We prepared microarrays that contain genomic sequences of a heterocyst-forming filamentous cyanobacterium Anabaena sp. PCC 7120. The complete genome of this cyanobacterium codes for about 5,368 protein-coding genes in the main chromosome of 6.4 Mbp. In total, 2,407 DNA segments were selected from the sequencing clones, and amplified by PCR, then spotted on glass slides in duplicate. These microarrays differ from the widely used commercial or custom-made ones for other microorganisms in that each DNA segment was 3–4 kbp long, and contained about 3–4 predicted genes on average. This feature, however, did not decrease the usefulness of the microarrays, since we were able to detect a number of potentially novel genes that are induced in response to nitrogen deprivation, low temperature and drought. In addition, we found some genomic regions in which dozens of contiguous genes are simultaneously regulated. These results suggest that these segment-based microarrays are useful especially for such large genomes as Anabaena, for which the number of genes exceeds either technical or practical limitations.
Thirteen reference strains, including the type strains of the type species of the genus Gluconobacter, Gluconobacter oxydans (NBRC 14819T), Gluconobacter cerinus (NBRC 3267T), and Gluconobacter frateurii (IFO 3264T) were examined for their species identification based on the sequence and the restriction analyses of the 16S–23S rDNA internal transcribed spacer (ITS) regions. A phylogenetic tree constructed by the neighbor-joining method represented three clusters corresponding respectively to the three species, G. oxydans, G. cerinus, and G. frateurii. The type strain of Gluconobacter asaii (NBRC 3276T), which is a junior subjective synonym of G. cerinus, was included completely in the G. cerinus cluster. Several restriction endonucleases discriminating the three species from one another were selected by computer analyses: Bsp1286I, MboII, SapI, Bpu10I, EarI, BsiHKAI, and FatI. On digestion of the PCR products with restriction endonucleases Bsp1286I and MboII, all the restriction patterns coincided with those of the type strains of the three species except for strain NBRC 3251. This strain gave a different pattern from the type strain of G. frateurii, when digested with MboII. However, strain 3251 was included phylogenetically in the G. frateurii cluster. All the reference strains were thus identified at the species level by the sequence and the restriction analyses of the 16S–23S rDNA ITS regions.
Ten strains of root nodule bacteria were isolated from the nodules of Acacia mangium grown in the Philippines and Thailand. Partial sequences (approx. 300 bp) of the 16S rRNA gene of each isolate were analyzed. The nucleotide sequences of strain DASA 35030 indicated high homology (>99%) with members of the genus Ochrobactrum in Brucellaceae, although the sequences of other isolates were homologous to those of two distinct genera Bradyrhizobium and Rhizobium. The strain DASA 35030 was strongly suggested to be a strain of Ochrobactrum by full length sequences of the 16S rRNA gene, fatty acids composition, G+C contents of the DNA, and other physiological characteristics. Strain DASA 35030 induced root nodules on A. mangium, A. albida and Paraserianthes falcataria. The nodules formed by strain DASA 35030 fixed nitrogen and the morphology of the nodules is the same as those of nodules formed by the other isolates. This is the first report that the strain of Ochrobactrum possesses complete symbiotic ability with Acacia.