David van der Ha

Energy recovery from energy rich vegetable products with microbial fuel cells

Two types of rapidly biodegradable vegetable products (the liquid fraction of clover and the glycerol-containing sidestream from biodiesel production) were selected for anodic oxidation in microbial fuel cells (MFC) equipped with a biocathode. As benchmark references, five abundant amino-acids in plant sap (l-glutamine, l-glutamic acid, l-asparagine, l-aspartic acid and l-alanine) were tested separately. Their performance was in the same order of magnitude of clover sap oxidation (145–225 A m−3 MFC; 39–95 W m−3 MFC). Glycerol oxidation resulted in competitive current and power outputs (111 A m−3 MFC; 23 W m−3 MFC).

A sustainable, carbon neutral methane oxidation by a partnership of methane oxidizing communities and microalgae

Effluents of anaerobic wastewater treatment plants are saturated with methane, an effective greenhouse gas. We propose a novel approach to treat such effluents using a coculture of methane oxidizing communities and microalgae, further indicated as methalgae, which would allow microbial methane oxidation with minimal CO(2) emissions. Coculturing a methane oxidizing community with microalgae in sequence batch reactors under continuous lightning yielded a factor of about 1.6 more biomass relative to the control without microalgae. Moreover, 55% less external oxygen supply was needed to maintain the methane oxidation, as oxygen was produced in situ by the microalgae. An overall methane oxidation rate of 171±27 mg CH(4) L(-1) liquid phase d(-1) was accomplished in a semi-batch setup, while the excess CO(2) production was lower than 1mg CO(2) L(-1) d(-1). Both nitrate and ammonium were feasible nitrogen sources for the methalgae. These results show that a coculture of microalgae and methane oxidizing communities can be used to oxidize dissolved methane under O(2)-limiting conditions, which could lead to a novel treatment for dissolved methane in anaerobic effluents.

Niche differentiation in nitrogen metabolism among methanotrophs within an operational taxonomic unit

BackgroundThe currently accepted thesis on nitrogenous fertilizer additions on methane oxidation activity assumes niche partitioning among methanotrophic species, with activity responses to changes in nitrogen content being dependent on the in situ methanotrophic community structure Unfortunately, widely applied tools for microbial community assessment only have a limited phylogenetic resolution mostly restricted to genus level diversity, and not to species level as often mistakenly assumed. As a consequence, intragenus or intraspecies metabolic versatility in nitrogen metabolism was never evaluated nor considered among methanotrophic bacteria as a source of differential responses of methane oxidation to nitrogen amendments.ResultsWe demonstrated that fourteen genotypically different Methylomonas strains, thus distinct below the level at which most techniques assign operational taxonomic units (OTU), show a versatile physiology in their nitrogen metabolism. Differential responses, even among strains with identical 16S rRNA or pmoA gene sequences, were observed for production of nitrite and nitrous oxide from nitrate or ammonium, nitrogen fixation and tolerance to high levels of ammonium, nitrate, and hydroxylamine. Overall, reduction of nitrate to nitrite, nitrogen fixation, higher tolerance to ammonium than nitrate and tolerance and assimilation of nitrite were general features.ConclusionsDifferential responses among closely related methanotrophic strains to overcome inhibition and toxicity from high nitrogen loads and assimilation of various nitrogen sources yield competitive fitness advantages to individual methane-oxidizing bacteria. Our observations proved that community structure at the deepest phylogenetic resolution potentially influences in situ functioning.

Conversion of biogas to bioproducts by algae and methane oxidizing bacteria.

Biogas produced by anaerobic digestion is typically converted into electricity and low value heat. In this study, biogas is microbially transformed into valuable bioproducts. As proof of principle, the production of feed additives, i.e. lipids and polyhydroxybutyrate, out of biogas was evaluated. In a first stage, the CO₂ in a synthetic biogas was photosynthetically fixed by an algae Scenedesmus sp. culture at an average rate of 192 ± 9 mg CO₂ L⁻¹ liquid d⁻¹, resulting in concomitant O₂ production. After N-depletion, more than 30% of the 220 ± 7 mg lipids g⁻¹ total organic carbon were unsaturated. In a second stage, the theoretical resulting gas mixture of 60% CH₄ and 40% O₂ was treated by a methane oxidizing Methylocystis parvus culture, with oxidation rates up to 452 ± 7 mg⁻¹ CH₄-C L⁻¹ liquid d⁻¹. By repeated N-limitation, concentrations of 295 ± 50 mg intracellular polyhydroxybutyrate g⁻¹ cell dry weight were achieved. Finally, a one-stage approach with controlled coculturing of both microbial groups resulted in harvestable bioflocs. This is the first time that a total microbial conversion of both greenhouse gases into biomass was achieved without external O₂ provision. Based on these results, a biotechnological approach is discussed whereby all kinds of biogas can be transformed into valuable bioproducts.

Methyloparacoccus murrellii gen. nov., sp. nov., a methanotroph isolated from pond water.

Two novel methanotrophic strains, R-49797(T) and OS501, were isolated from pond water in South Africa and Japan, respectively. Strains R-49797(T) and OS501 shared 99.7% 16S rRNA gene sequence similarity. Cells were Gram-stain-negative, non-motile cocci with a diplococcoid tendency and contained type I methanotroph intracytoplasmic membranes. The pmoA gene encoding particulate methane monooxygenase was present. Soluble methane monoooxygenase (sMMO) activity, the mmoX gene encoding sMMO and the nifH gene encoding nitrogenase were not detected. Methane and methanol were utilized as sole carbon source. The strains grew optimally at 25-33 °C (range 20-37 °C) and at pH 6.3-6.8 (range 5.8-9.0). The strains did not support growth in media supplemented with 1% (w/v) NaCl. For both strains, the two major fatty acids were C(16 : 1)ω7c and C(16 : 0) and the DNA G+C content was 65.6 mol%. The isolates belong to the family Methylococcaceae of the class Gammaproteobacteria and cluster most closely among the genera Methylocaldum, Methylococcus and Methylogaea, with a 16S rRNA gene sequence similarity of 94.2% between strain R-49797(T) and its closest related type strain (Methylocaldum gracile VKM 14L(T)). Based on the low 16S rRNA gene sequence similarities with its nearest phylogenetic neighbouring genera, the formation of a separate lineage based on 16S rRNA and pmoA gene phylogenetic analysis, and the unique combination of phenotypic characteristics of the two isolated strains compared with the genera Methylocaldum, Methylococcus and Methylogaea, we propose to classify these strains as representing a novel species of a new genus, Methyloparacoccus murrellii gen. nov., sp. nov., within the family Methylococcaceae. The type strain of Methyloparacoccus murrellii is R-49797(T) ( = LMG 27482(T) = JCM 19379(T)).

Miniaturized extinction culturing is the preferred strategy for rapid isolation of fast‐growing methane‐oxidizing bacteria

Methane‐oxidizing bacteria (MOB) have a large potential as a microbial sink for the greenhouse gas methane as well as for biotechnological purposes. However, their application in biotechnology has so far been hampered, in part due to the relative slow growth rate of the available strains. To enable the availability of novel strains, this study compares the isolation of MOB by conventional dilution plating with miniaturized extinction culturing, both performed after an initial enrichment step. The extinction approach rendered 22 MOB isolates from four environmental samples, while no MOB could be isolated by plating. In most cases, extinction culturing immediately yielded MOB monocultures making laborious purification redundant. Both type I (Methylomonas spp.) and type II (Methylosinus sp.) MOB were isolated. The isolated methanotrophic diversity represented at least 11 different strains and several novel species based on 16S rRNA gene sequence dissimilarity. These strains possessed the particulate (100%) and soluble (64%) methane monooxygenase gene. Also, 73% of the strains could be linked to a highly active fast‐growing mixed MOB community. In conclusion, miniaturized extinction culturing was more efficient in rapidly isolating numerous MOB requiring little effort and fewer materials, compared with the more widely applied plating procedure. This miniaturized approach allowed straightforward isolation and could be very useful for subsequent screening of desired characteristics, in view of their future biotechnological potential.

Enhanced disinfection efficiencies of solar irradiation by biogenic silver

Solar disinfection (SODIS) is a very inexpensive and easy-to-run water-treatment process that is widely used in third world countries to decrease the number of waterborne diseases and mortality. However, it does have a number of disadvantages, including the long time needed for complete disinfection, especially during cloudy days, and the possible regrowth of germs during subsequent storage of the water. We tested whether the addition of low concentrations of biogenic silver, which is nanosilver produced on a bacterial scaffold of Lactobacillus fermentum, to the treatment process would improve the disinfection process in general and, more specifically, retard the growth of germs during water storage. Biogenic silver was found to accelerate the inactivation of Escherichia coli by SODIS by approximately twofold. This effect was more pronounced during the first 3 h of the disinfection process and was better than when TiO2 was added. Biogenic silver which was immobilized on zeolite or polysulphone (PSF) to create a reusable formulation enhanced SODIS during the first 3 h, with the Ag–PSF formulation giving the best results. Ag–PSF released silver more slowly to the surrounding water, making it a more suitable formulation for drinking water disinfection, and it prevented germ regrowth during storage of the treated water.