Microbial Petroleum Degradation: The Role of Cladosporium Resinae

Cladosporium resinae is probably the most prevalent hydrocarbon-utilizing fungus. It has been isolated in fresh water and marine environments. It utilizes aliphatic and aromatic hydrocarbons, as well as alcohols and acids. Growth on aliphatic hydrocarbons is slow, and yields are lower than for cells cultured on acids. However, degradation of hydrocarbons is not slow, since most of the hydrocarbon is mineralized (converted to CO₂) and not assimilated to cellular carbon. Growth of the fungus was not supported by organo-phosphorus-, chlorinated hydrocarbon-, or natural pesticides as sole carbon source. However, the fungus was resistant to or stimulated by high concentrations (20,000 ppm) of these pesticides when cultured on hydrocarbons. This suggests that high concentrations of pesticides occurring in oil slicks would not inhibit oil degradation by Cladosporium resinae. Hydrocarbon-oxidation is constitutive in Cladosporium resinae. Cells oxidize aldehydes, although they did not grow on them. Release of ¹⁴C0₂ from D-glucose-l-¹⁴ C labeled cells was not greater in the presence of hydrocarbons than under endogenous conditions, indicating that intermediate and long-chain hydrocarbons are oxidized and do not stimulate endogenous respiration. Comparison of hydrocarbon oxidation by whole cells and cell-free preparations revealed the presence of an efficient cell-free oxidizing system. The pathway of hydrocarbon oxidation has been reported for hydrocarbon-utilizing bacteria and yeasts but not for fungi. Temperature, pH and co-enzyme requirements were determined for the oxidation of hydrocarbons by C. resinae. Isolation of intermediates and results of experiments utilizing electron transport inhibitors support the conclusion that in C. resinae alkanes are oxidized to their homologous alcohol, aldehyde and acid. The range of hydrocarbon substrates degraded by constitutive enzymes of Cladosporium resinae coupled with the ability to degrade hydrocarbons in the presence of high concentrations of pesticides suggests that C. resinae may be one of the most important microorganisms capable of degrading oil in the natural environment.