Although molecular phylogenetic studies of cyanobacteria on the basis of the 16S rRNA gene sequence have been reported, the topologies were unstable, especially in the inner branchings. Our analysis of 16S rRNA gene phylogeny by the maximum-likelihood and neighbor-joining methods combined with rate homogeneous and heterogeneous models revealed seven major evolutionary lineages of the cyanobacteria, including prochlorophycean organisms. These seven lineages are always stable on any combination of these methods and models, fundamentally corresponding to phylogenetic relationships based on other genes, e.g., psbA, rbcL, rnpB, rpoC, and tufA. Moreover, although known genotypic and phenotypic characters sometimes appear paralleled in independent lineages, many characters are not contradictory within each group. Therefore we propose seven evolutionary groups as a working hypothesis for successive taxonomic reconstruction. New 16S rRNA sequences of five unicellular cyanobacterial strains, PCC 7001, PCC 7003, PCC 73109, PCC 7117, and PCC 7335 of Synechococcus sp., were determined in this study. Although all these strains have been assigned to "marine clusters B and C," they were separated into three lineages. This suggests that the organisms classified in the genus Synechococcus evolved diversely and should be reclassified in several independent taxonomic units. Moreover, Synechococcus strains and filamentous cyanobacteria make a monophyletic group supported by a comparatively high statistical confidence value (80 to 100%) in each of the two independent lineages; therefore, these monophylies probably reflect the convergent evolution of a multicellular organization.

Proposal of Lysinibacillus boronitolerans gen. nov. sp. nov., and transfer of Bacillus fusiformis to Lysinibacillus fusiformis comb. nov. and Bacillus sphaericus to Lysinibacillus sphaericus comb. nov. SORST, JST, Chiyoda-ku, Tokyo, JapanThree strains of a spore-forming, Gram-positive, motile, rod-shaped and boron-tolerant bacterium were isolated from soil. The strains, designated 10a T , 11c and 12B, can tolerate 5 % (w/v) NaCl and up to 150 mM boron, but optimal growth was observed without addition of boron or NaCl in Luria-Bertani agar medium. The optimum temperature for growth was 37 6C (range 16-45 6C) and the optimum pH was 7.0-8.0 (range pH 5.5-9.5). A comparative analysis of the 16S rRNA gene sequence demonstrated that the isolated strains were closely related to Bacillus fusiformis DSM 2898 T (97.2 % similarity) and Bacillus sphaericus DSM 28 T (96.9 %). DNA-DNA relatedness was greater than 97 % among the isolated strains and 61.1 % with B. fusiformis DSM 2898 T and 43.2 % with B. sphaericus IAM 13420 T . The phylogenetic and phenotypic analyses and DNA-DNA relatedness indicated that the three strains belong to the same species, that was characterized by a DNA G+C content of 36.5-37.9 mol%, MK-7 as the predominant menaquinone system and iso-C 15 : 0 (32 % of the total) as a major cellular fatty acid. In contrast to the type species of the genus Bacillus, the strains contained peptidoglycan with lysine, aspartic acid, alanine and glutamic acid. Based on the distinctive peptidoglycan composition, phylogenetic analyses and physiology, the strains are assigned to a novel species within a new genus, for which the name Lysinibacillus boronitolerans gen. nov., sp. nov. is proposed. The type strain of Lysinibacillus boronitolerans is strain 10aIt is also proposed that Bacillus fusiformis and Bacillus sphaericus be transferred to this genus as Lysinibacillus fusiformis comb. nov. and Lysinibacillus sphaericus comb. nov., respectively.

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