Biosorption and Biomineralization of U(VI) by the marine bacterium Idiomarina loihiensis MAH1: effect of background electrolyte and pH.

The main goal of this study is to compare the effects of pH, uranium concentration, and background electrolyte (seawater and NaClO4 solution) on the speciation of uranium(VI) associated with the marine bacterium Idiomarina loihiensis MAH1. This was done at the molecular level using a multidisciplinary approach combining X-ray Absorption Spectroscopy (XAS), Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), and High Resolution Transmission Electron Microscopy (HRTEM). We showed that the U(VI)/bacterium interaction mechanism is highly dependent upon pH but also the nature of the used background electrolyte played a role. At neutral conditions and a U concentration ranging from 5·10(-4) to 10(-5) M (environmentally relevant concentrations), XAS analysis revealed that uranyl phosphate mineral phases, structurally resembling meta-autunite [Ca(UO2)2(PO4)2 2-6H2O] are precipitated at the cell surfaces of the strain MAH1. The formation of this mineral phase is independent of the background solution but U(VI) luminescence lifetime analyses demonstrated that the U(VI) speciation in seawater samples is more intricate, i.e., different complexes were formed under natural conditions. At acidic conditions, pH 2, 3 and 4.3 ([U] = 5·10(-4) M, background electrolyte  = 0.1 M NaClO4), the removal of U from solution was due to biosorption to Extracellular Polysaccharides (EPS) and cell wall components as evident from TEM analysis. The LIII-edge XAS and TRLFS studies showed that the biosorption process observed is dependent of pH. The bacterial cell forms a complex with U through organic phosphate groups at pH 2 and via phosphate and carboxyl groups at pH 3 and 4.3, respectively. The differences in the complexes formed between uranium and bacteria on seawater compared to NaClO4 solution demonstrates that the actinide/microbe interactions are influenced by the three studied factors, i.e., the pH, the uranium concentration and the chemical composition of the solution.

Deep-sea bacteria enriched by oil and dispersant from the Deepwater Horizon spill.

The Deepwater Horizon oil spill resulted in a massive influx of hydrocarbons into the Gulf of Mexico (the Gulf). To better understand the fate of the oil, we enriched and isolated indigenous hydrocarbon-degrading bacteria from deep, uncontaminated waters from the Gulf with oil (Macondo MC252) and dispersant used during the spill (COREXIT 9500). During 20 days of incubation at 5°C, CO(2) evolution, hydrocarbon concentrations and the microbial community composition were determined. Approximately 60% to 25% of the dissolved oil with or without COREXIT, respectively, was degraded, in addition to some hydrocarbons in the COREXIT. FeCl(2) addition initially increased respiration rates, but not the total amount of hydrocarbons degraded. 16S rRNA gene sequencing revealed a succession in the microbial community over time, with an increase in abundance of Colwellia and Oceanospirillales during the incubations. Flocs formed during incubations with oil and/or COREXIT in the absence of FeCl(2) . Synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectromicroscopy revealed that the flocs were comprised of oil, carbohydrates and biomass. Colwellia were the dominant bacteria in the flocs. Colwellia sp. strain RC25 was isolated from one of the enrichments and confirmed to rapidly degrade high amounts (approximately 75%) of the MC252 oil at 5°C. Together these data highlight several features that provide Colwellia with the capacity to degrade oil in cold, deep marine habitats, including aggregation together with oil droplets into flocs and hydrocarbon degradation ability.

Ca-Mg kutnahorite and struvite production by Idiomarina strains at modern seawater salinities.

The production of Mg-rich carbonates by Idiomarina bacteria at modern seawater salinities has been investigated. With this objective, four strains: Idiomarina abyssalis (strain ATCC BAA-312), Idiomarina baltica (strain DSM 15154), Idiomarina loihiensis (strains DSM 15497 and MAH1) were used. The strain I. loihiensis MAH1 is a new isolate, identified in the scope of this work. The four moderately halophilic strains precipitated struvite (NH4MgPO4 x 6H2O) crystals that appear encased by small Ca-Mg kutnahorite [CaMg(CO3)2] spheres and dumbbells, which are also regularly distributed in the bacterial colonies. The proportion of Ca-Mg kutnahorite produced by the bacteria assayed ranged from 50% to 20%, and I. abyssalis also produced monohydrocalcite. All precipitated minerals appeared to be related to the bacterial metabolism and, consequently, can be considered biologically induced. Amino acid metabolism resulted in a release of ammonia and CO2 that increase the pH and CO(3)(2-) concentration of the culture medium, creating an alkaline environment that favoured carbonate and struvite precipitation. This precipitation may be also related to heterogeneous nucleation on negatively charged points of biological structures. Because the nature of the organic matrix determines which ion is preferentially adsorbed and, consequently, which mineral phase is formed, the uniquely high content in odd-iso-branched fatty acids of the Idiomarina suggests that their particular membrane characteristics could induce Ca-Mg kutnahorite production. The Ca-Mg kutnahorite, a mineral with a dolomite-ordered structure, production at seawater salinities is noticeable. To date, such precipitation in laboratory cultures, has only been described in hypersaline conditions. It has also been the first time that biomineralization processes have been related to Idiomarina bacteria.

Idiomarina loihiensis sp. nov., a halophilic gamma-Proteobacterium from the Lo'ihi submarine volcano, Hawai'i.

During an investigation of bacterial diversity at hydrothermal vents on the Lo'ihi Seamount, Hawai'i, a novel bacterium (designated L2-TR(T)) was cultivated, which shares 99.9 % 16S rRNA gene sequence similarity over 1415 nt with an uncultured eubacterium from sediment at a depth of 11 000 m in the Mariana Trench. The nearest cultivated neighbour of L2-TR(T), however, is Idiomarina abyssalis KMM 227(T), with which it shares 98.9 % 16S rRNA sequence similarity. L2-TR(T) differed from I. abyssalis KMM 227(T) in several phenotypic respects, including growth at 46 degrees C and in medium that contained 20 % (w/v) NaCl. DNA-DNA hybridization data showed that L2-TR(T) did not belong to the species I. abyssalis (43.4 % DNA-DNA reassociation). Cells of L2-TR(T) were Gram-negative rods, 0.35 microm wide and 0.7-1.0 microm long, which were occasionally up to 1.8 microm in length. Cells were motile by a single polar or subpolar flagellum. The major fatty acid in L2-TR(T) was iso-C(15 : 0) (32.6 %). The DNA G+C content was 47.4 mol%. Phenotypic and genotypic analyses indicated that L2-TR(T) could be assigned to the genus Idiomarina but, based on significant phenotypic and genotypic differences, constituted a novel species within this genus, Idiomarina loihiensis sp. nov., of which L2-TR(T) (=ATCC BAA-735(T)=DSM 15497(T)) is the type strain.

Marinobacter excellens sp. nov., isolated from sediments of the Sea of Japan.

Five strains of halophilic, Gram-negative marine bacteria (KMM 3809(T), KMM 3814, KMM 3815, KMM 3817 and KMM 3818) were isolated from sediments collected from Chazhma Bay, Sea of Japan. Phylogenetic 16S rRNA gene sequence-based analysis placed these bacteria in a clade within the genus Marinobacter in the gamma-Proteobacteria. KMM 3809(T) showed highest 16S rRNA gene sequence similarity of 97.3 % to Marinobacter litoralis and 96.9 % to Marinobacter hydrocarbonoclasticus and Marinobacter aquaeolei. DNA-DNA hybridization between the five isolates was at the conspecific level (94-96 %) and that among the closest phylogenetic neighbours ranged from 45.0 to 62.5 %. The new organisms were susceptible to polymyxin. Predominant fatty acids were C(16 : 0), C(16 : 1)omega9c, C(16 : 1)omega7c and C(18 : 1)omega9c. Phylogenetic evidence, along with phenotypic and genotypic characteristics, showed that the bacteria constituted a novel species of the genus Marinobacter. The name Marinobacter excellens sp. nov. is proposed for this species, with the type strain KMM 3809(T) (=CIP 107686(T)).