Bacterial biofilms may form on all surface-associated natural and many industrial environments. Biofilm formation requires particular notice due to its associated risks for human health and its impact on environmental contamination and pollution. In this work, we investigated the effects of Mg2+ and Ca2+ ions on biofilm formation by Sphingomonas paucimobilis from an industrial environment. The biofilm formation on coupons within nutrient broth medium was significantly enhanced after addition of 0, 100, 250 and 500 mu M Mg2+. Similarly, the addition of Ca2+ caused a significant increase in S. paucimobilis biofilm formation when the above concentration levels for Ca2+ were tested. In contrast, the same concentrations of these ions had no effect on growth of free-living (planktonic) S. paucimobilis cells in the medium. Hence, Mg2+ and Ca2+ increased the biofilm formation as adherent-cells on the coupons. Both ion types were significantly effective on S. paucimobilis biofilm formation, particularly at 100 and 250 mu M (P <= 0.05). These firstly reported data for S. paucimobilis biofilms are important in the elucidation of the roles of divalent cations, such as Mg2+ and Ca2+, in bacterial adhesion to the environmental surfaces for biofilm formation, and prevention of environmental contamination by this bacterium.