R. M. Kroppenstedt

The genus Nocardiopsis was shown to be phylogenetically coherent and to represent a distinct lineage within the radiation of the order Actinomycetales. The closest relatives of the genus Nocardiopsis are members of the genera Actinomadura, Thermomonospora, Streptosporangium, and Microtetraspora. The intrageneric structure of the genus Nocardiopsis is shown to consist of a highly related species group containing Nocardiopsis dassonvillei, Nocardiopsis alborubida, and Nocardiopsis antarctica and a second group of less highly related species comprising Nocardiopsis alba subsp. alba, Nocardiopsis alba subsp. prasina, and Nocardiopsis listeri. Nocardiopsis lucentensis occupies a position intermediate between the two species groups. The results of a 16S ribosomal DNA sequence analysis are generally consistent with the available chemotaxonomic, phenotypic, and DNA-DNA hybridization data. The phylogenetic position and the morpho- and chemotaxonomic properties of Nocardiopsis species support the creation of a family for the genus Nocardiopsis, Nocardiopsaceae fam. nov.

Eight hundred and twenty-one strains of the genera Streptomyces and Streptoverticillium were physiologically characterized using a total of 329 miniaturized tests. Overall similarities of all strains were determined by numerical taxonomic techniques using the UPGMA algorithm and the SSM and the S J coefficients as measures of similarity. Test error was within acceptable limits. Comparison of photometric and visual test reading revealed overall differences of 7·45%. A total of 15 major clusters (six or more strains), 34 minor clusters (less than six strains) and 40 single-member clusters were defined at the 81.5% similarity level (S SM). Two clusters containing physiologically, and in some cases morphologically and genetically, different groups could be further subdivided at the 84·0% similarity level (S SM). Generally, similar groupings were obtained with the Jaccard coefficient at similarity levels ranging from 59·6% to 64·6% similarity (S J), with changes in the definition of clusters and subclusters. The cophenetic correlation coefficients r CS for the UPGMA/S J and the UPGMA/S sm analysis were 0·6929 and 0·8239, respectively. Several phena showed significant overlap with others, indicating the physiological variability within the species. The phenetic data in most cases confirm the major phena of the study of Williams et al. (1983), Journal of General Microbiology 129, 1743-1813 (although the cluster-groups defined in that study could only be detected in part) and the results indicate that the genus Streptomyces is still overspeciated. Some of the major groupings obtained were very much in line with chemotaxonomic and genetical data. However, several clusters containing only a few strains should be regarded as preliminary ‘species’ until further information is available. The majority of Streptoverticillium strains presently assigned to different species formed a homogeneous subcluster defined at the 84·0% similarity level (S SM). Thus, on the basis of numerical phenetic and (published) molecular genetic and chemotaxonomic data, our study supports the suggestion that members of the genus Streptoverticillium be reclassified into the genus Streptomyces.

Using natural rubber latex as the sole source of carbon and energy 50 rubber-degrading bacteria were isolated. Out of those 50 isolates, 33 were identified as Streptomyces species and 8 as Micromonospora species. Screening of 1220 bacteria obtained from different culture collections revealed 46 additional rubber-degrading bacteria (Streptomyces 31 strains, Micromonospora 5, Actinoplanes 3, Nocardia 2, Dactylosporangium 1, Actinomadura 1, unidentified 3). All rubber-degrading isolates were identified as members of the actinomycetes, a large group of mycelium-forming Gram-positive bacteria. Interestingly no Gram-negative bacterium could be isolated. In most strains expression of extracellular rubber-degrading enzymes was repressed by glucose and/or succinate. The reduction of the average molecular mass of solution-cast films of natural rubber from 640000 to 25000 in liquid culture upon bacterial growth indicates the participation of an endo-cleavage mechanism of degradation.

Lipoproteins are a subgroup of secreted bacterial proteins characterized by a lipidated N-terminus, processing of which is mediated by the consecutive activity of prolipoprotein diacylglyceryl transferase (Lgt) and lipoprotein signal peptidase (LspA). The study of LspA function has been limited mainly to non-pathogenic microorganisms. To study a potential role for LspA in the pathogenesis of bacterial infections, we have disrupted lspA by allelic replacement in Mycobacterium tuberculosis, one of the world's most devastating pathogens. Despite the presence of an impermeable lipid outer layer, it was found that LspA was dispensable for growth under in vitro culture conditions. In contrast, the mutant was markedly attenuated in virulence models of tuberculosis. Our findings establish lipoprotein metabolism as a major virulence determinant of tuberculosis and define a role for lipoprotein processing in bacterial pathogenesis. In addition, these results hint at a promising new target for therapeutic intervention, as a highly specific inhibitor of bacterial lipoprotein signal peptidases is available.