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Available online xxx Keywords: Biopolymer Polyhydroxyalkanoates Microbial polyesters Poly((R)-3-hydroxybutyrate) Poly((R)-3-hydroxybutyrate-co-3hydroxyvalerate) Mechanical properties a b s t r a c tMicrobially produced polyhydroxyalkanoates (PHAs) are fully biodegradable biopolyesters that have attracted much attention recently as alternative polymeric materials that can be produced from biorenewable and biowaste resources. The properties of these biological polymers are affected by the same fundamental principles as those of fossil-fuel derived polyolefins, with a broad range of compositions available based on the incorporation of different monomers into the PHA polymer structure, and with this broad range tailoring subsequent properties. This review comprehensively covers current understanding with respect to PHA biosynthesis and crystallinity, and the effect of composition, microstructure and supramacromolecular structures on chemomechanical properties. While polymer composition and microstructure are shown to affect these properties, the review also finds that a key driver for determining polymer performance properties is compositional distribution. From this review it follows that PHA-PHA blend compositions are industrially important, and the performance properties of such blends are discussed. A particular need is identified for further research into the effect of chemical compositional distribution on macromolecular structure and end-use properties, advanced modeling of the PHA accumulation process and chain growth kinetics for better process control.

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The microorganisms responsible for anaerobic oxidation of methane (AOM) coupled to denitrification have not been clearly elucidated. Three recent publications suggested it can be achieved by a denitrifying bacterium with or without the involvement of anaerobic methanotrophic archaea. A key factor limiting the progress in this research field is the shortage of enrichment cultures performing denitrifying anaerobic methane oxidation (DAMO). In this study, DAMO cultures were enriched from mixed inoculum including sediment from a freshwater lake, anaerobic digester sludge and return activated sludge from a sewage treatment plant. Two reactors, operated at 35°C and at 22°C, respectively, showed simultaneous methane oxidation and nitrate reduction after several months of operation. Analysis of 16S rRNA gene clone libraries from the 35°C enrichment showed the presence of an archaeon closely related to other DAMO archaea and a dominated bacterium belonging to the yet uncultivated NC10 phylum. This culture preferred nitrite to nitrate as the electron acceptor. The present study suggests that the archaea are rather methanotrophs than methanogens. The highest denitrification rate achieved was 2.35 mmol NO3 (-) -N gVSS(-1)  day(-1) . The culture enriched at 22°C contained the same NC10 bacterium observed in the culture enriched at 35°C but no archaea.