Physicochemical characterization of the brown pigment produced by Azospirillum brasilense HM053 using tryptophan as precursor.

Microorganisms are known to be a promising source of biopigments because they are easy to obtain, can be produced on a commercial scale, and are environmentally friendly. Therefore, the aim of this work was to characterize a brown pigment (BP) produced by HM053 in NFbHPN-lactate medium. The BP was extracted from the pellet (BPP) or supernatant (BPS), in the presence (BPPTrp, BPSTrp) or absence (BPPw, BPSw) of tryptophan (Trp). The UV-vis results were similar among all BP samples and compared with commercial melanin used as a standard, and the maximum absorption was observed around 200-220 nm. FTIR spectra showed that BP and commercial melanin had slight differences, with a small band between 3000-2840 cm- 1, related to C-H in the CH2 and CH3 aliphatic groups, which is not observed in the commercial melanin. Between BPP and BPS showed a different structure with bands in the region 1230-1070 cm- 1 related to groups C-O. The thermogravimetric curves for BPSw and BPSTrp showed similar behavior, with 4 stages of mass loss. The similarity between BPPw and BPPTrp with 2 stages of mass loss was also observed. Scanning electron microscopy results showed morphological differences between BPP and BPS, where BPP had a physical structure more homogeneous and a regular flat surface, while the BPS physical structure did not seem homogeneous and the surface was uneven with some spherical structures as commercial melanin.

Polyphasic characterization of bacteria obtained from upland rice cultivated in Cerrado soil

ABSTRACT This work aimed to characterize 20 isolates obtained from upland rice plants, based on phenotypic (morphology, enzymatic activity, inorganic phosphate solubilization, carbon source use, antagonism), genotypic assays (16S rRNA sequencing) and plant growth promotion. Results showed a great morphological, metabolic and genetic variability among bacterial isolates. All isolates showed positive activity for catalase and protease enzymes and, 90% of the isolates showed positive activity for amylase, catalase and, nitrogenase. All isolates were able to metabolize sucrose and malic acid in contrast with mannitol, which was metabolized only by one isolate. For the other carbon sources, we observed a great variability in its use by the isolates. Most isolates showed antibiosis against Rhizoctonia solani (75%) and Sclerotinia sclerotiorum (55%) and, 50% of them showed antibiosis against both pathogens. Six isolates showed simultaneous ability of antibiosis, inorganic phosphate solubilization and protease activity. Based on phylogenetic analysis of the 16S rRNA gene all the isolates belong to Bacillus genus. Under greenhouse conditions, two isolates (S4 and S22) improved to about 24%, 25%, 30% and 31% the Total N, leaf area, shoot dry weight and root dry weight, respectively, of rice plants, indicating that they should be tested for this ability under field conditions.

Polyphasic characterization of bacteria obtained from upland rice cultivated in Cerrado soil.

This work aimed to characterize 20 isolates obtained from upland rice plants, based on phenotypic (morphology, enzymatic activity, inorganic phosphate solubilization, carbon source use, antagonism), genotypic assays (16S rRNA sequencing) and plant growth promotion. Results showed a great morphological, metabolic and genetic variability among bacterial isolates. All isolates showed positive activity for catalase and protease enzymes and, 90% of the isolates showed positive activity for amylase, catalase and, nitrogenase. All isolates were able to metabolize sucrose and malic acid in contrast with mannitol, which was metabolized only by one isolate. For the other carbon sources, we observed a great variability in its use by the isolates. Most isolates showed antibiosis against Rhizoctonia solani (75%) and Sclerotinia sclerotiorum (55%) and, 50% of them showed antibiosis against both pathogens. Six isolates showed simultaneous ability of antibiosis, inorganic phosphate solubilization and protease activity. Based on phylogenetic analysis of the 16S rRNA gene all the isolates belong to Bacillus genus. Under greenhouse conditions, two isolates (S4 and S22) improved to about 24%, 25%, 30% and 31% the Total N, leaf area, shoot dry weight and root dry weight, respectively, of rice plants, indicating that they should be tested for this ability under field conditions.

Labeled Azospirillum brasilense wild type and excretion-ammonium strains in association with barley roots.

Soil bacteria colonization in plants is a complex process, which involves interaction between many bacterial characters and plant responses. In this work, we labeled Azospirillum brasilense FP2 (wild type) and HM053 (excretion-ammonium) strains by insertion of the reporter gene gusA-kanamycin into the dinitrogenase reductase coding gene, nifH, and evaluated bacteria colonization in barley (Hordeum vulgare). In addition, we determined inoculation effect based on growth promotion parameters. We report an uncommon endophytic behavior of A. brasilense Sp7 derivative inside the root hair cells of barley and highlight the promising use of A. brasilense HM053 as plant growth-promoting bacterium.