The effect of different substrates and humic acid on power generation in microbial fuel cell operation

Electricity production from acetate, glucose and xylose with humic acid as mediator was investigated in two chambers microbial fuel cells (MFCs). Acetate produced the highest voltage (570 mV with 1000 Omega) and maximum power density (P(maxd)=123 mW/m(2)) due to a simpler metabolism than with glucose and xylose. Glucose and xylose resulted in P(maxd) of 28 mW/m(2) and 32 mW/m(2) at lower voltage of 380 mV and 414 mV, respectively. P(maxd) increased by 84% and 30%, for glucose and xylose respectively, when humic acid (2g/l) was present in the medium. No significant effect was found with acetate since the internal resistance possessed a limiting effect. The increase of P(maxd) due to humic acid presence was attributed to its ability to act as mediator. Even though pH decreased to 5 with glucose and xylose, due to production of acetate and propionate, the voltage remained on the same level of 250-350 mV.     

Bioethanol,biohydrogen and biogas production from wheat straw in a biorefinery concept

The production of bioethanol, biohydrogen and biogas from wheat straw was investigated within a biorefinery framework. Initially, wheat straw was hydrothermally liberated to a cellulose rich fiber fraction and a hemicellulose rich liquid fraction (hydrolysate). Enzymatic hydrolysis and subsequent fermentation of cellulose yielded 0.41 g-ethanol/g-glucose, while dark fermentation of hydrolysate produced 178.0 ml-H₂/g-sugars. The effluents from both bioethanol and biohydrogen processes were further used to produce methane with the yields of 0.324 and 0.381 m³/kg volatile solids (VS)_added, respectively. Additionally, evaluation of six different wheat straw-to-biofuel production scenaria showed that either use of wheat straw for biogas production or multi-fuel production were the energetically most efficient processes compared to production of mono-fuel such as bioethanol when fermenting C6 sugars alone. Thus, multiple biofuels production from wheat straw can increase the efficiency for material and energy and can presumably be more economical process for biomass utilization.     

Submersible microbial fuel cell sensor for monitoring microbial activity and BOD in groundwater: Focusing on impact of anodic biofilm on sensor applicability

A sensor, based on a submersible microbial fuel cell (SUMFC), was developed for in situ monitoring of microbial activity and biochemical oxygen demand (BOD) in groundwater. Presence or absence of a biofilm on the anode was a decisive factor for the applicability of the sensor. Fresh anode was required for application of the sensor for microbial activity measurement, while biofilm‐colonized anode was needed for utilizing the sensor for BOD content measurement. The current density of SUMFC sensor equipped with a biofilm‐colonized anode showed linear relationship with BOD content, to up to 250 mg/L (～233 ± 1 mA/m²), with a response time of <0.67 h. This sensor could, however, not measure microbial activity, as indicated by the indifferent current produced at varying active microorganisms concentration, which was expressed as microbial adenosine‐triphosphate (ATP) concentration. On the contrary, the current density (0.6 ± 0.1 to 12.4 ± 0.1 mA/m²) of the SUMFC sensor equipped with a fresh anode showed linear relationship, with active microorganism concentrations from 0 to 6.52 nmol‐ATP/L, while no correlation between the current and BOD was observed. It was found that temperature, pH, conductivity, and inorganic solid content were significantly affecting the sensitivity of the sensor. Lastly, the sensor was tested with real contaminated groundwater, where the microbial activity and BOD content could be detected in <3.1 h. The microbial activity and BOD concentration measured by SUMFC sensor fitted well with the one measured by the standard methods, with deviations ranging from 15% to 22% and 6% to 16%, respectively. The SUMFC sensor provides a new way for in situ and quantitative monitoring contaminants content and biological activity during bioremediation process in variety of anoxic aquifers. Biotechnol. Bioeng. 2011;108: 2339–2347. © 2011 Wiley Periodicals, Inc.     

Immune Activation Is Associated with CD8 T Cell Interleukin-21 Production in HIV-1-Infected Individuals

Interleukin-21 (IL-21) can be produced by CD8 T cells from HIV-1-infected individuals and those with autoimmune disease, but the mechanism remains poorly understood. Here we demonstrate that IL-21-producing CD8 T cells are not associated with CD4 depletion and are absent in patients with idiopathic CD4 lymphocytopenia. Instead, IL-21 production by CD8 T cells was associated with high levels of activation, suggesting that these cells emerge as a consequence of excessive chronic immune activation rather than CD4 lymphopenia.     

Tomato Fruit Chromoplasts Behave as Respiratory Bioenergetic Organelles during Ripening

During tomato (Solanum lycopersicum) fruit ripening, chloroplasts differentiate into photosynthetically inactive chromoplasts. It was recently reported that tomato chromoplasts can synthesize ATP through a respiratory process called chromorespiration. Here we show that chromoplast oxygen consumption is stimulated by the electron donors NADH and NADPH and is sensitive to octyl gallate (Ogal), a plastidial terminal oxidase inhibitor. The ATP synthesis rate of isolated chromoplasts was dependent on the supply of NAD(P)H and was fully inhibited by Ogal. It was also inhibited by the proton uncoupler carbonylcyanide m-chlorophenylhydrazone, suggesting the involvement of a chemiosmotic gradient. In addition, ATP synthesis was sensitive to 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, a cytochrome b₆f complex inhibitor. The possible participation of this complex in chromorespiration was supported by the detection of one of its components (cytochrome f) in chromoplasts using immunoblot and immunocytochemical techniques. The observed increased expression of cytochrome c₆ during ripening suggests that it could act as electron acceptor of the cytochrome b₆f complex in chromorespiration. The effects of Ogal on respiration and ATP levels were also studied in tissue samples. Oxygen uptake of mature green fruit and leaf tissues was not affected by Ogal, but was inhibited increasingly in fruit pericarp throughout ripening (up to 26% in red fruit). Similarly, Ogal caused a significant decrease in ATP content of red fruit pericarp. The number of energized mitochondria, as determined by confocal microscopy, strongly decreased in fruit tissue during ripening. Therefore, the contribution of chromoplasts to total fruit respiration appears to increase in late ripening stages.Chromoplasts are plastids specialized in the production and accumulation of carotenoids, conferring color to many fruits and flowers. During tomato (Solanum lycopersicum) fruit ripening, chloroplasts differentiate into chromoplasts in a process that involves the dismantling of the photosynthetic apparatus and a massive synthesis and deposition of lycopene (Camara et al., 1995). Chromoplasts show a barely studied respiratory process, first reported for daffodil (Narcissus pseudonarcissus) chromoplasts and called chromorespiration, which consists of a membrane-bound redox pathway associated with carotenoid desaturation and results in oxygen uptake activity (Nievelstein et al., 1995). The most likely oxidase involved in this respiratory activity is the plastidial terminal oxidase (PTOX), a plastoquinol oxidase homologous to the mitochondrial alternative oxidase (AOX; Carol et al., 1999; Wu et al., 1999). According to its role in chromorespiration and in carotenoid biosynthesis, the expression of PTOX increases during the ripening process of tomato and bell pepper (Capsicum annuum) fruits (Josse et al., 2003), in parallel to chromoplast differentiation. PTOX has been characterized in vitro and it has been reported to be inhibited by pyrogallol analogs, specially by octyl gallate (Ogal; Josse et al., 2000). In vivo, PTOX has been studied mainly in chloroplasts. PTOX not only participates in carotenoid biosynthesis in chloroplasts but is also involved in chlororespiration, an electron transport chain present in thylakoids that shares plastoquinone with the photosynthetic electron transport chain (Carol and Kuntz, 2001; McDonald et al., 2011).In daffodil chromoplast homogenates (Nievelstein et al., 1995) as well as in isolated tomato fruit chromoplasts (Pateraki et al., 2013), NAD(P)H acts as an electron donor for chromorespiration, indicating the participation of NAD(P)H plastoquinone oxidoreductase activity. Considering that tomato fruit chromoplasts derive from chloroplasts, it is possible that some components of the chromoplastic redox pathway could originate from chlororespiration, such as the NAD(P)H:plastoquinone-reductase complex (NDH), which could act as the electron entrance. However, the enzymes involved in chromorespiration are not well known. It was also reported that the oxygen uptake activity of daffodil chromoplast homogenates was sensitive to the classic uncoupler 2,4-dinitrophenol (Nievelstein et al., 1995), and this observation led to the proposal that chromorespiration could be linked to membrane energization. Morstadt et al. (2002) found that liposomes containing daffodil chromoplast proteins and energized by an acid-base transition were able to produce ATP through a chemiosmotic mechanism, demonstrating that daffodil chromoplasts contain a functional H⁺-ATP synthase complex. We recently reported that isolated chromoplasts from tomato fruits can synthesize ATP de novo (Pateraki et al., 2013). This process is dependent on an ATP synthase complex containing an atypical γ-subunit without the regulatory dithiol domain, which may be active using lower proton gradients than those present in the chloroplast (Pateraki et al., 2013). This finding is consistent with proteomic analyses that reveal that several proteins related to electron transport and ATP production are present in chromoplasts of ripe fruits, like ATP synthase, some subunits of the NDH complex, and the cytochrome b₆f complex (Barsan et al., 2012; Wang et al., 2013).Several anabolic pathways that require ATP and reducing agents are active in ripe fruit chromoplasts, such as synthesis of carotenoids, lipids (glycolipids, phospholipids, and sterols), and the shikimate pathway (Bian et al., 2011; Angaman et al., 2012). On the other hand, the ATP synthesis capacity of mitochondria in ripe fruit is low, because its membrane potential diminishes during ripening as a result of the increasing activity of the mitochondrial uncoupling protein (Almeida et al., 1999; Costa et al., 1999). This fact raised the question of whether chromorespiration could play a significant role in the production of ATP at the last stages of ripening. To our knowledge, the ATP synthesis rates of chromoplasts have not been quantified; therefore, it was uncertain whether the endogenous production could provide ATP in significant amounts to address the energy requirements of the chromoplasts. Moreover, there was no information about the quantitative contribution of chromorespiration to total fruit tissue respiration. This work aimed to deepen the study of the chromorespiratory process in isolated tomato fruit chromoplasts and to analyze the relative participation of this pathway in the overall respiration and ATP levels of fruit pericarp in vivo.     

Cutting edge: L-selectin (CD62L) expression distinguishes small resting memory CD4+ T cells that preferentially respond to recall antigen

Naive CD4+ T cells use L-selectin (CD62L) expression to facilitate immune surveillance. However, the reasons for its expression on a subset of memory CD4+ T cells are unknown. We show that memory CD4+ T cells expressing CD62L were smaller, proliferated well in response to tetanus toxoid, had longer telomeres, and expressed genes and proteins consistent with immune surveillance function. Conversely, memory CD4+ T cells lacking CD62L expression were larger, proliferated poorly in response to tetanus toxoid, had shorter telomeres, and expressed genes and proteins consistent with effector function. These findings suggest that CD62L expression facilitates immune surveillance by programming CD4+ T cell blood and lymph node recirculation, irrespective of naive or memory CD4+ T cell phenotype.     

CD2AP regulates SUMOylation of CIN85 in podocytes

Podocytes are highly differentiated and polarized epithelial cells located on the visceral side of the glomerulus. They form an indispensable component of the glomerular filter, the slit diaphragm, formed by several transmembrane proteins and adaptor molecules. Disruption of the slit diaphragm can lead to massive proteinuria and nephrotic syndrome in mice and humans. CD2AP is an adaptor protein that is important for the maintenance of the slit diaphragm. Together with its paralogue, CIN85, CD2AP belongs to a family of adaptor proteins that are primarily described as being involved in endocytosis and downregulation of receptor tyrosine kinase activity. We have shown that full-length CIN85 is upregulated in podocytes in the absence of CD2AP, whereas in wild-type cells, full-length CIN85 is not detectable. In this study, we show that full-length CIN85 is postranslationally modified by SUMOylation in wild-type podocytes. We can demonstrate that CIN85 is SUMOylated by SUMO-1, -2, and -3 and that SUMOylation is enhanced in the presence of CD2AP. Conversion of lysine 598 to arginine completely abolishes SUMOylation and leads to increased binding of CIN85 to nephrin. Our results indicate a novel role for CD2AP in regulating posttranslational modification of CIN85.