Hydrocarbon-utilizing microorganisms naturally associated with sawdust

Sawdust, one of the materials used as sorbent for removing spilled oil from polluted environments was naturally colonized by hydrocarbon-utilizing fungi, 1 × 105–2 × 105 colony forming units (CFU) g−1, depending on the hydrocarbon substrate. This sorbent was initially free of hydrocarbon-utilizing bacteria. Incubating wet sawdust at 30 °C resulted in gradually increasing the fungal counts to reach after 6 months between 5 × 106 and 7 × 106 CFU g−1, and the appearance of hydrocarbon-utilizing bacteria in numbers between 8 × 104 and 3 × 105 cells g−1. The fungi belonged to the genera Candida (32% of the total), Penicillium (21%), Aspergillus (15%), Rhizopus (12%), Cladosporium (9%), Mucor (7%) and Fusarium (4%). Based on their 16S rRNA gene sequences the bacteria were affiliated to Actinobacterium sp. (38%), Micrococcus luteus (30%), Rhodococcus erythropolis, (19%) and Rhodococcus opacus (13%). Individual pure fungal and bacterial isolates grew on a wide range of individual pure aliphatic (n-alkanes with chain lengths between C9 and C40) and aromatic (benzene, biphenyl, anthracene, naphthalene and phenanthrene) hydrocarbons as sole sources of carbon and energy. Quantitative determinations revealed that all fungal and bacterial isolates could consume considerable proportions of crude oil, phenanthrene (an aromatic hydrocarbon) and n-hexadecane (an aliphatic hydrocarbon) in batch cultures. It was concluded that when sawdust is used as a sorbent, the associated microorganisms probably contribute to the bioremediation of oil and hydrocarbon pollutants in the environment.

► Sawdust is in use among other sorbents for physical removal of oil.
► The core finding of this study is that sawdust harbors hydrocarbon-utilizing fungi and bacteria in considerable-numbers.
► Incubating wet sawdust resulted in enriching this sorbent with hydrocarbon-utilizing microorganisms.
► Individual fungi and bacteria isolated from sawdust could consume aliphatic and aromatic hydrocarbons in batch cultures.
► It was concluded that this sorbent, not only removes oil from polluted environments but, is also associated with microorganisms which can in situ biodegrade the hydrocarbon pollutants.