Poly(3-hydroxybutyrate) biosynthesis under non-sterile conditions: Piperazine as nitrogen substrate control switch

Biosynthesis of poly(3-hydroxybutyrate) by N,N-dimethylformamide degrading strain Paracoccus sp. PXZ: A strategy for resource utilization of pollutants

N,N-dimethylformamide is a toxic chemical solvent, which widely exists in industrial wastewater. Nevertheless, the relevant methods merely achieved non-hazardous treatment of N,N-dimethylformamide. In this study, one efficient N,N-dimethylformamide degrading strain was isolated and developed for pollutant removal coupling with poly(3-hydroxybutyrate) (PHB) accumulation. The functional host was characterized as Paracoccus sp. PXZ, which could consume N,N-dimethylformamide as the nutrient substrate for cell reproduction. Whole-genome sequencing analysis confirmed that PXZ simultaneously possesses the essential genes for poly(3-hydroxybutyrate) synthesis. Subsequently, the approaches of nutrient supplementation and various physicochemical variables to strengthen poly(3-hydroxybutyrate) production were investigated. The optimal biopolymer concentration was 2.74 g·L^-1 with a poly(3-hydroxybutyrate) proportion of 61%, showing a yield of 0.29 g-PHB·g^-1-fructose. Furthermore, N,N-dimethylformamide served as the special nitrogen matter that could realize a similar poly(3-hydroxybutyrate) accumulation. This study provided a fermentation technology coupling with N,N-dimethylformamide degradation, offering a new strategy for resource utilization of specific pollutants and wastewater treatment.

Bioconversion of waste activated sludge hydrolysate into polyhydroxyalkanoates using Paracoccus sp. TOH: Volatile fatty acids generation and fermentation strategy

The expensive carbon matrix is a bottleneck restricting the industrialization of polyhydroxyalkanoates (PHAs). Volatile fatty acids (VFAs) derived from waste activated sludge via anaerobic fermentation might be alternative carbon matters for PHAs synthesis. In this study, the effect of enzymes on VFAs yields and the feasibility of the produced VFAs for PHAs fermentation by Paracoccus sp. TOH were investigated. The optimum cumulative VFAs concentration reached 4076.6 mg-COD·L^-1 in the lysozyme treatment system. Correspondingly, the highest poly(3-hydroxybuturate-co-3-hydroxyvalerate) (PHBV) concentration (119.1 mg·L^-1) containing 20.3 mol% 3-hydroxyvalerate was obtained. It proved that Paracoccus sp. TOH possesses the capability for PHBV accumulation. The functional hydrolytic-acidogenic microorganisms, such as Clostridium sensu stricto and Bacteroides sp. were accumulated. The functional genes encoding hydrolysis, carbohydrates metabolism, VFAs generation were enriched. This study offered a possible strategy for VFAs production and verified the feasibility of sludge hydrolysate as a high-quality carbon substrate for PHAs fermentation.

Nitrogen contribution and microbial community of size-fractionated anammox sludge in continuous stirred-tank reactors

In this study, the microbial diversity of size-fractionated anammox sludge in a well-mixed system and their contribution to nitrogen transformation were investigated. Results showed that small granules (0.2-1.0 mm) contributed to the major part of the nitrogen removal rate (56 %) due to its largest mixed liquor volatile suspended solids (1240 ± 80 mg·L^-1). However, large granules (>1.0 mm) possessed the highest relative abundances of Ca. Kuenenia stuttgartiensis and specific anammox activity, representing 49.34 % and 24.45 ± 0.01 mg-N·g^-1-mixed liquor volatile suspended solids·h^-1, respectively. The microbial diversity decreased as the increase of granular size, resulting in microbial community shifting to a simpler model. Metagenomic analysis showed that fine sludge might be the potential major for NO/N₂O production in the mature well-mixed system under inorganic conditions. This study provides guidance for the evaluation of nitrogen contribution by anammox size-fractionated sludge and the inhibition of the potential NO/N₂O emission in anammox processes.