Influence of external resistance on electrogenesis, methanogenesis, and anode prokaryotic communities in microbial fuel cells

The external resistance (R(ext)) of microbial fuel cells (MFCs) regulates both the anode availability as an electron acceptor and the electron flux through the circuit. We evaluated the effects of R(ext) on MFCs using acetate or glucose. The average current densities (I) ranged from 40.5 mA/m(2) (9,800 Ω) to 284.5 mA/m(2) (150 Ω) for acetate-fed MFCs (acetate-fed reactors [ARs]), with a corresponding anode potential (E(an)) range of -188 to -4 mV (versus a standard hydrogen electrode [SHE]). For glucose-fed MFCs (glucose-fed reactors [GRs]), I ranged from 40.0 mA/m(2) (9,800 Ω) to 273.0 mA/m(2) (150 Ω), with a corresponding E(an) range of -189 to -7 mV. ARs produced higher Coulombic efficiencies and energy efficiencies than GRs over all tested R(ext) levels because of electron and potential losses from glucose fermentation. Biogas production accounted for 14 to 18% of electron flux in GRs but only 0 to 6% of that in ARs. GRs produced similar levels of methane, regardless of the R(ext). However, total methane production in ARs increased as R(ext) increased, suggesting that E(an) might influence the competition for substrates between exoelectrogens and methanogens in ARs. An increase of R(ext) to 9,800 Ω significantly changed the anode bacterial communities for both ARs and GRs, while operating at 970 Ω and 150 Ω had little effect. Deltaproteobacteria and Bacteroidetes were the major groups found in anode communities in ARs and GRs. Betaproteobacteria and Gammaproteobacteria were found only in ARs. Bacilli were abundant only in GRs. The anode-methanogenic communities were dominated by Methanosaetaceae, with significantly lower numbers of Methanomicrobiales. These results show that R(ext) affects not only the E(an) and current generation but also the anode biofilm community and methanogenesis.     

TPR proteins: the versatile helix

Tetratrico peptide repeat (TPR) proteins have several interesting properties, including their folding characteristics, modular architecture and range of binding specificities. In the past five years, many 3D structures of TPR domains have been solved, revealing at a molecular level the versatility of this basic fold. Here, we discuss the structure of TPRs and highlight the diversity of arrangements and functions that are associated with these ubiquitous domains. Genomic analyses of the distribution of TPR domains are presented along with implications for protein engineering.     

Osmoregulatory bicarbonate secretion exploits H+-sensitive haemoglobins to autoregulate intestinal O2 delivery in euryhaline teleosts

Marine teleost fish secrete bicarbonate (HCO₃ ^?) into the intestine to aid osmoregulation and limit Ca²⁺ uptake by carbonate precipitation. Intestinal HCO₃ ^? secretion is associated with an equimolar transport of protons (H⁺) into the blood, both being proportional to environmental salinity. We hypothesized that the H⁺-sensitive haemoglobin (Hb) system of seawater teleosts could be exploited via the Bohr and/or Root effects (reduced Hb-O₂ affinity and/or capacity with decreasing pH) to improve O₂ delivery to intestinal cells during high metabolic demand associated with osmoregulation. To test this, we characterized H⁺ equilibria and gas exchange properties of European flounder (Platichthys flesus) haemoglobin and constructed a model incorporating these values, intestinal blood flow rates and arterial–venous acidification at three different environmental salinities (33, 60 and 90). The model suggested red blood cell pH (pH_i) during passage through intestinal capillaries could be reduced by 0.14–0.33 units (depending on external salinity) which is sufficient to activate the Bohr effect (Bohr coefficient of ?0.63), and perhaps even the Root effect, and enhance tissue O₂ delivery by up to 42 % without changing blood flow. In vivo measurements of intestinal venous blood pH were not possible in flounder but were in seawater-acclimated rainbow trout which confirmed a blood acidification of no less than 0.2 units (equivalent to ?0.12 for pH_i). When using trout-specific values for the model variables, predicted values were consistent with measured in vivo values, further supporting the model. Thus this system is an elegant example of autoregulation: as the need for costly osmoregulatory processes (including HCO₃ ^? secretion) increases at higher environmental salinity, so does the enhancement of O₂ delivery to the intestine via a localized acidosis and the Bohr (and possibly Root) effect.     

Behavioural Repertoire of Working Donkeys and Consistency of Behaviour over Time,as a Preliminary Step towards Identifying Pain-Related Behaviours

Background

The donkey has a reputation for stoicism and its behavioural repertoire in clinical contexts is under-reported. Lack of understanding of the norms of donkey behaviour and how it may vary over time can compromise use of behavioural measures as indicators of pain or emotional state. The objective of this study was to find out whether the behaviour of working donkeys was influenced by gender, the time of day or differed between days with a view to assessing how robust these measures are for inclusion in a working donkey ethogram.

Methodology/Principal Findings

Frequency and consistency of postural and event behaviours were measured in 21 adult working donkeys (12 females; 9 males). Instantaneous (scan) and focal sampling were used to measure maintenance, lying, ingestive and investigative behaviours at hourly intervals for ten sessions on each of two consecutive days. High head carriage and biting were seen more frequently in male donkeys than females (P<0.001). Level head carriage, licking/chewing and head-shaking were observed more frequently in female donkeys (P<0.001). Tail position, ear orientation, foot stamping, rolling/lying and head-shaking behaviours were affected by time of day (P<0.001). However, only two variations in ear orientation were found to be significantly different over the two days of observations (P<0.001). Tail swishing, head shaking, foot stamping, and ears held sideways and downwards were significantly correlated (P<0.001) and are assumed to be behaviours to discourage flies.

Conclusions/Significance

All donkeys expressed an extensive behavioural repertoire, although some differences in behaviour were evident between genders. While most behaviours were consistent over time, some behaviours were influenced by time of day. Few behaviours differed between the two test days. The findings can be used to inform the development of a robust, evidence-based ethogram for working donkeys.     

Change in microbial communities in acetate- and glucose-fed microbial fuel cells in the presence of light

Power densities produced by microbial fuel cells (MFCs) in natural systems are changed by exposure to light through the enrichment of photosynthetic microorganisms. When MFCs with brush anodes were exposed to light (4000 lx), power densities increased by 8–10% for glucose-fed reactors, and 34% for acetate-fed reactors. Denaturing gradient gel electrophoresis (DGGE) profiles based on the 16S rRNA gene showed that exposure to high light levels changed the microbial communities on the anodes. Based on 16S rRNA gene clone libraries of light-exposed systems the anode communities using glucose were also significantly different than those fed acetate. Dominant bacteria that are known exoelectrogens were identified in the anode biofilm, including a purple nonsulfur (PNS) photosynthetic bacterium, Rhodopseudomonas palustris, and a dissimilatory iron-reducing bacterium, Geobacter sulfurreducens. Pure culture tests confirmed that PNS photosynthetic bacteria increased power production when exposed to high light intensities (4000 lx). These results demonstrate that power production and community composition are affected by light conditions as well as electron donors in single-chamber air-cathode MFCs.