Submarine Basaltic Glass Colonization by the Heterotrophic Fe(II)-Oxidizing and Siderophore-Producing Deep-Sea Bacterium

Phylogenetically and metabolically diverse bacterial communities have been found in association with submarine basaltic glass surfaces. The driving forces behind basalt colonization are for the most part unknown. It remains ambiguous if basalt provides ecological advantages beyond representing a substrate for surface colonization, such as supplying nutrients and/or energy. Pseudomonas stutzeri VS-10, a metabolically versatile bacterium isolated from Vailulu'u Seamount, was used as a model organism to investigate the physiological responses observed when biofilms are established on basaltic glasses. In Fe-limited heterotrophic media, P. stutzeri VS-10 exhibited elevated growth in the presence of basaltic glass. Diffusion chamber experiments demonstrated that physical attachment or contact of soluble metabolites such as siderophores with the basaltic glass plays a pivotal role in this process. Electrochemical data indicated that P. stutzeri VS-10 is able to use solid substrates (electrodes) as terminal electron donors and acceptors. Siderophore production and heterotrophic Fe(II) oxidation are discussed as potential mechanisms enhancing growth of P. stutzeri VS-10 on glass surfaces. In correlation with that we discuss the possibility that metabolic versatility could represent a common and beneficial physiological trait in marine microbial communities being subject to oligotrophic and rapidly changing deep-sea conditions

Patterns of in situ Mineral Colonization by Microorganisms in a ~60°C Deep Continental Subsurface Aquifer

The microbial ecology of the deep biosphere is difficult to characterize, owing in part to sampling challenges and poorly understood response mechanisms to environmental change. Pre-drilled wells, including oil wells or boreholes, offer convenient access, but sampling is frequently limited to the water alone, which may provide only a partial view of the native diversity. Mineral heterogeneity demonstrably affects colonization by deep biosphere microorganisms, but the connections between the mineral-associated and planktonic communities remain unclear. To understand the substrate effects on microbial colonization and the community response to changes in organic carbon, we conducted an 18-month series of in situ experiments in a warm (57°C), anoxic, fractured carbonate aquifer at 752 m depth using replicate open, screened cartridges containing different solid substrates, with a proteinaceous organic matter perturbation halfway through this series. Samples from these cartridges were analyzed microscopically and by Illumina (iTag) 16S rRNA gene libraries to characterize changes in mineralogy and the diversity of the colonizing microbial community. The substrate-attached and planktonic communities were significantly different in our data, with some taxa (e.g., Candidate Division KB-1) rare or undetectable in the first fraction and abundant in the other. The substrate-attached community composition also varied significantly with mineralogy, such as with two Rhodocyclaceae OTUs, one of which was abundant on carbonate minerals and the other on silicic substrates. Secondary sulfide mineral formation, including iron sulfide framboids, was observed on two sets of incubated carbonates. Notably, microorganisms were attached to the framboids, which were correlated with abundant Sulfurovum and Desulfotomaculum sp. sequences in our analysis. Upon organic matter perturbation, mineral-associated microbial diversity differences were temporarily masked by the dominance of putative heterotrophic taxa in all samples, including OTUs identified as Caulobacter, Methyloversatilis, and Pseudomonas. Subsequent experimental deployments included a methanogen-dominated stage (Methanobacteriales and Methanomicrobiales) 6 months after the perturbation and a return to an assemblage similar to the pre-perturbation community after 9 months. Substrate-associated community differences were again significant within these subsequent phases, however, demonstrating the value of in situ time course experiments to capture a fraction of the microbial assemblage that is frequently difficult to observe in pre-drilled wells

A review of advancements in black soldier fly (Hermetia illucens) production for dietary inclusion in salmonid feeds

It is globally recognized that the development and growth of aquaculture is necessary to supply an increasing shortfall in protein for human consumption. The production of salmonids, like many cultured finfish species, relies on fish meal, as a source of protein, essential amino acids, fatty acids, and other micronutrients. Recently, alternative sources such as black soldier fly larvae (BSFL) have been investigated as a more environmentally sustainable option for dietary protein. In recent years, there have been significant advancements in BSFL production techniques to provide adequate nutritional value for animal feeds and ensure optimal digestibility and gut health of BSFL-fed species. Feeding trials with salmonids have shown that BSFL meal can be included in up to 100 g/kg of dry feed, while some studies have shown success at 300 g/kg. The production method of BSFL meal used in different feeding trials varies between studies, which affects the bulk composition of the meal and consequently on the results on growth performance, fish health, and tissue biochemical composition. This review summarizes the main findings on the advancement on BSFL production methods and their use in salmonid aquaculture, and highlights the importance of BSFL rearing procedures and processing on the outcome of a nutritious protein source for salmonids. Further research into idealistic rearing and processing procedures for BSFL destined for aquafeeds, and standardizing BSFL sourcing based upon these findings may help future feed trials create more comparable and consistent results. These results will also be useful for determining BSFL inclusion levels in other cultured species, further developing innovative, sustainable nutrient sources for aquafeeds

Ecological implications of hypoxia-triggered shifts in secondary metabolism.

Members of the actinomycete genus Streptomyces are non-motile, filamentous bacteria that are well-known for the production of biomedically relevant secondary metabolites. While considered obligate aerobes, little is known about how these bacteria respond to periods of reduced oxygen availability in their natural habitats, which include soils and ocean sediments. Here, we provide evidence that the marine streptomycete strain CNQ-525 can reduce MnO2 via a diffusible mechanism. We investigated the effects of hypoxia on secondary metabolite production and observed a shift away from the antibiotic napyradiomycin towards 8-amino-flaviolin, an intermediate in the napyradiomycin biosynthetic pathway. We purified 8-amino-flaviolin and demonstrated that it is reversibly redox-active (midpoint potential -474.5 mV), indicating that it has the potential to function as an endogenous extracellular electron shuttle. This study provides evidence that environmentally triggered changes in secondary metabolite production may provide clues to the ecological functions of specific compounds, and that Gram-positive bacteria considered to be obligate aerobes may play previously unrecognized roles in biogeochemical cycling through mechanisms that include extracellular electron shuttling

Bacterial nanowires: conductive as silicon, soft as polymer

It was recently discovered that Shewanella oneidensis MR-1, a dissimilatory metal-reducing bacterium, can grow electrically conductive extracellular appendages. Such bacterial nanowires, as they are termed, function as electron-transfer conduits to far-field electron acceptors or among neighbouring cells. A recent advance in the field was the characterization of bacterial nanowires' resistivity along their length, which is on the order of 1 Ω cm. This finding has motivated the exploration of their potential use in biofuel cells, bionanoelectronics and other bionanodevices. Along with conductivity measurements, it is also important to characterize the nature of these nanowires and their mechanical properties. In this work, we have confirmed the nature of these nanowires is protein. In addition, we have investigated the elasticity of bacterial nanowires using two independent atomic force microscopy techniques: (i) real-time elastic modulus mapping by AFM HarmoniX using T-shaped cantilevers with an offset tip and (ii) conventional AFM nanoindentation by force-distance curve fitting based on Hertz model. Results from both techniques demonstrated that the Young's modulus of bacterial nanowires is on the order of 1 GPa. This work inspires us with new applications of bacterial nanowires: with electrical conductivity comparable to that of moderately doped inorganic semiconductors and elasticity similar to polymeric materials, bacterial nanowires can function as electron-transfer conduits for biofuel cells and building blocks for bionanoelectronics and flexible nanoelectronics

Shewanella oneidensis MR-1 Bacterial Nanowires Exhibit p-Type, Tunable Electronic Behavior

The study of electrical transport in biomolecular materials is critical to our fundamental understanding of physiology and to the development of practical bioelectronics applications. In this study, we investigated the electronic transport characteristics of Shewanella oneidensis MR-1 nanowires by conducting-probe atomic force microscopy (CP-AFM) and by constructing field-effect transistors (FETs) based on individual S. oneidensis nanowires. Here we show that S. oneidensis nanowires exhibit p-type, tunable electronic behavior with a field-effect mobility on the order of 10 cm /(V s), comparable to devices based on synthetic organic semiconductors. This study opens up opportunities to use such bacterial nanowires as a new semiconducting biomaterial for making bioelectronics and to enhance the power output of microbial fuel cells through engineering the interfaces between metallic electrodes and bacterial nanowires

Electrical transport along bacterial nanowires from Shewanella oneidensis MR-1

Bacterial nanowires are extracellular appendages that have been suggested as pathways for electron transport in phylogenetically diverse microorganisms, including dissimilatory metal-reducing bacteria and photosynthetic cyanobacteria. However, there has been no evidence presented to demonstrate electron transport along the length of bacterial nanowires. Here we report electron transport measurements along individually addressed bacterial nanowires derived from electron-acceptor–limited cultures of the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. Transport along the bacterial nanowires was independently evaluated by two techniques: (i) nanofabricated electrodes patterned on top of individual nanowires, and (ii) conducting probe atomic force microscopy at various points along a single nanowire bridging a metallic electrode and the conductive atomic force microscopy tip. The S. oneidensis MR-1 nanowires were found to be electrically conductive along micrometer-length scales with electron transport rates up to 109/s at 100 mV of applied bias and a measured resistivity on the order of 1 Ω·cm. Mutants deficient in genes for c-type decaheme cytochromes MtrC and OmcA produce appendages that are morphologically consistent with bacterial nanowires, but were found to be nonconductive. The measurements reported here allow for bacterial nanowires to serve as a viable microbial strategy for extracellular electron transport

The complete genome of the uncultivated ultra-deep subsurface bacterium Desulforudis audaxviator obtained by environmental genomics

A more complete picture of life on Earth, and even life in the Earth, has recently become possible through the application of environmental genomics. We have obtained the complete genome sequence of a new genus of the Firmicutes, the uncultivated sulfate reducing bacterium Desulforudis audaxviator, by filtering fracture water from a borehole at 2.8 km depth in a South African gold mine. The DNA was sequenced at the JGI using a combination of traditional Sanger sequencing and 454 pyrosequencing, and assembled into just one genome, indicating the planktonic community is extremely low in diversity. We analyzed the genome of D. audaxviator using the MicrobesOnline annotation pipeline and toolkit (http://www.microbesonline.org, and see MicrobesOnline abstract), which offers powerful resources for comparative genome analysis, including operon predictions and tree-based comparative genome browsing. MicrobesOnline allowed us to compare the D. audaxviator genome with other sequenced members of the Firmicutes in the same clade (primarily Pelotomaculum thermoproprionicum, Desulfotomaculum reducens, Carboxydothermus hydrogenoformans, and Thermoanaerobacter tengcongensis), as well as other known sulfate reducers (including Archaeoglobus fulgidus and Desulfovibrio vulgaris). D. audaxviator gives a view to the set of tools necessary for what appears to be a self-contained, independent lifestyle deep in the Earth's crust. The genome is not very streamlined, and indicates a motile, endospore forming sulfate reducer with pili that can fix its own nitrogen and carbon. D. audaxviator is an obligate anaerobe, and lacks obvious homologs of many of the traditional O2 tolerance genes, consistent with the low concentration of O2 in the fracture water and its long-term isolation from the surface. D. audaxviator provides a complete genome representative of the Gram-positive bacteria to further our understanding of dissimilatory sulfate reducing bacteria and archaea, and offers the full complement of genes necessary for an independent lifestyle based solely on interactions with the geochemistry of the deep subsurface