The enrichment of Rhizobium from a model system using immunomagnetic separation

Molecular assay to identifyAcetobacter diazotrophicusand detect its occurrence in plant tissues

The occurrence of Acetobacter diazotrophicus was directly demonstrated in plant tissues using a species-specific oligonucleotide probe and polymerase chain reaction (PCR) amplification of a 411-bp product. The oligonucleotide probe was derived from the sequence of a highly variable region of 23S rDNA and its specificity was tested with membrane-bound nucleic acids of 112 different microorganisms in hybridization experiments. It was found to be able to discriminate Acetobacter diazotrophicus from other Acetobacter spp. and other reference organisms. PCR amplification from pure cultured cells or colonies showed that the method was sensitive enough to detect as few as 200 cells in the reaction. The presence of Acetobacter diazotrophicus in tissues of micropropagated sugarcane plants inoculated with either this bacterium or a mixture of this bacterium and Herbaspirillum seropedicae was demonstrated by PCR amplification. Acetobacter diazotrophicus could also be detected by the PCR method in field-grown sugarcane plants, as well as in certain cultivars of Pennisetum purpureum Schumach but not in\i maize, sweet potato, and two samples of weed plants grown within or outside of a sugarcane field. The addition of 1% polyvinylpolypyrrolidone during preparation of the field samples, especially with root tissues, improved the amplificability of the target sequence. The minimum level of detection of this bacterium in sugarcane tissue using the universal 1440 and AD species-specific primers was about 105bacterial cells/g of fresh plant material. The sensitivity could be improved 10-fold by probing immobilized PCR products containing the target region with the32P-labeled oligonucleotide AD.Key words: Acetobacter diazotrophicus, diazotrophic endophytes, specific rRNA-targeting oligonucleotides, polymerase chain reaction (PCR).

The use of immunological methods to detect and identify bacteria in the environment

Immunological detection methods have become increasingly important in microbial ecology for the tracking of specific microorganisms and for community analysis. For a reliable application of these techniques, the monoclonal antibodies or polyclonal antisera used have to fulfill several quality criteria. Cross reactivity, cellular localization of the antigenic determinant, affinity characteristics and the expression of the antigenic determinant at environmental conditions have to be determined. Immunological methods can be used for the identification, quantification and enrichment of specific bacteria in extracts as well as for the visualization of cells in situ. The sensitivity of advanced immunological methods can be compared to PCR techniques. Using image processing of epifluorescence micrographs or confocal laser scanning microscopy, the immunofluorescence approach can now be applied to study complex environmental samples.