Genomic Analysis of Carbon Monoxide Utilization and Butanol Production by Clostridium carboxidivorans Strain P7T

Increasing demand for the production of renewable fuels has recently generated a particular interest in microbial production of butanol. Anaerobic bacteria, such as Clostridium spp., can naturally convert carbohydrates into a variety of primary products, including alcohols like butanol. The genetics of microorganisms like Clostridium acetobutylicum have been well studied and their solvent-producing metabolic pathways characterized. In contrast, less is known about the genetics of Clostridium spp. capable of converting syngas or its individual components into solvents. In this study, the type of strain of a new solventogenic Clostridium species, C. carboxidivorans, was genetically characterized by genome sequencing. C. carboxidivorans strain P7T possessed a complete Wood-Ljungdahl pathway gene cluster, involving CO and CO2 fixation and conversion to acetyl-CoA. Moreover, with the exception of an acetone production pathway, all the genetic determinants of canonical ABE metabolic pathways for acetate, butyrate, ethanol and butanol production were present in the P7T chromosome. The functionality of these pathways was also confirmed by growth of P7T on CO and production of CO2 as well as volatile fatty acids (acetate and butyrate) and solvents (ethanol and butanol). P7T was also found to harbour a 19 Kbp plasmid, which did not include essential or butanol production related genes. This study has generated in depth knowledge of the P7T genome, which will be helpful in developing metabolic engineering strategies to improve C. carboxidivorans's natural capacity to produce potential biofuels from syngas

Biodegradation of benzene in a laboratory-scale biobarrier at low dissolved oxygen concentrations

NRC publication: Ye

Anaerobic digestion as an effective biofuel production technology

The methane produced from the anaerobic digestion of organic wastes and energy crops represents an elegant and economical mean of generating renewable biofuel. Anaerobic digestion is a mature technology and is already used for the conversion of the organic fraction of municipal solid wastes and primary and secondary sludge from wastewater treatment plant. High methane yield up to 0.45 Nm3 CH<inf>4</inf>/kg volatile solids (VS) or 12,390 Nm3 CH<inf>4</inf>/ha can be achieved with sugar and starch crops, although these cultures are competing for high quality land with food and feed crops. The cultivation of lignocellulosic crops on marginal and set-aside lands is a more environmentally sound and sustainable option for renewable energy production. The methane yield obtained from these crops is lower, 0.17-0.39 Nm3 CH<inf>4</inf>/kg VS or 5,400 Nm3 CH<inf>4</inf>/ha, as its conversion into methane is facing the same initial barrier as for the production of ethanol, e.g., hydrolysis of the crops. Intensive research and development on efficient pretreatments is ongoing to optimize the net energy production, which is potentially greater than for liquid biofuels, since the whole substrate excepted lignin is convertible into methane. Algal biomass is another alternative to food and feed crops. Their relatively high methane potential (up to 0.45 Nm3 CH<inf>4</inf>/kg VS fed) combined with their higher areal biomass productivity make them particularly attractive as a feedstock for an anaerobic digestion-based biorefinery concept.Peer reviewed: YesNRC publication: Ye

Characterization of the protein fraction of the extracellular polymeric substances of three anaerobic granular sludges

Abstract Extracellular polymeric substances (EPS) play major roles in the efficacy of biofilms such as anaerobic granules, ranging from structural stability to more specific functions. The EPS of three granular anaerobic sludges of different origins were studied and compared. Particularly, the peptides from the protein fraction were identified by mass spectrometry. Desulfoglaeba and Treponema bacterial genera and Methanosaeta and Methanobacterium archaeal genera were prominent in all three sludges. Methanosaeta concilii proteins were the most represented in EPS of all three sludges studied. Principally, four proteins found in the three sludges, the S-layer protein, the CO-methylating acetyl-CoA synthase, an ABC transporter substrate-binding protein and the methyl-coenzyme M reductase, were expressed by Methanosaeta concilii. Mainly catabolic enzymes were found from the 45 proteins identified in the protein fraction of EPS. This suggests that EPS may have a role in allowing extracellular catabolic reactions

Biomethane production from starch and lignocellulosic crops : a comparative review

The methane produced from the anaerobic digestion of organic wastes and energy crops represents an elegant and economical means of generating renewable biofuel. Anaerobic digestion is a mature technology and is already used for the conversion of the organic fraction of municipal solid wastes and excess primary and secondary sludge from waste-water treatment plants. High methane yield up to 0.45 m3 STP CH4/kg volatile solids (VS) or 12 390 m3 STP CH4/ ha can be achieved with sugar and starch crops, although these cultures are competing with food and feed crops for high-quality land. The cultivation of lignocellulosic crops on marginal and set-aside lands is a more environmentally sound and sustainable option for renewable energy production. The methane yield obtained from these crops is lower, 0.17-0.39 m3 STP CH4/kg VS or 5400 m3 STP CH4/ha, as its conversion into methane is facing the same initial barrier as for the production of ethanol, for example, hydrolysis of the crops. Intensive research and development on efficient pre-treatments is ongoing to optimize the net energy production, which is potentially greater than for liquid biofuels, since the whole substrate excepted lignin is convertible into methane.La production de m\ue9thane \ue0 partir de la digestion ana\ue9robie de d\ue9chets organiques et de plantes \ue9nerg\ue9tiques repr\ue9sente un moyen \ue9l\ue9gant et \ue9conomique d\u2019obtenir du biocarburant renouvelable. La digestion ana\ue9robie est une technologie \ue9prouv\ue9e que l\u2019on utilise d\ue9j\ue0 pour la conversion de la fraction organique des d\ue9chets urbains solides et de l\u2019exc\ue9dent de boues primaires et secondaires provenant des stations d\u2019\ue9puration des eaux us\ue9es. Il est possible d\u2019obtenir un rendement de m\ue9thane \ue9lev\ue9 qui peut atteindre 0,45 m3 de CH4 (TPN)/kg de solides volatils (SV) ou 12 390 m3 de CH4 (TPN)/ha en utilisant des cultures riches en sucre et en amidon, bien que ces cultures se disputent les terres de premi\ue8re qualit\ue9 avec les cultures alimentaires et fourrag\ue8res. La culture des plantes lignocellulosiques sur des terres marginales ou retir\ue9es de la culture constitue une option plus \ue9cologique et durable pour la production d\u2019\ue9nergie renouvelable. Le rendement de m\ue9thane obtenu \ue0 partir de ces cultures est moins \ue9lev\ue9, \ue0 savoir, de 0,17 \ue0 0,39 m3 de CH4 (TPN)/kg de SV ou 5400 m3 de CH4 (TPN)/ha, car sa conversion en m\ue9thane se heurte au m\ueame obstacle initial que dans le cas de la production d\u2019\ue9thanol qui est de proc\ue9der \ue0 une hydrolyse de la plante. Des travaux de recherche et de d\ue9veloppement intensifs sur des pr\ue9traitements efficaces sont en cours pour optimiser la production nette d\u2019\ue9nergie, qui est potentiellement plus \ue9lev\ue9e que dans le cas des biocarburants liquides, car le substrat en entier, sauf la lignine, se convertit en m\ue9thane.Peer reviewed: YesNRC publication: Ye

Thermophilic adaptation of a mesophilic anaerobic sludge for food waste treatment

As opposed to mesophilic, thermophilic anaerobic digestion of food waste can increase the biogas output of reactors. To facilitate the transition of anaerobic digesters, this paper investigated the impact of adapting mesophilic sludge to thermophilic conditions. A 5L bench scale reactor was seeded with mesophilic granular sludge obtained from an up-flow anaerobic sludge blanket digester. After 13 days of operation at 35 degrees C, the reactor temperature was instantaneously increased to 55 degrees C and operated at this temperature until day 21. The biomass was then fed food waste on days 21, 42 and 63, each time with an F/M (Food/Microorganism) ratio increasing from 0.12 to 4.43 gVS/gVSS. Sludge samples were collected on days 0, 21, 42 and 63 to conduct substrate activity tests, and reactor biogas production was monitored during the full experimental period. The sludge collected on day 21 demonstrated that the abrupt temperature change had no pasteurization effect, but rather lead to a biomass with a fermentative activity of 3.58 g Glucose/gVSS/d and a methanogenic activity of 0.47 and 0.26 g Substrate/gVSS/d, related respectively, to acetoclastic and hydrogenophilic microorganisms. At 55 degrees C, an ultimate gas production (Go) and a biodegradation potential (Bo) of 0.2-1.4 L(STP)/gVS(fed) and of 0.1-0.84 L(STP) CH(4)/gVS(fed) were obtained, respectively. For the treatment of food waste, a fully adapted inoculum was developed by eliminating the initial time-consuming acclimatization stage from mesophilic to thermophilic conditions. The feeding stage was initiated within 20 days, but to increase the population of thermophilic methanogenic microorganisms, a substrate supply program must be carefully observed.NRC publication: Ye

Animal digestive strategies versus anaerobic digestion bioprocesses for biogas production from lignocellulosic biomass

Herbivorous mammals and wood-eating insects are fairly effective in the digestion of plant polymers, such as lignocellulosics. In order to improve methane production from the lignocellulosic biomass, several kinds of anaerobic digestion processes derived from animal models have been devised. However, the rates of biodegradation occurring in the anaerobic bioreactors still remain lower than in animal guts. The effectiveness of the digestive systems of those animals results from the concerted action of the various enzymes (e.g. cellulases, xylanases, esterases, ligninases) produced in their guts as well as their integration with mechanical and chemical actions. Powerful pretreatment (prefermentation) operations are integrated to and support efficiently the microbial fermentation system, e.g. the rumination (i.e. mechanical) in ruminants and the secretion of endogenous cellulases (i.e. enzymatic) or the alkaline treatment (chemical) at mid-way in xylophagous insects. The oxygen gradients along the gastrointestinal tract may also stimulate the hydrolytic activities of some microbial populations. In addition, the solid retention time, the digesta flow and the removal of the end-products are well ordered to enable animals to thrive on a complex polymer such as lignocellulose. At the same time, technologies were developed to degrade lignocellulosic biomass, such as the rumen derived anaerobic digestion (RUDAD) process and the rumen simulating technique (RUSITEC), more elaborated and using rumen microbial consortia. Overall, they showed that the fermentation taking place in the rumen fermentation and even in the hindgut are biological processes that go beyond the limited environmental conditions generally found in anaerobic digesters. Hence, knowledge on herbivores' digestion mechanisms might be better exploited in the design and operation of anaerobic digesters. This literature review is a cross-analysis of the relevant information about the digestive strategies of herbivorous and wood-eating animals and the bioengineering techniques in lignocelluloses degradation. The aim is to highlight strategies of animals' digestion simulation for more effective anaerobic digestion of lignocellulosic compounds and other solid residues. \ua9 2010 Her Majesty.Peer reviewed: YesNRC publication: Ye

Direct interspecies electron transfer in anaerobic digestion: a review

Direct interspecies electrons transfer (DIET) is a syntrophic metabolism in which free electrons flow from one cell to another without being shuttled by reduced molecules such as molecular hydrogen or formate. As more and more microorganisms show a capacity for electron exchange, either to export or import them, it becomes obvious that DIET is a syntrophic metabolism that is much more present in nature than previously thought. This article reviews literature related to DIET, specifically in reference to anaerobic digestion. Anaerobic granular sludge, a biofilm, is a specialized microenvironment where syntrophic bacterial and archaeal organisms grow together in close proximity. Exoelectrogenic bacteria degrading organic substrates or intermediates need an electron sink and electrotrophic methanogens represent perfect partners to assimilate those electrons and produce methane. The granule extracellular polymeric substances by making the biofilm matrix more conductive, play a role as electrons carrier in DIET.Peer reviewed: YesNRC publication: Ye

Anaerobic co-digestion of dairy manure with mulched switchgrass for improvement of the methane yield

The owners of farm-scale anaerobic digesters are relying on off-farm wastes or energy crops as a co-digestion feedstock with animal manure in order to increase their production of methane and thus revenues. Switchgrass represents an interesting feedstock for Canadian digesters owners as it is a high-yielding low-maintenance perennial crop, well adapted to northern climate. Methane potential assays in batch tests showed methane production of 19.4 \ub1 3.6, 28.3 \ub1 1.7, 37.3 \ub1 7.1 and 45.7 \ub1 0.8 L kg -1, for raw manure, blended manure, manure and mulched switchgrass, manure and pretreated switchgrass, respectively. Two 6-L lab-scale anaerobic digesters were operated for 130 days in order to assess the benefit of co-digesting switchgrass with bovine manure (digester #2), at a 20% wet mass fraction, compared with a manure-only operation (digester #1) The digesters were operated at an hydraulic retention time of 37 \ub1 6 days and at loads of 2.4 \ub1 0.6 and 2.6 \ub1 0.6 kg total volatile solids (TVS) L\u207b\ub9 day\u207b\ub9 for digesters #1 (D1) and #2 (D2), respectively. The TVS degradation reached 25 and 39%, which resulted in a methane production of 1.18 \ub1 0.18 and 2.19 \ub1 0.31 L day\u207b\ub9 for D1 and D2, respectively. The addition of 20% on a wet mass ratio of switchgrass to a manure digester increased its methane production by 86%. The co-digestion of switchgrass in a 500 m\ub3 manure digester could yield up to 10.2 GJ day\u207b\ub9 of purified methane or 1.1 MWh day\u207b\ub9 of electricity.Peer reviewed: YesNRC publication: Ye

High-rate biomethane production from microalgal biomass in a UASB reactor

Biomethane production from the microalga Scenedesmus sp. AMDD was demonstrated in an upflow anaerobic sludge bed (UASB) reactor. A full factorial design experiment was used to identify the effect of organic loading rate (OLR) of algal biomass and hydraulic retention time (HRT) on the volumetric rate of methane production. At an HRT of 4days and an OLR of 3.23gTVSLR -1d-1 corresponding to an influent microalgae concentration of 12g total volatile solids (TVS) L-1, the volumetric rate of CH4 production reached 0.6LSTPL-1 Rd-1. A methane yield of 0.18-0.2L per gTVS of fed microalgae was estimated. A stable performance was observed throughout 3months of UASB reactor operation. Due to the short HRT and the good performance of UASB reactor, operated at influent microalgae concentrations in a range of 4-12gTVSL-1, this reactor type is suitable for coupling with photobioreactors equipped with gravitational settlers.Peer reviewed: YesNRC publication: Ye