Three Lampropedia hyalina strains from different habitats were compared by phenotypic, chemotaxonomic and molecular characteristics. All strains form coccoid cells and have been reported to grow as square tablets of eight to 64 cells. However, two of these strains (ATCC 11041T and ATCC 43383) have apparently lost this ability, and the third strain may temporarily lose this capacity under certain cultivation conditions. The three strains showed only minor differences in metabolic characteristics: the main significant physiological difference was the ability to accumulate polyphosphate under alternating anaerobic-aerobic conditions found for DSM 15336. The three strains showed high similarity in fatty acid composition and only slight differences in the G+C content (63-67 mol%) and DNA-DNA reassociation (90-95% relatedness). Comparative 16S rRNA gene sequence analyses on these three strains and three Lampropedia hyalina 16S rRNA gene sequences deposited at NCBI showed that they are all very similar (> 98.8%) and that they form a distinct group among the 'Betaproteobacteria', showing between 94.6 and 93% 16S rRNA gene similarity to members of various genera such as Acidovorax, Aquaspirillum, Brachymonas, Comamonas, Delftia and Xenophilus. Fluorescent in situ hybridization with oligonucleotide probes targeting betaproteobacteria on the 16S rRNA and 23S rRNA gene level further supported the conclusion that all investigated strains are members of the 'Betaproteobacteria'. Two oligonucleotide probes were designed and successfully applied for culture-independent identification of Lampropedia hyalina by means of fluorescent in situ hybridization.
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