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We investigated the outcome of the interaction between the arbuscular mycorrhizal fungus (AMF) Rhizophagus (R) irregularis DAOM 197198 and the Plant-Growth-Promoting Rhizobacteria (PGPR) (mix of Bacillus megaterium , Burkholdria cedrus and Streptomyces beta-vulgaris) by conducting an olive field experiment. Our data provide evidence that the co-inoculation of R. irregularis and PGPR has important effects on the rhizosphere microbial community. The largest proportional increase was found for the PLFA biomarkers indicative of Gram-negative bacteria (16:1ω9, 18:1ω7 and 18:1ω9), fungi (18:2ω6) and actinobacteria (10Me16:0 and 10Me18:0). Microbial inoculants application of all tested treatments caused a significant decrease in the level of trehalose in the olive rhizosphere. The most pronounced decrease was observed in the plant inoculated with R. intraradices only, suggesting that the presence of AMF may have relaxed the bacterial stress. Co-inoculation of PGPR and AMF significantly improved the nutritional status of olive roots. Specifically, the interaction of PGPR and R. intraradices led to an increase in N (26 %), P (60 %), Fe (25 %), Mn (18 %), Zn (26 %), B (22 %) and Cu (14 %) compared with the control. We also found that the co-inoculation of AMF with PGPR causes a shift in the accumulation of secondary metabolites in olive roots. In particular, the most important effect induced by AMF was an improvement of oleuropein concentration, while co-inoculation of R. irregularis and PGPR positively modulated verbascoside concentration. The novelty of the present work lies in the use of microbial inoculants in the field of olive trees. This approach provided direct information regarding the advantages of using AMF and PGPR inoculants, allowing the reduction of chemical inputs and positively influencing the olive tree performance. • AM fungi and PGPR modified the microbial community of the olive rhizosphere. • AM fungi and PGPR enhanced mineral nutrient concentrations of olive roots. • AM fungi and PGPR modified the phenolic profiles of olive roots. • AM fungi and PGPR reduced the accumulation of trehalose and relaxed bacterial stress. [ABSTRACT FROM AUTHOR]

Abstract: Two Gram (+) bacterial strains, BSB6 and BSB12, showing resistance and potential for Se(IV) reduction among 26 moderately halotolerant isolates from the Bhitarkanika mangrove soil were characterized by biochemical and 16S rDNA sequence analyses. Both of them were strictly aerobic and able to grow in a wide range of pH (4–11), temperature (4–40°C) and salt concentration (4–12%) having an optimum growth at 37°C, pH ∼7.5 and 7% salt (NaCl). The biochemical characteristics and 16S rDNA sequence analysis of BSB6 and BSB12 showed the closest phylogenetic similarity with the species Bacillus megaterium. Both the strains effectively reduced Se(IV) and complete reduction of selenite (up to 0.25mM) was achieved within 40h. SEM with energy dispersive X-ray and TEM analyses revealed the formation of nano size spherical selenium particles in and around the bacterial cells which were also supported by the confocal micrograph study. The UV–Vis diffuse reflectance spectra and XRD of selenium precipitates revealed that the selenium particles are in the nanometric range and crystalline in nature. These bacterial strains may be exploited further for bioremediation process of Se(IV) at relatively high salt concentrations and green synthesis of selenium nanoparticles. [Copyright &y& Elsevier]

• At an optimal concentration of 25 ppm, Padina pavonica and Sargassum tenerrimuman obtained 75 and 73% inhibitory efficiency, respectively. • The Extracellular Electron Transfer (EET) of Bacillus megaterium was inhibited using the methanolic extraction of seaweeds. • The bioactive compounds of seaweeds are more potential to inhibit bacterial growth and prevent the biofilm layer. • MEPP and MEST revealed the existence of organic compounds like N, S, O blocking electron transfers reduce the corrosion rate. Biocorrosion is an aggregation of microbes on the metal surface that induces ion degradation by oxidation and reduction of chemical and electrochemical reactions. Extracellular electron transfer (EET) process was a significant phenomenon in ion deterioration. To block the EET process, the inhibitor was used to destroy or prevent extracellular electron transfer during microbial metabolism. In the present study, methanolic extraction of two different seaweeds acts as a bio-inhibitor against the corrosive biofilm forming bacteria B.megaterium SKR7 on the mild steel. The optimized concentration of biofilm inhibition efficiency of methanolic extract P.pavonica (MEPP) and S.tenerrimum (MEST) was found to be 75% and 73% at 25 ppm respectively. It was confirmed by assay of antimicrobial activity and weight loss measurement which is represented the reduction of corrosion rate S3 (A) 0.355 mm/y and S3 (B) 0.442 mm/y of both seaweed extracts than control (1.598 mm/y). This observation was confirmed by the electrochemical studies by the significant decrease in charge transfer resistance (R ct) and the surface analysis of FTIR and SEM analysis were confirmed the seaweeds inhibit the biofilm. MEPP and MEST revealed the existence of organic and bioactive compounds like N, S, O blocks the electron transfers during the biofilm formation on a metal surface and thus inhibits corrosion rate. The study concluded seaweed extracts act as mixed-type of inhibitors, thus effectivley inhibit the biofilm formation and are easily accessible at low cost, eco-friendly. [ABSTRACT FROM AUTHOR]

Cyclic voltabsorptometry is used for the first time to distinguish and characterize electrochemically the active (P450) and inactive (P420) forms of cytochromes P450 immobilized on an electrode during voltammetry experiments. This was achieved by using the heme domain (BMP) of the bacterial cytochrome P450 BM3 from Bacillus megaterium(CYP102A1) immobilized on mesopouros tin-oxide (SnO 2) electrodes. We demonstrate that the formation of either the P450 form or the P420 one can be obtained by modifying the mesoporous electrode surface with polycations with different properties such as polyethylenimmine (PEI) and polydiallyldimethylammonium chloride (PDDA). Potential step spectroelectrochemistry allowed measurement of reduction potentials of the active P450 form. Values of −0.39 ± 0.01 V and −0.58 ± 0.01 V (both versus Ag/AgCl) were calculated for the active P450 form immobilized on the BMP/PDDA−SnO 2and BMP/PEI−SnO 2electrodes, respectively. The cyclic voltabsorptometric experiments showed how, when both the active and inactive forms are present on the PEI film, the inactive P420 species tends to dominate the cyclic voltammetric signal. [ABSTRACT FROM AUTHOR]