Among the tens of thousands of known terpenoids,only a relative handful have been isolated from bacterial species.Mining of genomic data from Streptomyces and other bacteria and identification of the biochemical function of The presumptive terpene synthase genes has revealed a rich treasure trove of novel biochemistry as well as new terpenoid metabolites.For example,among the 7575 predicted proteins from the 9.05 Mb linear chromosome of S.avermitilis four Open Reading Frames encode enzymes mediating terpenoid cyclizations.One of these,ptlA (sav2998) encodes a protein of 335 amino acids that catalyzes the cyclization of farnesyl diphosphate to pentalenene.the parent hydrocarbon of the pentalenolactone family of antibiotics.