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Autonomous platforms that support low-power sensors represent one approach to expanding ocean observing. This paper describes a unique autonomous platform designed to deliver long-term sensor measurements from the benthic boundary layer at low cost. The platform, called a Benthic Observer (BeOb), is powered by energy harvested with a benthic microbial fuel cell (BMFC), and it uses an acoustic modem to both store and transmit data organized in daily reports of hourly measurements. A BeOb equipped with sensors to measure dissolved oxygen, temperature, and conductivity ~1 m above the seabed has been active for over 14 months on the Oregon slope at a location within the core of the oxygen minimum zone. During this observation period, the system's battery reserves have been kept fully charged by the BMFC. A 90-day time series of sensor data are compared to simultaneous high-frequency measurements at a neighboring Ocean Observatories Initiative cabled Benthic Experiment Package to examine the expected quality and confidence levels for seasonal or annual means of continued measurements. An ocean observing system incorporating arrays of BMFC-powered platforms transmitting to central gateway modems is proposed for future ocean-property monitoring programs. Such arrays may be especially helpful for tracking expansions of ocean oxygen minimum zones. [ABSTRACT FROM AUTHOR]

Multicellular, filamentous, sulfur-oxidizing bacteria, known as cable bacteria, were discovered attached to fibers of a carbon brush electrode serving as an anode of a benthicmicrobial fuel cell (BMFC). The BMFC had been operated in a temperate estuarine environment for over a year before collecting anode samples for scanning electron microscopy and phylogenetic analyses. Individual filaments were attached by single terminus cells with networks of pilus-like nano-filaments radiating out from these cells, across the anode fiber surface, and between adjacent attachment locations. Current harvesting by the BMFC poised the anode at potentials of ~170-250mV vs. SHE, and these surface potentials appear to have allowed the cable bacteria to use the anode as an electron acceptor in a completely anaerobic environment. A combination of catalyzed reporter deposition fluorescent in situ hybridization (CARD-FISH) and 16S rRNA gene sequence analysis confirmed the phylogeny of the cable bacteria and showed that filaments often occurred in bundles and in close association with members of the genera Desulfuromonas. However, the Desulfobulbaceae Operational Taxonomic Units (OTUs) from the 16S sequencing did not cluster closely with other putative cable bacteria sequences suggesting that the taxonomic delineation of cable bacteria is far from complete. [ABSTRACT FROM AUTHOR]

Most oceanographic instruments on the seafloor have no connections with the surface and therefore have to run on batteries and store data until recovery. To demonstrate a developing technology, sensors and acoustic modems were powered with energy harvested from the seafloor, and data were relayed acoustically in near-real time to the Monterey Accelerated Research System (MARS) observatory in Monterey Bay, California, and to surface research vessels. MARS is a cabled observatory in deep water (~890 m) at the edge of Monterey Canyon. An acoustic modem was attached to the MARS node and configured to send out commands to, and relay data received from, remote modems. Two benthic microbial fuel cells (BMFCs) positioned approximately 0.5 km away from MARS supplied power to the remote modems and sensors. At their peak performance, these BMFCs produced continuous power densities of ~35 mW m−2 (footprint area). The modems utilized in this study contained an integrated power management platform (PMP) designed to manage and store the electrical energy generated by each BMFC and to record BMFC performance parameters and sensor data on an hourly basis. Temperature and either oxygen or conductivity sensors were chosen because of their common use and environmental relevance. Acoustically transmitted data records show that the BMFCs renewed energy stores and that the oceanographic sensors measured dissolved oxygen, temperature, and conductivity reliably throughout the operational life of each BMFC system (~6 months). These systems remained in place for more than 12 months. [ABSTRACT FROM AUTHOR]

This study examines changes in diversity and abundance of bacteria recovered from the anodes of microbial fuel cells (MFCs) in relation to anode potential, power production and geochemistry. MFCs were batch-fed with plankton, and two systems were maintained at different potentials whereas one was at open circuit for 56.8 days. Bacterial phylogenetic diversity during peak power was assessed from 16S rDNA clone libraries. Throughout the experiment, microbial community structure was examined using terminal restriction fragment length polymorphism. Changes in cell density of key phylotypes, including representatives of δ-, ɛ-, γ-proteobacteria and Flavobacterium-Cytophaga-Bacteroides, were enumerated by quantitative PCR. Marked differences in phylogenetic diversity were observed during peak power versus the final time point, and changes in microbial community structure were strongly correlated to dissolved organic carbon and ammonium concentrations within the anode chambers. Community structure was notably different between the MFCs at different anode potentials during the onset of peak power. At the final time point, however, the anode-hosted communities in all MFCs were similar. These data demonstrate that differences in growth, succession and population dynamics of key phylotypes were due to anode potential, which may relate to their ability to exploit the anode as an electron acceptor. The geochemical milieu, however, governs overall community diversity and structure. These differences reflect the physiological capacity of specific phylotypes to catabolize plankton-derived organic matter and exploit the anode of an MFC for their metabolism directly or indirectly through syntrophy.The ISME Journal (2009) 3, 635–646; doi:10.1038/ismej.2009.12; published online 26 February 2009 [ABSTRACT FROM AUTHOR]

Energy sources that may be converted to electric power are elusive at the seafloor. This communication describes the design of a compact benthic microbial fuel cell (BMFC) and a power management platform (PMP) that have been used to recharge lithium-ion batteries with energy harvested in situ from biomass enclosed in the BMFC's anode chamber. The primary power produced was typically between 5 and 50 mW with 42% of the energy transferred to battery storage. The batteries in turn were used to sustain environmental sensors and acoustic communication devices during three experiments in contrasting marine locations. The programmable PMP permitted control of sensor duty cycles and monitoring of BMFC performance. One of the experiments occurred at an ocean depth of 580 m for 1,045 days. It suggested a need for longer lasting biomass supplies to sustain elevated power levels beyond 2–3 years. Based on the lessons learned from these experiments, we conclude that BMFC systems are now sufficiently mature to be applied within marine observing networks. They represent an alternative power source that may be integrated readily with many kinds of innovative sensors. [Display omitted] • Energy harvesting has been demonstrated for 1,045 days at an ocean depth of 580 m. • A power management platform provides options for control and data. • Sensors have been powered at 7V after transfer of energy to rechargeable batteries. • Operation necessitates an organic matter source to fuel anode-reducing biofilms. [ABSTRACT FROM AUTHOR]

Members in the family of Desulfobulbaceae may be influential in various anaerobic microbial communities, including those in anoxic aquatic sediments and water columns, and within wastewater treatment facilities and bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs). However, the diversity and roles of the Desulfobulbaceae in these communities have received little attention, and large portions of this family remain uncultured. Here we expand on findings from an earlier study (Li, Reimers, and Alleau, 2020) to more fully characterize Desulfobulbaceae that became prevalent in biofilms on oxidative electrodes of bioelectrochemical reactors. After incubations, DNA extraction, microbial community analyses, and microscopic examination, we found that a group of uncultured Desulfobulbaceae were greatly enriched on electrode surfaces. These Desulfobulbaceae appeared to form filaments with morphological features ascribed to cable bacteria, but the majority were taxonomically distinct from recognized cable bacteria genera. Thus, the present study provides new information about a group of Desulfobulbaceae that can exhibit filamentous morphologies and respire on the oxidative electrodes. While the phylogeny of cable bacteria is still being defined and updated, further enriching these members can contribute to the overall understanding of cable bacteria and may also lead to identification of successful isolation strategies. [ABSTRACT FROM AUTHOR]

Supported by the natural potential difference between anoxic sediment and oxic seawater, benthic microbial fuel cells (BMFCs) promise to be ideal power sources for certain low-power marine sensors and communication devices. In this study a chambered BMFC with a 0.25 m² footprint was used to power an acoustic modem interfaced with an oceanographic sensor that measures dissolved oxygen and temperature. The experiment was conducted in Yaquina Bay, Oregon over 50 days. Several improvements were made in the BMFC design and power management system based on lessons learned from earlier prototypes. The energy was harvested by a dynamic gain charge pump circuit that maintains a desired point on the BMFC's power curve and stores the energy in a 200 F supercapacitor. The system also used an ultralow power microcontroller and quartz clock to read the oxygen/temperature sensor hourly, store data with a time stamp, and perform daily polarizations. Data records were transmitted to the surface by the acoustic modem every 1-5 days after receiving an acoustic prompt from a surface hydrophone. After jump-starting energy production with supplemental macroalgae placed in the BMFC's anode chamber, the average power density of the BMFC adjusted to 44 mW/m² of seafloor area which is better than past demonstrations at this site. The highest power density was 158 mW/m², and the useful energy produced and stored was ≥1.7 times the energy required to operate the system. [ABSTRACT FROM AUTHOR]

This research investigated whether the addition of an exogenous electron donor would affect power production in laboratory-scale benthic microbial fuel cells (BMFC) by differentially influencing microbially mediated electron transfer processes. Six BMFCs were operated for over one year in a temperature- controlled laboratory. Three BMFCs relied on endogenous electron donors, and three were supplemented with lactate. The supplemented BMFCs generated more cumulative charge, but did not generate higher average current between periods of lactate enrichment. Coulombic efficiencies during the lactate treatments ranged from 25 to 65% suggesting that lactate utilization was variably coupled to power production. Cumulative electron flux resulting from lactate additions and chemical changes within the anode chamber, as well as a difference in the anode-hosted microbial communities indicated that lactate supplementation promoted sulfate reduction. After the addition of molybdate to suppress sulfate reduction and sulfur disproportionation, all BMFCs continued to produce current but no longer responded to lactate additions. Chemical data support a two-step cycle in which endogenous organic carbon and/or supplemented lactate fuel sulfate reduction resulting in sulfide and simple organic molecules (such as acetate) that can act as the electron donors for the BMFC. [ABSTRACT FROM AUTHOR]