For example, other species of any genus of the Nocardioforms including Rhodococcus NCIB 10554, R. erythropolis NCIB 9158, Nocardia erythropolis ATCC 17895 and Nocardia erythropolis ATCC 4277 could be used to prepare the genomic library; or the libraries could be screened for other useful metabolic activities such as the assimilation of alkanes and aromatic hydrocarbons; the degradation of lignin,