Effect of linear alkylbenzene sulfonates on the growth of aerobic heterotrophic cultivable bacteria isolated from an agricultural soil

An enrichment culture technique was used to isolate soil bacteria capable of growing in the presence of two different concentrations of linear alkylbenzene sulfonates (LAS) (10 and 500 μg ml⁻¹). Nine bacterial strains, representatives of the major colony types of aerobic heterotrophic cultivable bacteria in the enriched samples, were isolated and subsequently identified by PCR-amplification and partial sequencing of the 16S rRNA gene. Amongst the isolates, strains LAS05 (Pseudomonas syringae), LAS06 (Staphylococcus epidermidis), LAS07 (Delftia tsuruhatensis), LAS08 (Staphylococcus epidermidis) and LAS09 (Enterobacter aerogenes), were able to grow in pure culture in dialysed soil media amended with LAS (50 μg ml⁻¹). The three Gram-negative strains grew to higher cell numbers in the presence of 50 μg ml⁻¹ of LAS, compared to LAS-unamended dialysed soil medium, and were selected for further testing of their ability to use LAS as carbon source. However, HPLC analysis of culture supernatants showed that the three strains can tolerate but not degrade LAS when grown in pure cultures. A higher concentration of soluble phosphates was recorded in dialysed soil media amended with LAS (50 μg ml⁻¹) compared to unamended control media, suggesting an effect of the surfactant that enhanced the bioavailability of P from soil. The presence of LAS at a concentration of 50 μg ml⁻¹ had an important impact on growth of selected aerobic heterotrophic soil bacteria, a deleterious effect which may be relevant for the normal function and evolution of agricultural soil.