Screening of Phytophagous and Xylophagous Insects Guts Microbiota Abilities to Degrade Lignocellulose in Bioreactor

Microbial consortia producing specific enzymatic cocktails are present in the gut of phytophagous and xylophagous insects; they are known to be the most efficient ecosystems to degrade lignocellulose. Here, the ability of these consortia to degrade ex vivo lignocellulosic biomass in anaerobic bioreactors was characterized in term of bioprocess performances, enzymatic activities and bacterial community structure. In a preliminary screening, guts of Ergates faber (beetle), Potosia cuprea (chafer), Gromphadorrhina portentosa (cockroach), Locusta migratoria (locust), and Gryllus bimaculatus (cricket) were inoculated in anaerobic batch reactors, in presence of grounded wheat straw at neutral pH. A short duration fermentation of less than 8 days was observed and was related to a drop of pH from 7 to below 4.5, leading to an interruption of gas and metabolites production. Consistently, a maximum of 180 mgeq.COD of metabolites accumulated in the medium, which was related to a low degradation of the lignocellulosic biomass, with a maximum of 5 and 2.2% observed for chafer and locust gut consortia. The initial cell-bound and extracellular enzyme activities, i.e., xylanase and β-endoglucanase, were similar to values observed in the literature. Wheat straw fermentation in bioreactors leads to an increase of cell-bounded enzyme activities, with an increase of 145% for cockroach xylanase activity. Bacterial community structures were insect dependent and mainly composed of Clostridia, Bacteroidia and Gammaproteobacteria. Improvement of lignocellulose biodegradation was operated in successive batch mode at pH 8 using the most interesting consortia, i.e., locust, cockroaches and chafer gut consortia. In these conditions, lignocellulose degradation increased significantly: 8.4, 10.5, and 21.0% of the initial COD were degraded for chafer, cockroaches and locusts, respectively in 15 days. Consistently, xylanase activity tripled for the three consortia, attesting the improvement of the process. Bacteroidia was the major bacterial class represented in the bacterial community for all consortia, followed by Clostridia and Gammaproteobacteria classes. This work demonstrates the possibility to maintain apart of insect gut biological activity ex vivo and shows that lignocellulose biodegradation can be improved by using a biomimetic approach. These results bring new insights for the optimization of lignocellulose degradation in bioreactors

Similar PAH fate in anaerobic digesters inoculated with three microbial communities accumulating either volatile fatty acids or methane.

Urban sludge produced on wastewater treatment plants are often contaminated by organic pollutants such as polycyclic aromatic hydrocarbons (PAH). Their removal under methanogenic conditions was already reported, but the factors influencing this removal remain unclear. Here, we determined the influence of microbial communities on PAH removal under controlled physico-chemical conditions. Twelve mesophilic anaerobic digesters were inoculated with three microbial communities extracted from ecosystems with contrasting pollution histories: a PAH contaminated soil, a PCB contaminated sediment and a low contaminated anaerobic sludge. These anaerobic digesters were operated during 100 days in continuous mode. A sterilised activated sludge, spiked with 13 PAH at concentrations usually encountered in full-scale wastewater treatment plants, was used as substrate. The dry matter and volatile solid degradation, the biogas production rate and composition, the volatile fatty acids (VFA) production and the PAH removals were monitored. Bacterial and archaeal communities were compared in abundance (qPCR), in community structure (SSCP fingerprinting) and in dominant microbial species (454-pyrosequencing). The bioreactors inoculated with the community extracted from low contaminated anaerobic sludge showed the greater methane production. The PAH removals ranged from 10% to 30%, respectively, for high and low molecular weight PAH, whatever the inoculums tested, and were highly correlated with the dry matter and volatile solid removals. The microbial community structure and diversity differed with the inoculum source; this difference was maintained after the 100 days of digestion. However, the PAH removal was not correlated to these diverse structures and diversities. We hence obtained three functional stable consortia with two contrasted metabolic activities, and three different pictures of microbial diversity, but similar PAH and matter removals. These results confirm that PAH removal depends on the molecule type and on the solid matter removal. But, as PAH elimination is similar whether the solid substrate is degraded into VFA or into methane, it seems that the fermentative communities are responsible for their elimination

Correlation of the Electrochemical Kinetics of High-Salinity-Tolerant Bioanodes with the Structure and Microbial Composition of the Biofilm

International audienceIncreasing the conductivity of the electrolytes used in microbial electrochemical systems is an essential prerequisite to large‐scale application of these technologies. Microbial anodes formed on carbon felt from a salt marsh inoculum under polarisation at 0.1 V (versus a saturated calomel electrode), generated up to 85 A m−2 in media that contained 30–45 g L−1 of NaCl. Analyses of microbial populations showed a stringent selection of the two microbial genera Marinobacter and Desulfuromonas. Currents decreased if NaCl concentration was increased to 60 g L−1. This highest salinity was shown to consistently impact the bioanode performance in three ways: voltammetry indicated degraded electron‐transfer kinetics, confocal laser scanning microscopy showed a modified biofilm structure and DNA pyrosequencing detected a decrease in the level of Desulfuromonas spp. relative to Marinobacter spp. A consistent correlation was, thus, found between electrochemical kinetics, biofilm structure and the composition of the microbial community

Halotolerant bioanodes: The applied potential modulates the electrochemical characteristics, the biofilm structure and the ratio of the two dominant genera

The development of economically-efficient microbial electrochemical technologies remains hindered by the low ionic conductivity of the culture media used as the electrolyte. To overcome this drawback, halotolerant bioanodes were designed with salt marsh sediment used as the inoculum in electrolytes containing NaCl at 30 or 45 g/L (ionic conductivity 7.0 or 10.4 S·m− 1). The bioanodes were formed at four different potentials − 0.4, − 0.2, 0.0 and 0.2 V/SCE to identify the effect on the electrochemical kinetic parameters, the biofilm structures and the composition of the microbial communities. The bioanodes formed at − 0.4 V/SCE were largely dominated by Marinobacter spp. Voltammetry showed that they provided higher currents than the other bioanodes in the range of low potentials, but the maximum currents were limited by the poor surface colonization. The bioanodes formed at − 0.2, 0.0 and 0.2 V/SCE showed similar ratios of Marinobacter and Desulfuromonas spp. and higher values of the maximum current density. The combined analysis of kinetic parameters, biofilm structure and biofilm composition showed that Marinobacter spp., which ensured a higher electron transfer rate, were promising species for the design of halotolerant bioanodes. The challenge is now to overcome its limited surface colonization in the absence of Desulfuromonas spp

Average enumeration according to the inoculum origin (<i>eco1</i> in white, <i>eco2</i> in grey, <i>eco3</i> in black) of <i>Bacteria</i> (left) and <i>Archaea</i> (right) by q-PCR.

<p>The x axis represents the hydraulic retention time. Standard errors are displayed. HRT4 and HRT 5 represent the steady state based on the reactors performances.</p

Similar PAH Fate in Anaerobic Digesters Inoculated with Three Microbial Communities Accumulating Either Volatile Fatty Acids or Methane - Fig 6

<p><b>(A)</b> Influence of the inoculum origin (<i>eco1</i>, <i>eco</i>2, <i>eco3</i>) and time (HRT0, HRT3, HRT4 and HRT5) on the difference in genetic structure of bacterial (on the left) and archaeal (on the right) communities through a PCA. The percentage variation explained by each principal component and the principal component scores of the sample are plotted on their respective axes. Changes over time are graphically represented by arrows.<b>(B)</b> Principal Component Analysis (PCA) biplot of bacterial (on the left) and archaeal (on the right) communities. PCA displayed 65.4% of variance for bacterial CE-SSCP fingerprints and 74.3% of variance for archaeal CE-SSCP fingerprints. Only significant correlations with operational characteristics were presented as arrows.</p

Principal Component Analysis (PCA) biplot at steady state of microbial communities (<i>eco1</i>, <i>eco2</i>, <i>eco3</i>) obtained with the CE-SSCP data (on the left) and with the sequencing data (on the right).

<p>PCA displayed 92% and 92.3% of variance for microbial fingerprints and sequencing respectively. Most discriminant CE-SSCP peaks (on the left) and most discriminant species (on the right) were highlighted as arrows that were directed according to their explanatory outputs. 1, 2, 3: <i>Clostridium sp</i>. (88%), 4: <i>Parabacteroides sp</i>. (87%), 5: <i>Dysgonomas sp</i>. (90%), 6: <i>Parabacteroides sp</i>. (86%), 7: <i>Clostridium sp</i> (93%), 8: <i>Anaerobaculum mobile</i> (99%), 9: <i>Thiohalomonas sp</i>. (82%), 10: <i>Op9</i> (99%), 11: <i>Pseudomonas stutzeri</i> (99%).</p

Correlation between DM (black square) or VS (grey triangle) removals and PAH removal.

<p>Correlation between DM (black square) or VS (grey triangle) removals and PAH removal.</p

Characteristics of the feeding sludge (FS) and of the outlet sludge (<i>eco 1</i>, <i>2 or 3</i>) from the mesophilic bioreactors inoculated with the three microbial communities at steady state.

<p>COD_tot is measured on the total sample and COD_DCM on the DCM fraction. COD*: degraded COD, nd: not detectable. The VFA_tot is the total concentration of the VFA measured on the DCM fraction. The different parameters were averaged on two HRT at steady state.</p><p>Characteristics of the feeding sludge (FS) and of the outlet sludge (<i>eco 1</i>, <i>2 or 3</i>) from the mesophilic bioreactors inoculated with the three microbial communities at steady state.</p

<i>Archaea</i> / <i>Bacteria</i> ratio depending on the methane production at steady state.

<p>The ratio is either calculated with the q-PCR or the 454-pyrosequencing data.</p