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Conzattia multiflora is a leguminous tree present only in Mexico and Guatemala. There is no record about its symbiotic or pathogenic microbes. In this study, we found that numerous bacteria with 104-106 individuals per gram of fresh epidermis were distributed in the tissue of this plant. All the bacteria isolated from the Conzattia epidermis were Gram-negative, facultative anaerobic rods and formed yellow or colorless colonies. They were identified as endophytes by inoculation tests. Some of the bacteria could significantly promote the growth of Conzattia seedlings. Nine different groups were defined by PCR-based RFLP, which were classified as Pantoea, Erwinia, Salmonella, Enterobacter, Citrobacter and Klebsiella by the phylogenetic analysis of 16S rRNA genes. The existence of plant-borne lineages of Salmonella indicates that the unexplored plants may harbor some unknown microbes. [ABSTRACT FROM AUTHOR]

Forty-six Mesorhizobium strains associated with the leguminous plants Leucaena leucocephala and Sesbania herbacea in an uncultivated Mexican field were characterized using a polyphasic approach. The strains were identified as Mesorhizobium plurifarium based upon the close relationships with the reference strains for this species in PCR-based restriction fragment length polymorphism analyses, sequencing of 16S rRNA genes, multilocus enzyme electrophoresis, and DNA-DNA hybridization. Although the strains isolated from both plants formed the same group in multilocus enzyme electrophoresis and cross-nodulations were observed in the laboratory, different electrophoretic types were obtained from the two plants grown in natural soils, indicating the existence of a preferable association between the plants and the rhizobia. The M. plurifarium strains from Mexico and the reference strains from Africa and Brazil formed different phenotypic clusters in a numerical taxonomy. The Mexican strains did not grow at 37 °C and were sensitive to salty-alkaline conditions, while the reference strains from Africa and Brazil grew at 42 °C and were more resistant to salty-alkaline conditions. These results demonstrate that both the plants and environmental factors affected the evolution of rhizobia and that the Mexican strains had adapted to the neutral soils and the cool climate where they were isolated. [ABSTRACT FROM AUTHOR]

Examines the genetic diversity of rhizobia from Leucaena leucocephala nodules in Mexico. Identification of rDNA types; Impact of soil cultivation on the soil populations of rhizobia; Differences in rhizobial populations in cultivated and uncultivated soils.