Comparative study of tributyltin toxicity on two bacteria of the genus Bacillus

Abstract

Tributyltin is a potent biocide mainly used in marine antifouling paints. Owing to its widespread distribution in coast areas and its high toxicity to aquatic organisms, the use of this compound is generally restricted and under government regulation. Despite of that, it persists in the aquatic environment. Organotins used in industry have also been detected in terrestrial environments. The persistence and high lipophilicity explain bioaccumulation. The role of bacteria in recycling organic matter prompted us to study the interaction of tributyltin with two ubiquitous bacilli, B. stearothermophilus and B. subtilis, proposed as biological indicators of pollutants with ecological impact. These bacteria have been used as suitable models for the study of toxicity mechanisms of unselective lipophilic compounds (e.g., DDT and endosulfan). Drug effects on growth parameters, oxygen consumption and membrane organization were assessed. Bacteria growth in a liquid complex medium was disturbed by concentrations of TBT as low as 25 nM (8 lg L À1 ), close to the concentration in polluted environments. The respiratory activity is affected by TBT in both microorganisms. Membrane organization, assessed by fluorescence polarization of two fluidity probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and a propionic acid derivative (DPH-PA), was also perturbed by the xenobiotic. Alterations on growth, oxygen consumption and physical properties of membrane lipids are stronger in B. stearothermophilus as compared to B. subtilis. A putative relationship between growth inhibition and respiratory activity impairment induced by TBT and its effects on the physical behaviour of bacterial membrane lipids is suggested.

Toxicity assessment of the herbicide metolachlor comparative effects on bacterial and mitochondrial model systems

“…In our laboratory, a strain of the thermophilic Gram-positive eubacterium Bacillus stearothermophilus has been used as a predictive model for assessing the toxicity of different compounds. Toxicity tests using B. stearothermophilus have allowed to establishing toxicity correlations for insecticides and organometals, regarding effects on energy metabolism and cell viability (Donato et al, 1997;Martins et al, 2003Martins et al, , 2005Monteiro et al, 2003). On the other hand, mitochondria are recognized as a suitable model to evaluate in vitro toxicological actions of several xenobiotics, providing data well correlated with toxicity parameters derived from cell cultures and whole organisms (Eisenbrand et al, 2002;Bragadin, 2006).…”

Herbicides: the Face and the Reverse of the Coin. An in Vitro Approach to the Toxicity of Herbicides in Non-Target Organisms

“…Accordingly, the herbicide effects on the bacterial respiratory activity, evaluated in terms of the oxygen consumption rate in protoplasts, also denote a moderate toxicity. Thus, for oxygen consumption supported by NADH, metolachlor and alachlor EC 50 of 1.2 µmol/mg protein or 1.2 mM (Pereira et al, 2009) and 2.2 µmol/mg protein or 2.2 mM (Pereira et al, 2010), respectively, are two order of magnitude higher than those found for DDT (Donato et al, 1997b) or the organotin TBT (Martins et al, 2005). The respiratory activity elicited by ascorbate/TMPD showed to be insensitive to both herbicides in the range of 0.5 to 5.0 µmol/mg protein (0.5 to 5.0 mM), suggesting that the herbicides act upstream the cytochrome c oxidase segment.…”

“…The effective concentrations which alter these growth parameters by 50% compared to the control (EC 50 ) are around 400 to 450 µM for metolachlor and slightly higher than 500 µM for alachlor. Comparing these values of EC 50 with those determined in identical conditions for other pesticides, such as DDT (Donato et al, 1997b), methoprene (Monteiro et al, 2005) or tributyltin (TBT) (Martins et al, 2005), it is clear that the herbicides metolachlor and alachlor have a much lower toxicity. Accordingly, the herbicide effects on the bacterial respiratory activity, evaluated in terms of the oxygen consumption rate in protoplasts, also denote a moderate toxicity.…”

“…The effective concentration of linuron of 98 nmol/mg protein or 98 µM (unpublished data) to reduce for a half the protoplast oxygen consumption rate relatively to the control (protoplast preparation without herbicide, containing a correspondent amount of DMSO, i.e. the herbicide vehicle solvent) is also one order of magnitude lower than the equivalent concentrations of alachlor and metolachlor (see above) and one order of magnitude higher than the concentration of TBT to produce the same effect (Martins et al, 2005). These results are also in accordance with those obtained using the mitochondrial model system (see above).…”

“…In our laboratory, a strain of the thermophile Bacillus stearothermophilus, grown in a liquid medium (L-Broth) at 65ºC (within the optimal temperature range), has been extensively used as a model system for assessing the cytotoxicity of different groups of environmental pollutants, as herbicides (Pereira et al, 2009;, insecticides (Donato et al, 1997a,b;Martins et al, 2003;Monteiro et al, 2005) and organometals (Martins et al, 2005). Toxicity indicators have been taken from parameters of growth (lag time, specific growth rate and bacterial yield in the stationary phase) when growth is followed by turbidity measurements or by counting the colony-forming units (c.f.u.)…”