Toxicity of organotins towards the marine yeast Debaryomyces hansenii

Of nine organotin compounds tested towards the marine yeast Debaryomyces hansenii, only triphenyltin chloride (Ph₃SnCl) and mono-, di-, and tributyltin chloride induced significant K⁺ release from cells which was symptomatic of viability loss. The general order of toxicity of the butylated compounds was tributyltin chloride (Bu₃SnCl) > monobutyltin chloride (BuSnCl₃) ≫ dibutyltin chloride (Bu₂SnCl₂). The overall toxicity of Ph₃SnCl was similar to BuSnCl₃. Release of K⁺ induced by butylated tin compounds or by Ph₃SnCl was strongly dependent on the external pH. Maximal toxicity occurred at pH 6.5 for Bu₃SnCl, BuSnCl₃, and Ph₃SnCl, whereas maximal toxicity of Bu₂SnCl₂ occurred at pH 5.0. Toxicity was decreased above or below these values. The toxicity of BuSnCl₃, Bu₃SnCl, and Ph₃SnCl was reduced at salinity levels approximating to sea water conditions. Prior growth of D. hansenii in 3% (w/v) NaCl also resulted in reduced sensitivity to Bu₃SnCl as evidenced by a decreased rate and extent of K⁺ efflux. Bu₃SnCl-induced Na⁺ release from cells grown in the absence or presence of 3% (w/v) NaCl was low and similar in both cases. It appeared that the monovalent cation was important in the reduction of Bu₃SnCl toxicity since Na₂SO₄ had a similar protective effect as NaCl while CsCl completely prevented K⁺ efflux. Thus, the effects of external NaCl were related both to Na⁺ and to Cl^-. These results emphasize that cellular and environmental factors influence the toxic effects of organotins and suggests that these compounds may be more effective antimicrobial agents in some environmental niches than in others.