Separation of bacteria from a methanogenic wastewater population by utilizing a self-generating Percoll gradient

Biomass density-function relationships in suspended growth biological processes - A critical review

Good settling performance in suspended growth biomass systems, for example in activated sludge (AS) process, leads to efficient wastewater and sludge treatment. Factors that cause the differences in settleablility of AS include the morphology of bacteria, microbial community structure, and the density of bacteria and flocs. Density of AS at three levels, namely, cell, floc, and process, have been discussed here to explain the variations in AS settleability. Dense materials, inside or outside the cell, significantly increase density of AS bacteria or flocs. Functional bacteria, defined as those performing N and P removal and recovery such as phosphate accumulating organisms, nitrifiers, and anammox contain cellular inclusions that increase their density, and consequently a dense and well-settling biomass results at the process level in those systems. A density based selector of AS can be used to enrich functional bacteria in the process through the wasting and sludge age control operations in AS process. This paper critically reviews the latest literature to elucidate mechanisms of density enhancement from cell to process level, and identifies needs/strategies to improve the AS process through a biomass density selector.

Colloidal and bacterial deposition: role of gravity

The role of gravitational force on the deposition of 0.5, 1.1, and 1.8 mum carboxylate-modified polystyrene latex (CML) microspheres and bacterium Burkholderia cepacia G4g has been evaluated using a parallel plate flow chamber system. This experimental system utilized an inverted and an upright optical microscope attached with image-capturing devices to directly observe and determine the deposition kinetics onto glass surfaces located at the top and bottom of the flow chamber. Deposition kinetics was quantified at 10 mM KCl under electrostatically unfavorable and favorable attachment conditions and at two flow rates (0.06 and 3 mL/min), simulating the range of flow velocities from groundwater to rapid granular filtration. Comparing the particle deposition kinetics on the top and bottom surfaces under identical flowing exposure time, fluid chemistries, and hydrodynamic conditions, results showed that significant differences were observed between the two surfaces, suggesting that gravity was a significant driving force for the initial stages of deposition of particles that were larger than 1 mum size. Simulation results utilizing a particle trajectory model confirmed these experimental observations. This was further supported by additional deposition experiments with 1.1 mum microspheres suspended in a deuterium oxide (D(2)O)/water mixture (heavy water) where the density of colloid and the suspending heavy water were effectively the same. Under this condition, deposition rates were observed to be identical between the top and bottom surfaces. Results from normal and heavy water solutions indicated that the greater deposition of colloidal particles larger than 1 mum on the bottom in normal water solutions is due to gravity. Finally, the experimental results were compared with deposition studies using smaller 0.5 mum colloids as well as some theoretical calculations of expected rates of particle deposition.

Monitoring granule formation in anaerobic upflow bioreactors using oligonucleotide hybridization probes

The process of granule formation in upflow anaerobic sludge blanket (UASB) reactors was studied using oligonucleotide hybridization probes. Two laboratory-scale UASB reactors were inoculated with sieved primary anaerobic digester sludge from a municipal wastewater treatment plant and operated similarly except that reactor G was fed glucose, while reactor GP was fed glucose and propionate. Size measurements of cell aggregates and quantification of different populations of methanogens with membrane hybridization targeting the small-subunit ribosomal RNA demonstrated that the increase in aggregate size was associated with an increase in the abundance of Methanosaeta concilii in both reactors. In addition, fluorescence in situ hybridization showed that the major cell components of small aggregates collected during the early stages of reactor startup were M. concilii cells. These results indicate that M. concilii filaments act as nuclei for granular development. The increase in aggregate size was greater in reactor GP than in reactor G during the early stages of startup, suggesting that the presence of propionate-oxidizing syntrophic consortia assisted the formation of granules. The mature granules formed in both reactors exhibited a layered structure with M. concilii dominant in the core, syntrophic consortia adjacent to the core, and filamentous bacteria in the surface layer. The excess of filamentous bacteria caused delay of granulation, which was corrected by increasing shear through an increase of the recycling rate.

Antigen recognition by rainbow trout (Oncorhynchus mykiss) of whole cell proteins expressed by Lactococcus garvieae when obtained directly from fish and under iron limited culture conditions

Infection by Lactococcus garvieae has become a widely recognised problem associated with intensively cultured fish. Long-term control of fish infections may be possible by vaccination providing a suitable and efficacious epitope is expressed during production of cells used for vaccine preparation. The identification of novel vaccine candidates must, therefore, consider how the host species recognises and responds to bacterial cell components. L. garvieae was cultured in iron deficient, limited and haem iron enriched media and the whole cell proteins expressed under these conditions were compared with those expressed in bacteria extracted with Percoll gradients directly from spleen tissue of infected rainbow trout (Oncorhynchus mykiss). SDS-PAGE of the cell proteins showed the existence of several different electropherotypes according to the iron status of the culture media. Only minor differences in cell protein profile were detected in bacteria obtained directly from fish spleens, but when the electropherograms were analysed by Western blots using L. garvieae hyperimmune fish sera, several proteins could be identified that were expressed only when L. garvieae was growing in vivo. Siderophore could be detected in culture supernatant of iron deficient, limited and haem iron enriched media but not in media with higher nutrient concentrations. The siderophore could not be identified as a type of catechol or hydroxymate. Rainbow trout recognise proteins in the range of approximately 50-80 kDa for bacterial cells obtained without subculture from infected fish and culture conditions can influence protein profiles for this pathogen.

Differential expression of methanogenesis genes of Methanothermobacter thermoautotrophicus (formerly Methanobacterium thermoautotrophicum) in pure culture and in cocultures with fatty acid-oxidizing syntrophs

The expression of genes involved in methanogenesis in a thermophilic hydrogen-utilizing methanogen, Methanothermobacter thermoautotrophicus strain TM, was investigated both in a pure culture sufficiently supplied with H(2) plus CO(2) and in a coculture with an acetate-oxidizing hydrogen-producing bacterium, Thermacetogenium phaeum strain PB, in which hydrogen partial pressure was constantly kept very low (20 to 80 Pa). Northern blot analysis indicated that only the mcr gene, which encodes methyl coenzyme M reductase I (MRI), catalyzing the final step of methanogenesis, was expressed in the coculture, whereas mcr and mrt, which encodes methyl coenzyme M reductase II (MRII), the isofunctional enzyme of MRI, were expressed at the early to late stage of growth in the pure culture. In contrast to these two genes, two isofunctional genes (mtd and mth) for N(5),N(10)-methylene-tetrahydromethanopterin dehydrogenase, which catalyzes the fourth step of methanogenesis, and two hydrogenase genes (frh and mvh) were expressed both in a pure culture and in a coculture at the early and late stages of growth. The same expression pattern was observed for Methanothermobacter thermoautotrophicus strain DeltaH cocultured with a thermophilic butyrate-oxidizing syntroph, Syntrophothermus lipocalidus strain TGB-C1. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole proteins of M. thermoautotrophicus strain TM obtained from a pure culture and a coculture with the acetate-oxidizing syntroph and subsequent N-terminal amino acid sequence analysis confirmed that MRI and MRII were produced in the pure culture, while only MRI was produced in the coculture. These results indicate that under syntrophic growth conditions, the methanogen preferentially utilizes MRI but not MRII. Considering that hydrogenotrophic methanogens are strictly dependent for growth on hydrogen-producing fermentative microbes in the natural environment and that the hydrogen supply occurs constantly at very low concentrations compared with the supply in pure cultures in the laboratory, the results suggest that MRI is an enzyme primarily functioning in natural methanogenic ecosystems.