SDS-DEGRADING BACTERIA ATTACH TO RIVERINE SEDIMENT IN RESPONSE TO THESURFACTANT OR ITS PRIMARY BIODEGRADATION PRODUCT DODECAN-1-OL

A laboratory-scale river microcosm was used to investigate the effect of the anionic surfactant sodium dodecyl sulphate (SDS) on the attachm ent of five Pseudomonas strains to natural river-sediment surfaces. Th ree of the Pseudomonas strains were chosen for their known ability to express alkylsulphatase enzymes capable of hydrolysing SDS, and the ot her two for their lack of such enzymes. One strain from each category was isolated from the indigenous bacterial population present in the r iver sediment used; other isolates were from soil or sewage. The alkyl sulphatase phenotypes were confirmed by gel zymography of cell extract s. Addition of SDS to mixed suspensions of river sediment with any one of the biodegradation-competent strains stimulated the attachment of bacteria to the sediment particles. In contrast, the attachment of bio degradation-incompetent strains was weak and, moreover, was unaffected by SDS. The SDS-stimulated attachment for competent organisms coincid ed with rapid biodegradation of the surfactant. The primary intermedia te of SDS biodegradation, dodecan-1-ol, accumulated transiently, and t he numbers of attached bacteria correlated closely with the amount of dodecan-1-ol present. Direct addition of dodecan-1-ol also stimulated attachment but the effect was more immediate compared with SDS, when t here was a lag period of approximately 2 h. To account for these obser vations, a model is proposed in which SDS stimulates the attachment of biodegradation-competent bacteria through its conversion to dodecan-1 -ol, and it is hypothesized that the observed reversibility of the att achment is due to the subsequent removal of dodecan-1-ol by further ba cterial metabolism.