Short Communication Polyhydroxyalkanoates accumulation by Methylobacterium organophilum CZ-2 during methane degradation using citrate or propionate as cosubstrates Cristal Zuñiga a , Marcia Morales b , Sergio Revah b,⇑ a Posgrado de Biotecnología, Universidad Autónoma Metropolitana-Iztapalapa, Mexico b Departamento de Procesos y Tecnología, Universidad Autónoma Metropolitana-Cuajimalpa, Artificios # 40, Col. Miguel Hidalgo, CP 01120, México DF, Mexico highlights " Methylobacterium organophilum CZ-2 accumulated polyhydroxyalkanoates by CH4 uptake. " Citrate or propionate was concurrently metabolized during CH4 consumption. " Propionate induced the accumulation of 3-hydroxybutyrate and 3-hydroxyvalerate. " Accumulation of PHA of 88% w w-1 was reached with the pulse of citrate. " The consumption of CH4 and citrate led to PHA unreported for a methanotrophs. article info Article history: Received 9 September 2012 Received in revised form 26 November 2012 Accepted 28 November 2012 Available online 6 December 2012 Keywords: Methane Methylobacterium Poly-b-hydroxybutyrate Polyhydroxyalkanoates Copolymer abstract Methylobacterium organophilum CZ-2 synthesized polyhydroxyalkanoates (PHAs) under nitrogen limita- tion with CH 4 as carbon source and when either citrate or propionate was added as cosubstrates. The highest PHAs content (y PHA ) in closed flasks was obtained in the CH 4 -citrate and CH 4 -propionate exper- iments attaining values of 0.82 and 0.68, respectively. M. organophilum CZ-2 cultivated in bioreactors with citrate and continuous CH 4 addition yielded a final PHAs concentration of 143 g m À3 containing hydroxybutyrate (HB), hydroxyvalerate (HV) and hydroxyoctanoate (HO), in a 55:35:10 ratio, with, y PHA of 0.88 and a CH 4 elimination capacity (EC) of 20 g m À3 h À1 . With propionate, the y PHA was 0.3 and the EC around 8 g m À3 h À1 . From 1 H and 13 C NMR experiments it was found that the polymer produced with CH 4 -citrate contained six different monomers: 3HB, 3HV, 4HV, 4-hydroxyheptanoate (4HH), 3HO and 4HO, showing the great versatility of this PHAs producing bacterium. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Methane (CH 4 ) is one of the most important greenhouse gases (GHG) and the most abundant organic compound in the atmo- sphere. Streams with high CH 4 concentration can be used for en- ergy production as it is often the case of landfill biogas, (Themelis and Ulloa, 2007) or simply flared. Reduction of lower concentrations (below 5% which is the LEL for CH 4 in air) requires different control technologies and biological methods using met- hanotrophic microorganisms have been proposed (Rocha-Ríos et al., 2009; Nikiema et al., 2007). Bacterial methanotrophs are present in many environments and some have been found to pro- duce polyhydroxyalkanoates (PHAs) under nitrogen limitation when carbon and energy source is in excess (Zúñiga et al., 2011). The most reported biopolymer is polyhydroxybutyrate (PHB) which is a highly brittle crystalline material. Incorporating differ- ent monomeric units other than hydroxybutyrate (HB), such as hydroxyvalerate (HV) or hydroxyoctanoate (HO), results in PHAs copolymers with better mechanical properties and higher com- mercial potential (Gandini and Belgacem, 2008). The synthesis of copolymers is favored by the addition of precursors such as low molecular weight organic acids. HB and HV copolymers have been obtained from mixtures of acetate, propionate and lactate (Dionisi et al., 2004) including butyrate and valerate (Beccari et al.,1998) using activated sludge. However, scant information is available about copolymer formation in methanotrophs. The objective of this work was to evaluate the effect of cosub- strates on PHAs accumulation and the formation of copolymers during CH 4 degradation by our previously isolated strain Methylobacterium organophilum CZ-2 (Zúñiga et al., 2011). Propionate was selected as cosubstrate because it promotes 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.11.120 ⇑ Corresponding author. Tel.: +52 5526363801; fax: +52 5526363834. E-mail address: srevah@correo.cua.uam.mx (S. Revah). Bioresource Technology 129 (2013) 686–689 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech