The attachment of the cells of Pseudomonas syringae pv. atropurpurea NIAES 1309 onto the leaf surface of Italian ryegrass (Loium multiflorum Lam.) was analyzed by using two strains, wild-type strain (WT strain) and the strain containing the plasmid pBPW1:: Tn7 (pBPW1 strain), which gives the microbial cell surface a more negative charge and allows the microbes to attach more easily to inert surfaces. The leaf surface facing the ground (the dorsal side) was as hydrophobic as the Teflon membrane, whereas the surface facing the sky (the frontal side) had hydrophilicity intermediate between the Teflon and glass surface, i. e., the polar component of the surface tension of the frontal side of leaf was ca. half of that of a conventional glass slide. The cells were suspended in medium at various pHs and salt concentrations and allowed to be in contact with the leaf surfaces. In almost all medium conditions, more cells of both strains attached to the frontal side of the leaf than to the dorsal side. More pBPW1 cells attached at either surface of the leaf compared with the WT cells. Both strains showed the maximum cell attachment to the frontal side of the leaf around pH 5 to 6. The number of attached cells decreased under a high salt concentration (100mM). The pBPW1 cells attached more firmly to the leaf surface compared with WT cells, indicating a specific interaction between the cell surface and the leaf surface.
Survival of antibiotic resistant Bradyrhizobium japonicum (streptomycin, 200μg ml-1; spectinomycin, 200μg ml-1), Rhizobium leguminosarum (streptomycin, 100μg ml-1; spectinomycin, 100μg ml-1; rifampicin, 100μg ml-1) and Rhizobium meliloti (streptomycin, 200μg ml-1; spectinomycin, 200μg ml-1; rifampicin, 200μg ml-1) associated with the application of two commercially prepared composts, Bark and Tenporon, in an acid soil was investigated. Population changes were monitored using antibiotic media and the rhizobial number was enumerated by the plate count method. Populations of the three rhizobium strains generally decreased between 1 and 3 weeks and thereafter remained constant. The soil carrying capacity (asymptotic number of rhizobia reached) for the three rhizobium strains was significantly (p<0.05) elevated by Bark compost, but a significant (p<0.05) decrease for R. leguminosarum and R. meliloti was noted in the soils treated with Tenporon. The effects of these composts on extractable NH4+ and NO3-, fluorescein diacetic acid (FDA) hydrolytic activity and amount of Ca released were also examined. Addition of Tenporon compost resulted in a high amount of extractable NH4+ and NO3-. Bark did not affect them, although FDA hydrolytic activity was high. Both composts increased the amount of exchangeable Ca, however, the amount in the Bark-treated soil was higher than that of Tenporon. Investigation of the survival of the three rhizobium strains indicated that application of some organic materials can increase soil carrying capacity for rhizobia in acid soil for subsequent nodulation without liming.
Because of the importance of microorganisms as participants in ecosystems on the Earth, the International Union of Biological Sciences in cooperation with the international Union of Microbiological Societies have urged the initiation of a global diversity survey, provisionally called MICROBIAL DIVERSITY 21, aimed at the ultimate full identification of all species (10). The cataloguing of soil bacteria requires: 1) the estimation of microbial diversity in soil on a global scale; 2) the development of standard systems for sampling, identification and quantification of all known bacterial forms in any terrestrial habitat. The focus of our review is current taxonomic knowledge of soil inhabitants as a prerequisite for the inventory of microbial communities.