Conjugal transfer of a series of incompatibility group P and Q plasmids has been studied in the acetic acid bacterium, Gluconobacter oxydans ssp. suboxydans. Transfer frequencies for the IncP/Q vectors ranged from 10(-5)-10(-9) exconjugants per recipient cell. It was found in the case of the IncP vector, pRK290, that BglII insert constructs displayed increased conjugal transfer frequenceis over pRK290 per se, the parent plasmid. A gentamycin-resistant encoding pRK290 vector which was constructed offers considerable potential as a versatile gene delivery system for Gluconobacter. The lactose transposon, Tn951, was used as a model to examine heterologous gene expression in G. oxydans ssp. suboxydans. The expression level of Tn951 encoded beta-galactosidase in this strain was found to be less than 5% of that found in the parent Escherichia coli strain, JC3272.