Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A & M University, College Station, TX 77843-4467, USA.
BMC Microbiol. 2010 Jun 8;10:167. doi: 10.1186/1471-2180-10-167.
Quorum sensing is a communication system that regulates gene expression in response to population density and often regulates virulence determinants. Deletion of the luxR homologue vjbR highly attenuates intracellular survival of Brucella melitensis and has been interpreted to be an indication of a role for QS in Brucella infection. Confirmation for such a role was suggested, but not confirmed, by the demonstrated in vitro synthesis of an auto-inducer (AI) by Brucella cultures. In an effort to further delineate the role of VjbR to virulence and survival, gene expression under the control of VjbR and AI was characterized using microarray analysis.
Analyses of wildtype B. melitensis and isogenic DeltavjbR transciptomes, grown in the presence and absence of exogenous N-dodecanoyl homoserine lactone (C12-HSL), revealed a temporal pattern of gene regulation with variances detected at exponential and stationary growth phases. Comparison of VjbR and C12-HSL transcriptomes indicated the shared regulation of 127 genes with all but 3 genes inversely regulated, suggesting that C12-HSL functions via VjbR in this case to reverse gene expression at these loci. Additional analysis using a DeltavjbR mutant revealed that AHL also altered gene expression in the absence of VjbR, up-regulating expression of 48 genes and a luxR homologue blxR 93-fold at stationary growth phase. Gene expression alterations include previously un-described adhesins, proteases, antibiotic and toxin resistance genes, stress survival aids, transporters, membrane biogenesis genes, amino acid metabolism and transport, transcriptional regulators, energy production genes, and the previously reported fliF and virB operons.
VjbR and C12-HSL regulate expression of a large and diverse number of genes. Many genes identified as virulence factors in other bacterial pathogens were found to be differently expressed, suggesting an important contribution to intracellular survival of Brucella. From these data, we conclude that VjbR and C12-HSL contribute to virulence and survival by regulating expression of virulence mechanisms and thus controlling the ability of the bacteria to survive within the host cell. A likely scenario occurs via QS, however, operation of such a mechanism remains to be demonstrated.
群体感应是一种调节基因表达的通讯系统，它根据种群密度的变化而反应，通常调节毒力决定因子。缺失 luxR 同源物 vjbR 会极大地降低布鲁氏菌属细胞内的生存能力，这被解释为群体感应在布鲁氏菌属感染中的作用的一个迹象。虽然通过布鲁氏菌属培养物体外合成一种自体诱导物 (AI) 得到了证实，但并没有得到证实。为了进一步阐述 VjbR 对毒力和生存能力的作用，使用微阵列分析对 VjbR 和 AI 控制下的基因表达进行了表征。
分析野生型 B. melitensis 和同源缺失 vjbR 的转录组，在存在和不存在外源 N-十二酰基高丝氨酸内酯 (C12-HSL) 的情况下生长，显示出基因调控的时间模式，在指数和静止生长阶段检测到方差。VjbR 和 C12-HSL 转录组的比较表明，有 127 个基因受到共同调控，只有 3 个基因受到相反调控，这表明在这种情况下，C12-HSL 通过 VjbR 来逆转这些基因座的基因表达。使用 DeltavjbR 突变体的进一步分析表明，AHL 也会在没有 VjbR 的情况下改变基因表达，在静止生长阶段上调 48 个基因和 luxR 同源物 blxR 的表达 93 倍。基因表达的改变包括以前未描述的黏附素、蛋白酶、抗生素和毒素抗性基因、应激生存辅助物、转运体、膜生物发生基因、氨基酸代谢和运输、转录调节剂、能量产生基因以及以前报道的 fliF 和 virB 操纵子。
VjbR 和 C12-HSL 调节大量多样的基因表达。在其他细菌病原体中被鉴定为毒力因子的许多基因的表达情况不同，这表明它们对布鲁氏菌属细胞内的生存有重要贡献。根据这些数据，我们得出结论，VjbR 和 C12-HSL 通过调节毒力机制的表达来促进毒力和生存，从而控制细菌在宿主细胞内的生存能力。一种可能的情况是通过群体感应发生的，但是，这种机制的运作仍有待证明。
