Functionalized medium-chain-length polyhydroxyalkanoates (mcIPHAs) have gained much interest in research on biopolymers because of their ease of chemical modification. Tailored olefinic mcIPHA production from mixtures of octanoic acid and 10-undecenoic acid was investigated in batch and dual (C,N) nutrient limited chemostat cultures of Pseudomonas putida GPo1 (ATCC 29347). In a batch culture, where P. putida GPo1 was grown on a mixture of octanoic acid (58 mol%) and 10-undecenoic acid (42 mol%), it was found that the fraction of aliphatic monomers was slightly lower in mcIPHA produced during exponential growth than during late stationary phase. Thus, the total monomeric composition changed over time indicating different kinetics for the two carbon substrates. Chemostat experiments showed that the dual (C,N) nutrient limited growth regime (DNLGR) for 10-undecenoic acid coincided with the one for octanoic acid. Five different chemostats on equimolar mixtures of octanoic acid and 10-undecenoic acid within the DNLGR revealed that the monomeric composition of mcIPHA was not a function of the carbon to nitrogen (C-0/N-0) ratio in the feed medium but rather of the dilution rate. The fraction of aliphatic monomers in the accumulated mcIPHA was slightly lower at high dilution rates and increased towards low dilution rates, again indicating different kinetics for the two carbon substrates in P. putida GPo1. (c) 2005 Wiley Periodicals, Inc.