or secretion were isolated following Tn10 mutagenesis. Three phenotypic classes of mutants were identified. Class I mutants were defective in the surface localization and secretion of pullulanase. Class II mutants did not secrete detectable levels of pullulanase but were able to export pullulanase to the cell surface. Class II mutants also expressed pullulanase and other maltose-regulated genes at markedly lower levels than those found in the parent strain under non-inducing conditions. The single class III mutant was intermediate between K21 and class I mutants; most of the cell-associated pullulanase was localized at the cell surface whilst a significant amount was secreted into the medium. Mapping indicated that all but three of the Tn10 insertions were adjacent to, and at either side of, pulA. One class II mutant carried a Tn10 insertion in or close to malT whereas in the remaining class II mutants the insertions were located at least 4 kb upstream of pulA in a region which may define a new regulatory locus of the maltose operon.
本研究表明，肺炎克雷伯菌K21菌株与先前鉴定的密切相关的肺炎克雷伯菌PAP996菌株不同，支链淀粉酶基因（pulA）和麦芽糖调节子的其他基因的表达部分独立于外源诱导物（麦芽糖/麦芽三糖）。通过Tn10诱变分离出支链淀粉酶合成和/或分泌有缺陷的K21菌株突变体。鉴定出三类表型突变体。I类突变体在支链淀粉酶的表面定位和分泌方面存在缺陷。II类突变体不分泌可检测水平的支链淀粉酶，但能够将支链淀粉酶输出到细胞表面。II类突变体在非诱导条件下表达支链淀粉酶和其他麦芽糖调节基因的水平也明显低于亲本菌株。唯一的III类突变体介于K21和I类突变体之间；大多数与细胞相关的支链淀粉酶定位于细胞表面，同时有大量分泌到培养基中。定位表明，除三个Tn10插入外，其余均与pulA相邻且位于其两侧。一个II类突变体在malT内或其附近有一个Tn10插入，而在其余II类突变体中，插入位于pulA上游至少4 kb的一个区域，该区域可能定义了麦芽糖操纵子的一个新调控位点。
