Ulrich Szewzyk

In situ identification of Legionellaceae using 16s rRNA-targeted oligonucleotide probes and confocal laser scanning microscopy

Bacteria of the family Legionellaceae form a monophyletic group within the gamma-subclass of Proteobacteria. Based on comparative sequence analysis we constructed two oligonucleotide probes complementary to regions of 16S rRNA characteristic for Legionellaceae. Probe specificities were tested by whole-cell or dot-blot hybridization against 14 serogroups of Legionella pneumophila, 22 different Legionella spp. and 72 non-legionellae reference strains. Using optimized conditions both probes hybridized to all tested strains of L. pneumophila. Probes LEG226 and LEG705 hybridized to 71% and 90% of the Legionella species tested, respectively. With the exception of Methylomonas alba none of the non-target strains showed complete sequence homology within the target molecule. In a preliminary evaluation the results of classical techniques employing selective media, immunofluorescence and the probe assay were in good accordance for routine environmental and clinical isolates. L. pneumophila suspended in drinking water at approximately 10(3)-10(4) c.f.u. ml-1 could be rapidly detected by a combination of membrane filtration on polycarbonate filters and whole-cell hybridization. Even after incubation for 1 year a proportion of the released cells was still detectable. In situ hybridization also facilitated visualization of Legionella spp, cells in model biofilms. A combination of in situ hybridization and confocal laser scanning microscopy (CLSM) was used to analyse the three-dimensional arrangement of L. pneumophila within cells of the ciliated protozoan Tetrahymena pyriformis. Whole-cell probing with 16S rRNA-targeted oligonucleotides could, in the future, complement established techniques like immunofluorescence and PCR in ecological and epidemiological studies of Legionellaceae.

Neutrophilic Iron-Depositing Microorganisms

Neutrophilic iron-depositing microorganisms include various groups of bacteria, algae, and protozoa. The most striking feature of these microorganisms is their ability to precipitate ferric iron around their cells and colonies in many different forms. Growth of these microorganisms has various practical implications, for example, formation of iron ore in many parts of the world, aging of water wells, and clogging of drinking water pipes. Morphological description of many genera and species of iron-depositing bacteria by microscopy dates back to the nineteenth century, but only very few pure cultures of bacteria such as Leptothrix discophora and Gallionella ferruginea have been obtained in the last decades. Therefore, little has been known on the physiology or phylogeny of these bacteria.