The Escherichia coli genes sspA and rnk can functionally replace the Pseudomonas aeruginosa alginate regulatory gene algR2

The algR2 (also known as algQ) gene of Pseudomonas aeruginosa has previously been identified as being necessary for alginate production at 37°C. We have cloned two genes, from a cosmid library of Escherichia coli, which can restore mucoidy to an algR2 mutant of P. aeruginosa. The complementing regions of both cosmids were localized by subcloning restriction fragments. One of the E. coli genes identified here has not previously been described; we have named this gene rnk (regulator of nucleoside diphosphate kinase). It encodes a 14.9 kDa protein with no homo-logy to any other protein. The other gene, sspA, is a regulator involved in stationary-phase regulation in E. coli. Either gene will restore mucoidy to an algR2-deficient strain of P. aeruginosa. AlgR2 has been shown to regulate at least two enzymes, succinyl-CoA synthetase (Scs) and nucleoside diphosphate kinase (Ndk), which form a complex in P. aeruginosa. When we examined the ability of the E. coli analogues to regulate Ndk, we found that rnk but not sspA was able to restore Ndk activity to the P. aeruginosa algR2 mutant. Furthermore, rnk was able to restore growth of the algR2 mutant in the presence of Tween 20, which inhibits other Ndk-like activities.