Antisense RNA strategies for metabolic engineering of Clostridium acetobutylicum.
We examined the effectiveness of antisense RNA (as RNA) strategies for metabolic engineering of Clostridium acetobutylicum. Strain ATCC 824(pRD4) was developed to produce a 102-nucleotide asRNA with 87% complementarity to the butyrate kinase (BK) gene. Strain ATCC 824(pRD4) exhibited 85 to 90% lower BK and acetate kinase specific activities than the control strain. Strain ATCC 824(pRD4) also exhibited 45 to 50% lower phosphotransbutyrylase (PTB) and phosphotransacetylase specific activities than the control strain. This strain exhibited earlier induction of solventogenesis, which resulted in 50 and 35% higher final concentrations of acetone and butanol, respectively, than the concentrations in the control. Strain ATCC 824(pRD1) was developed to putatively produce a 698-nucleotide asRNA with 96% complementarity to the PTB gene. Strain ATCC 824(pRD1) exhibited 70 and 80% lower PTB and BK activities, respectively, than the control exhibited. It also exhibited 300% higher levels of a lactate dehydrogenase activity than the control exhibited. The growth yields of ATCC 824(pRD1) were 28% less than the growth yields of the control. While the levels of acids were not affected in ATCC 824(pRD1) fermentations, the acetone and butanol concentrations were 96 and 75% lower, respectively, than the concentrations in the control fermentations. The lower level of solvent production by ATCC 824(pRD1) was compensated for by approximately 100-fold higher levels of lactate production. The lack of any significant impact on butyrate formation fluxes by the lower PTB and BK levels suggests that butyrate formation fluxes are not controlled by the levels of the butyrate formation enzymes. (+info)
Steady-state nitrogen isotope effects of N2 and N2O production in Paracoccus denitrificans.
Nitrogen stable-isotope compositions (delta15N) can help track denitrification and N2O production in the environment, as can knowledge of the isotopic discrimination, or isotope effect, inherent to denitrification. However, the isotope effects associated with denitrification as a function of dissolved-oxygen concentration and their influence on the isotopic composition of N2O are not known. We developed a simple steady-state reactor to allow the measurement of denitrification isotope effects in Paracoccus denitrificans. With [dO2] between 0 and 1.2 microM, the N stable-isotope effects of NO3- and N2O reduction were constant at 28.6 per thousand +/- 1.9 per thousand and 12.9 per thousand +/- 2.6 per thousand, respectively (mean +/- standard error, n = 5). This estimate of the isotope effect of N2O reduction is the first in an axenic denitrifying culture and places the delta15N of denitrification-produced N2O midway between those of the nitrogenous oxide substrates and the product N2 in steady-state systems. Application of both isotope effects to N2O cycling studies is discussed. (+info)
Immobilization patterns and dynamics of acetate-utilizing methanogens immobilized in sterile granular sludge in upflow anaerobic sludge blanket reactors.
Sterile granular sludge was inoculated with either Methanosarcina mazeii S-6, Methanosaeta concilii GP-6, or both species in acetate-fed upflow anaerobic sludge blanket (UASB) reactors to investigate the immobilization patterns and dynamics of aceticlastic methanogens in granular sludge. After several months of reactor operation, the methanogens were immobilized, either separately or together. The fastest immobilization was observed in the reactor containing M. mazeii S-6. The highest effluent concentration of acetate was observed in the reactor with only M. mazeii S-6 immobilized, while the lowest effluent concentration of acetate was observed in the reactor where both types of methanogens were immobilized together. No changes were observed in the kinetic parameters (Ks and mumax) of immobilized M. concilii GP-6 or M. mazeii S-6 compared with suspended cultures, indicating that immobilization does not affect the growth kinetics of these methanogens. An enzyme-linked immunosorbent assay using polyclonal antibodies against either M. concilii GP-6 or M. mazeii S-6 showed significant variations in the two methanogenic populations in the different reactors. Polyclonal antibodies were further used to study the spatial distribution of the two methanogens. M. concilii GP-6 was immobilized only on existing support material without any specific pattern. M. mazeii S-6, however, showed a different immobilization pattern: large clumps were formed when the concentration of acetate was high, but where the acetate concentration was low this strain was immobilized on support material as single cells or small clumps. The data clearly show that the two aceticlastic methanogens immobilize differently in UASB systems, depending on the conditions found throughout the UASB reactor. (+info)
The role of benzoate in anaerobic degradation of terephthalate.
The effects of acetate, benzoate, and periods without substrate on the anaerobic degradation of terephthalate (1, 4-benzene-dicarboxylate) by a syntrophic methanogenic culture were studied. The culture had been enriched on terephthalate and was capable of benzoate degradation without a lag phase. When incubated with a mixture of benzoate and terephthalate, subsequent degradation with preference for benzoate was observed. Both benzoate and acetate inhibited the anaerobic degradation of terephthalate. The observed inhibition is partially irreversible, resulting in a decrease (or even a complete loss) of the terephthalate-degrading activity after complete degradation of benzoate or acetate. Irreversible inhibition was characteristic for terephthalate degradation only because the inhibition of benzoate degradation by acetate could well be described by reversible noncompetitive product inhibition. Terephthalate degradation was furthermore irreversibly inhibited by periods without substrate of only a few hours. The inhibition of terephthalate degradation due to periods without substrate could be overcome through incubation of the culture with a mixture of benzoate and terephthalate. In this case no influence of a period without substrate was observed. Based on these observations it is postulated that decarboxylation of terephthalate, resulting in the formation of benzoate, is strictly dependent on the concomitant fermentation of benzoate. In the presence of higher concentrations of benzoate, however, benzoate is the favored substrate over terephthalate, and the culture loses its ability to degrade terephthalate. In order to overcome the inhibition of terephthalate degradation by benzoate and acetate, a two-stage reactor system is suggested for the treatment of wastewater generated during terephthalic acid production. (+info)
Identification of a novel group of bacteria in sludge from a deteriorated biological phosphorus removal reactor.
The microbial diversity of a deteriorated biological phosphorus removal reactor was investigated by methods not requiring direct cultivation. The reactor was fed with media containing acetate and high levels of phosphate (P/C weight ratio, 8:100) but failed to completely remove phosphate in the effluent and showed very limited biological phosphorus removal activity. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S ribosomal DNA was used to investigate the bacterial diversity. Up to 11 DGGE bands representing at least 11 different sequence types were observed; DNA from the 6 most dominant of these bands was further isolated and sequenced. Comparative phylogenetic analysis of the partial 16S rRNA sequences suggested that one sequence type was affiliated with the alpha subclass of the Proteobacteria, one was associated with the Legionella group of the gamma subclass of the Proteobacteria, and the remaining four formed a novel group of the gamma subclass of the Proteobacteria with no close relationship to any previously described species. The novel group represented approximately 75% of the PCR-amplified DNA, based on the DGGE band intensities. Two oligonucleotide rRNA probes for this novel group were designed and used in a whole-cell hybridization analysis to investigate the abundance of this novel group in situ. The bacteria were coccoid and 3 to 4 microm in diameter and represented approximately 35% of the total population, suggesting a relatively close agreement with the results obtained by the PCR-based DGGE method. Further, based on electron microscopy and standard staining microscopic analysis, this novel group was able to accumulate granule inclusions, possibly consisting of polyhydroxyalkanoate, inside the cells. (+info)
Fluorescence in situ hybridization using 16S rRNA-targeted oligonucleotides reveals localization of methanogens and selected uncultured bacteria in mesophilic and thermophilic sludge granules.
16S rRNA-targeted in situ hybridization combined with confocal laser scanning microscopy was used to elucidate the spatial distribution of microbes within two types of methanogenic granular sludge, mesophilic (35 degrees C) and thermophilic (55 degrees C), in upflow anaerobic sludge blanket reactors fed with sucrose-, acetate-, and propionate-based artificial wastewater. The spatial organization of the microbes was visualized in thin sections of the granules by using fluorescent oligonucleotide probes specific to several phylogenetic groups of microbes. In situ hybridization with archaeal- and bacterial-domain probes within granule sections clearly showed that both mesophilic and thermophilic granules had layered structures and that the outer layer harbored mainly bacterial cells while the inner layer consisted mainly of archaeal cells. Methanosaeta-, Methanobacterium-, Methanospirillum-, and Methanosarcina-like cells were detected with oligonucleotide probes specific for the different groups of methanogens, and they were found to be localized inside the granules, in both types of which dominant methanogens were members of the genus Methanosaeta. For specific detection of bacteria which were previously detected by whole-microbial-community 16S ribosomal DNA (rDNA)-cloning analysis (Y. Sekiguchi, Y. Kamagata, K. Syutsubo, A. Ohashi, H. Harada, and K. Nakamura, Microbiology 144:2655-2665, 1998) we designed probes specific for clonal 16S rDNAs related to unidentified green nonsulfur bacteria and clones related to Syntrophobacter species. The probe designed for the cluster closely related to Syntrophobacter species hybridized with coccoid cells in the inner layer of the mesophilic granule sections. The probe for the unidentified bacteria which were clustered with the green nonsulfur bacteria detected filamentous cells in the outermost layer of the thermophilic sludge granule sections. These results revealed the spatial organizations of methanogens and uncultivated bacteria and their in situ morphologies and metabolic functions in both mesophilic and thermophilic granular sludges. (+info)
High-rate anaerobic treatment of wastewater at low temperatures.
Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8 degrees C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids-1 day-1, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40 degrees C. (+info)
Functional arteries grown in vitro.
A tissue engineering approach was developed to produce arbitrary lengths of vascular graft material from smooth muscle and endothelial cells that were derived from a biopsy of vascular tissue. Bovine vessels cultured under pulsatile conditions had rupture strengths greater than 2000 millimeters of mercury, suture retention strengths of up to 90 grams, and collagen contents of up to 50 percent. Cultured vessels also showed contractile responses to pharmacological agents and contained smooth muscle cells that displayed markers of differentiation such as calponin and myosin heavy chains. Tissue-engineered arteries were implanted in miniature swine, with patency documented up to 24 days by digital angiography. (+info)