Leech, D. | Search bioRxiv

bioRxiv2020

Electroactive biofilms on surface functionalized anodes: the anode respiring behavior of a novel electroactive bacterium, Desulfuromonas acetexigens

Surface chemistry is known to influence the formation, composition and electroactivity of electron-conducting biofilms with however limited information on the variation of microbial composition and electrochemical response during biofilm development to date. Here we present voltammetric, microscopic and microbial community analysis of biofilms formed under fixed applied potential for modified graphite electrodes during early (90 h) and mature (340 h) growth phases. Electrodes modified to introduce hydrophilic groups (-NH2, -COOH and -OH) enhance early-stage biofilm formation compared to unmodified or electrodes modified with hydrophobic groups (-C2H5). In addition, early-stage films formed on hydrophilic electrodes were dominated by the gram-negative sulfur-reducing bacterium Desulfuromonas acetexigens while Geobacter sp. dominated on -C2H5 and unmodified electrodes. As biofilms mature, current generation becomes similar, and D. acetexigens dominates in all biofilms irrespective of surface chemistry. Electrochemistry of pure culture D. acetexigens biofilms reveal that this microbe is capable of forming electroactive biofilms producing considerable current density of > 9 A/m2 in a short period of potential induced growth (~19 h followed by inoculation) using acetate as an electron donor. The inability of D. acetexigens biofilms to use H2 as a sole source electron donor for current generation shows promise for maximizing H2 recovery in single-chambered microbial electrolysis cell systems treating wastewaters. HighlightsO_LIAnode surface chemistry affects the early stage biofilm formation. C_LIO_LIHydrophilic anode surfaces promote rapid start-up of current generation. C_LIO_LICertain functionalized anode surfaces enriched the Desulfuromonas acetexigens. C_LIO_LID. acetexigens is a novel electroactive bacteria. C_LIO_LID. acetexigens biofilms can produce high current density in a short period of potential induced growth C_LIO_LID. acetexigens has the ability to maximize the H2 recovery in MEC. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/974261v1_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@1a9c7a5org.highwire.dtl.DTLVardef@1722697org.highwire.dtl.DTLVardef@143b996org.highwire.dtl.DTLVardef@14d4a60_HPS_FORMAT_FIGEXP M_FIG TOC - Graphical abstract C_FIG

bioengineering↗

bioRxiv2019

Indirect versus Direct Effects of Freshwater Browning on Larval Fish Foraging

Fish foraging and energy flow are both predicted to decline with freshwater browning due to reductions in light availability. Studies investigating these predictions have focused on juveniles and adults; however, the larval stage represents a critical period in fish development. We investigated the indirect versus direct effects of browning on zooplankton-larval fish interactions by altering water color with SuperHume (absorbance at 440 nm = 1.6 - 10.8 m-1). Phytoplankton and zooplankton densities were monitored across experimental tanks in the laboratory for one month leading up to fish spawning. Larval largemouth bass were then introduced to assess indirect effects on fish feeding rates and growth. Direct effects on foraging of largemouth bass and bluegill were determined with separate short-term feeding experiments. Browning did not directly alter the ability of larval fish to capture prey. However, significant indirect effects on larval fish foraging, growth, and survival were observed as phytoplankton and zooplankton decreased with increased browning. Our data suggest lake browning will reduce energy transfer to larval fish due to a reduction in prey availability but not visual foraging.

ecology↗