Occurrence of lignin degradation genotypes and phenotypes among prokaryotes.

A number of prokaryotes actively contribute to lignin degradation in nature and their activity could be of interest for many applications including the production of biogas/biofuel from lignocellulosic biomass and biopulping. This review compares the reliability and efficiency of the culture-dependent screening methods currently used for the isolation of ligninolytic prokaryotes. Isolated prokaryotes exhibiting lignin-degrading potential are presented according to their phylogenetic groups. With the development of bioinformatics, culture-independent techniques are emerging that allow larger-scale data mining for ligninolytic prokaryotic functions but today, these techniques still have some limits. In this work, two phylogenetic affiliations of isolated prokaryotes exhibiting ligninolytic potential and laccase-encoding prokaryotes were determined on the basis of 16S rDNA sequences, providing a comparative view of results obtained by the two types of screening techniques. The combination of laboratory culture and bioinformatics approaches is a promising way to explore lignin-degrading prokaryotes.

Electrochemical analysis of a microbial electrochemical snorkel in laboratory and constructed wetlands.

Microbial electrochemical snorkel (MES) is a short-circuited microbial fuel cell applicable to water treatment that does not produce energy but requires lower cost for its implementation. Few reports have already described its water treatment capabilities but no deeper electrochemical analysis were yet performed. We tested various materials (iron, stainless steel and porous graphite) and configurations of snorkel in order to better understand the rules that will control in a wetland the mixed potential of this self-powered system. We designed a model snorkel that was studied in laboratory and on the field. We confirmed the development of MES by identifying anodic and cathodic parts, by measuring the current between them and by analyzing microbial ecology in laboratory and field experiments. An important application is denitrification of surface water. Here we discuss the influence of nitrate on its electrochemical response and denitrification performances. Introducing nitrate caused the increase of the mixed potential of MES and of current at a potential value relatively more positive than for nitrate-reducing biocathodes described in the literature. The major criteria for promoting application of MES in artificial wetland dedicated to mitigation of non-point source nitrate pollution from agricultural water are considered.

Biorefinery for heterogeneous organic waste using microbial electrochemical technology.

Environmental biorefineries aim to produce biofuels and platform biomolecules from organic waste. To this end, microbial electrochemical technologies theoretically allow controlled microbial electrosynthesis (MES) of organic molecules to be coupled to oxidation of waste. Here, we provide a first proof of concept and a robust operation strategy for MES in a microbial electrolysis cell (MEC) fed with biowaste hydrolysates. This strategy allowed stable operation at 5 A/m2 for more than three months in a labscale reactor. We report a two to four-fold reduction in power consumption compared to microbial electrosynthesis with water oxidation at the anode. The bioelectrochemical characterizations of the cells were used to compute energy and matter balances for biorefinery scenarios in which anaerobic digestion (AD) provides the electricity and CO2 required for the MEC. Calculations shows that up to 22% of electrons (or COD) from waste may be converted to organic products in the AD-MEC process.

Cellulose accessibility and microbial community in solid state anaerobic digestion of rape straw.

Solid state anaerobic digestion (SSAD) with leachate recirculation is an appropriate method for the valorization of agriculture residues. Rape straw is a massively produced residue with considerable biochemical methane potential, but its degradation in SSAD remains poorly understood. A thorough study was conducted to understand the performance of rape straw as feedstock for laboratory solid state anaerobic digesters. We investigated the methane production kinetics of rape straw in relation to cellulose accessibility to cellulase and the microbial community. Improving cellulose accessibility through milling had a positive influence on both the methane production rate and methane yield. The SSAD of rape straw reached 60% of its BMP in a 40-day pilot-scale test. Distinct bacterial communities were observed in digested rape straw and leachate, with Bacteroidales and Sphingobacteriales as the most abundant orders, respectively. Archaeal populations showed no phase preference and increased chronologically.

Impact of wet aerobic pretreatments on cellulose accessibility and bacterial communities in rape straw.

A new pretreatment method of lignocellulosic biomass was explored by using a wet aerobic process with an alkaline lignin and a mineral salt solution. This treatment significantly improved structural modification of rape straw used as substrate model in this study. Change in cellulose accessibility to cellulase of rape straw rose up to six fold within the first days of this pretreatment without generated significant modification of van Soest lignocellulose fractionation. The biological pretreatment apply to rape straw induced a high microbial activity revealed by quantitative PCR and sequencing techniques, suggesting that bacteria including Xanthomonadales and Sphingobacteriales may be involved in this lignocellulosic biomass transformation. Moreover, results of this work demonstrate that the endogenous microbial community associated with rape straw plays a key role in its alteration.