- Volume 142, Issue 2, 1996

Summary: This paper reports the adaptation of Rhizobium leguminosarum bv. phaseoli to oxidative stress and the investigation of its overlap with other environmental stress responses. Treatment of R. leguminosarum bv. phaseoli cells with low concentrations of either menadione (MD, a superoxide generating agent) or 1-chloro-2,4-dinitrobenzene (CDNB, which depletes GSH levels) induced an adaptive response which resulted in cells becoming resistant to subsequent treatment with high concentrations of these oxidative stress compounds. There was overlap between the adaptive response to MD-generated superoxide stress and the response previously demonstrated in this organism to H2O2 (A. J. Crockford, G. A. Davis & H. D. Williams, 1995, Microbiology 141, 843-851); pretreatment with H2O2 was protective against cell killing by MD and vice versa. In contrast, similar experiments indicated only a limited overlap between the responses to H2O2 and CDNB-mediated GSH depletion. It was also found that H2O2, but not MD or CDNB, adaptation protected cells against subsequent osmotic challenge and heat shock. Carbon-starved cells were more resistant to H2O2 and MD killing than exponentially growing cultures, but were more sensitive to CDNB-mediated GSH depletion. Therefore, this work shows that there is a substantial, but incomplete overlap between the responses of R. leguminosarum to different forms of oxidative and other environmental stresses.

Summary: Our previous studies revealed that rsmA of Erwinia carotovora subsp. carotovora strain 71 suppressed the synthesis of the cell density (quorum) sensing signal N-(3-oxohexanoyl)-L-homoserine lactone, the production of extracellular enzymes and tissue macerating ability in soft-rotting Erwinia species and that homologues of this negative regulator gene were present in other Erwinia species. Northern blot data presented here demonstrate that rsmA and rsmA-like genes are also expressed in soft-rotting and non-soft-rotting Erwinia spp. such as E. amylovora, E. carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, E. carotovora subsp. carotovora, E. chrysanthemi, E. herbicola and E. stewartii. A low-copy plasmid carrying rsmA of E. carotovora subsp. carotovora strain 71 caused suppression of antibiotic production in E. carotovora subsp. betavasculorum, flagellum formation in E. carotovora subsp. carotovora, carotenoid production in E. herbicola and E. stewartii, and indigoidine production in E. chrysanthemi. In E. amylovora, rsmA of E. carotovora subsp. carotovora suppressed the elicitation of the hypersensitive reaction in tobacco leaves and the production of disease symptoms in apple shoots, in addition to repressing motility and extracellular polysaccharide production. We conclude that rsmA homologues function as global regulators of secondary metabolic pathways as well as factors controlling host interaction of Erwinia species.

Summary: As part of a larger taxonomic investigation of the genus Capnocytophaga, 50 strains, including reference strains as well as clinical isolates, were subjected to multilocus enzyme electrophoretic (MLEE) analysis of 12 intracellular metabolic enzymes and characterization of their immunoglobulin A1 (IgA1) proteases by enzyme-neutralizing antibodies raised in rabbits. The dendrogram derived from cluster analysis of the MLEE data discriminated between the five known human Capnocytophaga species and separated the strains into two major divisions. Division A comprised C. gingivalis and C. granulosa strains, and division B comprised C. ochracea, C. sputigena and C. haemolytica strains. Immunoglobulin A1 (IgA1) protease activity, a known feature of C. ochracea, C. sputigena and C. gingivalis, was present in all strains except the type strain of C. haemolytica and two clinical isolates. Inhibition typing of IgA1 proteases of all active strains with enzyme-neutralizing antibodies against protease preparations of the type strains of C. ochracea, C. sputigena and C. gingivalis separated the strains into two major groups identical to the two divisions based on the MLEE data. Thus, the IgA1 proteases of C. granulosa and C. gingivalis seemed to be antigenically similar to one another, and different from the IgA1 proteases of C. ochracea and C. sputigena, which had similar characteristics. The clustering of the clinical isolates based on the MLEE analyses, which was confirmed by the antigenic characterization of IgA1 proteases, was in good agreement with the results of previous studies.

Summary: We have constructed refined physical maps of the chromosome (1.82 Mb) and the large plasmid pTT27 (250 kb) of Thermus thermophilus HB27. A total of 49 cleavage sites with five restriction enzymes, EcoRI, SspI, MunI, EcoRV and ClaI, were determined on the maps. The location of 61 genes was determined by using as probes 64 genes cloned from T. thermophilus or other Thermus strains. Comparison of the genomic organization of the chromosomes of T. thermophilus HB27 and HB8 revealed that they were basically identical, but some genes were located in different regions. Among 32 genes whose locations were determined on both the HB27 and the HB8 chromosomes, the copy number of rpsL-rpsG-fus-tufA, the locations of glyS, pol, and one copy of nusG-rplK-rplA were different. The IS1000 sequence was located only in one region on the HB27 chromosome. In contrast, IS1000 sequences were scattered over four regions on the chromosome of HB8. As each region in which glyS, pol, or one copy of nusG-rplK-rplA are present also contained IS1000 in HB8, it is suggested that IS1000 may play an important role in genomic rearrangements in Thermus strains.