Phenotypic and genetic diversity within a colony morphotype.

Isolates showing different and similar colony morphologies were selected from spread plates of bacteria from seawater samples taken in the northern Adriatic Sea. All isolates were characterised by restriction fragment length polymorphism (RFLP) patterns of their PCR-amplified 16S rRNA gene and by 95 physiological tests (Biolog system). Cluster analysis of both genetic and phenotypic patterns showed that different colony morphotypes were related to different species or biotypes. However, isolates belonging to the more well-defined, conspicuous colony types had a high similarity, whereas those from the less conspicuous colony morphotypes showed high genetic diversity. Although colony morphotypes clearly underestimate taxonomic diversity, they can be used combined with PCR-RFLP analysis and as a preliminary approach for ecological studies aimed at the isolation of different species. Furthermore, for some species forming very conspicuous pigmented colonies, such as some photosynthetic aerobic bacteria, colony morphology may be useful for a rapid and low-cost screening of their distribution in the natural environment, especially when combined with other molecular techniques.

A New Sensitive, Whole-Cell Hybridization Technique for Detection of Bacteria Involving a Biotinylated Oligonucleotide Probe Targeting rRNA and Tyramide Signal Amplification.

A tyramide signal amplification system with biotinylated oligonucleotide probes and streptavidin-horseradish peroxidase was used to increase the sensitivity of fluorescent in situ hybridization techniques. When applied to both gram-negative and -positive bacteria immobilized on glass slides, a 7- to 12-fold amplification of the fluorescence signal was observed relative to that of cells hybridized with fluorescently monolabeled probes. A large proportion (62 to 78%) of bacteria could be detected under starvation conditions and in natural samples from the marine environment. This amplification procedure allows new investigations in marine oligotrophic ecosystems and water quality control.