Biological Nitrogen Fixation (BNF) process benefits the agriculture sector especially for reducing cost of nitrogen fertilizer. In the process, the diazotrophs convert N2 into ammonia (NH3) which is useable by plants. The BNF process is catalysed by nitrogenase enzyme that involved protons and electrons together with evolution of H2 therefore, the assessment of N2 fixation is also available via H2 production and electron allocation analysis. Thus, the aims of this experiment were to estimate the nitrogenase enzyme activities and observe the influence of diazothrophs on growth of legume (soybean) and non legume (rice) plants. Host plants were inoculated with respective inocula; Bradyrhizobium japonicum (strain 532C) for soybean while Azospirillum brasilense (Sp7) and locally isolated diazotroph (isolate 5) for rice. At harvest, the plants were observed for plant growth parameters, H2 evolution, N2 fixation and electron allocation coefficient (EAC) values. The experiment recorded N2 fixation activities of inoculated soybean plants at 141.2 μmol N2 h-1 g-1 dry weight nodule, and the evolution of H2 at 144.4 μmol H2 h-1 g-1 dry weight nodule. The electron allocation coefficient (EAC) of soybean was recorded at 0.982. For inoculated rice plants, none of the observations was successfully recorded. However, results for chlorophyll contents and plant dry weight of both plants inoculated with respective inocula were similar to the control treatments supplied with full nitrogen fertilization (+N). The experiment clearly showed that inoculation of diazotrophic bacteria could enhance growth of the host plants similar to plants treated with nitrogenous fertilizer due to efficient N2 fixation process

Aims: The purpose of this experiment was to determine the artificial symbiosis interaction of Herbaspirillum seropedicae (Z78) on oil palm embryogenic calli. Methodology and results: For this purpose, symbiotic associations were established between Z78 and embryogenic calli of oil palm tissue cultured. A total of five treatments involved, in particular: i) + 3.0 mg/L 2,4-D + 100% N MS medium (control), ii) + Z78 pellet cells (1 mL) + 25% N MS medium, iii) + Z78 supernatant (1 mL) + 25% N MS medium, iv) + Z78 broth culture (1 mL) + 25% N MS medium, and v) + Z78 sonicated cells (1 mL) + 25% N MS medium. All treatments were supplied with minimal N sources (25% N), ammonium nitrate and potassium nitrate, while the control was treated with 100% N sources. Treated samples were harvested on D80 and observed for biomass and diameter increment (%), formation of embryoids, and Z78 colonization. The results showed embryogenic calli in the inoculated treatments that contained depleted N produced similar result to the control treatment which contained 100% N nutrients. Positive interactions occurred between the diazotroph and host plant tissues as viewed under FESEM and EFTEM. Among the treatments, Z78 sonicated cell showed better growth of embryogenic calli compared to others. Conclusion, significance and impact study: The in vitro nitrogen-depleted artificial symbiosis environment allowed the diazotroph (Z78) to be expressed and provide the nitrogen sources and indole-3-acetic acid for cell growth. This study represents beneficial co-culture interaction effects of different inocula of diazotrophic bacterial cells with in vitro embryogenic calli of oil palm.

Aims: The purpose of this research was to explore the composition and genomic functions of bacterial community inhabiting the rhizosphere of Mimosa pudica, which were naturally growing on tailing and non-tailing soils of an ex-tin mining area. Methodology and results: DNA were extracted from rhizosphere soils and PCR targeting the hypervariable region V3-V4 was carried out by Illumina 16S metagenomic library. Libraries were sequenced using Illumina MiSeq. The Operational Taxonomic Units (OTUs) were assigned to 23 bacterial phyla, 72 classes, 165 orders, 248 families and 357 genera. The most represented and dominant phylum was Proteobacteria, with an average abundance value of 41.2%. The most represented genera included Paraburkholderia, Bradyrhizobium, Bacillus, Candidatus, Acidothermus, Acidibacter and Nitrospira. Non-tailing soils had more number and richness of species while the tailings had more diversity of species. The metagenomes accommodate suspected genes for heavy metal tolerance of microbes (As, Cr, Co, Zn, Ni, Cu, Cd, Fe and Hg) and microbial plant-growth-promoting traits for hyperaccumulator plants (synthesis of indole acetic acid (IAA), siderophore and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase; solubilization of phosphate and potassium and nitrogen fixation). Conclusion, significance and impact of study Bacteria and predicted genes discovered could be part of major factors influencing growth of M. pudica in heavy metal-contaminated soils. The study provides the first report and a basis into the bacterial community associated with M. pudica in ex-tin mining soils from the studied geographical location. The findings also provide fundamental knowledge on phytoremediation potential of heavy metal contaminated soils involving indigenous beneficial microbial populations.
Bacteria ; Rhizosphere ; Mimosa ; Plant Growth Regulators