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Background Bacteria have developed different mechanisms for the transformation of metalloid oxyanions to non-toxic chemical forms. A number of bacterial isolates so far obtained in axenic culture has shown the ability to bioreduce selenite and tellurite to the elemental state in different conditions along with the formation of nanoparticles—both inside and outside the cells—characterized by a variety of morphological features. This reductive process can be considered of major importance for two reasons: firstly, toxic and soluble (i.e. bioavailable) compounds such as selenite and tellurite are converted to a less toxic chemical forms (i.e. zero valent state); secondly, chalcogen nanoparticles have attracted great interest due to their photoelectric and semiconducting properties. In addition, their exploitation as antimicrobial agents is currently becoming an area of intensive research in medical sciences. Results In the present study, the bacterial strain Ochrobactrum sp. MPV1, isolated from a dump of roasted arsenopyrites as residues of a formerly sulfuric acid production near Scarlino (Tuscany, Italy) was analyzed for its capability of efficaciously bioreducing the chalcogen oxyanions selenite (SeO 3 2− ) and tellurite (TeO 3 2− ) to their respective elemental forms (Se 0 and Te 0 ) in aerobic conditions, with generation of Se- and Te-nanoparticles (Se- and TeNPs). The isolate could bioconvert 2 mM SeO 3 2− and 0.5 mM TeO 3 2− to the corresponding Se 0 and Te 0 in 48 and 120 h, respectively. The intracellular accumulation of nanomaterials was demonstrated through electron microscopy. Moreover, several analyses were performed to shed light on the mechanisms involved in SeO 3 2− and TeO 3 2− bioreduction to their elemental states. Results obtained suggested that these oxyanions are bioconverted through two different mechanisms in Ochrobactrum sp. MPV1. Glutathione (GSH) seemed to play a key role in SeO 3 2− bioreduction, while TeO 3 2− bioconversion could be ascribed to the catalytic activity of intracellular NADH-dependent oxidoreductases. The organic coating surrounding biogenic Se- and TeNPs was also characterized through Fourier-transform infrared spectroscopy. This analysis revealed interesting differences among the NPs produced by Ochrobactrum sp. MPV1 and suggested a possible different role of phospholipids and proteins in both biosynthesis and stabilization of such chalcogen-NPs. Conclusions In conclusion, Ochrobactrum sp. MPV1 has demonstrated to be an ideal candidate for the bioconversion of toxic oxyanions such as selenite and tellurite to their respective elemental forms, producing intracellular Se- and TeNPs possibly exploitable in biomedical and industrial applications.

We explored how Ochrobactrum sp. MPV1 can convert up to 2.5 mM selenite within 120 h, surviving the challenge posed by high oxyanion concentrations. The data show that thiol-based biotic chemical reaction(s) occur upon bacterial exposure to low selenite concentrations, whereas enzymatic systems account for oxyanion removal when 2 mM oxyanion is exceeded. The selenite bioprocessing produces selenium nanomaterials, whose size and morphology depend on the bacterial physiology. Selenium nanoparticles were always produced by MPV1 cells, featuring an average diameter ranging between 90 and 140 nm, which we conclude constitutes the thermodynamic stability range for these nanostructures. Alternatively, selenium nanorods were observed for bacterial cells exposed to high selenite concentration or under controlled metabolism. Biogenic nanomaterials were enclosed by an organic material in part composed of amphiphilic biomolecules, which could form nanosized structures independently. Bacterial physiology influences the surface charge characterizing the organic material, suggesting its diverse biomolecular composition and its involvement in the tuning of the nanomaterial morphology. Finally, the organic material is in thermodynamic equilibrium with nanomaterials and responsible for their electrosteric stabilization, as changes in the temperature slightly influence the stability of biogenic compared to chemogenic nanomaterials.

A Gram stain negative, motile, non-spore-forming, rod-shaped, strictly aerobic, beige-pigmented bacterium, designated strain BO-7T, was isolated from soil of cattle farm, in Seosan, Republic of Korea. On the basis of 16S rRNA gene sequencing, strain BO-7T clustered with species of the genus Ochrobactrum and appeared closely related to O. haematophilum CCUG 38531T (98.9%), O. daejeonense KCTC 22458T (98.1%), O. rhizosphaerae DSM 19824T (98.1%), O. pituitosum DSM 22207T (98.0%), and O. pecoris DSM 23868T (98.0%). The digital DNA-DNA hybridization and average nucleotide identity between strain BO-7T and the closely related strains were 21.9–39.1%, 78.5–89.5%, respectively, indicating that BO-7T is a novel species of the genus Ochrobactrum. The DNA G + C content of the genomic DNA was 57.1 mol%, and ubiquinone Q-10 was the predominant respiratory quinone. The polar lipids consisted of phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylmonomethyl-ethanolamine, di-phosphatidylglycerol, the major polyamines were spermidine, putrescine, and sym-homospermidine. The major cellular fatty acids (> 5%) were C16:0, C19:0 cycle ω7c, and C18:1ω7c and/or C18:1ω6c (summed feature 8). ANI calculation, digital DNA-DNA hybridization, physiological and biochemical characteristics indicated that strain BO-7T represents a novel species of the genus Ochrobactrum, for which the name Ochrobactrum soli sp. nov. is proposed. The type strain is BO-7T (= KACC 19676T = LMG 30809T).

Microbial bioreporters offer excellent potentialities for the detection of the bioavailable portion of pollutants in contaminated environments, which currently cannot be easily measured. This paper describes the construction and evaluation of two microbial bioreporters designed to detect the bioavailable chromate in contaminated water samples. The developed bioreporters are based on the expression of gfp under the control of the chr promoter and the chrB regulator gene of TnOtChr determinant from Ochrobactrum tritici 5bvl1. pCHRGFP1 Escherichia coli reporter proved to be specific and sensitive, with minimum detectable concentration of 100 nM chromate and did not react with other heavy metals or chemical compounds analysed. In order to have a bioreporter able to be used under different environmental toxics, O. tritici type strain was also engineered to fluoresce in the presence of micromolar levels of chromate and showed to be as specific as the first reporter. Their applicability on environmental samples (spiked Portuguese river water) was also demonstrated using either freshly grown or cryo-preserved cells, a treatment which constitutes an operational advantage. These reporter strains can provide on-demand usability in the field and in a near future may become a powerful tool in identification of chromate-contaminated sites.

A novel bacterial cells immobilized carrier (ZnONPs/PVA), polyvinyl alcohol (PVA) composites decorated with ZnO nanoparticles (ZnO NPs), was prepared and used for immobilization of the strain Ochrobactrum sp. LC-1, and subsequently for quinoline degrading in water. Characterization of ZnONPs/PVA by using X-ray diffractometer and scanning electron microscopy demonstrated that ZnO NPs were coated on the surface of PVA cubes evenly and the bacterium grew well on the ZnONPs/PVA. Quinoline biodegradation results showed that the degradation effect of quinoline by ZnONPs/PVA immobilized cells was superior to the free cells significantly. The structure and physical properties of ZnNPs/PVA were maintained steady after the reuse of ZnNPs/PVA for cells immobilization several times. Reusability of the ZnONPs/PVA immobilized cells revealed that the quinoline removal ratio was above 97% within 8 h under the conditions of pH neutral, 37 °C when the initial quinoline concentration was 300 mg/L.

Fast hexavalent chromium (Cr(VI)) determination is important for environmental risk and health-related considerations. We used a microbial fuel cell-based biosensor inoculated with a facultatively anaerobic, Cr(VI)-reducing, and exoelectrogenic Ochrobactrum anthropi YC152 to determine the Cr(VI) concentration in water. The results indicated that O. anthropi YC152 exhibited high adaptability to pH, temperature, salinity, and water quality under anaerobic conditions. The stable performance of the microbial fuel cell (MFC)-based biosensor indicated its potential as a reliable biosensor system. The MFC voltage decreased as the Cr(VI) concentration in the MFC increased. Two satisfactory linear relationships were observed between the Cr(VI) concentration and voltage output for various Cr(VI) concentration ranges (0.0125–0.3 mg/L and 0.3–5 mg/L). The MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in drinking water, groundwater, and electroplating wastewater in 45 min with low deviations (<10%). The use of the biosensor can help in preventing the violation of effluent regulations and the maximum allowable concentration of Cr(VI) in water. Thus, the developed MFC biosensor has potential as an early warning detection device for Cr(VI) determination even if O. anthropi YC152 is a possible opportunistic pathogen.

ω-Transaminase (ω-TA) is an industrially important enzyme for production of chiral amines. About 20 (S)-specific ω-TAs known to date show remarkably similar substrate selectivity characterized by stringent steric constraint precluding entry of a substituent larger than an ethyl group in the small binding pocket (S) and dual recognition of an aromatic substituent as well as a carboxylate group in the large pocket (L). The strictly defined substrate selectivity of the available ω-TAs remains a limiting factor in the production of structurally diverse chiral amines. In this work, we cloned, purified, and characterized three new ω-TAs from Ochrobactrum anthropi, Acinetobacter baumannii, and Acetobacter pasteurianus that were identified by a BLASTP search using the previously studied ω-TA from Paracoccus denitrificans. All the new ω-TAs exhibited similar substrate specificity, which led us to explore whether the molecular determinants for the substrate specificity are conserved among the ω-TAs. To this end, key active site residues were identified by docking simulation using the X-ray structure of the ω-TA from Pseudomonas putida. We found that the dual recognition in the L pocket is ascribed to Tyr23, Phe88*, and Tyr152 for hydrophobic interaction and Arg414 for recognition of a carboxylate group. In addition, the docking simulation indicates that Trp60 and Ile262 form the S pocket where the substituent size up to an ethyl group turns out to be sterically allowed. The six key residues were found to be essentially conserved among nine ω-TA sequences, underlying the molecular basis for the high similarity in the substrate selectivity. [PUBLICATION ABSTRACT]

Ochrobactrum anthropi strain AD2 was isolated from the waste water treatment plant of an oil refinery and was identified by analysis of the sequence of the gene encoding 16S rDNA. This bacterium produced exopolysaccharides in glucose nutrient broth media supplemented with various hydrocarbons (n-octane, mineral light and heavy oils and crude oils). The exopolysaccharide AD2 (EPS emulsifier) synthesized showed a wide range of emulsifying activity but none of them had surfactant activity. Yield production varied from 0.47 to 0.94 g of EPS l⁻¹ depending on the hydrocarbon added. In the same way, chemical composition and emulsification activity of EPS emulsifier varied with the culture conditions. Efficiency of the EPS emulsifier as biostimulating agent was assayed in soil microcosms and experimental biopiles. The AD2 biopolymer was added alone or combined with commercial products frequently used in oil bioremediation such as inorganic NPK fertilizer and oleophilic fertilizer (S200 C). Also, its efficiency was tested in mixture with activated sludge from an oil refinery. In soil microcosms supplemented with S200 C + EPS emulsifier as combined treatment, indigenous microbial populations as well as hydrocarbon degradation was enhanced when compared with microcosms treated with NPK fertilizer or EPS emulsifier alone. In the same way EPS emulsifier stimulated the bioremediation effect of S200 C product, increasing the number of bacteria and decreasing the amount of hydrocarbon remained. Finally, similar effects were obtained in biopile assays amended with EPS emulsifier plus activated sludge. Our results suggest that the bioemulsifier EPS emulsifier has interesting properties for its application in environment polluted with oil hydrocarbon compounds and may be useful for bioremediation purposes.

Metal nanoparticle synthesis is an interesting area in nanotechnology due to their remarkable optical, magnetic, electrical, catalytic and biomedical properties, but there needs to develop clean, non-toxic and environmental friendly methods for the synthesis and assembly of nanoparticles. Biological agents in the form of microbes have emerged up as efficient candidates for nanoparticle synthesis due to their extreme versatility to synthesize diverse nanoparticles with varying size and shape. In the present study, an eco favorable method for the biosynthesis of silver nanoparticles using marine bacterial isolate has been attempted. Very interestingly, molecular identification proved it as a strain of Ochrobactrum anhtropi. In addition, the isolate was found to have the potential to form silver nanoparticles intracellularly at room temperature within 24 h. The biosynthesized silver nanoparticles were characterized by UV-Vis spectroscopy, transmission electron microscope (TEM) and scanning electron microscope (SEM). The UV-visible spectrum of the aqueous medium containing silver nanoparticles showed a peak at 450 nm corresponding to the plasmon absorbance of silver nanoparticles. The SEM and TEM micrographs revealed that the synthesized silver nanoparticles were spherical in shape with a size range from 38 nm - 85 nm. The silver nanoparticles synthesized by the isolate were also used to explore its antibacterial potential against pathogens like Salmonella Typhi, Salmonella Paratyphi, Vibrio cholerae and Staphylococcus aureus.

Background Alkaline thermostable lipase and biosurfactant producing bacteria are very interested at detergent applications, not only because of their eco-friendly characterize, but alsoproduction lipase and biosurfactant by using cheap materials. Ochrobactrum intermedium strain MZV101 was isolated as washing powder resistant, alkaline thermostable lipase and biosurfactant producing bacterium in order to use at detergent applications. Methods O. intermedium strain MZV101 produces was lipase and biosurfactant in the same media with pH 10 and temperature of 60 °C. Washing test and some detergent compatibility character of lipase enzyme and biosurfactant were assayed. The antimicrobial activity evaluated against various bacteria and fungi. Results Lipase and biosurfactant produced by O. intermedium strain MZV101 exhibited high stability at pH 10–13 and temperature of 70–90 °C, biosurfactant exhibits good stability at pH 9–13 and thermostability in all range. Both lipase and biosurfactant were found to be stable in the presence of different metal ions, detergents and organic solvents. The lipase enzyme extracted using isopropanol with yield of 69.2% and biosurfactant with ethanol emulsification index value of 70.99% and yield of 9.32 (g/l). The single band protein after through from G-50 Sephadex column on SDS-PAGE was calculated to be 99.42 kDa. Biosurfactant O. intermedium strain MZV101 exhibited good antimicrobial activity against Gram-negative bacteria and against various bacterial pathogens. Based upon washing test biosurfactant and lipase O. intermedium strain MZV101considered being strong oil removal. Conclusion The results of this study indicate that isolated lipase and biosurfactant with strong oil removal, antimicrobial activity and good stability could be useful for detergent applications. Graphical abstract