A total of 63 strains of rhizobia isolated from Hainan Province, a tropical region of the People's Republic of China, and 27 representative strains belonging to the genera Rhizobium, Bradyrhizobium, and Agrobacterium were compared by performing numerical taxonomy, DNA hybridization, and DNA base composition analysis to determine the relationships among these rhizobia. The results indicated that the strains isolated from Hainan Province fell into two distinct phena, the slowly growing rhizobia and the fast-growing rhizobia. The slowly growing rhizobia, which formed three subphena that seemed to be three subspecies, are Bradyrhizobium japonicum strains. The fast-growing strains belong to the genus Rhizobium and might be further divided into three specific groups. Sometimes both slowly growing rhizobia and fast-growing rhizobia were isolated from host plants belonging to the same genus or species or even from the same nodule. There was no correlation between hosts and the distribution of rhizobia in the subphena. Isolates obtained from members of the same host genus or species fell into different groups or subgroups.The root nodule bacteria of tropical leguminous plants have been investigated by workers in many laboratories (1,(5)(6)(7)(8)10,23,25), but taxonomic studies of these bacteria have been sparse and have been limited to a few leguminous symbionts (16,19,24,27,28). Dreyfus and Dommergues (6) classified 13 Acacia species into three groups on the basis of effective nodulation with fast-growing and slowly growing tropical strains of rhizobia. The first group formed nodules effectively with slow growers; the second group formed effective nodules with fast growers; and the third group formed effective nodules with both fast and slow growers. Zhang et al. (27) obtained 12 clusters by using numerical taxonomy to study 97 strains isolated from root nodules of Acacia senagal, Prospopis chilensis, and other legumes. Thus, it is interesting to study the taxonomy of rhizobia isolated from a wide range of tropical legumes.In this work 63 rhizobial strains were isolated from various legumes, including trees, herbs, and vines, growing in different geographic regions of Hainan Province of the People's Republic of China, a tropical region south of latitude 20" N. These strains were compared with previously described species of rhizobia by performing numerical taxonomy, DNA composition, and DNA-DNA hybridization analysis. MATERIALS AND METHODSBacterial strains. A total of 90 strains were used in this study (Table 1); 27 of these strains were type and representative strains of Rhizobium, Bradyrhizobium, and Agrobacterium species, and 63 strains were isolated from root nodules collected in different geographic regions of Hainan Province. The purity of the cultures was assured by using single-colony isolates and checking colony morphology, bacterial morphology, and the Gram stain reaction. The identity of each strain was checked by performing a plant infection test with the original host plant.

Patients with Parkinson's disease (PD) often have non-motor symptoms related to gastrointestinal (GI) dysfunction, such as constipation and delayed gastric emptying, which manifest prior to the motor symptoms of PD. Increasing evidence indicates that changes in the composition of the gut microbiota may be related to the pathogenesis of PD. However, it is unclear how GI dysfunction occurs and how gut microbial dysbiosis is caused. We investigated whether a neurotoxin model of PD induced by chronic low doses of MPTP is capable of reproducing the clinical intestinal pathology of PD, as well as whether gut microbial dysbiosis accompanies this pathology. C57BL/6 male mice were administered 18 mg/kg MPTP twice per week for 5 weeks via intraperitoneal injection. GI function was assessed by measuring the 1-h stool frequency and fecal water content; motor function was assessed by pole tests; and tyrosine hydroxylase and alpha-synuclein expression were analyzed. Furthermore, the inflammation, intestinal barrier and composition of the gut microbiota were measured. We found that MPTP caused GI dysfunction and intestinal pathology prior to motor dysfunction. The composition of the gut microbiota was changed; in particular, the change in the abundance of Lachnospiraceae, Erysipelotrichaceae, Prevotellaceae, Clostridiales, Erysipelotrichales and Proteobacteria was significant. These results indicate that a chronic low-dose MPTP model can be used to evaluate the progression of intestinal pathology and gut microbiota dysbiosis in the early stage of PD, which may provide new insights into the pathogenesis of PD.

A novel Gram-stain-negative strain, designated ZYY5T, was isolated from rice roots. Results of 16S rRNA gene analysis indicated that strain ZYY5T was a member of the genus Dickeya , with a highest similarity to Dickeya zeae DSM 18068T (98.5%). The major fatty acids were summed feature 3 (C16:1 ω7c and/or C16:1 ω6c), C16:0 and summed feature 8 (C18:1 ω7c and/or C18:1 ω6c). Multi-locus sequence analysis using five concatenated genes (16S rRNA, atpD, infB, recA and gyrB) and phylogenomic analysis based on 2940 core gene sequences showed that strain ZYY5T formed a robust cluster with strains EC1, ZJU1202, DZ2Q, NCPPB 3531 and CSL RW192, while separated from the other strains of D. zeae . The orthologous average nucleotide identity (ANI) and digital DNA–DNAhybridization (dDDH) values among these six strains ranged from 96.8–99.9% and 73.7–99.8%, which supported that they were belonged to the same species. However, strain ZYY5T shared 58.4 of dDDH and 94.5% of ANI values with type strain D. zeae DSM 18068T, which were lower than the proposed species boundary cut-off for dDDH and ANI. The genomic analysis revealed that strain ZYY5T contained virulence-associated genes, which is same as the phylogenetic-related strains of the genus Dickeya . Based on the results of the polyphasic approaches, we propose that strain ZYY5T represents a novel species in the genus Dickeya , for which the name Dickeya oryzae sp. nov. (=JCM 33020 T=ACCC 61554 T) is proposed. Strains EC1, ZJU1202, DZ2Q, NCPPB 3531 and CSL RW192 should also be classified in the same genomospecies of D. oryzae same as ZYY5T.