Waterstof uit biomassa

De eerste voorzichtige tekenen van een waterstofeconomie zijn al zichtbaar. In België kun je waterstof tanken, Brabantse boeren overwegen hun windmolen in de daluren in te zetten voor de productie van de brandstof en vorig jaar lanceerde autofabrikant Honda een apparaat waar je thuis waterstof mee kunt maken voor de Honda FCX Clarity

Dark hydrogen fermentations

The production of hydrogen is a ubiquitous, natural phenomenon under anoxic or anaerobic conditions. A wide variety of bacteria, in swamps, sewage, hot springs, the rumen of cattle etc. is able to convert organic matter to hydrogen, CO2 and metabolites like acetic acid, lactate, ethanol and alanine. In general, these bacteria live in the close vicinity of other bacteria which consume these metabolites, including hydrogen, producing their own endproducts like methane and CO2. In this way, a stable ecosystem is formed where potential feedback inhibition of the hydrogen producers by hydrogen, is annulled by the action of the hydrogen consumers. In view of the design of a bioprocess for the production of hydrogen from biomass, extreme thermophilic anaerobic bacteria have been selected because of their high yield with respect to hydrogen production. The yield is reported to be approximately 83-100¿f the maximal theoretical value of 4 mol hydrogen/mol glucose, in contrast to the strict anaerobic Clostridia which produce hydrogen with an approximate yield of 2 mol/mol and the facultative anaerobes which show a H2 yield of less than 2. Besides optimal H2 molar yields, high hydrogen production rates are needed. Product formation appeared to be dependent on cell densities. Thermophiles usually grow to low densities and, therefore production rates are expected to be low. High production rates are reported for Clostridia and Enterobacter of maximal 23 and 58 mmol/L.h, respectively. Hydrogen fermentations by co- and mixed cultures showed production rates of approximately 30-50 mmol/L.h

Biobest products : openbaar eindrapport : Technische Ontwikkeling voor de Productie van Acetaatzouten als Alternatief Strooimiddel : TOPAAS

De technisch-economische evaluatie van een conceptueel calcium-magnesium-acetaat (CMA) productie proces op basis van biomassa leidt tot een minimale verkoopprijs van CMA die competitief is met de marktprijs van CMA dat uit fossiele grondstoffen is geproduceerd. Dit gunstige resultaat wordt veroorzaakt door de economische winst die verkregen wordt doordat in TOPAAS niet alleen CMA maar ook waterstof wordt geproduceerd. De geschiktheid van bermgras voor de productie van CMA en waterstof is, op kleine schaal, experimenteel bewezen. Er is een aanzet gemaakt voor de optimalisatie van de voorbehandeling. Diverse organische restfracties zoals overdatum-producten of restanten voedsel uit grootkeukens en voedingsmiddelenindustrie zijn geanalyseerd. De samenstelling ervan wijst op geschiktheid voor acetaatproductie. De fermentatieve productie van acetaat en waterstof is op continue schaal bewerkstelligd tot en met een aanvaardbare acetaat concentratie. TOPAAS is het acroniem van “Technische Ontwikkeling voor de Productie van Acetaatzouten als Alternatief Strooimiddel”

Acetate metabolisme in Thiobacillus versutus

Thiobacillusversutus was chosen as a modelorganism to study the metabolism of acetate in isocitrate lyase negative organisms.The potential operation of the tricarboxylic acid cycle was established after investigation of the oxidation of acetate by chemolithoautotrophically and heterotrophically grown cells and by measuring the enzyme activities involved in this oxidative cycle. Isocitrate lyase activity, the first enzyme of the glyoxylate cycle, was never observed in calls grown under aerobic conditions whereas malate synthase, catalyzing the second step in this assimilative cycle, was always highest in acetate-grown cells.However, when T.versutus was grown on acetate under denitrifying conditions, isocitrate lyase activity was induced after a certain lag phase during which denitrifying growth took place without the presence of this enzyme. This isocitrate lyase activity was directly linked to the metabolism of acetate during denitrification. Following transition to aerobic growth on this substrate, the activity was actively repressed.Malate synthase activity during denitrifying growth was again highest in acetate-grown cells and the amount was independent of the terminal electron acceptor present, indicating a physiological role of glyoxylate during denitrifying as well as during aerobic growth.The authenticity of the observed isocitrate lyase activity was investigated and appeared to be comparable to isocitrate lyases from other organisms.Although it was found during this study that T.versutus possesses the capacity to synthesize an authentic isocitrate lyase, the reason why this is linked to denitrifying growth and the way acetate is assimilated during aerobic growth remain to be solved

Substrate-induced production and secretion of cellulases by Clostridium acetobutylicum

Clostridium acetobutylicum ATCC 824 is a solventogenic bacterium that grows heterotrophically on a variety of carbohydrates, including glucose, cellobiose, xylose, and lichenan, a linear polymer of beta-1,3- and beta-1,4-linked beta-D-glucose units. C. acetobutylicum does not degrade cellulose, although its genome sequence contains several cellulase-encoding genes and a complete cellulosome cluster of cellulosome genes. In the present study, we demonstrate that a low but significant level of induction of cellulase activity occurs during growth on xylose or lichenan. The celF gene, located in the cellulosome-like gene cluster and coding for a unique cellulase that belongs to glycoside hydrolase family 48, was cloned in Escherichia coli, and antibodies were raised against the overproduced CelF protein. A Western blot analysis suggested a possible catabolite repression by glucose or cellobiose and an up-regulation by lichenan or xylose of the extracellular production of CelF by C. acetobutylicum. Possible reasons for the apparent inability of C. acetobutylicum to degrade cellulose are discussed