Enhancement of PHA Production by a Mixed Microbial Culture Using VFA Obtained from the Fermentation of Wastewater from Yeast Industry

Wastewater from the yeast production industry (WWY) is potentially harmful to surface water due to its high nitrogen and organic matter content; it can be used to produce compounds of higher commercial value, such as polyhydroxyalkanoates (PHA). PHA are polyester-type biopolymers synthesized by bacteria as energy reservoirs that can potentially substitute petrochemical-derived plastics. In this exploratory work, effluent from WWY was used to produce PHA, using a three-step setup of mixed microbial cultures involving one anaerobic and two aerobic reactors. First, volatile fatty acids (VFA; 2.5 g/L) were produced on an anaerobic batch reactor (reactor A) fed with WWY, using a heat pretreated sludge inoculum to eliminate methanogenic activity. Concurrently, PHA-producing bacteria were enriched using synthetic VFA in a sequencing batch reactor (SBR, reactor C) operated for 78 days. Finally, a polyhydroxybutyrate (PHB)-producing reactor (reactor B) was assembled using the inoculum enriched with PHA-producing bacteria and the raw and distilled effluent from the anaerobic reactor as a substrate. A maximum accumulation of 17% of PHB based on cell dry weight was achieved with a yield of 1.2 g PHB/L when feeding with the distilled effluent. Roche 454 16S rRNA gene amplicon pyrosequencing of the PHA-producing reactor showed that the microbial community was dominated by the PHA-producing bacterial species Paracoccus alcalophilus (32%) and Azoarcus sp. (44%). Our results show promising PHB accumulation rates that outperform previously reported results obtained with real substrates and mixed cultures, demonstrating a sustainable approach for the production of PHA less prone to contamination than a pure culture

Individual Steps of the Mizoroki—Heck Reaction and Intrinsic Reactivity of Intermediate Organopalladium Complexes Studied in the Gas Phase

The mechanism of the Mizoroki-Heck reaction (MHR) was analyzed by collision-induced dissociation (CID) tandem-mass spectrometry and gas-phase ion/molecule reactions (IMRs) as well as by DFT computational analysis. The MHR was performed in the gas phase and the intrinsic reactivity of important intermediates was examined individually. Kinetics and substituent effects of cationic palladiumPCy(3)-aryl complexes (Cy = cyclohexyl) with 2,3-dimethylbutadiene in the MHR were analyzed via IMRs and CID. The kinetics and ion structures of the species involved in the olefin insertion, i.e., the carbopalladation, were investigated. Moreover, linear free-energy correlations-were applied and a concerted mechanism proceeding via a four-membered transition state for the carbopalladation step that exhibited only a minor charge separation was deduced