Microbiological Transformation of Terpenes

PREMA B. R. (National Chemical Laboratory, Poona, India) AND P. K. BHATTACHARYYA. Microbiological transformation of terpenes. II. Transformations of apinene. Appl. Microbiol. 10:524-528. 1962.-Several strains of fungi were tested for their ability to metabolize a-pinene in shake cultures. A strain of Aspergillus niger showing marked efficiency in this respect was selected for further studies. The optimal conditions for fermentation were established with respect to substrate concentration, time, and temperature. From the fermentation products three major metabolites of ca-pinene were isolated: a ketone, CioH140, identified as d-verbenone; an alcohol, CloH160, identified as d-cis-verbenol; and a crystalline diol, CioH1802, characterized as d-trans-sobrerol. The yields of some essential oils from plant origin are affected by the microorganisms infecting the plant. A case in point is that of Aquilaria agallocha, commonly known in India as "agarwood" (Sadgopal and Varma, 1952). Wood from the green healthy tree is odorless; odoriferous wood is found in comparatively mature trees, and has widespread fungal infection associated with irregular patches and dark streaks highly impregnated with an oleoresin. The microorganisms associated with the production of this oleoresin, commonly called "agar" or "aguru," were isolated by earlier workers (Tunstall, quoted by Sadgopal and Varma, 1952; Bose, 1938) and identified as an Aspergillus sp. believed to be primarily responsible for the production of "agar," a Penicillium sp., and a Fusarium sp. One of the main odoriferous principles in agar has been identified as a monohydroxy compound, agarol (Bhattacharyya and Jain, 1959), the hydroxylation probably being a direct effect of microbial action on a suitable hydrocarbon precursor of the eudesmane system. A clear-cut experimental proof for this biogenetic formulation of agarol is not, however, available. Among the few isolated reports on the biological conversion of terpenoids by microorganisms are the oxidation of camphor (Bradshaw et al., 1959; Conrad, DeBus, and Gunsalus, 1961) and the degradation of citronellol (Seubert, 1960) by soil pseudomonads. The fungi extensively used in the hydroxylation of steroids do not appear to have been applied to transformations of monoor sesquiterpenes. Since it was not possible to obtain agarwood hydrocarbon in sufficient quantities, studies were undertaken to investigate the capability of microorganisms, particularly fungi, to convert some easily available monoand sesquiterpene hydrocarbons to oxygenated products which might be of potential interest in the perfumery industry. This communication deals mainly with the selection of microorganisms and studies on the transformation of ca-pinene (Fig. 1) by a selected strain of A. niger. A preliminary note on these studies has appeared elsewhere (Bhattacharyya et al., 1960).