Mini-transposon-induced mutants with defects in utilization of linear terpenes such as citronellol and citronellic acid were isolated from Pseudomonas citronellolis. Mutants with strongly reduced growth on citronellol and citronellic acid (class I) were obtained together with mutants growing normally on citronellic acid but with impairment in growth on citronellol (class II) and auxotroph mutants (class III). The transposon carrying DNA fragments of two class I mutants were cloned and malate:quinone oxidoreductase gene (mqoB) was identified as the transposon insertion site in both mutants. The mqoB genes of P. aeruginosa and of P. citronellolis wild types were cloned. Conjugative transfer of the mqoB genes to the two P. citronellolis mutants increased the strongly reduced levels of MqoB activity in cell extracts of the mutants to the level of the wild type and restored the ability of the mutants to grow on citronellol and citronellic acid. Physiological analysis of the wild type and of mutants showed that MqoB is part of the glyoxylate cycle in P. citronellolis and is necessary for growth on C(2)-compounds and linear terpenes such as citronellol or citronellic acid.