Anaerobic bioprocessing of organic wastes

Anaerobic digestion of dissolved, suspended and solid organics has rapidly evolved in the last decades but nevertheless still faces several scientific unknowns. In this review, some fundamentals of bacterial conversions and adhesion are addressed initially. It is argued in the light of G-values of reactions, and in view of the minimum energy quantum per mol, that anaerobic syntrophs must have special survival strategies in order to support their existence: redistributing the available energy between the partners, reduced end-product fermentation reactions and special cell-to-cell physiological interactions. In terms of kinetics, it appears that both reaction rates and residual substrate thresholds are strongly related to minimum G-values. These new fundamental insights open perspectives for efficient design and operation of anaerobic bioprocesses. Subsequently, an overview is given of the current anaerobic biotechnology. For treating wastewaters, a novel and high performance new system has been introduced during the last decade; the upflow anaerobic sludge blanket system (UASB). This reactor concept requires anaerobic consortia to grow in a dense and eco-physiologically well-organized way. The microbial principles of such granular sludge growth are presented. Using a thermodynamic approach, the formation of different types of aggregates is explained. The application of this bioprocess in worldwide wastewater treatment is indicated. Due to the long retention times of the active biomass, the UASB is also suitable for the development of bacterial consortia capable of degrading xenobiotics. Operating granular sludge reactors at high upflow velocities (5–6 m/h) in expanded granular sludge bed (EGSB) systems enlarges the application field to very low strength wastewaters (chemical oxygen demand < 1 g/l) and psychrophilic temperatures (10°C). For the treatment of organic suspensions, there is currently a tendency to evolve from the conventional mesophilic continuously stirred tank system to the thermophilic configuration, as the latter permits higher conversion rates and easier sanitation. Integration of ultrafiltration in anaerobic slurry digestion facilitates operation at higher volumetric loading rates and at shorter residence times. With respect to organic solids, the recent trend in society towards source separated collection of biowaste has opened a broad range of new application areas for solid state anaerobic fermentation.W. Verstraete and D. de Beer are with the Center for Environmental Sanitation, University of Gent, Coupure L 653, B-9000 Gent, Belgium; D. de Beer is also with the Max Plank Institut für Marine Mikrobiologie-Microzensor Group, Fahrenstrasse 1, 28359 Bremen, Germany. M. Pena is with the Groupo de Biotechnologia Ambiental, Departamento de Ingenieria Quimica, Universidad de Valladolid, Prado de la Magdalena, 47005 Valladolid, Spain. G. Lettinga is with the Department of Environmental Technology, Wageningen Agricultural University, Bomenweg 2, 6703 HD Wageningen, The Netherlands. P. Lens is with the Environmental Research Unit. Department of Microbiology, University College Galway, Galway, Ireland.     

Developmental regulation of aldoxime formation in seedlings and mature plants of Chinese cabbage (Brassica campestris ssp. pekinensis) and oilseed rape (Brassica napus): Glucosinolate and IAA biosynthetic enzymes

The first steps in the biosynthesis of glucosinolates and indole-3-acetic acid (IAA) in oilseed rape (Brassica napus L.) and Chinese cabbage (Brassica campestris ssp. pekinensis) involve the formation of aldoximes. In rape the formation of aldoximes from chain-extended amino acids, for aromatic and aliphatic glucosinolate biosynthesis, is catalysed by microsomal flavin-containing monooxygenases. The formation of indole-3-aldoxime from l-tryptophan, the potential precursor of both indole-3-acetic acid and indolyl-glucosinolates, is catalysed by several microsomal peroxidases. The biosynthesis of glucosinolates and indole-3-acetic acid was shown to be under developmental control in oilseed rape and Chinese cabbage. No monooxygenase activities were detected in cotyledons or old leaves of either species. The highest monooxygenase activities were found in young expanding leaves; as the leaves reached full expansion and matured the activities decreased rapidly. The indole-aldoxime-forming activity was found in all of the tissues analysed, but there was also a clear decrease in foliar activity with maturity in leaves of rape and Chinese cabbage. Partial characterisation of the Chinese cabbage monooxygenases showed that they have essentially identical properties to the previously characterised rape enzymes; they are not cytochrome P450-type enzymes, but resemble flavin-containing monooxygenases. No monooxygenase inhibitors were detected in microsomes prepared from either cotyledons or old leaves.Abbreviations DHMet dihomomethionine - FMO flavin-containing monooxygenase - HPhe homophenylalanine - IAA indole-3-acetic acid - l-Phe l-phenylalanine - l-Trp l-tryptophan - MO monooxygenase - IAALD indole-3-acetaldehyde - IAOX indole-3-aldoxime - THMet trihomomethionine     

Granular sludge growth under different reactor liquid surface tensions in lab-scale upflow anaerobic sludge blanket reactors treating wastewater from sugar-beet processing

The formation of anaerobic granular sludge on wastewater from sugar-beet processing was examined in upflow anaerobic sludge blanket reactors. Two strategies were investigated: addition of high-energy substrate, i.e. sugars, and varying the reactor liquid surface tension. When there were insufficient amounts of sugars i.e. less than 7% of the chemical O₂ demand of the influent, no granulation was observed; moreover lowering the reactor liquid surface tension below 48 mN/m was found to increase biomass wash-out. On the other hand, when there were sufficient sugars, granular sludge growth occurred; moreover operating the reactor at a low reactor liquid surface tension reduced biomass wash-out and increased granular yield.     

The impact of the Scheldt input on the trace metal distribution in the Belgian coastal area (results of 1981–1983 and 1995–1996)

Offshore fluxes of Cu, Zn, Cd, Pb and Hg were calculated based onresidual flow patterns and salinity gradients along the Belgian coast. Theresidual flow lines along the Belgian coast are more or less parallel to thecoast except in the area where the north-easterly flowing watermass comingfrom the Channel encounters the south-westerly-oriented Scheldt outflow,forming a residual hydrodynamical front. From the steady-state salinitypattern, diffusion coefficients perpendicular to the residual flow werededuced; they ranged from 21 to 108 m² s^-1. Offshore fluxes of dissolved and particulate trace metals based on diffusiveand mixing processes are calculated. The steady state profiles of dissolvedmetals show a dilution effect in the coastal waters, reaching an almostconstant concentration in the marine watermass in the 1981–1983dataset. The ratios of the Scheldt input of trace metals to the totaldissolved offshore flux vary from 38 to 55% (1981–1983),depending on the kind of metal, and from 55 to 91% (1995–1996).The ratio of the Scheldt input to the dissolved metal flow parallel to thecoast, is in both periods (1981–1983 and 1995–1996), smallerthan 1%. The steady-state concentration profiles of particular metalsversus salinity are fairly constant in the coastal-estuarine and marinewatermasses, but decrease very abruptly from the first to the secondwatermass. Assuming a conservative behaviour of the particular metals,offshore fluxes and the resulting concentration increases agree fairly wellwith the observed values. The ratios of the Scheldt input to the particulatetrace metal offshore flux vary between 30 to 46% (1981–1983)and 13 to 37% (1995–1996). The contribution of the Scheldtestuary to the flows parallel to the coast ranges from 1.6 to 2.9%(1981–1983) and from 0.6 to 1.6% (1995). This revised version was published online in July 2006 with corrections to the Cover Date.     

Calcium concretions in the pineal gland of aged rats: an ultrastructural and microanalytical study of their biogenesis

The genesis of calcium concretions in aged rats was studied by means of transmission and scanning electron microscopy. The potassium pyroantimonate method, combined with X-ray microanalysis, allowed us to study the distribution of cations and calcium. Notable accumulations of calcium (associated with phosphorus) were localized in vesicles, vacuoles, lipid droplets, lipopigments, and mitochondria of dark pinealocytes. The results obtained in the present investigation suggest that these organelles are involved in the genesis of the concretions. The presence of sulfur indicates the existence of an organic matrix. We propose that genesis takes place in dark pinealocytes, which contain more calcium than light pinealocytes. Mineralization foci are some-times associated with cellular debris and enlarge by further apposition of material. Two types of concretions, as determined by electron microscopy and confirmed by electron diffraction, could be observed: the amorphous type with concentric layers and the crystalline type with needle-shaped crystals. Once formed, the concretions reach the extracellular space and the cell breaks down. Possible extracellular calcification is suggested in the extracellular calcium-rich floculent material. The mineralization process is interpreted as being an age-related phenomenon and mainly a consequence of the degeneration of pinealocytes.     

Synthesis and evaluation of azaproline peptides as potential inhibitors of dipeptidyl peptidase IV and prolyl oligopeptidase

Summary A series of azaproline dipeptides with various N-substituents were synthesized as possible active-site-directed inhibitors of two proline-specific serine proteases, dipeptidyl peptidase IV and prolyl oligopeptidase. Compounds with semicarbazide, carbazate, acylhydrazine and sulphonylhydrazine structures were tested. Some compounds show moderate activity, i.e., in the millimolar range.     

Ionophore-mediated Ca2+ countertransport: role of Na+, Li+ or H+ gradient

Summary In an artificial system, the ionophore A23187, which transports Ca²⁺ but not Na⁺, is able to mediate the uphill translocation of Ca²⁺ from one aqueous medium to another across an organic immiscible phase, provided that a Na⁺, Li⁺ or H⁺ gradient is imposed on the system. Therefore, in the process known as Na-Ca countertransport, the downhill influx of Na⁺ may not be necessary for causing Ca²⁺ extrusion against its electrochemical gradient.     

Ionomycin-mediated calcium transport in rigid and fluid liposomes

The antibiotic ionophore ionomycin translocates Ca from an aqueous medium into or across an organic immiscible phase. At pH 8.0, ionomycin translocates less Ca than A23187, the effects of these ionophores being additive to one another. The capacity of ionomycin to translocate Ca across the organic phase is dramatically decreased when the pH of the aqueous media is reduced from 8.0 to 7.5 or lower values. Ionomycin also mediates Ca exchange-diffusion in liposomes, the magnitude of such a process being greater in fluid than in rigid liposomes. At a physiological pH (7.4), ionomycin is unexpectedly as potent as A23187 in mediating Ca transport in fluid liposomes. These findings suggest that the capacity of ionophores to translocate Ca across model membranes depends on both the transverse and lateral mobility of the ionophoretic molecules. The relative importance of the latter phenomenon itself largely depends on the stoichiometry of the Ca-ionophore complex.     

Insulin release: Reconciliation of the receptor and metabolic hypotheses

Summary Nutrients which stimulate insulin secretion are currently thought to initiate the series of cellular events eventually leading to insulin release either by interacting with a stereospecific receptor system (the regulatory site hypothesis) or by acting as a fuel (the substrate site hypothesis) in the pancreaticB-cell. The latter hypothesis is supported by a number of observations indicating that the capacity of nutrients to stimulate insulin release is indeed highly dependent on their capacity to increase catabolic fluxes in isolated pancreatic islets. However, these observations do not rule out the existence of nutrient receptors in islet cells. For instance, a nonmetabolized analog of L-leucine stimulates insulin release by causing allosteric activation of glutamate dehydrogenase, which should be considered, therefore, as a receptor for certain amino acids. Likewise, the increase in glycolytic flux, which is associated with the process of glucose-stimulated insulin release, is attributable not solely to a mass action phenomenon but also to the activation of phosphofructokinase by fructose 2.6-bisphosphate. The biosynthesis of this activator may involve a glucose receptor system. The fact that certain nutrient secretagogues (e.g D-glucose and L-leucine) act in the B-cell both as substrates and enzyme activators permits reconciliation of the substrate site and regulatory site hypotheses for insulin release.     

Bacteriophage MS2 RNA: A correlation between the stability of the codon: Anticodon interaction and the choice of code words

Summary The non-random distribution of degenerate code words in Bacteriophage MS2 RNA can be explained partially by considerations of the stability of the codon-anticodon complex in prokaryotic systems. Supporting this hypothesis we note that wobble codons are positively selected in codons having G and/or C in the first two positions. In contrast, wobble codons are statitically less likely in codons composed of A and U in the first two positions. Analyses of nucleotides adjacent to 5 and 3 ends of codons indicate a nonrandom distribution as well. It is thus likely that some elements of RNA evolution are independent of the structural needs of the RNA itself and of the translated protein product.This work was supported by grants from the Belgian Government Actions concertées - Gekon-certéerde Acties, N.F.W.O. and F.K.F.O. as well as from le Ministère de l'éducation du Québec. A preliminary report of this work was given at the EMBO ribosome workshop, Brussels 1976