The omlA gene is involved in multidrug resistance and its expression is inhibited by coumarins in Xanthomonas campestris pv. phaseoli

Abstract

A gene encoding the outer membrane lipoprotein, OmlA, from the bacterial phytopathogen Xanthomonas campestris pv. phaseoli was isolated and characterized. An omlA insertion mutant showed an increased susceptibility to novobiocin and coumermycin, antibiotics with gyrase inhibitor activity. The omlA mutant accumulated novobiocin. Additionally, the omlA mutant was more sensitive than the wild type to chloramphenicol, a protein synthesis inhibitor; SDS, a detergent; and menadione, a superoxide generator. The susceptibility of the mutant to unrelated chemicals indicated a general role for OmlA in maintaining membrane integrity. Transcription of omlA was downregulated in the presence of both gyrase inhibitors, suggesting that DNA supercoiling might regulate the synthesis of OmlA. The omlA gene was divergently transcribed from the gene encoding the ferric uptake regulator Fur. Although the promoters of omlA and fur overlapped, Fur did not play any regulatory role in the expression of omlA due to the fact that inactivation of Fur did not affect the expression of omlA either in the presence or absence of iron. © 2007 Springer-Verlag.