Departamento de Radiobiología, Comisión Nacional de Energía Atómica, Avda. General Paz 1499, 1650 San Martín, Argentina.
Can J Microbiol. 2009 Nov;55(11):1284-93. doi: 10.1139/w09-086.
A transcriptional fusion (opgG1::MudJ) to the opgGH operon of Salmonella enterica serovar Typhimurium (S. Typhimurium) LT2, isolated by resistance to mecillinam, was used to study the influence of global regulators RpoS, ppGpp, and cAMP/cAMP-receptor protein (CRP) on expression of the opgGH operon and osmoregulated periplasmic glucan (OPG) content. Neither high growth medium osmolarity nor absence of ppGpp or CRP had important effects on opgG1::MudJ expression in exponential cultures. However, under the same conditions, OPG content was strongly decreased by high osmolarity or cAMP/CRP defectiveness, and reduced to a half by lack of ppGpp. In stationary cultures, high osmolarity as well as CRP loss caused significant descents in opgG1::MudJ expression that were compensated by inactivation of RpoS sigma factor. No effect of RpoS inactivation on OPG content was observed. It is concluded that opgGH expression in S. Typhimurium is only slightly affected by high osmolarity, but is inversely modulated by RpoS level. On the other hand, osmolarity and the cAMP/CRP global regulatory system appear to control OPG content, either directly or indirectly, mainly at the post-transcriptional level.
鼠伤寒沙门氏菌（S. Typhimurium）LT2 的 opgGH 操纵子的转录融合（opgG1::MudJ）对 mecillinam 抗性分离，用于研究全局调控因子 RpoS、ppGpp 和 cAMP/cAMP 受体蛋白 (CRP) 对 opgGH 操纵子表达和渗透压调节周质聚糖 (OPG) 含量的影响。高生长培养基渗透压或缺乏 ppGpp 或 CRP 对指数培养物中 opgG1::MudJ 表达没有重要影响。然而，在相同条件下，高渗透压或 cAMP/CRP 缺陷会强烈降低 OPG 含量，并使 OPG 含量降低至一半。在静止培养物中，高渗透压以及 CRP 缺失导致 opgG1::MudJ 表达显著下降，但 RpoS σ 因子失活可补偿这种下降。RpoS 失活对 OPG 含量没有影响。因此，鼠伤寒沙门氏菌中 opgGH 的表达仅受高渗透压轻微影响，但受 RpoS 水平的反向调节。另一方面，渗透压和 cAMP/CRP 全局调控系统似乎直接或间接主要在转录后水平控制 OPG 含量。
