Biodiversity and Geographic Distribution of Rhizobia Nodulating With Vigna minima

Vigna minima is a climbing annual plant widely distributed in barren wilderness, grass land, and shrub bush of China and other countries such as Japan. However, the rhizobia nodulating with this plant has never been systematically studied. In order to reveal the biodiversity of nodulating rhizobia symbiosis with V. minima, a total of 874 rhizobium isolates were obtained from root nodules of the plant spread in 11 sampling sites of Shandong Peninsula, China, and they were designated as 41 haplotypes in the genus Bradyrhizobium based upon recA sequence analyses. By multilocus sequence analysis (MLSA) of five housekeeping genes (dnaK, glnII, gyrB, recA, and rpoB), the 41 strains representing different recA haplotypes were classified into nine defined species and nine novel genospecies. Bradyrhizobium elkanii, Bradyrhizobium ferriligni, and Bradyrhizobium pachyrhizi were the predominant and universally distributed groups. The phylogeny of symbiotic genes of nodC and nifH showed similar topology and phylogenetic relationships, in which all the representative strains were classified into two clades grouped with strains nodulating with Vigna spp., demonstrating that Vigna spp. shared common nodulating groups in the natural environment. All the representative strains formed nodules with V. minima in a nodulation test performed in green house conditions. The correlation between V. minima nodulating rhizobia and soil characteristics analyzed by CANOCO indicates that available nitrogen, total nitrogen, and organic carbon in the soil samples were the main factors affecting the distribution of rhizobia isolated in this study. This study systematically uncovered the biodiversity and distribution characteristics of V. minima nodulating rhizobia for the first time, which provided novel information for the formation of the corresponding rhizobium community.

Phenotypic diversity of bacteria in root nodules of Dalbergia ecastaphyllum (L.) Taub. (Fabaceae)

Many species belonging to family Fabaceae are able to establish symbiotic relationships with nitrogen-fixing bacteria. Studies developed with Dalbergia ecastaphyllum (L.) Taub., for example, have demonstrated the symbiotic potential of this species. In this sense, this study aimed to analyze the phenotypic characteristics of rhizobia isolated from D. ecastaphyllum and to identify whether these bacterial isolates are capable of establishing symbiotic relationships with Vigna unguiculata (L.) Walp. D. ecastaphyllum seeds were sown in soil samples collected in Japaratinga, Alagoas, Brazil, in three zones located at different distances from the high tide line. At 60 days after the emergence of the plants, nodulation in the roots of D. ecastaphyllum was analyzed and the bacteria were isolated. Subsequently, the phenotypic characterization of the bacteria was carried out based on some criteria (growth time, type of pH, colony color, type of mucus and amount of mucus). For the nodulation test, the species V. unguiculata was used. In total, 17 phenotypic types of bacterial isolates were identified, of which 8 are fast-growing and 9 are intermediate-growth. Regarding the type of pH, 7 phenotypes are acidic pH, 8 are neutral pH and 2 are alkaline pH. As for the coloring of the bacterial colonies, 5 are yellow, 7 white and 5 pink. It was also observed the presence of consistent and aqueous mucus in colonies from the three different areas. Only 7 bacterial phenotypic types and the commercial inoculant were efficient in the nodulation of V. unguiculata.

Isolation, Identification and Production of Encapsulated Bradyrhizobium japonicum and Study on their Viability

Rhizobium, a nitrogen-fixing bacteria is the essential feature of leguminous plants which is essential for the regeneration of nutrient-deficient soil. This study was aimed to isolate, identify, mass culture and immobilize Bradyrhizoium japonicum in encapsulated form and test their viability. Root nodules were sterilized, grinded and cultured aseptically in YEMA media containing Congo red. The obtained colon was sub-cultured to get a pure culture and different biochemical tests were conducted which proved Bradyrhizobium japonicum as the slow-growing species. The test shows a positive result of catalase production and nodulation test whereas the pH tolerance test shows more tolerance to the acidic pH. Similarly, Bradyrhizaobium japonicum can tolerate 1% and 2% NaCl concentration and it doesn’t show resistance to the penicillin disc of 10mg. The mass culture and encapsulation with sodium alginate adding sucrose as nutrient proved the simplicity for handling. Altogether 548 beads were prepared from the 100ml of the cultured broths which were viable for more than 190 days at 1%, 2% and 3% sucrose concentration but less viable at 5% and 10% sucrose concentration under room temperature.

Production Bacteriosin by Rhizobia obtained from Root nodules of Macrotyloma uniflorum (Lam.) Verdc. (Horse Gram)

Thirty two Rhizobium isolates obtained from the root nodules of Horse gram plants grown in 32 different soil samples collected from various regions in Andhra Pradesh, India. They were identified as rhizobia by nodulation test. These isolates were used to study the production of bacteriocins. All the isolates produced bacteriocins against the remaining isolates. The isolates HGR-4 and 9 showed maximum activity/inhibition zone among all the isolates, and also found to be inhibiting more number of isolates than that of other bacteriocin producing isolates. The bacteriocin protein substance produced by the isolates HGR-4 and 9 showed a molecular weight of ~ 50 kDa by SDS-AGE and bacteriocin plasmids molecular weight is > 22 kb and 24 kb. DOI: http://dx.doi.org/10.3329/bjm.v28i2.11820 Bangladesh J Microbiol, Volume 28, Number 2, December 2011, pp 76-79

Devosia yakushimensis sp. nov., isolated from root nodules of Pueraria lobata (Willd.) Ohwi

A Gram-negative, strictly aerobic bacterium, comprising non-endospore-forming motile rods (1.2–2.0 μm × 0.4–0.6 μm) with polar flagellae was isolated from root nodules of the leguminous plant Pueraria lobata (Willd.) Ohwi growing on the coast of Yakushima Island, Kagoshima Prefecture, Japan. The novel strain, designated Yak96BT, grew at an optimum pH of 7.0 and an optimum temperature of 28 °C. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that the new strain was closely related to Devosia neptuniae J1T and Devosia chinhatensis IPL18T, with sequence similarities of 98.1 % and 97.8 %, respectively. However, the DNA–DNA relatedness values of strain Yak96BT with D. neptuniae LMG 21357T and D. chinhatensis CCM 7426T were 53.6 % and 34 %, respectively. The DNA G+C content of strain Yak96BT was 65.3 mol%, the predominant isoprenoid quinone was Q10 (85 %) and the polar lipids were phosphatidylglycerol and diphosphatidylglycerol. The major fatty acids (>5 %) were 11-methyl C18 : 1 ω7c (35.0 %), C16 : 0 (22.4 %), C18 : 1 ω7c (21.8 %), C19 : 0 cyclo ω8c (6.8 %) and C18 : 0 (5.4 %). The infection/nodulation test was negative and nifH and nodD genes were not detected. Based on its chemotaxonomic and physiological characteristics, strain Yak96BT represents a novel species of the genus Devosia, for which the name Devosia yakushimensis sp. nov. is proposed. The type strain is Yak96BT (=KCTC 22147T=NBRC 103855T=LMG 24299T).

Bacteriocin production by rhizobia isolated from root nodules of Horse gram

Thirty two Rhizobium strains were isolated from the root nodules of Horse gram plants grown in 32 soil samples collected from various regions in Andhra Pradesh, India. They were identified as rhizobia by nodulation test. These isolates were used to study the production of bacteriocins. All the isolates produced bacteriocins against the remaining isolates. The isolates HGR-4 and 9 showed maximum activity/inhibition zone among all the isolates, and also found to be inhibiting more number of isolates than that of other bacteriocin producing isolates. The bacteriocin protein substance produced by the isolates HGR-4 and 9 showed a molecular weight of ~ 50 kDa by SDS-AGE and bacteriocin plasmids molecular weight is > 22 kb and > 24 kb. DOI: http://dx.doi.org/10.3329/bjms.v11i1.9819 BJMS 2012; 11(1): 28-32