Williamsia aurantiacus sp. nov. a novel actinobacterium producer of antimicrobial compounds isolated from the marine sponge.

An antibiotic-producing actinobacterium, designated isolate B375T, was isolated from marine sponge Glodia corticostylifera collected from Praia Guaecá, São Paulo, Brazil (23°49S; 45°25W), and its taxonomic position established using data from a polyphasic study. The organism showed a combination of morphological, physiological, biochemical and chemotaxonomic characteristics consistent with its classification in the genus Williamsia. Comparative 16S rRNA gene sequence analysis indicated that the strain B375T was most closely related to Williamsia serinedens DSM 45037T and Williamsia spongiae DSM 46676T and having 99.43% and 98.65% similarities, respectively, but was distinguished from these strains by a low level of DNA-DNA relatedness (53.2-63.2%) and discriminatory phenotypic properties. Chemotaxonomic investigations revealed the presence of cell-wall chemotype IV and N-glycolated muramic acid residues present in the wall cells. The cells contained C16:0 (23.3%), C18:0 10-methyl (23.2%) and C18:1 ω9c (21.6%) as the major cellular fatty acids. The strain B375T inhibited growing of Staphylococcus aureus and Colletotrichum gloeosporioides strains and was considered a producer of antimicrobial compounds. Based on the data obtained, the isolate B375T (= CBMAI 1090T = DSM 46677T) should, therefore, be classified as the type strain of a novel species of the genus Williamsia, for which the name Williamsia aurantiacus sp. nov. is proposed.

Bradyrhizobium sacchari sp. nov., a legume nodulating bacterium isolated from sugarcane roots.

Members of the genus Bradyrhizobium are well-known as nitrogen-fixing microsymbionts of a wide variety of leguminous species, but they have also been found in different environments, notably as endophytes in non-legumes such as sugarcane. This study presents a detailed polyphasic characterization of four Bradyrhizobium strains (type strain BR 10280T), previously isolated from roots of sugarcane in Brazil. 16S rRNA sequence analysis, multilocus sequence analysis (MLSA) and analysis of the 16S-23S rRNA internal transcribed spacer showed that these strains form a novel clade close to, but different from B. huanghuaihaiense strain CCBAU 23303T. Average nucleotide identity (ANI) analyses confirmed that BR 10280T represents a novel species. Phylogenetic analysis based on nodC gene sequences also placed the strains close to CCBAU 23303T, but different from this latter strain, the sugarcane strains did not nodulate soybean, although they effectively nodulated Vigna unguiculata, Cajanus cajan and Macroptilium atropurpureum. Physiological traits are in agreement with the placement of the strains in the genus Bradyrhizobium as a novel species for which the name Bradyrhizobium sacchari sp. nov. is proposed.

Bradyrhizobium stylosanthis sp. nov., comprising nitrogen-fixing symbionts isolated from nodules of the tropical forage legume Stylosanthes spp.

The introduction of legumes and nitrogen-fixing bacteria in tropical areas under pasture is a key factor for improvement of soil fertility. However, there are still very few studies concerning the symbionts of tropical forage legumes. We performed a polyphasic study with three strains representing the genus Bradyrhizobium (BR 446T, BR 510 and BR 511) isolated from the tropical perennial forage legume of the genus Stylosanthes. On the basis of 16S rRNA gene sequences, the three strains showed highest similarity with B. huanghuaihaiense, and in the analysis of the intergenic transcribed spacer (ITS) they showed less than 93.4 % similarity to all described species of the genus Bradyrhizobium. Multilocus sequence analysis (MLSA) with three, four or five (dnaK, glnII, gyrB, recA and rpoB) housekeeping genes confirmed that the BR strains belong to a distinct clade, with <96.5 % nucleotide identity with other members of the genus Bradyrhizobium. Average nucleotide identity (ANI) of genome sequences between strain BR 446T and B.huanghuaihaiense was below the threshold for species circumscription (90.7 %). DNA-DNA hybridization resulted in ΔTm values over 6.7 °C with the most closely related species. Similarities among the BR strains and differences from other species were confirmed by rep-PCR analysis. Interestingly, the BR strains were grouped in the analysis of nifH and nodC genes, but showed higher similarity with B. iriomotense and B. manausense than with B.huanghuaihaiense, indicating a different evolutionary history for nitrogen-fixation genes. Morpho-physiological, genotypic and genomic data supported that these BR strains represent a novel species for which the name Bradyrhizobium stylosanthis sp. nov. is suggested. The type strain is BR 446T (=CNPSo 2823T=HAMBI 3668T=H-8T), isolated from Stylosanthes guianensis.

Bradyrhizobium tropiciagri sp. nov. and Bradyrhizobium embrapense sp. nov., nitrogen-fixing symbionts of tropical forage legumes.

Biological nitrogen fixation is a key process for agricultural production and environmental sustainability, but there are comparatively few studies of symbionts of tropical pasture legumes, as well as few described species of the genus Bradyrhizobium, although it is the predominant rhizobial genus in the tropics. A detailed polyphasic study was conducted with two strains of the genus Bradyrhizobium used in commercial inoculants for tropical pastures in Brazil, CNPSo 1112T, isolated from perennial soybean (Neonotonia wightii), and CNPSo 2833T, from desmodium (Desmodium heterocarpon). Based on 16S-rRNA gene phylogeny, both strains were grouped in the Bradyrhizobium elkanii superclade, but were not clearly clustered with any known species. Multilocus sequence analysis of three (glnII, gyrB and recA) and five (plus atpD and dnaK) housekeeping genes confirmed that the strains are positioned in two distinct clades. Comparison with intergenic transcribed spacer sequences of type strains of described species of the genus Bradyrhizobium showed similarity lower than 93.1 %, and differences were confirmed by BOX-PCR analysis. Nucleotide identity of three housekeeping genes with type strains of described species ranged from 88.1 to 96.2 %. Average nucleotide identity of genome sequences showed values below the threshold for distinct species of the genus Bradyrhizobium ( < 90.6 %), and the value between the two strains was also below this threshold (91.2 %). Analysis of nifH and nodC gene sequences positioned the two strains in a clade distinct from other species of the genus Bradyrhizobium. Morphophysiological, genotypic and genomic data supported the description of two novel species in the genus Bradyrhizobium, Bradyrhizobium tropiciagri sp. nov. (type strain CNPSo 1112T = SMS 303T = BR 1009T = SEMIA 6148T = LMG 28867T) and Bradyrhizobium embrapense sp. nov. (type strain CNPSo 2833T = CIAT 2372T = BR 2212T = SEMIA 6208T = U674T = LMG 2987).

Screening of Brazilian cacti rhizobacteria for plant growth promotion under drought.

Drought is one of the major problems worldwide. The search for new and efficient microorganisms, from unexplored environments, to be used in association with plants to alleviate the negative effects imposed by water stress, is an interesting alternative. Thus, cacti-associated bacteria from the Brazilian semi-arid region were isolated based on their ability to grow in medium with reduced water availability. Strains were tested for the production of exopolysaccharides (EPS), as well as in vitro plant growth promotion traits. A great proportion of the isolates belong to the genus Bacillus. From a total of forty-eight bacteria, 65% were able to grow in medium with reduced water availability (0.919Aw), exopolysaccharide production was observed for 65% of the strains. The production of indole acetic acid (IAA) exceeding 51µgmL(-1) was observed for 4% and the high solubilization of Ca-P was verified for 6% of the isolates. No strain was able to produce hydrogen cyanide (HCN), 71% produced ammonia and 79% showed a halo of carboxymethyl cellulose (CMC) degradation. Zea mays L. growth promotion under water stress (30% of field capacity) was achieved by two strains of Bacillus spp. This is the first report to describe cacti-associated bacteria from Brazilian semi-arid with plant growth-promoting abilities.