title: Lon protease of Azorhizobium caulinodans ORS571 is required for suppression of reb gene expression.
abstract: Bacterial Lon proteases play important roles in a variety of biological processes in addition to housekeeping functions. In this study, we focused on the Lon protease of Azorhizobium caulinodans, which can fix nitrogen both during free-living growth and in stem nodules of the legume Sesbania rostrata. The nitrogen fixation activity of an A. caulinodans lon mutant in the free-living state was not significantly different from that of the wild-type strain. However, the stem nodules formed by the lon mutant showed little or no nitrogen fixation activity. By microscopic analyses, two kinds of host cells were observed in the stem nodules formed by the lon mutant. One type has shrunken host cells containing a high density of bacteria, and the other type has oval or elongated host cells containing a low density or no bacteria. This phenotype is similar to a praR mutant highly expressing the reb genes. Quantitative reverse transcription-PCR analyses revealed that reb genes were also highly expressed in the lon mutant. Furthermore, a lon reb double mutant formed stem nodules showing higher nitrogen fixation activity than the lon mutant, and shrunken host cells were not observed in these stem nodules. These results suggest that Lon protease is required to suppress the expression of the reb genes and that high expression of reb genes in part causes aberrance in the A. caulinodans-S. rostrata symbiosis. In addition to the suppression of reb genes, it was found that Lon protease was involved in the regulation of exopolysaccharide production and autoagglutination of bacterial cells.
authors: Biotechnology Research Center, The University of Tokyo, Tokyo, Japan.
authors: Azusa
authors: A
authors: Nakajima
authors: Toshihiro
authors: T
authors: Aono
authors: Shuhei
authors: S
authors: Tsukada
authors: Lowela
authors: L
authors: Siarot
authors: Tetsuhiro
authors: T
authors: Ogawa
authors: Hiroshi
authors: H
authors: Oyaizu
mesh_terms: D020599:Azorhizobium caulinodans / Q000201:enzymology* / Q000235:genetics* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D009586:Nitrogen Fixation; D018547:Plant Stems / Q000382:microbiology; D049070:Protease La / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D049931:Sesbania / Q000382:microbiology / Q000502:physiology; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D049070:Protease La