Toxic effects of tin compounds on microorganisms

Summary Organotins are used for industrial and agricultural purposes and in antibiologic agents. They are significantly more toxic than inorganic tins, and eventually reach the environment where they can be toxic to a wide variety of organisms. Particular attention has been given to tributyltins which are highly toxic components of antifouling paints. Realization that the molecular species of organotin influences fate and effects of organotins led to development of sensitive methods for quantifying individual molecular species. Even though such methods are now available, little information has been obtained on the ability of microorganisms to bioaccumulate tin compounds. Trisubstituted alkyl and aryltins (R₃Sn's) are more toxic than disubstituted compounds (R₂Sn's) while monosubstituted organotins (RSn's) are still less toxic. R₄Sn's are toxic only if they are metabolized to R₃Sn's. Among trisubstituted compounds propyl-, butyl-, pentyl-, phenyl-, and cyclohexyl Sn's are generally the most toxic to microorganisms. Toxicity in the R₃Sn series is related to total molecular surface area of the tin compound and to the octanol:water partition coefficient,K _ow, which is a measure of hydrophobicity; a highK _ow indicates greater hydrophobicity and predicts greater toxicity. Care must be taken when testing the toxicity of tin compounds, for a number of biological, physical and chemical factors can influence the apparent toxicity. Although little is known of the effects of tin compounds on microbial processes, a number of bacterial processes can be inhibited by organotins and all relate to membrane functions. They include effects on energy transduction, solute transport and retention and oxidation of substrates. Very little is known of how organotins exert their toxic effects on algae and fungi; Information on effects on chloroplasts and mitochondria stems principally from animal systems and from higher plants. Triorganotins act against chloroplasts and mitochondria by causing swelling, by acting as ionophores and by acting against ATPase, while diorganotins appear to act by binding to dithiol groups on enzymes and cofactors. Nucleic acids do not seem to be affected at environmentally relevant concentrations. Virtually nothing is known of the action of tin compounds on microbial enzymes, but resistant mutants are easy to obtain and should facilitate work to understand modes of microbial interaction with tin compounds and mechanisms of resistance.     

Organotin compounds and aquatic bacteria: A review

Organotins are toxic to microorganisms. Trisubstituted organotins (R₃SnX) are considered more toxic than disubstituted (R₂SnX₂) or monosubstituted (RSnX₃) compounds, and tetrasubstituted compounds (R₄Sn) are not considered toxic. In the R₃Sn series propyl-, butyl-, pentyl-, phenyl- and cyclohexyltins are the most toxic to microorganisms. Toxicity towards aerobes in the R₃Sn series is related to total molecular surface area and to the octanol: water partition coefficient,Kow, which is a measure of hydrophobicity. Care must be taken when testing the toxicity of tin compounds in the laboratory, for a number of biological, chemical and physical factors can influence the apparent toxicity. Although TBT is generally the most toxic of the butyltins, there are instances where monobutyltin (MBT) is as toxic, or more toxic, than TBT to microorganisms. Thus, debutylation in the sequence TBT→DBT→MBT→Sn does not detoxity TBT for all microorganisms. Some microorganisms can methylate inorganic or organic tins under aerobic or anaerobic conditions. Methylation can also occur by chemical means and the relative contributions of biotic and abiotic mechanisms are not clear. It is difficult to isolate a pure culture which can methylate tin compounds aerobically, and it is difficult to isolate a pure culture which degrades TBT, suggesting that microbial consortiums may be involved in transformations of organotins in the aquatic environment. Methylation and debutylation alter the adsorbtivity and solubility of tin compounds; thus microorganisms can influence the environmental mobility of tin. TBT-resistant microorganisms can be isolated, and in some of them resistance to TBT can be plasmid-mediated. The literature review for this paper was completed in July, 1992.     

Organotin compounds and their interactions with microorganisms.

Organotin compounds are ubiquitous in the environment. The general order of toxicity to microorganisms increases with the number and chain length of organic groups bonded to the tin atom. Tetraorganotins and inorganic tin have little toxicity. Because of their lipophilicity, organotins are regarded as membrane active. There is evidence that the site of action of organotins may be both at the cytoplasmic membrane and intracellular level. Consequently, it is not known whether cell surface adsorption or accumulation within the cell, or both is a prerequisite for toxicity. Biosorption studies on a fungus, cyanobacteria, and microalgae indicates that cell surface binding alone occurred in these organisms, while studies on the effects of TBT (tributyltin) on certain microbial enzymes indicated that in some bacteria TBT can interact with cytosolic enzymes. Microorganism-organotin interactions are influenced by environmental conditions. In aquatic systems, both pH and salinity can determine organotin speciation and therefore reactivity. These environmental factors may also alter selectivity for resistant microorganisms in polluted systems. Tin-resistant microorganisms have been identified, and resistance can be either plasmid or chromosomally mediated. In one TBT-resistant organism, an Altermonas sp., an efflux system was suggested as the resistance mechanism. Biotransformation of organotin compounds by debutylation or methylation has been observed. These reactions may influence the toxicity, mobility, and environmental fate of organotin compounds.     

Anaerobic microbial methylation of inorganic tin in estuarine sediment slurries

Estuarine sediment slurries and microorganisms were examined for the ability to methylate inorganic tin. Under controlled redox conditions, tin was methylated only in oxygen-free sediment slurries. Monomethyltin usually comprised greater than 90% of the alkyltin products formed, although dimethyltin was also produced. Autoclaved anoxic sediments did not produce organotins. Several bacterial cultures, most notably sulfate-reducing bacteria isolated from anoxic estuarine sediments, formed monoand dimethyltin from inorganic tin in the absence of sediment. The results suggest that inorganic tin methylation in estuarine environments is an anaerobic process catalyzed primarily by sulfate-reducing microorganisms.     

Microbial formation and transformation of organometallic and organometalloid compounds

Abstract: Microbial formation and transformation of organometallic and organometalloid compounds comprise significant components of biogeochemical cycles for the metals mercury, lead and tin and the metalloids arsenic, selenium, tellurium and germanium. Methylated derivatives of such elements can arise as a result of chemical and biological mechanisms and this frequently results in altered volatility, solubility, toxicity and mobility. The major microbial methylating agents are methylcobalamin (CH₃CoB₁₂), involved in the methylation of mercury, tin and lead, and S -adenosylmethionine (SAM), involved in the methylation of arsenic and selenium. Evidence for the methylation of other toxic metal(loid)s is sparse. Biomethylation may result in metal(loid) detoxification since methylated derivatives may be excreted readily from cells, are often volatile and may be less toxic, e.g. organoarsenicals. However, for mercury, low yields of methylated derivatives and the existence of more efficient resistance mechanisms, e.g. reduction of Hg²⁺ to Hg⁰, suggest a lower significance in detoxification. Bioalkylation has only been characterised in detail for arsenic. Microorganisms can accumulate organometal(loid)s, a phenomenon relevant to toxicant transfer to higher organisms. As well as bioaccumulation, many microorganisms are capable of the degradation and detoxification of organometal(loid) compounds by, e.g. demethylation and dealkylation. Several organometal(loid) transformations have potential for environmental bioremediation.     

Inhibition of biofouling by marine microorganisms and their metabolites

Development of microbial biofilms and the recruitment of propagules on the surfaces of man-made structures in the marine environment cause serious problems for the navies and for marine industries around the world. Current antifouling technology is based on the application of toxic substances that can be harmful to the natural environment. For this reason and the global ban of tributyl tin (TBT), there is a need for the development of "environmentally-friendly" antifoulants. Marine microbes are promising potential sources of non-toxic or less-toxic antifouling compounds as they can produce substances that inhibit not only the attachment and/or growth of microorganisms but also the settlement of invertebrate larvae and macroalgal spores. However, so far only few antilarval settlement compounds have been isolated and identified from bacteria. In this review knowledge about antifouling compounds produced by marine bacteria and diatoms are summarised and evaluated and future research directions are highlighted.     

Inorganic tin and organotin interactions with<Emphasis Type="Italic"> Candida maltosa</Emphasis>

As a consequence of the widespread industrial and agricultural applications of organotins, contamination of various ecosystems has occurred in recent decades. Understanding how these compounds interact with microorganisms is important in assessing the risks of organotin pollution. The organotins, tributyltin (TBT), trimethyltin (TMT) and inorganic tin, Sn(IV), were investigated for their physical interactions with non-metabolising cells and protoplasts of the yeast Candida maltosa, an organism that is often associated with contaminated environments. Uptake, toxicity and membrane-acting effects of these compounds, at concentrations approximating those found in polluted environments, were assessed. Sn(IV) and TBT uptake occurred by different mechanisms. Uptake of Sn(IV) was 2-fold greater in intact cells than protoplasts, underlining the importance of cell wall binding, whereas TBT uptake levels by both cell types were similar. TBT uptake resulted in cell death and extensive K⁺ leakage, while Sn(IV) uptake had no effect. TMT did not interact with cells. Of the three compounds, TBT alone altered membrane fluidity, as measured by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene incorporated into cells. Anisotropy of 1-(4-trimethylaminophenyl-6-phenyl-1,3,5-hexatriene) was not affected, implying that TBT is not confined to the surface of the cytoplasmic membrane, but acts within membrane lipids. These results indicate that the cell wall is the dominant site of Sn(IV) interactions with yeast, while lipophilic interactions play an important role in uptake and toxicity of TBT.     

The environment,microbes and bioremediation: microbial activities modulated by the environment

Microorganisms in nature are largely responsible for the biodegradation and removal of toxic and non-toxic chemicals. Many organisms are also known to have specific ecological niches for proliferation and colonization. The nature of the environment dictates to a large extent the biodegradability of synthetic compounds by modulating the evolutionary processes in microorganisms for new degradative genes. Similarly, environmental factors often determine the extent of microbial gene expression by activating or repressing specific gene or sets of genes through a sensory signal transduction process. Understanding how the environment modulates microbial activity is critical for successful bioremediative applications.     

Metabolism of fluoroorganic compounds in microorganisms: impacts for the environment and the production of fine chemicals

Incorporation of fluorine into an organic compound can favourably alter its physicochemical properties with respect to biological activity, stability and lipophilicity. Accordingly, this element is found in many pharmaceutical and industrial chemicals. Organofluorine compounds are accepted as substrates by many enzymes, and the interactions of microorganisms with these compounds are of relevance to the environment and the fine chemicals industry. On the one hand, the microbial transformation of organofluorines can lead to the generation of toxic compounds that are of environmental concern, yet similar biotransformations can yield difficult-to-synthesise products and intermediates, in particular derivatives of biologically active secondary metabolites. In this paper, we review the historical and recent developments of organofluorine biotransformation in microorganisms and highlight the possibility of using microbes as models of fluorinated drug metabolism in mammals.     

Extremophiles as a source for novel enzymes

Microbial life does not seem to be limited to specific environments. During the past few decades it has become clear that microbial communities can be found in the most diverse conditions, including extremes of temperature, pressure, salinity and pH. These microorganisms, called extremophiles, produce biocatalysts that are functional under extreme conditions. Consequently, the unique properties of these biocatalysts have resulted in several novel applications of enzymes in industrial processes. At present, only a minor fraction of the microorganisms on Earth have been exploited. Novel developments in the cultivation and production of extremophiles, but also developments related to the cloning and expression of their genes in heterologous hosts, will increase the number of enzyme-driven transformations in chemical, food, pharmaceutical and other industrial applications.     

Gas chromatographic determination of inorganic tin in rat urine after a single oral administration of stannous chloride and mono-, di-, and triphenyltin chloride

A method is described for the determination of inorganic tin by gas chromatography with flame photometric detection. The inorganic tins, stannous and stannic, were extracted with hydrochloric acid and n-hexane—benzene in the presence of 0.05% tropolone, and both inorganic tins were pentylated to tetrapentyltin with a Grignard reagent prior to gas chromatography. The absolute limit of detection for tetrapentyltin was 3 pg as tin. The recovery of stannous chloride added to rat urine samples was 80.2 ± 2.4% (mean ± S.D., n = 8). The application of this method to the study of urinary excretion of inorganic tin and organotin compounds in rats following oral administration of tin compounds is presented. The urinary excretion of tin compounds was observed over a period of 96 h following administration of stannous chloride or phenyltin compounds. Most of the inorganic tin was excreted into urine within 24 h after administration of stannous chloride. In the experiments on organotin administration, the level of the excretion as total tin for monophenyltin reached a maximum ca. 0–24 h after administration, whereas the maxima for di- and triphenyltin were found after 24–48 h and 48–72 h, respectively. The predominant excretion product of these tin compounds found in urine was monophenyltin.     

叶际微生物研究进展

植物的叶际是一个复杂的生态系统,微生物的生存环境条件严苛。其可被利用的营养成分较少,温湿度波动大。此外,较强的紫外线辐射对于叶际微生物的生存也有很大影响。但是植物叶际却有着丰富的微生物多样性,其中还有许多有益细菌和真菌。它们通过和植物寄主的互作,改善着叶际微生物的栖居环境;其对植物病原体的拮抗亦可提高植物的抗病性。植物叶际的微生物还可以产生激素以促进植物生长,还有一些微生物可以利用农药等污染有机物作为营养物质,在污染物的环境生物修复方面显示巨大的潜力。此外,叶际微生物作为一种生态学指标在生态稳定与环境安全评价中开始发挥显著的作用。     

Volatile affairs in microbial interactions

Microorganisms are important factors in shaping our environment. One key characteristic that has been neglected for a long time is the ability of microorganisms to release chemically diverse volatile compounds. At present, it is clear that the blend of volatiles released by microorganisms can be very complex and often includes many unknown compounds for which the chemical structures remain to be elucidated. The biggest challenge now is to unravel the biological and ecological functions of these microbial volatiles. There is increasing evidence that microbial volatiles can act as infochemicals in interactions among microbes and between microbes and their eukaryotic hosts. Here, we review and discuss recent advances in understanding the natural roles of volatiles in microbe–microbe interactions. Specific emphasis will be given to the antimicrobial activities of microbial volatiles and their effects on bacterial quorum sensing, motility, gene expression and antibiotic resistance.     

环境激素类有机污染物的微生物降解和药物类化合物的残留问题

合成有机物在环境中的残留和危害已不仅仅局限于其毒性、富集、致畸和致突变,同时还能干扰包括人类在内的生物的内分泌调节作用.近年来发达国家已开始逐渐有了环境方面的条例,限制和控制这类化合物在水及食物链中的含量.现已清楚地知道,部分除草剂和杀虫剂(如阿特拉津、DDT),塑料的添加增塑剂均有内分泌激素活性,从而对生物的正常生长发育造成不良的影响.而这些化合物不但广泛存在于环境中,在特定的环境中其含量更是非常之高.以增塑剂邻苯二甲酸和邻苯二甲酸二甲酯为例,它们在填埋渗出液中的含量可高达10g·L^-1.在我们研究这类化合物的微生物降解时发现,从活性污泥和红树林中富集到的好氧微生物能将这类化合物完全矿化,且反应速度很快.同时也发现,在降解邻苯二甲酸二甲酯时,单一的纯菌不能完全降解这类化合物,而二种或三种组合的纯菌可以在一周内将500mg·L^-1的底物完全矿化.我们已分离、鉴定出中间产物,建立起了降解途径.研究的结果证实,邻苯二甲酸二甲酯类环境激素是能够在排放前通过微生物的作用达到完全矿化的.另一方面,药物类化合物的残留问题也是一个逐渐显现出的环境问题,这方面的研究应引起更多的关注和重视.     

微生物硫循环网络的研究进展

硫元素是所有生物的基本组成成分,是生物体必需的营养元素之一。硫氧化还原微生物的数量多、分布广、代谢途径多样化,硫化合物之间的平衡依赖于微生物代谢网络中的各种硫转化反应与代谢过程。此外,硫循环与碳、氮循环紧密相关,对地球生态循环起到了至关重要的作用。本文综述了近期微生物硫循环网络的研究进展,包括所涉及的主要微生物、硫循环的生物化学途径、硫循环的环境意义和工业应用潜能等,深入了解自然和人工生态系统中存在的硫循环过程,可为控制工农业生产中硫元素的增减与利用提供理论基础与应用方案。     

Microbial decolorization of spentwash: a review

Spentwash is one of the most complex and cumbersome wastewater with very high BOD, COD and other organic and inorganic toxic constituents. It is dark brown colored and difficult to treat by normal biological process such as activated sludge or anaerobic lagooning. The color is due to the presence of melanoidins, caramels and other polymers. These compounds have anti oxidant properties which render them toxic to microorganisms. Spentwash disposal into the environment is hazardous and has a considerable pollution potential. It affects the aesthetic merit. Its decolorization by physical or chemical methods have been investigated and were found unsuitable. In the recent past, increasing attention has been directed towards utilizing microbial activity for decolorization of spentwash. This review reveals various groups of microorganisms which have potential in spentwash decolorization. The role of enzymes in decolorization and the microbial degradation of individual compounds imparting color to spentwash are also discussed.     

Enhancement of metal bioremediation by use of microbial surfactants

Metal pollution all around the globe, especially in the mining and plating areas of the world, has been found to have grave consequences. An excellent option for enhanced metal contaminated site bioremediation is the use of microbial products viz. microbial surfactants and extracellular polymers which would increase the efficiency of metal reducing/sequestering organisms for field bioremediation. Important here is the advantage of such compounds at metal and organic compound co-contaminated site since microorganisms have long been found to produce surface-active compounds when grown on hydrocarbons. Other options capable of proving efficient enhancers include exploiting the chemotactic potential and biofilm forming ability of the relevant microorganisms. Chemotaxis towards environmental pollutants has excellent potential to enhance the biodegradation of many contaminants and biofilm offers them a better survival niche even in the presence of high levels of toxic compounds.     

Natural product antifoulants: One perspective on the challenges related to coatings development

Fouling of surfaces by abiotic and biotic substances has molecular, microbial, and macro-organismal levels of organization. Fouling involves molecular bonding and biological adhesives. Existing commercial solutions to fouling are antifouling or foul-release. Antifouling uses broad-spectrum biocides which kill foulers by virtue of oxidation or toxic metal ions. Foul-release coatings are dimethyl silicone polymers that foul, but clean easily. The best foul-release coatings also contain additives that kill organisms. Environmentally unacceptable consequences of toxic antifouling coatings, especially those based on organotins, have prompted interest in antifoulants found in living organisms. Laboratories worldwide now use bioassays with target fouling organisms to direct purification and identification of antifoulant compounds. Natural antifoulants are common and include toxins, anesthetics, surface-active agents, attachment and/or metamorphosis inhibitors and repellents. Development of commercial coatings using natural products is blocked by cost, the time horizon to meet government regulations and performance standards based upon coatings with unacceptable environmental impacts. If blocks are removed, the potential for environmentally acceptable solutions that combine natural products with organic biocides is high.     

Interactions of chromium with microorganisms and plants

Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.