Supernatants of rhamnose-induced Erwinia chrysanthemi strain 3937 cultures contain a principal secreted protein named RhiE. A rhiE mutant has been found among a set of rhamnose-induced MudI1681 lacZ fusions. RhiE is a 62-kDa protein that has rhamnogalacturonate lyase activity on rhamnogalacturonan I (RG-I). It does not require a divalent cation for its activity and has an optimal pH of 6.0. rhiE expression is strongly induced in the presence of rhamnose but is also regulated by PecT and Crp, two regulators of the transcription of pectinolytic enzyme genes. RhiE is secreted through the type II Out secretion pathway. RhiE has no disulfide bond. The absence of RhiE secretion in a dsb mutant indicated that disulfide bond formation is required for the biogenesis of the secretion apparatus. RhiE was searched for in several E. chrysanthemi strains by using antibodies, and it was found to be present in one-third of the strains tested. However, the reduced virulence of the rhiE mutant indicates that degradation of the RG-I region of pectin is important for full virulence of E. chrysanthemi.Pectin is one of the main components present in plant cell walls. The pectin molecule can have three types of backbone: homogalacturonan, rhamnogalacturonan I (RG-I), and RG-II. Homogalacturonan (polygalacturonate [PGA]) is a polymer of galacturonic acid residues linked by ␣ 1-4 bonds which are partially methylated and acetylated. Homogalacturonan forms the smooth regions of pectin which are interspersed with hairy regions of RG-I and RG-II. RG-I has a backbone composed of as many as 100 repeats of the disaccharide ␣-L-rhamnose-␣-1,4-galacturonic acid. Side chains of arabinan or galactan are attached to O-4 of the rhamnosyl residues. RG-II is a complex polysaccharide with a short homogalacturonan backbone to which are linked side chains containing more than 10 different types of sugars (1).Plant-pathogenic microorganisms often secrete enzymes that are able to degrade the polysaccharides of cell walls in order to disorganize the plant tissue and obtain carbon sources for their growth. The enzymes that degrade the smooth regions of pectin have been extensively studied (26). The action of pectin methylesterases and of pectin acetylesterases liberates PGA. PGA is then degraded by pectate lyases or polygalacturonases that cleave either in an endo or in an exo mode. These enzymes have been characterized in bacteria as well in fungi. Much less is known about the enzymes degrading RG-I and RG-II. It seems that the presence of side chains prevents the degradation of the homogalacturonan backbone of RG-II by polygalacturonase and pectate lyases, and the debranching enzymes have not yet been characterized. Only a few enzymes that are able to cleave the RG-I backbone have so far been characterized, mostly in Aspergillus aculeatus. A rhamnogalacturonate lyase (18) cleaves inside the chain between a rhamnose and a galacturonate, creating an unsaturation on the galacturonate at the nonreducing end. A rhamnogalacturonate rhamnohydrolase (17) and a rha...

The Finnish C. hyointestinalis subsp. hyointestinalis strains are susceptible to a majority of the antimicrobials of veterinary importance. The mechanism of ciprofloxacin resistance at lower levels (< or = 32 mg/L) is not associated with a specific mutation in the quinolone resistance-determining region of the gyrA gene. Finally, there are distinct differences in the mechanisms of ciprofloxacin resistance compared with nalidixic acid resistance within the studied species.