Differential expression of virulence genes and motility in Ralstonia (Pseudomonas) solanacearum during exponential growth
Differential expression of virulence genes and motility in Ralstonia (Pseudomonas) solanacearum during exponential growth
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DOI：
10.1128/aem.63.3.844-850.1997
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发表时间：
1997-03-01
影响因子：
4.4
通讯作者：
Denny, TP
中科院分区：
文献类型：
--
作者：
Clough, SJ;Flavier, AB;Denny, TP
青枯雷尔氏菌(原青枯假单胞菌)的毒力由一个复杂的网络调控；该系统的核心是PhcA，一种LysR型转录调节因子，我们在这里报道了两种PhcA调节的毒力因子，内切葡聚糖酶(Eg1)和酸性胞外多糖I(EPS I)，以及在分批培养的指数生长过程中表达的差异。在野生型遗传背景下与携带LacZ融合的菌株进行的测试表明，phcA的表达(以每个细胞为基础)保持不变，但EGL和epsB的表达在从1×10(7)到5×10(8)cfu/ml的增殖过程中增加了20-50倍，在EPS表达的调节级联中PhcA下游的中间调节因子xpsR的表达，随着细胞密度的增加，30%~50%的野生型细胞在10(7)~10(8)cfu/ml之间运动，但在10(9)cfu/ml时，这个群体又变得不活动。相比之下，phcB和phcA突变体中约60%的细胞在10(9)cfu/ml时保持运动。phcB的表达不受PhcA正调控，与epsB、EGL和xpsR相反(即，在高细胞密度时，它减少了20倍)。PhcB是产生胞外因子所必需的，暂定为3-OH PAME，它可能作为指数期信号激活毒力基因的运动或表达，然而，融合菌株在含有过量3-OH PAME的培养基中生长并不导致毒力基因在极低的细胞密度下运动或表达，这表明3-OH PAME不是控制这些特性的唯一因素。
A complex network regulates virulence in Ralstonia solanacearum (formerly Pseudomonas solanacearum); central to this system is PhcA, a LysR-type transcriptional regulator, We report here that two PhcA-regulated virulence factors, endoglucanase (Egl) and acidic exopolysaccharide I (EPS I), and motility are expressed differentially during exponential growth in batch cultures, Tests with strains carrying lacZ fusions in a wild-type genetic background revealed that expression (on a per-cell basis) of phcA was constant but expression of egl and epsB increased 20- to 50-fold during multiplication from 1 x 10(7) to 5 x 10(8) CFU/ml, Expression of xpsR, an intermediate regulator downstream of PhcA in the regulatory cascade for eps expression, was similar to that of epsB and egl, Motility track photography revealed that all strains were essentially nonmotile at 10(6) CFU/ml, As cell density increased, 30 to 50% of wild-type cells were motile between 10(7) and 10(8) CFU/ml, but this population was again nonmotile at 10(9) CFU/ml, In contrast, about 60% of the cells of phcB and phcA mutants remained motile at 10(9) CFU/ml. Expression of phcB which is not positively regulated by PhcA, was the inverse of epsB, egl, and xpsR (i.e., it decreased 20-fold at high cell density). PhcB is essential for production of an extracellular factor, tentatively identified as 3-hydroxypalmitic acid methyl ester (3-OH PAME), that might act as an exponential-phase signal to activate motility or expression of virulence genes, However, growth of the lacZ fusion strains in medium containing excess 3-OH PAME did not result in motility or expression of virulence genes at dramatically lower cell densities, suggesting that 3-OH PAME is not the only factor controlling these traits.