Anaerobic degradation of 2-propanol: Laboratory and pilot-scale studies

The anaerobic degradation of 2-propanol, an important industrial solvent, was scaled-up from batch assays to a pilot expanded granular sludge bed (EGSB) reactor at 25 °C. Batch studies indicated that 2-propanol followed Haldane kinetics, with a maximum rate at 10 g COD L−1. Concentrations as high as 25 g COD L−1 did not inhibit the degradation of ethanol, a common co-solvent. Similar specific methanogenic activities (SMA) were obtained for water-solvent and water-brewery sludges (88 and 77 ml CH4 g-VS−1 d−1 at 5 g COD L−1). Continuous degradation showed a lag-phase of three weeks with water-brewery sludge. Increases in 2-propanol load from 0.05 to 0.18 kg COD kg-VS−1 d−1 caused a shift from the consumption of soluble matter to methane production, indicating polyhydroxybutyrates (PHB) accumulation. Conversely, smooth increases of up to 0.29 kg COD kg-VS−1 d−1 allowed 2-propanol degradation without PHB accumulation. The slowdown rate of 2-propanol-oxidizer and acetate-utilizing methanogen bacteria below 20 °C adversely impacted both removal and CH4 yield

Intracellular PHB conversion in a type II methanotroph studied by 13 C NMR

Poly-g-hydroxybutyrate (PHB) formation under aerobic conditions via incorporation of [13C-2]acetate as a cosubstrate and its intracellular degradation under anaerobic conditions in a Type II methanotroph was studied by 13C NMR. During PHB synthesis in the presence of labelled acetate, low levels of g-hydroxybutyrate, butyrate, acetone, isopropanol, 2,3-butanediol and succinate were observed. Subsequent anaerobic PHB breakdown showed enhanced levels of these products at the expense of PHB. Fermentative metabolism occurring during anaerobic PHB degradation was confirmed in experiments with fully 13C-enriched cells, which were grown on 13C-labelled methane. g-hydroxybutyrate, butyrate, acetate, acetone, isopropanol, 2,3-butanediol and succinate were detected as multiple 13C-labelled compounds in the culture medium. Our results suggest that intracellular PHB degradation can be used as a reserve energy source by methanotrophs under anoxic conditions

Microaerobic and anaerobic metabolism of a Methylocystis parvus strain isolated from a denitrifying bioreactor

An obligate methanotrophic bacterium, strain MTS, was isolated from a methane-fed microaerobic denitrifying bioreactor. 16S rRNA and DNA–DNA hybridization analysis revealed that this organism was most closely related to Methylocystis parvus, a Type II methanotroph, belonging to the a-subclass of the Proteobacteria. The metabolism of the bacterium under microaerobic and anaerobic conditions was studied by 13C-NMR. 13C-labelled poly-ß-hydroxybutyrate (PHB) formation occurred in cell suspensions incubated with 13C-labelled methane at low (5–10%) oxygen concentration. Under these conditions low levels of succinate, acetate and 2,3-butanediol were formed and excreted into the culture medium. Intracellular PHB degradation was observed in intact cells under anaerobic conditions in the absence of an exogenous carbon source during a long-term incubation of 90 days. Multiple 13C-labelled ß-hydroxybutyrate, butyrate, acetate, acetone, isopropanol, 2,3-butanediol and succinate were identified as products in in vivo13C-NMR spectra and in the spectra of culture medium during the dynamic PHB degradation. The isolated obligate methanotroph clearly shows a fermentative metabolism of PHB under anaerobic conditions. The excreted products may serve as substrates for denitrifying bacteri

The effect of oxygen on methanol oxidation by an obligate metahnotrophic bacterium studied by in vivo 13C nuclear magnetic resonance spectroscopy

13C NMR was used to study the effect of oxygen on methanol oxidation by a type II methanotrophic bacterium isolated from a bioreactor in which methane was used as electron donor for denitrification. Under high (35-25€oxygen conditions the first step of methanol oxidation to formaldehyde was much faster than the following conversions to formate and carbon dioxide. Due to this the accumulation of formaldehyde led to a poisoning of the cells. A more balanced conversion of 13C-labelled methanol to carbon dioxide was observed at low (1-5€oxygen concentrations. In this case, formaldehyde was slowly converted to formate and carbon dioxide. Formaldehyde did not accumulate to inhibitory levels. The oxygen-dependent formation of formaldehyde and formate from methanol is discussed kinetically and thermodynamically

Phosphorus starvation and luxury uptake in green microalgae revisited

Phosphorus (P) is central to storing and transferring energy and information in living cells, including those of microalgae. Many microalgal species dwelling in low P environments are naturally equipped to take up and store P whenever it becomes available through a complex phenomenon known as “luxury P uptake.” Its research is required for better understanding of the nutrient geochemical cycles in aquatic environments but also for biotechnological applications such as sequestration of nutrients from wastewater and production of algal fertilizers. Here, we report on our recent insights into luxury P uptake and polyphosphate formation originating from physiological, ultrastructural, and transcriptomic evidence. The cultures pre-starved of P and re-fed with inorganic phosphate (Pi) exhibited a bi-phasic kinetics of Pi uptake comprising fast (1–2 h after re-feeding) and slow (1–3 d after re-feeding) phases. The rate of Pi uptake in the fast phase was ca. 10 times higher than in the slow phase with an opposite trend shown for the cell division rate. The transient peak of polyphosphate accumulation was determined 2–4 h after re-feeding and coincided with the period of slow cell division and fast Pi uptake. In this phase, the microalgal cells reached the highest P content (up to 5% of dry cell weight). The P re-feeding also reversed the characteristic changes in cell lipids induced by P starvation, namely increase in the major membrane glycolipid (DGDG/MGDG) ratio and betaine lipids. These changes were reversed upon Pi re-feeding of the starved culture. Electron microscopy revealed the ordered organization of vacuolar polyphosphate indicative of the possible involvement of an enzyme (complex) in their synthesis. A candidate gene encoding a protein similar to the vacuolar transport chaperone (VTC) protein, featuring an expression pattern corresponding to polyphosphate accumulation, was revealed. Implications of the findings for efficient biocapture of phosphorus are discussed. © 2019 Elsevier B.V

Genome Sequence of the Methanotrophic Alphaproteobacterium Methylocystis sp. Strain Rockwell (ATCC 49242) ▿

Methylocystis sp. strain Rockwell (ATCC 49242) is an aerobic methane-oxidizing alphaproteobacterium isolated from an aquifer in southern California. Unlike most methanotrophs in the Methylocystaceae family, this strain has a single pmo operon encoding particulate methane monooxygenase but no evidence of the genes encoding soluble methane monooxygenase. This is the first reported genome sequence of a member of the Methylocystis species of the Methylocystaceae family in the order Rhizobiales