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Research has been conducted on the dissimilatory iron-reducing bacteria. The use of microautoradiography and luorescence in situ hybridization for enumeration and phylogenetic characterization of these bacteria in activated sludge is described.

Comparative 16S rRNA and amoA sequence analysis was used to study the molecular diversity of ammonia-oxidizing bacteria. Using this technique, 122 amoA sequences from 11 nitrifying wastewater treatment plants showed the only nitrosomonads existed in most plants.

The performance of fluorescent in situ hybridization with rRNA-targeted oligonucleotide probes and microautoradiography for the identification and determination of substrate uptake patterns of individual microbial cells has been assessed. The method was tested using defined artificial mixtures of Escherichia coli and Herpetosiphon aurantiacus under aerobic conditions in the presence of (3H) glucose. Results indicate that the method can be used in identifying the uptake of labeled substrates for defined cell mixtures and activated sludge.

Four strains of filamentous bacteria that have been isolated from the slimes of paper mills have been studied by using a polyphasic approach. The isolates have physical characteristics similar to the Sphaerotilus species. However, the isolates differ from Sphaerotilus natans strains DSM 6575, DSM 565 and DSM 566 in their ability to metabolize complex polysaccharides, sugars, polyalcohols or organic acids as carbon sources. The isolates could be grown even at elevated temperatures of 40 degrees C. Their 16S ribosomal DNA sequences are similar to each other and with DSM 6575 and ATCC 15291.

In-situ hybridization has found increasing use in nucleic acid probes in studying the specific sequences of whole-fixed bacterial cells. The use of fluorescein-tyramide as a substrate for oligonucleotides labeled with horseradish peroxidase can improve the in situ hybridization of bacterial cells. Flow cytometry measurements show that the hybridized cells have a 10- to 20-fold signal amplifications.

The most important species of nitrifying bacteria present in activated sludge in an industrial sewage treatment plant has been identified. Bacterial diversity was studied through fluorescent in situ hybridization, sequence analysis of amoA gene sequences and characterization of the dominant ammonia oxidizer population. Results indicate that Nitrospira-like bacteria accounted to almost 9% of the total bacterial count and frequently existed in coaggregated microcolonies with Nitrosococcus mobilis.