• Energy Research

Corn stover has great potential as a biomass feedstock due its widespread availability. However, storage characteristics of moist corn stover harvested from single-pass harvesters have not been well quantified. In 2007, moist whole-plant corn stover at 19.1 to 40.3 % (w.b.) moisture content was stored for 237 days in aerobic piles, one covered and one uncovered, as well an anaerobic silo bag. In 2008, two moist stover materials – whole-plant and cob/husk from 31.7 to 58.1% (w.b.) moisture - were stored for 183 or 204 days in covered and uncovered anaerobic piles, ventilated bags, or anaerobic silo bags. Stover stored in uncovered piles was rehydrated from precipitation, which increased biological activity and produced DM losses from 8.2% to 39.1% with an average of 21.5%. Stover in covered piles was successfully conserved when the average moisture was less than 25% (w.b.) with DM losses of 3.3%. Stover above 36% (w.b.) and piled under a plastic cover had DM losses from 6.4% to 20.2% with an average of 11.9%. Localized heating to temperatures where spontaneous combustion might be a concern (i.e. > 70°C) occurred in the aerobic piles when moisture was above 45% (w.b.). Ambient air blown through a center tube in the ventilated bag dried stover near the tube to an average of 24.2% (w.b.), but the remainder of the bag averaged 46.8% (w.b.) at removal. Loss of DM ranged from 7.4% to 22.0% with an average of 11.8%. Stover was most successfully conserved in the bags where anaerobic conditions were maintained. Under anaerobic conditions DM losses ranged from 0.2% to 0.9%. When anaerobic conditions were not maintained in the silo bag DM losses averaged 6.1% of DM. Anaerobic storage is the best solution for conserving the value of moist corn stover.

Abstract This research investigated the harvest, ambient pre-treatment, and storage of whole-plant corn as an alternative to conventional systems where corn grain and stover are fractionated at harvest. Harvesting the whole-plant, both grain and most of the above ground stover, after physiological maturity can reduce the intense logistics challenges typically associated with corn harvest and expand the harvest window. To determine the feasibility of the proposed system, corn was harvested at 350–840 g kg −1 whole-plant dry matter (DM) using a forage harvester and then ensiled in pilot-scale silos. Ambient pretreatment during storage was investigated using both dilute acid and lime. Both pretreated and control whole-plant silages were very well conserved during anaerobic storage with DM losses generally less than 40 g kg −1 . Hydrodynamic separation of the grain and stover fractions after storage was found to be more effective at fractionating starch and fiber than conventional dry grain harvest, and both fractions had desirable composition. The effects of pretreatment on the silage were very pronounced at 30 and 100 g (kg DM) −1 sulfuric acid loading with less than 100 g (kg DM) −1 of the hemicellulose still bound in the cell wall at DM contents greater than 500 g kg −1 . The whole-plant harvest and storage system was shown to be a viable alternative to conventional corn grain and stover systems for producing feedstocks for biochemical conversion.

Mixed bacterial communities from the rumen ferment cellulosic biomass primarily to C2-C4 volatile fatty acids, and perform only limited chain extension to produce C5 (valeric) and C6 (caproic) acids. The aim of this study was to increase production of caproate and valerate in short-term in vitro incubations. Co-culture of mixed ruminal microbes with a rumen-derived strain of the bacterium Clostridium kluyveri converted cellulosic biomass (alfalfa stems or switchgrass herbage) plus ethanol to VFA mixtures that include valeric and caproic acids as the major fermentation products over a 48-72h run time. Concentrations of caproate reached 6.1gL(-1), similar to or greater than those reported in most conventional carboxylate fermentations that employ substantially longer run times.

The fermentation of cellulose and cellobiose by Clostridium thermocellum monocultures and C. thermocellum/Methanobacterium thermoautotrophicum cocultures was studied. All cultures were grown under anaerobic conditions in batch culture at 60 degrees C. When grown on cellulose, the coculture exhibited a shorter lag before initiation and growth and celluloysis than did the monoculture. Cellulase activity appeared earlier in the coculture than in the monoculture; however, after growth had ceased, cellulase activity was greater in the monoculture. Monocultures produced primarily ethanol, acetic acid, H2 and CO2. Cocultures produced more H2 and acetic acid and less ethanol than did the monoculture. In the coculture, conversion of H2 to methane was usually complete, and most of the methane produced was derived from CO2 reduction rather than from acetate conversion. Agents of fermentation stoppage were found to be low pH and high concentrations of ethanol in the monoculture and low pH in the coculture. Fermentation of cellobiose was more rapid than that of cellulose. In cellobiose medium, the methanogen caused only slight changes in the fermentation balance of the Clostridium, and free H2 was produced.

Bermuda grass is an attractive candidate as a feedstock for biofuel production because over four million hectares of Bermuda grass are already grown for forage in the Southern USA. Because both rumen digestion and biochemical conversion to ethanol depend upon enzymatic conversion of the cell wall polysaccharides into fermentable sugars, it is probable that grasses bred for increased forage quality would be more amenable for ethanol production. However, it is not known how variation in rumen digestibility and cell wall/fiber components correlates with efficiency of conversion to ethanol via fermentation. The objective of this research was to determine relationships between ethanol production evaluated by simultaneous saccharification and fermentation (SSF), 72-h in vitro ruminal dry matter digestibility (IVDMD), in vitro ruminal gas production after 24 and 96 h, and biomass composition for 50 genetically diverse Bermuda grass accessions. The Bermuda grass samples were subjected to standard 72-h IVDMD and forage fiber analyses. Also, in separate labs, gas production was measured in sealed volume-calibrated vials after 24 (NNG24) and 96 h (NNG96) of in vitro fermentation by ruminal fluid; ethanol and pentose sugar productions were measured from a bench-top SSF procedure; cell wall constituents were determined by the Uppsala Dietary Fiber Method; and total nitrogen, carbon, and ash concentrations were determined by using the LECO combustion method. Ethanol production was moderately correlated with IVDMD (r = 0.55) and NNG96 (r = 0.63) but highly correlated with NNG24 (r = 0.93). Ethanol was negatively correlated with neutral detergent fiber (NDF; r = −0.53) and pentose sugars (r = −0.60), but not correlated with glucose content. Regression models indicated that NDF and cell wall pentose sugar concentrations had significant negative effects on ethanol production. Variation among entries for IVDMD was affected by variability of NDF, pentose sugar concentrations, and biomass nitrogen content. Variation in Klason lignin content had only minor negative impacts on ethanol production and IVDMD. Biochemical conversion efficiency of Bermuda grass by SSF can be best estimated by NNG24 but not by IVDMD.

Arboreal herbivory is rare among mammals. The few species with this lifestyle possess unique adaptions to overcome size-related constraints on nutritional energetics. Sloths are folivores that spend most of their time resting or eating in the forest canopy. A three-toed sloth will, however, descend its tree weekly to defecate, which is risky, energetically costly and, until now, inexplicable. We hypothesized that this behaviour sustains an ecosystem in the fur of sloths, which confers cryptic nutritional benefits to sloths. We found that the more specialized three-toed sloths harboured more phoretic moths, greater concentrations of inorganic nitrogen and higher algal biomass than the generalist two-toed sloths. Moth density was positively related to inorganic nitrogen concentration and algal biomass in the fur. We discovered that sloths consumed algae from their fur, which was highly digestible and lipid-rich. By descending a tree to defecate, sloths transport moths to their oviposition sites in sloth dung, which facilitates moth colonization of sloth fur. Moths are portals for nutrients, increasing nitrogen levels in sloth fur, which fuels algal growth. Sloths consume these algae-gardens, presumably to augment their limited diet. These linked mutualisms between moths, sloths and algae appear to aid the sloth in overcoming a highly constrained lifestyle.

Les herbivores peuvent avoir un accès indirect au carbone récalcitrant présent dans les parois des cellules végétales grâce à des associations symbiotiques avec des microbes lignocellulolytiques. Un exemple paradigmatique est la fourmi coupeuse de feuilles (Tribu : Attini), qui utilise des feuilles fraîches pour cultiver un champignon pour se nourrir dans des jardins spécialisés. En utilisant une combinaison d'analyses de la composition du sucre, de la métagénomique et du séquençage du génome entier, nous révélons que le microbiome du champignon de jardin des fourmis coupeuses de feuilles est composé d'une communauté diversifiée de bactéries ayant une capacité élevée de dégradation de la biomasse végétale. La comparaison du profil enzymatique prédit de dégradation des glucides de ce microbiome avec d'autres métagénomes montre une similitude plus étroite avec le rumen bovin, indiquant une convergence évolutive du potentiel de dégradation de la biomasse végétale entre deux animaux herbivores importants. La caractérisation génomique et physiologique de deux bactéries dominantes dans le microbiome fongique du jardin fournit des preuves de leur capacité à dégrader la cellulose. Compte tenu de l'intérêt récent pour les biocarburants cellulosiques, comprendre comment la dégradation rapide et à grande échelle de la biomasse végétale se produit chez un insecte herbivore très évolué est particulièrement important pour la bioénergie. Los herbívoros pueden obtener acceso indirecto al carbono recalcitrante presente en las paredes celulares de las plantas a través de asociaciones simbióticas con microbios lignocelulolíticos. Un ejemplo paradigmático es la hormiga cortadora de hojas (Tribu: Attini), que utiliza hojas frescas para cultivar un hongo como alimento en jardines especializados. Usando una combinación de análisis de composición de azúcar, metagenómica y secuenciación del genoma completo, revelamos que el microbioma del jardín de hongos de las hormigas cortadoras de hojas está compuesto por una comunidad diversa de bacterias con alta capacidad de degradación de la biomasa vegetal. La comparación del perfil enzimático de degradación de carbohidratos predicho de este microbioma con otros metagenomas muestra la mayor similitud con el rumen bovino, lo que indica una convergencia evolutiva del potencial de degradación de la biomasa vegetal entre dos animales herbívoros importantes. La caracterización genómica y fisiológica de dos bacterias dominantes en el microbioma del jardín de hongos proporciona evidencia de su capacidad para degradar la celulosa. Dado el reciente interés en los biocombustibles celulósicos, la comprensión de cómo se produce la degradación rápida y a gran escala de la biomasa vegetal en un insecto herbívoro altamente evolucionado es de particular relevancia para la bioenergía. Herbivores can gain indirect access to recalcitrant carbon present in plant cell walls through symbiotic associations with lignocellulolytic microbes. A paradigmatic example is the leaf-cutter ant (Tribe: Attini), which uses fresh leaves to cultivate a fungus for food in specialized gardens. Using a combination of sugar composition analyses, metagenomics, and whole-genome sequencing, we reveal that the fungus garden microbiome of leaf-cutter ants is composed of a diverse community of bacteria with high plant biomass-degrading capacity. Comparison of this microbiome's predicted carbohydrate-degrading enzyme profile with other metagenomes shows closest similarity to the bovine rumen, indicating evolutionary convergence of plant biomass degrading potential between two important herbivorous animals. Genomic and physiological characterization of two dominant bacteria in the fungus garden microbiome provides evidence of their capacity to degrade cellulose. Given the recent interest in cellulosic biofuels, understanding how large-scale and rapid plant biomass degradation occurs in a highly evolved insect herbivore is of particular relevance for bioenergy. يمكن للحيوانات العاشبة الوصول بشكل غير مباشر إلى الكربون المتمرد الموجود في جدران الخلايا النباتية من خلال الارتباطات التكافلية مع الميكروبات المحللة للخلايا. ومن الأمثلة النموذجية على ذلك نملة قطع الأوراق (القبيلة: أتيني)، التي تستخدم أوراقًا طازجة لزراعة فطر للطعام في الحدائق المتخصصة. باستخدام مزيج من تحليلات تركيبة السكر، وعلم الوراثة، وتسلسل الجينوم الكامل، نكشف أن ميكروبيوم حديقة الفطريات من النمل القاطع للأوراق يتكون من مجموعة متنوعة من البكتيريا ذات القدرة العالية على تحلل الكتلة الحيوية للنبات. تُظهر مقارنة ملف تعريف إنزيم تحلل الكربوهيدرات المتوقع لهذا الميكروبيوم مع الميتاجينومات الأخرى أقرب تشابه مع الكرش البقري، مما يشير إلى التقارب التطوري لإمكانات تحلل الكتلة الحيوية النباتية بين اثنين من الحيوانات العاشبة المهمة. يوفر التوصيف الجيني والفسيولوجي لبكتيريا مهيمنة في ميكروبيوم حديقة الفطريات دليلاً على قدرتها على تحلل السليلوز. بالنظر إلى الاهتمام الأخير بالوقود الحيوي السليولوزي، فإن فهم كيفية حدوث تدهور الكتلة الحيوية النباتية على نطاق واسع وسريع في الحيوانات العاشبة الحشرية المتطورة للغاية له أهمية خاصة بالنسبة للطاقة الحيوية.

Corn stover was harvested with a modified combine that simultaneously harvested grain and stover in separate streams. The harvester was used to collect the following stover fractions using three different heads: cob and husk (ear-snapper head); stalk and leaves (stalk-gathering head); and stalks, leaves, husk, and cob (whole-plant head). Cob and husk were also collected when using the stalk-gathering head, but in a separate stream from the stalks and leaves. Material harvested with the ear-snapper, whole-plant, or stalk-gathering head had average moisture of 38.2%, 45.0%, and 46.7% (w.b.); particle size of 14, 22, and 90 mm; and density in the transport container of 98, 64, and 40 kg DM m-3, respectively. Area productivity was 3.4, 1.5, and 1.9 ha h-1; fraction of available stover DM actually harvested was 18%, 64%, and 49%; and total harvester specific fuel use was 1.46, 2.07, and 1.83 L Mg-1 DM or 17.0, 33.4, and 27.4 L ha-1 for the ear-snapper, whole-plant, and stalk-gathering head configurations, respectively. The untilled ground cover in the fall and spring was greater than the minimum requirement of 30% when using any of the three heads. Chisel plowing in the fall with twisted shovels buried too much residue no matter which harvester configuration was used. Chisel plowing in the spring with sweeps left sufficient residue when stover was harvested with either the ear-snapper or stalk-gathering heads. Material harvested with the ear-snapper, stalk-gathering, and whole-plant heads had an average density in a bag silo of 261, 111, and 160 kg DM m-3, respectively. Average loss in a bag silo was less than 4.3% of total stover DM after nine months of storage. Based on estimated cellulose and hemicellulose content, ethanol yield was 868, 1474, and 2804 L ha-1 from materials harvested with the ear-snapper, stalk-gathering, and whole-plant heads, respectively.

ABSTRACT Anaerobic cellulolytic bacteria are thought to adhere to cellulose via several mechanisms, including production of a glycocalyx containing extracellular polymeric substances (EPS). As the compositions and structures of these glycocalyces have not been elucidated, variable-pressure scanning electron microscopy (VP-SEM) and chemical analysis were used to characterize the glycocalyx of the ruminal bacterium Ruminococcus albus strain 7. VP-SEM revealed that growth of this strain was accompanied by the formation of thin cellular extensions that allowed the bacterium to adhere to cellulose, followed by formation of a ramifying network that interconnected individual cells to one another and to the unraveling cellulose microfibrils. Extraction of 48-h-old whole-culture pellets (bacterial cells plus glycocalyx [G] plus residual cellulose [C]) with 0.1 N NaOH released carbohydrate and protein in a ratio of 1:5. Boiling of the cellulose fermentation residue in a neutral detergent solution removed almost all of the adherent cells and protein while retaining a residual network of adhering noncellular material. Trifluoroacetic acid hydrolysis of this residue (G plus C) released primarily glucose, along with substantial amounts of xylose and mannose, but only traces of galactose, the most abundant sugar in most characterized bacterial exopolysaccharides. Linkage analysis and characterization by nuclear magnetic resonance suggested that most of the glucosyl units were not present as partially degraded cellulose. Calculations suggested that the energy demand for synthesis of the nonprotein fraction of EPS by this organism represents only a small fraction (<4%) of the anabolic ATP expenditure of the bacterium.