Manganese(II)-Oxidizing Bacillus Spores in Guaymas Basin Hydrothermal Sediments and Plumes

Microbial oxidation and precipitation of manganese at deep-sea hydrothermal vents are important oceanic biogeochemical processes, yet nothing is known about the types of microorganisms or mechanisms involved. Here we report isolation of a number of diverse spore-forming Mn(II)-oxidizing Bacillus species from Guaymas Basin, a deep-sea hydrothermal vent environment in the Gulf of California, where rapid microbially mediated Mn(II) oxidation was previously observed. mnxG multicopper oxidase genes involved in Mn(II) oxidation were amplified from all Mn(II)-oxidizing Bacillus spores isolated, suggesting that a copper-mediated mechanism of Mn(II) oxidation could be important at deep-sea hydrothermal vents. Phylogenetic analysis of 16S rRNA and mnxG genes revealed that while many of the deep-sea Mn(II)-oxidizing Bacillus species are very closely related to previously recognized isolates from coastal sediments, other organisms represent novel strains and clusters. The growth and Mn(II) oxidation properties of these Bacillus species suggest that in hydrothermal sediments they are likely present as spores that are active in oxidizing Mn(II) as it emerges from the seafloor.     

Enzymatic manganese(II) oxidation by metabolically dormant spores of diverse Bacillus species

Bacterial spores are renowned for their longevity, ubiquity, and resistance to environmental insults, but virtually nothing is known regarding whether these metabolically dormant structures impact their surrounding chemical environments. In the present study, a number of spore-forming bacteria that produce dormant spores which enzymatically oxidize soluble Mn(II) to insoluble Mn(IV) oxides were isolated from coastal marine sediments. The highly charged and reactive surfaces of biogenic metal oxides dramatically influence the oxidation and sorption of both trace metals and organics in the environment. Prior to this study, the only known Mn(II)-oxidizing sporeformer was the marine Bacillus sp. strain SG-1, an extensively studied bacterium in which Mn(II) oxidation is believed to be catalyzed by a multicopper oxidase, MnxG. Phylogenetic analysis based on 16S rRNA and mnxG sequences obtained from 15 different Mn(II)-oxidizing sporeformers (including SG-1) revealed extensive diversity within the genus Bacillus, with organisms falling into several distinct clusters and lineages. In addition, active Mn(II)-oxidizing proteins of various sizes, as observed in sodium dodecyl sulfate-polyacrylamide electrophoresis gels, were recovered from the outer layers of purified dormant spores of the isolates. These are the first active Mn(II)-oxidizing enzymes identified in spores or gram-positive bacteria. Although extremely resistant to denaturation, the activities of these enzymes were inhibited by azide and o-phenanthroline, consistent with the involvement of multicopper oxidases. Overall, these studies suggest that the commonly held view that bacterial spores are merely inactive structures in the environment should be revised.     

Localization of Mn(II)-oxidizing activity and the putative multicopper oxidase,MnxG, to the exosporium of the marine Bacillus sp. strain SG-1

Dormant spores of the marine Bacillus sp. strain SG-1 catalyze the oxidation of manganese(II), thereby becoming encrusted with insoluble Mn(III,IV) oxides. In this study, it was found that the Mn(II)-oxidizing activity could be removed from SG-1 spores using a French press and recovered in the supernatant following centrifugation of the spores. Transmission electron microscopy of thin sections of SG-1 spores revealed that the ridged outermost layer was removed by passage through the French press, leaving the remainder of the spore intact. Comparative chemical analysis of this layer with the underlying spore coats suggested that this outer layer is chemically distinct from the spore coat. Taken together, these results indicate that this outer layer is an exosporium. Previous genetic analysis of strain SG-1 identified a cluster of genes involved in Mn(II) oxidation, the mnx genes. The product of the most downstream gene in this cluster, MnxG, appears to be a multicopper oxidase and is essential for Mn(II) oxidation. In this study, MnxG was overexpressed in Escherichia coli and used to generate polyclonal antibodies. Western blot analysis demonstrated that MnxG is localized to the exosporium of wild-type spores but is absent in the non-oxidizing spores of transposon mutants within the mnx gene cluster. To our knowledge, Mn(II) oxidation is the first oxidase activity, and MnxG one of the first gene products, ever shown to be associated with an exosporium.     

锰氧化菌Bacillus sp. MK3-1的Mn(Ⅱ)氧化特性和除锰能力研究

锰氧化微生物能够将可溶的Mn(II)氧化为不溶的锰氧化物沉淀, 因此在生物除锰研究上具有重要的应用价值。本研究从锰污染土壤中分离到一株锰氧化菌Bacillus sp. MK3-1, 该菌对MnCl2有较高抗性, 其最低抑制浓度(Minimal inhibitory concentration, MIC)为20 mmol/L。实验表明该菌在培养基中Mn(Ⅱ)的去除率高达96%, 同时将其制成固体包埋菌剂应用于含0.15 mmol/L的MnCl2水溶液实验, 结果表明其仍然具有稳定的除锰能力, 去除率为87.12%, 使溶液的终锰浓度符合国家排放标准。扫描电子显微镜观察和能谱分析实验表明, 实验产生的锰氧化物均匀地分布在Bacillus sp. MK3-1的细胞表面, 细胞表面含锰量为19.60% (W/W)。用简并引物扩增目前被认为催化锰氧化的多铜氧化酶基因mnxG, 获得了903 bp的基因片段, 其基因产物与已报道的多铜氧化酶具有86%的同源性。     

Marine Bacillus spores as catalysts for oxidative precipitation and sorption of metals

The oxidation of soluble manganese(II) to insoluble Mn(III,IV) oxide precipitates plays an important role in the environment. These Mn oxides are known to oxidize numerous organic and inorganic compounds, scavenge a variety of other metals on their highly charged surfaces, and serve as electron acceptors for anaerobic respiration. Although the oxidation of Mn(II) in most environments is believed to be bacterially-mediated, the underlying mechanisms of catalysis are not well understood. In recent years, however, the application of molecular biological approaches has provided new insights into these mechanisms. Genes involved in Mn oxidation were first identified in our model organism, the marine Bacillus sp. strain SG-1, and subsequently have been identified in two other phylogenetically distinct organisms, Leptothrix discophora and Pseudomonas putida. In all three cases, enzymes related to multicopper oxidases appear to be involved, suggesting that copper may play a universal role in Mn(II) oxidation. In addition to catalyzing an environmentally important process, organisms capable of Mn(II) oxidation are potential candidates for the removal, detoxification, and recovery of metals from the environment. The Mn(II)-oxidizing spores of the marine Bacillus sp. strain SG-1 show particular promise, due to their inherent physically tough nature and unique capacity to bind and oxidatively precipitate metals without having to sustain growth.     

Identification and characterization of a gene cluster involved in manganese oxidation by spores of the marine Bacillus sp. strain SG-1.

The marine Bacillus sp. strain SG-1 forms spores that oxidize manganese(II) as a result of the activities of uncharacterized components of its spore coat. Nucleotide sequence analysis of chromosomal loci previously identified through insertion mutagenesis as being involved in manganese oxidation identified seven possible genes (designated mnxA to mnxG) in what appears to be an operon. A potential recognition site for the sporulation, mother-cell-specific, RNA polymerase sigma factor, sigmaK, was located just upstream of the cluster, and correspondingly, measurement of beta-galactosidase activity from a Tn917-lacZ insertion in mnxD showed expression at mid-sporulation to late sporulation (approximately stage IV to V of sporulation). Spores of nonoxidizing mutants appeared unaffected with respect to their temperature and chemical resistance properties and germination characteristics. However, transmission electron microscopy revealed alterations in the outermost spore coat. This suggests that products of these genes may be involved in the deposition of the spore coat structure and/or are spore coat proteins themselves. Regions of the deduced protein product of mnxG showed amino acid sequence similarity to the family of multicopper oxidases, a diverse group of proteins that use multiple copper ions to oxidize a variety of substrates. Similar regions included those that are involved in binding of copper, and the addition of copper at a low concentration was found to enhance manganese oxidation by the spores. This suggests that the product of this gene may function like a copper oxidase and that it may be directly responsible for the oxidation of manganese by the spores.     

Enzymatic Manganese(II) Oxidation by Metabolically Dormant Spores of Diverse Bacillus Species

Bacterial spores are renowned for their longevity, ubiquity, and resistance to environmental insults, but virtually nothing is known regarding whether these metabolically dormant structures impact their surrounding chemical environments. In the present study, a number of spore-forming bacteria that produce dormant spores which enzymatically oxidize soluble Mn(II) to insoluble Mn(IV) oxides were isolated from coastal marine sediments. The highly charged and reactive surfaces of biogenic metal oxides dramatically influence the oxidation and sorption of both trace metals and organics in the environment. Prior to this study, the only known Mn(II)-oxidizing sporeformer was the marine Bacillus sp. strain SG-1, an extensively studied bacterium in which Mn(II) oxidation is believed to be catalyzed by a multicopper oxidase, MnxG. Phylogenetic analysis based on 16S rRNA and mnxG sequences obtained from 15 different Mn(II)-oxidizing sporeformers (including SG-1) revealed extensive diversity within the genus Bacillus, with organisms falling into several distinct clusters and lineages. In addition, active Mn(II)-oxidizing proteins of various sizes, as observed in sodium dodecyl sulfate-polyacrylamide electrophoresis gels, were recovered from the outer layers of purified dormant spores of the isolates. These are the first active Mn(II)-oxidizing enzymes identified in spores or gram-positive bacteria. Although extremely resistant to denaturation, the activities of these enzymes were inhibited by azide and o-phenanthroline, consistent with the involvement of multicopper oxidases. Overall, these studies suggest that the commonly held view that bacterial spores are merely inactive structures in the environment should be revised.     

Direct Identification of a Bacterial Manganese(II) Oxidase, the Multicopper Oxidase MnxG, from Spores of Several Different Marine Bacillus Species

Microorganisms catalyze the formation of naturally occurring Mn oxides, but little is known about the biochemical mechanisms of this important biogeochemical process. We used tandem mass spectrometry to directly analyze the Mn(II)-oxidizing enzyme from marine Bacillus spores, identified as an Mn oxide band with an in-gel activity assay. Nine distinct peptides recovered from the Mn oxide band of two Bacillus species were unique to the multicopper oxidase MnxG, and one peptide was from the small hydrophobic protein MnxF. No other proteins were detected in the Mn oxide band, indicating that MnxG (or a MnxF/G complex) directly catalyzes biogenic Mn oxide formation. The Mn(II) oxidase was partially purified and found to be resistant to many proteases and active even at high concentrations of sodium dodecyl sulfate. Comparative analysis of the genes involved in Mn(II) oxidation from three diverse Bacillus species revealed a complement of conserved Cu-binding regions not present in well-characterized multicopper oxidases. Our results provide the first direct identification of a bacterial enzyme that catalyzes Mn(II) oxidation and suggest that MnxG catalyzes two sequential one-electron oxidations from Mn(II) to Mn(III) and from Mn(III) to Mn(IV), a novel type of reaction for a multicopper oxidase.     

Indirect oxidation of Co(II) in the presence of the marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1

Cobalt(II) oxidation in aquatic environments has been shown to be linked to Mn(II) oxidation, a process primarily mediated by bacteria. This work examines the oxidation of Co(II) by the spore-forming marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1, which enzymatically catalyzes the formation of reactive nanoparticulate Mn(IV) oxides. Preparations of these spores were incubated with radiotracers and various amounts of Co(II) and Mn(II), and the rates of Mn(II) and Co(II) oxidation were measured. Inhibition of Mn(II) oxidation by Co(II) and inhibition of Co(II) oxidation by Mn(II) were both found to be competitive. However, from both radiotracer experiments and X-ray spectroscopic measurements, no Co(II) oxidation occurred in the complete absence of Mn(II), suggesting that the Co(II) oxidation observed in these cultures is indirect and that a previous report of enzymatic Co(II) oxidation may have been due to very low levels of contaminating Mn. Our results indicate that the mechanism by which SG-1 oxidizes Co(II) is through the production of the reactive nanoparticulate Mn oxide.     

嗜中性微好氧铁氧化菌研究进展

在弱酸至近中性微氧条件下,嗜中性微好氧铁氧化菌能够通过依赖氧气的呼吸机制将二价亚铁氧化成三价铁,并获得生长所需能量。这一生物铁氧化过程的主要产物之一是无定形羟基氧化铁——一种异化铁还原作用(铁呼吸)的理想底物,故可加速铁元素在氧化还原分界层的地质循环。有关嗜中性微好氧铁氧化菌的记载可追溯到19世纪30年代,但对其生理、生态与系统发育学的研究自20世纪90年代中期才取得显著进展,主要得益于专性铁氧化菌新种、属的成功培养与分离。已知微好氧铁氧化菌广泛分布于弱酸及近中性富铁地下水、湿地和深海等环境,其参与调控的铁氧化过程对铁及其他元素(如碳、氮、磷、锰和砷等)的生物地球化学循环具有重要意义。这类古老微生物在金属成矿、地壳演变、全球气候变化及其它生源要素地球化学过程中的作用研究已逐渐受到关注,正成为地质与环境微生物学领域的研究热点。主要总结国外近15a对嗜中性微好氧铁氧化菌的研究进展,包括其代谢机理、种类和分布、生态学研究方法和技术、以及细菌铁氧化作用的实际应用和环境意义等,并对今后研究方向提出展望。     

Arsenite Oxidation Using Biogenic Manganese Oxides Produced by a Deep-Sea Manganese-Oxidizing Bacterium,Marinobacter sp. MnI7-9

Marinobacter sp. MnI7-9, a deep-sea manganese [Mn(II)]-oxidizing bacterium isolated from the Indian Ocean, showed a high resistance to Mn(II) and other metals or metalloids and high Mn(II) oxidation/removal abilities. This strain was able to grow well when the Mn(II) concentration reached up to 10 mM, and at that concentration, 76.4% of the added Mn(II) was oxidized and 23.4% of the Mn(II) was adsorbed by the generated biogenic Mn oxides (total 99.9% Mn removal). Scanning electron microscope observation and X-ray diffraction analysis showed that the biogenic Mn oxides were in stick shapes, adhered to the cell surface, and contained two typical crystal structures of γ-MnOOH and δ-MnO₂. In addition, the biogenic Mn oxides generated by strain MnI7-9 showed abilities to oxidize the highly toxic As(III) to the less toxic As(V), in both co-culture and after-collection systems. In the co-culture system containing 10 mM Mn(II) and 55 μM As(III), the maximum percentage of As(III) oxidation was 83.5%. In the after-collection system using the generated biogenic Mn oxides, 90% of the As(III) was oxidized into As(V), and the concentration of As(III) decreased from 55.02 to 5.55 μM. This study demonstrates the effective bioremediation by a deep-sea Mn(II)-oxidizing bacterium for the treatment of As-containing water and increases the knowledge of deep-sea bacterial Mn(II) oxidation mechanisms. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Enzymatic manganese(II) oxidation by a marine alpha-proteobacterium

A yellow-pigmented marine bacterium, designated strain SD-21, was isolated from surface sediments of San Diego Bay, San Diego, Calif., based on its ability to oxidize soluble Mn(II) to insoluble Mn(III, IV) oxides. 16S rRNA analysis revealed that this organism was most closely related to members of the genus Erythrobacter, aerobic anoxygenic phototrophic bacteria within the alpha-4 subgroup of the Proteobacteria (alpha-4 Proteobacteria). SD-21, however, has a number of distinguishing phenotypic features relative to Erythrobacter species, including the ability to oxidize Mn(II). During the logarithmic phase of growth, this organism produces Mn(II)-oxidizing factors of approximately 250 and 150 kDa that are heat labile and inhibited by both azide and o-phenanthroline, suggesting the involvement of a metalloenzyme. Although the expression of the Mn(II) oxidase was not dependent on the presence of Mn(II), higher overall growth yields were reached in cultures incubated with Mn(II) in the culture medium. In addition, the rate of Mn(II) oxidation appeared to be slower in cultures grown in the light. This is the first report of Mn(II) oxidation within the alpha-4 Proteobacteria as well as the first Mn(II)-oxidizing proteins identified in a marine gram-negative bacterium.     

劳盆地深海热液喷口沉积物中细菌多样性研究

采用PCR-RFLP技术调查了劳盆地深海热液喷口两位点沉积物中的细菌多样性。结果表明, 在劳盆地深海热液喷口沉积物环境中细菌多样性十分丰富, 样品DY1中发现6个细菌类群, DY2中则存在4个细菌类群, 其中Gammaproteobacteria细菌亚群和Epsilonproteobacteria细菌亚群在两文库中均占据最大比例, 为沉积物样品中的优势菌群。另外, 在克隆文库中还发现了一些与数据库中的已知序列同源性较低的类群, 从而说明劳盆地深海热液喷口沉积物中存在特有的微生物种属。     

Advances in Taxonomy,Ecology, and Biogeography of Dirivultidae (Copepoda) Associated with Chemosynthetic Environments in the Deep Sea

Background

Copepoda is one of the most prominent higher taxa with almost 80 described species at deep-sea hydrothermal vents. The unique copepod family Dirivultidae with currently 50 described species is the most species rich invertebrate family at hydrothermal vents.

Methodology/Principal Findings

We reviewed the literature of Dirivultidae and provide a complete key to species, and map geographical and habitat specific distribution. In addition we discuss the ecology and origin of this family.

Conclusions/Significance

Dirivultidae are only present at deep-sea hydrothermal vents and along the axial summit trough of midocean ridges, with the exception of Dirivultus dentaneus found associated with Lamellibrachia species at 1125 m depth off southern California. To our current knowledge Dirivultidae are unknown from shallow-water vents, seeps, whale falls, and wood falls. They are a prominent part of all communities at vents and in certain habitat types (like sulfide chimneys colonized by pompei worms) they are the most abundant animals. They are free-living on hard substrate, mostly found in aggregations of various foundation species (e.g. alvinellids, vestimentiferans, and bivalves). Most dirivultid species colonize more than one habitat type. Dirivultids have a world-wide distribution, but most genera and species are endemic to a single biogeographic region. Their origin is unclear yet, but immigration from other deep-sea chemosynthetic habitats (stepping stone hypothesis) or from the deep-sea sediments seems unlikely, since Dirivultidae are unknown from these environments. Dirivultidae is the most species rich family and thus can be considered the most successful taxon at deep-sea vents.     

Diversity of thiosulfate-oxidizing bacteria from marine sediments and hydrothermal vents

Species diversity, phylogenetic affiliations, and environmental occurrence patterns of thiosulfate-oxidizing marine bacteria were investigated by using new isolates from serially diluted continental slope and deep-sea abyssal plain sediments collected off the coast of New England and strains cultured previously from Galapagos hydrothermal vent samples. The most frequently obtained new isolates, mostly from 10(3)- and 10(4)-fold dilutions of the continental slope sediment, oxidized thiosulfate to sulfate and fell into a distinct phylogenetic cluster of marine alpha-Proteobacteria. Phylogenetically and physiologically, these sediment strains resembled the sulfate-producing thiosulfate oxidizers from the Galapagos hydrothermal vents while showing habitat-related differences in growth temperature, rate and extent of thiosulfate utilization, and carbon substrate patterns. The abyssal deep-sea sediments yielded predominantly base-producing thiosulfate-oxidizing isolates related to Antarctic marine Psychroflexus species and other cold-water marine strains of the Cytophaga-Flavobacterium-Bacteroides phylum, in addition to gamma-proteobacterial isolates of the genera Pseudoalteromonas and Halomonas-Deleya. Bacterial thiosulfate oxidation is found in a wide phylogenetic spectrum of Flavobacteria and Proteobacteria.     

Coupled photochemical and enzymatic Mn(II) oxidation pathways of a planktonic Roseobacter-Like bacterium

Bacteria belonging to the Roseobacter clade of the alpha-Proteobacteria occupy a wide range of environmental niches and are numerically abundant in coastal waters. Here we reveal that Roseobacter-like bacteria may play a previously unrecognized role in the oxidation and cycling of manganese (Mn) in coastal waters. A diverse array of Mn(II)-oxidizing Roseobacter-like species were isolated from Elkhorn Slough, a coastal estuary adjacent to Monterey Bay in California. One isolate (designated AzwK-3b), in particular, rapidly oxidizes Mn(II) to insoluble Mn(III, IV) oxides. Interestingly, AzwK-3b is 100% identical (at the 16S rRNA gene level) to a previously described Pfiesteria-associated Roseobacter-like bacterium, which is not able to oxidize Mn(II). The rates of manganese(II) oxidation by live cultures and cell-free filtrates are substantially higher when the preparations are incubated in the presence of light. The rates of oxidation by washed cell extracts, however, are light independent. Thus, AzwK-3b invokes two Mn(II) oxidation mechanisms when it is incubated in the presence of light, in contrast to the predominantly direct enzymatic oxidation in the dark. In the presence of light, production of photochemically active metabolites is coupled with initial direct enzymatic Mn(II) oxidation, resulting in higher Mn(II) oxidation rates. Thus, Roseobacter-like bacteria may not only play a previously unrecognized role in Mn(II) oxidation and cycling in coastal surface waters but also induce a novel photooxidation pathway that provides an alternative means of Mn(II) oxidation in the photic zone.     

The Role of Dissolved Organic Matter in the Nutrition of Deep-Sea Benthos

SYNOPSIS. Deep-sea sediments contain less particulate organicmatter and lower biomass than shallow-water sediments, but thedissolved organic matter in pore water varies less with depthand may provide a significant food source for deep-sea benthos.Pogonophora are a phylum of predominantly deep-sea animals,all without an internal digestive system. Experiments show thatone or two species ought to be able to live by uptake of dissolvedorganic matter from pore water in deep-sea deposits: some otherspecies may need local enrichment of the habitat for such uptaketo be useful. Less is known about nutrition of other deep-seaanimals, but dissolved organic matter may supplement a conventionaldiet in several groups. Chemoautotrophy, using endosymbioticbacteria, may be important for the large vestimentiferan Pogonophorain the high-sulfide conditions of the hydrothermal vents.     

Indirect Oxidation of Co(II) in the Presence of the Marine Mn(II)-Oxidizing Bacterium Bacillus sp. Strain SG-1

Cobalt(II) oxidation in aquatic environments has been shown to be linked to Mn(II) oxidation, a process primarily mediated by bacteria. This work examines the oxidation of Co(II) by the spore-forming marine Mn(II)-oxidizing bacterium Bacillus sp. strain SG-1, which enzymatically catalyzes the formation of reactive nanoparticulate Mn(IV) oxides. Preparations of these spores were incubated with radiotracers and various amounts of Co(II) and Mn(II), and the rates of Mn(II) and Co(II) oxidation were measured. Inhibition of Mn(II) oxidation by Co(II) and inhibition of Co(II) oxidation by Mn(II) were both found to be competitive. However, from both radiotracer experiments and X-ray spectroscopic measurements, no Co(II) oxidation occurred in the complete absence of Mn(II), suggesting that the Co(II) oxidation observed in these cultures is indirect and that a previous report of enzymatic Co(II) oxidation may have been due to very low levels of contaminating Mn. Our results indicate that the mechanism by which SG-1 oxidizes Co(II) is through the production of the reactive nanoparticulate Mn oxide.     

The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography

Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than previously recognised.     

Enzymatic Manganese(II) Oxidation by a Marine α-Proteobacterium

A yellow-pigmented marine bacterium, designated strain SD-21, was isolated from surface sediments of San Diego Bay, San Diego, Calif., based on its ability to oxidize soluble Mn(II) to insoluble Mn(III, IV) oxides. 16S rRNA analysis revealed that this organism was most closely related to members of the genus Erythrobacter, aerobic anoxygenic phototrophic bacteria within the α-4 subgroup of the Proteobacteria (α-4 Proteobacteria). SD-21, however, has a number of distinguishing phenotypic features relative to Erythrobacter species, including the ability to oxidize Mn(II). During the logarithmic phase of growth, this organism produces Mn(II)-oxidizing factors of ≈250 and 150 kDa that are heat labile and inhibited by both azide and o-phenanthroline, suggesting the involvement of a metalloenzyme. Although the expression of the Mn(II) oxidase was not dependent on the presence of Mn(II), higher overall growth yields were reached in cultures incubated with Mn(II) in the culture medium. In addition, the rate of Mn(II) oxidation appeared to be slower in cultures grown in the light. This is the first report of Mn(II) oxidation within the α-4 Proteobacteria as well as the first Mn(II)-oxidizing proteins identified in a marine gram-negative bacterium.