The thermophilic bacterium Thermus thermophilus HB8 is able to utilize lactose from whey-based media for the biosynthesis of polyhydroxyalkanoates (PHAs) under nitrogen limitation. T. thermophilus can utilize both, glucose and galactose, the products of lactose hydrolysis. When T. thermophilus HB8 was grown in culture media containing 24% (v/v) whey, PHA was accumulated up to 35% (w/w) of its biomass after 24 h of cultivation. The effect of initial phosphate concentration on the PHA production was also investigated. Using an initial phosphate concentration of 50 mM the PHA accumulation was enhanced. Analysis of the produced PHA from T thermophilous HB8 grown in whey-based media revealed a novel heteropolymer consisting of the short chain length 3-hydroxyvalerate (3HV; 38 mol%) and the medium chain length, 3-hydroxyheptanoate (3HHp: 9.89 mol%), 3-hydroxynanoate (3HN; 16.59 mol%) and 3-hydroxyundecanoate (3HU: 35.42 mol%). Despite the low molecular weight of the produced PHA by T thermophilus, whey could be an excellent substrate for the production of heteropolymers with unique properties. (C) 2009 Elsevier Ltd. All rights reserved.