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Taxonomic characterization of Ochrobactrum sp. isolates from soil samples and wheat roots, and description of Ochrobactrum tritici sp. nov. and Ochrobactrum grignonense sp. nov.

A large collection of bacterial strains, immunotrapped from soil and from the wheat rhizoplane, was subjected to polyphasic taxonomy by examining various pheno- and genotypic parameters. Strains were grouped on (inter) repetitive extragenic palindromic DNA (REP) PCR profiles at the intraspecies level. Pheno- and genotypic characters were assessed for representatives from 13 different REP groups. Strains of nine REP groups constituting two physiological BIOLOG clusters fell in the coherent DNA-DNA reassociation group of Ochrobactrum anthropi. Strains of two REP groups constituting a separate BIOLOG cluster fell in the coherent DNA-DNA reassociation group of Ochrobactrum intermedium. Additional phenotypic characters differentiating O. anthropi and O. intermedium were found. REP group K strains constituted a different BIOLOG cluster, a separate DNA-DNA reassociation group and a distinct phylogenetic lineage in 165 rDNA homology analysis, indicating that REP group K strains represent a new species. Diagnostic phenotypic characters were found. Closest relatives were Ochrobactrum species. The name Ochrobactrum grignonense sp. nov. is proposed (type strain OgA9aT = LMG 18954T = DSM 13338T). REP group J strains again constituted a different BIOLOG cluster, a separate DNA-DNA reassociation group and showed, as a biological particularity, a strict preference for the rhizoplane as habitat. Diagnostic phenotypic characters were found. This indicated that REP group J strains represent a further new species, although phylogenetic analyses using 16S rDNA homology were not able to separate the cluster of REP group J sequences significantly from 16S rDNA sequences of Ochrobactrum anthropi. The name Ochrobactrum tritici sp. nov. is proposed (type strain SCII24T = LMG 18957T = DSM 13340T).

Alphaproteobacteria↗

Evaluation of the relatedness of Brucella spp. and Ochrobactrum anthropi and description of Ochrobactrum intermedium sp. nov., a new species with a closer relationship to Brucella spp.

The relatedness of Brucella spp. and Ochrobactrum anthropi was studied by protein profiling, Western blot, immunoelectrophoresis and 16S rRNA analysis. Whole-cell and soluble proteins of brucellae and O. anthropi showed serological cross-reactivities quantitatively and qualitatively more intense than those existing with similar extracts of Agrobacterium spp. Numerical analysis of Western blot profiles of whole-cell extracts showed that O. anthropi LMG 3301 was closer to Brucella spp. than to O. anthropi LMG 3331T, a result not obtained by protein profiling. These differences were not observed by Western blot with soluble fractions, and immunoelectrophoretic analyses suggested that this was due to destruction of conformational epitopes in Western blot procedures with the subsequent simplification of antigenic profile. Analysis of the 16S rRNA sequences of strains previously used in the species definition confirmed that strain LMG 3301, and also LMG 3306, were closer to the brucellae, and that LMG 3331T was in a separate cluster. The LMG 3301 and the LMG 3331T clusters could also be separated by their different colistin sensitivity and by PCR with 16S rRNA Brucella primers, and both methods showed strains of both clusters among clinical isolates classified as O. anthropi by conventional tests. These results and those of previous DNA-DNA hybridization studies [Holmes, B., Popoff, M., Kiredjian, M. & Kersters, K. (1988). Int J Syst Bacteriol 38, 406-416] show that the LMG 3301 cluster and related clinical isolates should be given a new species status for which the name Ochrobactrum intermedium sp. nov. is proposed (type strain is LMG 3301T=NCTC 12171T = CNS 2-75T).

Animals↗

Brucella abortus and its closest phylogenetic relative, Ochrobactrum spp., differ in outer membrane permeability and cationic peptide resistance.

The outer membrane (OM) of the intracellular parasite Brucella abortus is permeable to hydrophobic probes and resistant to destabilization by polycationic peptides and EDTA. The significance of these unusual properties was investigated in a comparative study with the opportunistic pathogens of the genus Ochrobactrum, the closest known Brucella relative. Ochrobactrum spp. OMs were impermeable to hydrophobic probes and sensitive to polymyxin B but resistant to EDTA. These properties were traced to lipopolysaccharide (LPS) because (i) insertion of B. abortus LPS, but not of Escherichia coli LPS, into Ochrobactrum OM increased its permeability; (ii) permeability and polymyxin B binding measured with LPS aggregates paralleled the results with live bacteria; and (iii) the predicted intermediate results were obtained with B. abortus-Ochrobactrum anthropi and E. coli-O. anthropi LPS hybrid aggregates. Although Ochrobactrum was sensitive to polymyxin, self-promoted uptake and bacterial lysis occurred without OM morphological changes, suggesting an unusual OM structural rigidity. Ochrobactrum and B. abortus LPSs showed no differences in phosphate, qualitative fatty acid composition, or acyl chain fluidity. However, Ochrobactrum LPS, but not B. abortus LPS, contained galacturonic acid. B. abortus and Ochrobactrum smooth LPS aggregates had similar size and zeta potential (-12 to -15 mV). Upon saturation with polymyxin, zeta potential became positive (1 mV) for Ochrobactrum smooth LPS while remaining negative (-5 mV) for B. abortus smooth LPS, suggesting hindered access to inner targets. These results show that although Ochrobactrum and Brucella share a basic OM pattern, subtle modifications in LPS core cause markedly different OM properties, possibly reflecting the adaptive evolution of B. abortus to pathogenicity.

Alphaproteobacteria↗

Molecular and phenotypic features for identification of the opportunistic pathogens Ochrobactrum spp.

Among the six species characterized within the genus Ochrobactrum, Ochrobactrum anthropi and Ochrobactrum intermedium are currently reported as opportunistic pathogens in humans. Since the species identification is mainly based on 16S rDNA analysis, the aim of this study was to search for other characteristics useful for Ochrobactrum species discrimination. Ribotyping, morphological and biochemical analyses, and antimicrobial susceptibility testing were performed for a panel of 35 clinical isolates, first identified to the species level using 16S rDNA sequencing. Type and reference strains of five Ochrobactrum species were comparatively analysed. Commercial identification systems such as API 20NE and VITEK 2 were tested for their ability to identify Ochrobactrum anthropi and to detect other members of the genus Ochrobactrum. An improved protocol for the identification of Ochrobactrum spp. by routine medical microbiology practices is proposed: isolation of a non-fastidious non-fermenting oxidase-positive Gram-negative rod resistant to all beta-lactams except imipenem indicates the genus Ochrobactrum, and the API 20NE system confirms the genus identification for most strains, whereas the VITEK 2 system using ID-GNB cards was less powerful. Urease activity, the mucoidy of the colonies, growth at 45 degrees C on tryptic soy agar, and susceptibility to colistin, tobramycin and netilmicin should be considered as differential characteristics for identification of O. anthropi and O. intermedium to the species level. However, definitive identification depends on genotyping methods.

Anti-Bacterial Agents↗

Genetic and phenotypic microdiversity of Ochrobactrum spp.

The diversity of Ochrobactrum anthropi, Ochrobactrum intermedium, Ochrobactrum tritici and Ochrobactrum grignonense in agricultural soil and on the wheat rhizoplane was investigated. O. anthropi was isolated both from soil and from the rhizoplane, O. intermedium and grignonense only from bulk soil, and O. tritici only from the wheat rhizoplane. On the genetic level, the immunotrapped isolates and a number of strains from culture collection mainly of clinical origin were compared with rep-PCR profiling using BOX primers, and a subset of these isolates and strains using REP primers. The isolates clustered according to their species affiliation. There was no correlation between rep clusters of O. anthropi isolates and habitat (place of isolation). The genetic diversity of Ochrobactrum at the species level as well as microdiversity of O. anthropi (number of BOX groups) was higher in soil than on the rhizoplane. Similarity values from genetic rep-PCR profiles correlated positively with DNA-DNA reassociation percentages. Isolates with >80.7% similarity in BOX profile and >86.4% in rep profile clustered within the same species. Similarity analysis of rep-PCR profiles is hence an alternative to DNA-DNA hybridization as a genomic criterion for species delineation within the genus Ochrobactrum. We used the substrate utilization system BIOLOG-GN to compare the immunotrapped isolates on the phenetic level. For the isolates from bulk soil, substrate utilization versatility (number of utilized substrates) and substrate utilization capacity (mean conversion rate of substrates) were slightly but significantly higher than for the isolates from the rhizoplane. This trend was also seen using API 20E and 20NE systems. Plate counts of total bacteria and the number of immunotrapped Ochrobactrum isolates per gram dry weight were higher for the rhizoplane than for the soil samples. The results of genetic and phenotypic analyses indicated a 'rhizosphere effect'; the diversity and metabolic capacity of Ochrobactrum isolates were higher in bulk soil, and the population density was higher on the wheat rhizoplane.

Biodiversity↗

Pulsed-field gel electrophoresis to study the diversity of whole-genome organization in the genus Ochrobactrum.

The alpha-proteobacterial genus Ochrobactrum groups together organisms that display varied life-styles, such as free-living bacteria, members of rhizosphere and soil, nitrogen-fixing bacteria in plant nodules, xenobiotic-degrading bacteria, colonizers of nematodes and insects, and opportunistic human pathogens. The genomes of nine strains of Ochrobactrum anthropi and eight strains of Ochrobactrum intermedium were analyzed by pulsed-field gel electrophoresis of the whole genome and of I-CeuI digestion fragments. All isolates and type strains of O. anthropi and O. intermedium possessed two high-molecular-weight circular replicons identified as two independent chromosomes on the basis of 16S rDNA hybridization. The genome of the type strain of Ochrobactrum tritici, Ochrobactrum grignonense, and Ochrobactrum gallinifaecis also contained two circular chromosomes. The megaplasmid content was highly variable even among strains in the same species, leading to whole-genome sizes that ranged from 5.060 to 8.300 Mbp and from 4.690 to 7.680 Mbp for O. anthropi and O. intermedium, respectively. This exceptional level of genomic diversity could be related to the adaptability of Ochrobactrum spp. to various ecological niches.

Chromosomes, Bacterial↗

Towards a standardized format for the description of a novel species (of an established genus): Ochrobactrum gallinifaecis sp. nov.

A format for the description of single novel species is proposed, which should facilitate the reviewing process by assisting the provision of data in a standardized form. The abstract must be short and concise, highlighting phylogenetic position, morphology and chemotaxonomy for genus affiliation, the genotypic and phenotypic basis for species differentiation, and the name and deposition numbers from two public culture collections in different countries for the type strain: A Gram-negative, rod-shaped, non-spore-forming bacterium (Iso 196(T)) was isolated from chicken faeces. On the basis of 16S rRNA gene sequence similarity, strain Iso 196(T) was shown to belong to the alpha-2 subclass of the Proteobacteria related to Ochrobactrum tritici (95.6%), Ochrobactrum grignonense (95.0%) and Ochrobactrum anthropi (94.6%), and the phylogenetic distance from any validly described species within the genus Brucella was less than 95%. Chemotaxonomic data (major ubiquinone - Q-10; major polyamines - spermidine and putrescine; major polar lipids - phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine; major fatty acids - C(18 : 1)omega7c and C(19 : 0) cyclo omega8c) supported the affiliation of strain Iso 196(T) to the genus Ochrobactrum. The results of DNA-DNA hybridization and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain Iso 196(T) from the four validly published Ochrobactrum species. Iso 196(T) therefore represents a new species, for which the name Ochrobactrum gallinifaecis sp. nov. is proposed, with the type strain Iso 196(T) (= DSM 15295(T) = CIP 107753(T)).

Bacterial Typing Techniques↗

[Species identification and molecular epidemiology of bacteria belonging to Ochrobactrum genus].

Two species of medical interest belong to the genus Ochrobactrum, Ochrobactrum anthropi and Ochrobactrum intermedium. They are members of the microbiota of soil and an increasing number of works report the isolation of O. anthropi from clinical specimen, especially from immunocompromised patients and nosocomial infection. Involving of each species in human infection is poorly estimated due to unclear differential phenotypic characters. We performed 16S rDNA sequencing for identification of 20 clinical isolates of Ochrobactrum sp. to the species level. Then, we studied the phenotype of each isolate especially, morphology, culture onto different media and at different temperatures, biochemical characters and antibiotics resistance pattern. Colony morphology after growth onto Trypticase-Soy and McConkey agar, culture at 45 degrees C onto Trypticase-Soja agar, presence of urease, and netilmycin, tobramycin and colistin resistance allowed identification of species. Ribotyping using HindIII and EcoRI gave a supplementary criterion for species determination but did not allow typing at the infra-species level. In contrast, Pulsed-Field Gel Electrophoresis showed high degree of polymorphism between strains and proved the clonality of certain isolates. Thus, this method could be a useful tool for molecular epidemiology of Ochrobactrum infections.

DNA, Ribosomal↗

Complete mineralisation of dimethylformamide by Ochrobactrum sp. DGVK1 isolated from the soil samples collected from the coalmine leftovers.

A bacterial strain DGVK1 capable of using N,N-dimethylformamide (DMF) as sole source of carbon and nitrogen was isolated from the soil samples collected from the coalmine leftovers. The molecular phylogram generated using the complete sequence of 16S rDNA of the strain DGVK1 showed close links to the bacteria grouped under Brucellaceae family that belongs to alphaproteobacteria class. Specifically, the 16S rDNA sequence of strain DGVK1 has shown 97% similarity to Ochrobactrum anthropi LMG 3331 (D12794). This bacterium has also shown impressive growth on dimethylamine, methylamine, formaldehyde and formate that are considered to be the prominent catabolic intermediates of DMF. DMF degradation has led to the accumulation of ammonia and dimethylamine contributing to the increase of pH of the medium. The DMF-grown resting cells of Ochrobactrum sp. DGVK1 have also contributed for the release of ammonia when resting cell suspension was added to phosphate buffer containing DMF. Similar experiments done with the glucose-grown cultures have not produced ammonia and thus indicating the inducible nature of DMF-degrading enzymes in Ochrobactrum sp. DGVK1. Further, dimethylformamidase, dimethylamine dehydrogenase and methylamine dehydrogenase, the key enzymes involved in the degradation of DMF, were assayed, and the activities of these enzymes were found only in DMF-grown cultures further confirming the inducible nature of the DMF degradation. Based on these results, DMF degradation pathway found in Ochrobactrum sp. DGVK1 has been proposed.

Biodegradation, Environmental↗

Comparative sequence analysis of the internal transcribed spacer 1 of Ochrobactrum species.

The internal 16S/23S rDNA (rrs/rrl) internal spacer region 1 (ITS1) of 54 Ochrobactrum strains and close relatives was analysed. Separation of ITS1 containing PCR products by gel-electrophoresis, DGGE, cloning and sequencing revealed ITS1 length and sequence heterogeneity. We found up to 5 different allelic ITS1 stretches within a single strain (Ochrobactrum intermedium LMG 3301T), and 2-3 different ITS1 alleles in O. tritici. Within ITS1, ITS1c, being part of the conserved double-stranded rrn processing stem dsPS1, produced the most reliable segment tree. The overall ITS1, ITS1c and rrs phylogenetic tree topologies were generally consistent, but there was evidence for horizontal rrn (segment) transfer in O. tritici LMG 2134 (formerly O. anthropi). Good correlations were found between ITS1, ITS1c and rrs sequence similarity and DNA-DNA hybridization values indicating that phylogenetic analysis of ITS1 and ITS1c both can be used to preliminarily deduce the phylogenetic affiliation if HGT was excluded. Strains sharing > 96.19% ITS1c (> 95.11% ITS1) similarity fell within a species, and < or = 68.42% ITS1c (< or = 70.33% ITS1) similarity outside a genus. Both ITS1 and ITS1c analysis resolved microdiversity more profoundly than rrs analysis and revealed clades (genomovars) within O. anthropi that were also produced in rep cluster analysis. There was no evidence for habitat-specific ITS1 genomovars within Ochrobactrum species. Diversity of Ochrobactrum was higher in soil than at the rhizoplane below and at the species level. Isolates from soil contained only 1 rrn type whereas isolates from human clinical, animal and rhizoplane specimens could contain more.

Alleles↗

Endophytic colonization ability of two deep-water rice endophytes, Pantoea sp. and Ochrobactrum sp. using green fluorescent protein reporter.

Colonization ability of the two endophytic bacteria, isolated from surface sterilized seeds of Jaisurya variety of deep-water rice viz., Pantoea sp. and Ochrobactrum sp., was compared after genetically tagging them with a constitutively expressing green fluorescent protein gene (gfp). Confocal laser scanning microscopy (CLSM) of hydroponically grown seedlings of Jaisurya rice, inoculated with gfp-tagged endophytes, revealed that both Pantoea sp. and Ochrobactrum sp. colonized the intercellular spaces in the root cortex when inoculated separately. Colonization by gfp-tagged Ochrobactrum sp. was severely inhibited when co-inoculated with an equal number (10(5) c.f.u. ml(-1)) of wild type Pantoea sp., but the converse was not true. Pantoea sp. was a more aggressive endophytic colonizer of its host than Ochrobactrum sp. The potential of using GFP reporter and CLSM as tools in evaluating competitive ability of colonization among endophytes is herewith demonstrated.

Cell Division↗

Occurrence of natural dixenic associations between the symbiont Photorhabdus luminescens and bacteria related to Ochrobactrum spp. in tropical entomopathogenic Heterorhabditis spp. (Nematoda, Rhabditida).

Bacteria naturally associated with the symbiont Photorhabdus luminescens subsp. akhurstii were isolated from the entomopathogenic nematode Heterorhabditis indica. Bacterial isolates distinct from P. luminescens subsp. akhurstii were obtained from 33% of the samples. Fourteen bacterial isolates, from nematodes collected from three different Caribbean islands, were characterized by conventional phenotypic tests, restriction fragment length polymorphism and sequence analyses of PCR-amplified 16S rRNA genes (16S rDNAs). Isolates were grouped into three genotypes, each one being associated with one Caribbean island. Phenotypic characteristics and 16S rDNA analysis showed that the Photorhabdus-associated bacteria were closely related to Ochrobactrum anthropi for the group from Guadeloupe, and to Ochrobactrum intermedium for the two groups from the Dominican Republic and Puerto Rico. No pathogenicity of the Ochrobactrum spp. to the insects Galleria mellonella and Spodoptera littoralis (Lepidoptera) was detected. Since Ochrobactrum spp. are considered as human opportunist pathogens, the mass production of entomopathogenic nematodes for biological control requires strict vigilance.

Alphaproteobacteria↗

Ochrobactrum oryzae sp. nov., an endophytic bacterial species isolated from deep-water rice in India.

A non-pigmented, motile, Gram-negative bacterium designated MTCC 4195(T) was isolated from surface-sterilized seeds and plant tissue from deep-water rice (Oryza sativa) cultivated in Suraha Tal Lake in northern India. This isolate was shown to reinfect and colonize deep-water rice endophytically. The highest level of 16S rRNA sequence similarity (96.8 %) to strain MTCC 4195(T) was shown by Ochrobactrum gallinifaecis DSM 15295(T). Strain MTCC 4195(T) utilized gamma-hydroxybutyric acid, adonitol, d-glucosaminic acid and arabinose as carbon sources, but failed to use gentiobiose or citrate. The cell-wall fatty acids of strain MTCC 4195(T) were characterized by the presence of a relatively large proportion of C(18 : 1)omega7c and a relative small proportion of C(16 : 0) in comparison with Ochrobactrum species. DNA-DNA relatedness studies showed less than 52 % binding with the DNAs of type strains of other species of the genus Ochrobactrum. On the basis of phenotypic and genotypic characteristics and the results of 16S rRNA gene sequence analysis, the novel species Ochrobactrum oryzae sp. nov. is proposed, with MTCC 4195(T) (=DSM 17471(T)) as the type strain.

Carbohydrate Metabolism↗

Genotyping of Ochrobactrum anthropi by recA-based comparative sequence, PCR-RFLP, and 16S rRNA gene analysis.

A recA-PCR restriction fragment length polymorphism assay was developed to study intraspecies variation among Ochrobactrum anthropi. Primers deduced from the known recA gene sequence of the genetically closely related genus Brucella allowed the specific amplification of a 1065 bp recA fragment from each of the 38 O. anthropi and the eight Brucella strains investigated. RecA was also amplified from the type strains of O. intermedium, O. tritici, and O. lupini but could not be generated from O. grignonense and O. gallinifaecis. Subsequent comparative recA sequence- and HaeIII-recA restriction fragment length polymorphism analysis identified nine different genospecies among the tested 38 O. anthropi isolates, whereas the recA sequences of the Brucella spp. were indistinguishable. Furthermore, Brucella spp., O. anthropi, O. intermedium, and O. tritici were clearly separated from each other by means of their recA sequences and HaeIII restriction patterns. Five strains of uncertain species status listed in the Culture Collection University of Göteborg bacterial culture collection as O. anthropi were characterized by recA analysis, and their phylogenetic position within the Brucella-Ochrobactrum group was determined. In summary, recA-sequence analysis provides a new reliable molecular subtyping tool to study the phylogeny of the Ochrobactrum taxon at both the inter- and intraspecies level.

Animals↗

Evaluation of Ochrobactrum intermedium bacteremia in a patient with bladder cancer.

It is generally believed that Ochrobactrum anthropi is the only pathogenic species in the genus Ochrobactrum. We report a case of presumptive Ochrobactrum intermedium bacteremia in a patient with bladder cancer. Identification of a rare species using rapid commercial panel could lead to an erroneous result as this clinical isolate was initially reported to be Shewanella putrefaciens. The patient was successfully treated with imipenem and ciprofloxacin.

Aged↗

Specificity inversion of Ochrobactrum anthropi D-aminopeptidase to a D,D-carboxypeptidase with new penicillin binding activity by directed mutagenesis.

The serine penicillin-recognizing proteins have been extensively studied. They show a wide range of substrate specificities accompanied by multidomain features. Their adaptation capacity has resulted in the emergence of pathogenic bacteria resistant to beta-lactam antibiotics. The most divergent enzymatic activities in this protein family are those of the Ochrobactrum anthropi D-aminopeptidase and of the Streptomyces R61 D,D-carboxypeptidase/transpeptidase. With the help of structural data, we have attempted to identify the factors responsible for this opposite specificity. A loop deletion mutant of the Ochrobactrum anthropi D-aminopeptidase lost its original activity in favor of a new penicillin-binding activity. D-aminopeptidase activity of the deletion mutant can be restored by complementation with another deletion mutant corresponding to the noncatalytic domain of the wild-type enzyme. By a second step site-directed mutagenesis, the specificity of the Ochrobactrum anthropi D-aminopeptidase was inverted to a D,D-carboxypeptidase specificity. These results imply a core enzyme with high diversity potential surrounded by specificity modulators. It is the first example of drastic specificity change in the serine penicillin-recognizing proteins. These results open new perspectives in the conception of new enzymes with nonnatural specificities. The structure/specificity relationship in the serine penicillin-recognizing proteins are discussed.

Aminopeptidases↗

Nodulation of Lupinus albus by strains of Ochrobactrum lupini sp. nov.

The nodulation of legumes has for more than a century been considered an exclusive capacity of a group of microorganisms commonly known as rhizobia and belonging to the alpha-Proteobacteria. However, in the last 3 years four nonrhizobial species, belonging to alpha and beta subclasses of the Proteobacteria, have been described as legume-nodulating bacteria. In the present study, two fast-growing strains, LUP21 and LUP23, were isolated from nodules of Lupinus honoratus. The phylogenetic analysis based on the 16S and 23S rRNA gene sequences showed that the isolates belong to the genus Ochrobactrum. The strains were able to reinfect Lupinus plants. A plasmid profile analysis showed the presence of three plasmids. The nodD and nifH genes were located on these plasmids, and their sequences were obtained. These sequences showed a close resemblance to the nodD and nifH genes of rhizobial species, suggesting that the nodD and nifH genes carried by strain LUP21T were acquired by horizontal gene transfer. A polyphasic study including phenotypic, chemotaxonomic, and molecular features of the strains isolated in this study showed that they belong to a new species of the genus Ochrobactrum for which we propose the name Ochrobactrum lupini sp. nov. Strain LUP21T (LMG 20667T) is the type strain.

Base Sequence↗

Ochrobactrum tritici strain 5bvl1 - characterization of a Cr(VI)-resistant and Cr(VI)-reducing strain.

Bacterial strain 5bvl1, isolated from a chromium-contaminated wastewater treatment plant and identified as Ochrobactrum tritici, was resistant to a broad range of antibiotics, to Cr(VI), Ni(II), Co(II), Cd(II), and Zn(II), and was able to grow in the presence of 5% NaCl and within the pH range 4-10. Characterization showed that strain 5bvl1 could be considered a halotolerant and alkalitolerant microorganism resistant to high concentrations of Cr(VI). This strain was able to grow aerobically in up to 10 mmolxL(-1) Cr(VI). Cr(VI) resistance was independent of sulphate concentration. Under aerobic conditions strain 5bvl1 was also able to reduce high Cr(VI) concentrations (up to 1.7 mmolxL(-1)). Increasing concentrations of Cr(VI) in the medium lowered the growth rate of strain 5bv11 but the reduction in growth rate could not be directly correlated with the amount of Cr(VI) reduced. Unlike the type strain, which was only able to reduce Cr(VI), strain 5bvl1 was resistant to Cr(VI) and able to reduce it. Moreover, in strain 5bvl1, the rate and extent of Cr(VI)-reduction were higher than in the other strains of the genus Ochrobactrum. Ochrobactrum strain 5bvl1 resists high Cr(VI) concentrations and has a high Cr(VI)-reducing ability, making it a valuable tool in bioremediation.

Biodegradation, Environmental↗