Degradation of arsenobetaine to inorganic arsenic by bacteria in seawater

The substances suspended in seawater were fractionated by membrane filtration into three fractions. Fraction 1 was collected on a membrane filter of 0.22 µm pore-size, fraction 2 on a 5 µm pore-size and fraction 3 on 0.22 µm pore-size from the filtrate passed through the 5 µm membrane filter. Arsenobetaine was incubated with each of these fractions in two media (ZoBell 2216E and a solution of inorganic salts) at 25 °C in the dark under aerobic conditions. The mixture added with fraction 3 was considered to contain only bacteria. In every case, in the inorganic salt medium, inorganic arsenic(V) was derived from arsenobetaine via trimethylarsine oxide. In the ZoBell medium, arsenobetaine was not degraded to inorganic arsenic, although trimethylarsine oxide was derived in every case. We conclude that the degradation of arsenobetaine to trimethylarsine oxide or inorganic arsenic can be accomplished in seawater by bacteria alone.     

Degradation of arsenobetaine by microorganisms associated with marine macro algae,Monostroma nitidium and Hizikia fusiforme

• 1.1. Arsenobetaine-containing growth media (ZoBell 2216E; solution of inorganic salts) were mixed with each of two marine macro algae, a green alga Monostroma nitidum and a brown alga Hizikia fusiforme, as a source of microorganisms.
• 2.2. The conversion of arsenobetaine to trimethylarsine oxide and/or dimethylarsinic acid by the microorganisms associated with the marine macro algae was confirmed in both the media.
• 3.3. A striking contrast, however, in the conversion pattern was observed between the two algae: arsenobetaine was converted to trimethylarsine oxide and trimethylarsine oxide to dimethylarsine acid successively with M. nitidum, while the reverse was observed with H. fusiforme.

     

Proposal for novel metabolic pathway of highly toxic dimethylated arsenics accompanied by enzymatic sulfuration,desulfuration and oxidation

The International Agency for Research on Cancer (IARC) has concluded that dimethylarsinic acid [(CH₃)₂AsO(OH), DMA^V], a main metabolite of inorganic arsenic, is responsible for carcinogenesis in urinary bladder and lung in rodents, and various modes of carcinogenic action have been proposed. One theory concerning the mode of action is that the biotransformation of dimethylarsinous acid [(CH₃)₂AsOH, DMA^III] from DMA^V plays an important role in the carcinogenesis by way of reactive oxygen species (ROS) production. Furthermore, dimethylmonothioarsinic acid [(CH₃)₂AsS(OH), DMMTA^V], a metabolite of DMA^V, has also been noted because of its higher toxicity. However, the metabolic mechanisms of formation and disappearance of DMA^III and DMMTA^V, and their toxicity are not fully understood. Thus, the purpose of the present study was to clarify the mechanism of metabolic formation of DMMTA^V and DMA^V from DMA^III. The in vitro transformation of arsenicals by treatment with liver homogenate from rodents and sulfur transferase was detected by HPLC-ICP-MS and HPLC-tandem MS. DMMTA^V is produced from DMA^III but not DMA^V by cellular fractions from mouse liver homogenates and by rhodanese from bovine liver in the presence of thiosulfate, a sulfur donor. Not only DMMTA^V thus produced but also DMA^III are re-converted into DMA^V by an in vitro addition of S9 mix. These findings indicate that the metabolic process not only of DMA^III to DMA^V or DMMTA^V but also of DMMTA^V to DMA^V consists of a complicated mode of interaction between monooxygenase including cytochrome P450 (CYP) and/or sulfur transferase.     

Dimethylarsine likely acts as a mouse-pulmonary tumor initiator via the production of dimethylarsine radical and/or its peroxy radical

AimsRecent animal experiments have indicated that dimethylarsinic acid (DMA), a main metabolite of inorganic arsenic, is a complete carcinogen in the lung of mice and the urinary bladder of rats, nevertheless, no ultimate-active metabolite from DMA has been identified thus far. We have proposed that dimethylarsine ((CH₃)₂AsH), an ultimate reductive metabolite of DMA, is excreted in the expired air of mice administered DMA, and furthermore, was easily converted into dimethylarsine radical ((CH₃)₂As?) and dimethylarsine peroxy radical ((CH₃)₂AsOO?) by its reaction with O₂. The aim of the present study was to elucidate the possible mode of the tumorigenic action by dimethylated arsenic.Main methodsIn vitro experiments using GSH reductase as a two-electron donor of dimethylarsenic-glutathione conjugate ((CH₃)₂As-SG) and DNA adduct assay via a photochemical approach were performed. A lung tumorigenicity assay of (CH₃)₂AsH suspended in argon-atmospheric olive oil for 5 days was also conducted in mice.Key findingsThe results indicated that (CH₃)₂AsH was easily produced enzymatically from (CH₃)₂As-SG and showed tumor-initiating action in mouse lung via the production of (CH₃)₂As? and (CH₃)₂AsOO? by its reaction with O₂, and that these radicals have the ability to form DNA adducts.SignificanceThe carcinogenicity of DMA, at least in mouse lung, could be explained based on the proposal that oral administration of DMA induces pulmonary tumors in mice, and arises from the arsine radicals produced through (CH₃)₂AsH, which was enzymatically reduced from (CH₃)₂As-SG.     

Bacterial degradation of arsenobetaine via dimethylarsinoylacetate

Microorganisms from Mytilus edulis (marine mussel) degraded arsenobetaine, with the formation of trimethylarsine oxide, dimethylarsinate and methylarsonate. Four bacterial isolates from these mixed-cultures were shown by HPLC/hydride generation-atomic fluorescence spectroscopy (HPLC/HG-AFS) analysis to degrade arsenobetaine to dimethylarsinate in pure culture; there was no evidence of trimethylarsine oxide formation. Two of the isolates ( Paenibacillus sp. strain 13943 and Pseudomonas sp. strain 13944) were shown by HPLC/inductively coupled plasma-mass spectrometry (HPLC/ICPMS) analysis to degrade arsenobetaine by initial cleavage of a methyl-arsenic bond to form dimethylarsinoylacetate, with subsequent cleavage of the carboxymethyl-arsenic bond to yield dimethylarsinate. Arsenobetaine biodegradation by pure cultures was biphasic, with dimethylarsinoylacetate accumulating in culture supernatants during the culture growth phase and its removal accompanying dimethylarsinate formation during a carbon-limited stationary phase. The Paenibacillus sp. also converted exogenously supplied dimethylarsinoylacetate to dimethylarsinate only under carbon-limited conditions. Lysed-cell extracts of the Paenibacillus sp. showed constitutive expression of enzyme(s) capable of arsenobetaine degradation through methyl-arsenic and carboxymethyl-arsenic bond cleavage. The work establishes the capability of particular bacteria to cleave both types of arsenic-carbon bonds of arsenobetaine and demonstrates that mixed-community functioning is not an obligate requirement for arsenobetaine biodegradation.     

The reduction of trimethylarsine oxide to trimethylarsine by thiols: a mechanistic model for the biological reduction of arsenicals

Trimethylarsine oxide is reduced to trimethylarsine in aqueous solution by a variety of thiols and dithiols including cysteine, glutathione, and lipoic acid. Kinetic results and other observations suggest that the rate-determining step is the production of [Me₃AsSR]⁺ from an initially formed Me₃As(SR)OH species, and that the reduction occurs via a two-electron transfer from Me₃As(SR)₂ affording Me₃As and RS-SR. A simple model for the biological methylation of arsenic is proposed based on oxidative methylation of arsenic(III) by S-adenosylmethionine and reduction by a thiol such as lipoic acid.     

Structural analysis of the anti-arthritic drug Auranofin: Its complexes with cysteine, selenocysteine and their fragmentation products

Positive mode electrospray mass spectrometry was used to investigate complexes of cysteine and selenocysteine with the metallo-drug Auranofin and the analogous chlorotriethylphosphine gold. Evidence for all the complexes, with the exception of the Auranofin-selenocysteine complex, was obtained. Several fragmentation products were examined and their proposed structures reported. Structural details of many experimentally observed ions including [Auranofin + H]⁺, [(CH₃CH₂)₃P-Au-cysteine]⁺ and [(CH₃CH₂)₃P-Au-methylselenocysteine]⁺ were examined by means of hybrid density functional theory at the B3LYP/DZVP level. Structural information and relative free energies are presented for several isomers of each ion considered.     

Speciation of dimethyltin(IV) – and trimethyltin(IV) – carbocysteinate and – glutamate systems in aqueous media

Abstract

The formation of complex species in the dimethyltin(IV) and trimethyltin(IV)-carboxymethyl-L-cysteinate (carbocysteinate) systems in NaCl_aq, at different ionic strengths, and in a multicomponent Na⁺, K⁺, Ca²⁺ ,Mg²⁺, Cl^? and SO₄^2-? medium representative of the seawater major composition, is discussed. Experimental results give evidence for the formation of the following species (L = carbocysteinate): [(CH₃)₂Sn(L)]⁰, [(CH₃)₂Sn(HL)]⁺, [(CH₃)₂Sn(OH)(L)]^?, [(CH₃)₂Sn(OH)₂(L)]^2? in the DMT–CCYS system, and [(CH₃)₃Sn(HL)]⁰, [(CH₃)₃Sn(L)]^? and [(CH₃)₃Sn(OH)(L)]^2? in the TMT-CCYS system. The ionic strength dependence of formation constants was taken into account by an extended Debye Hückel type equation and by the SIT (Specific ion Interaction Theory). Measurements were carried out also on the dimethyltin(IV)-glutamate and trimethyltin(IV)-glutamate systems in NaCl_aq, owing the strict similarity of glutamate and carbocysteinate. Results obtained show the formation of complex species having the same stoichiometry as those formed in the DMT- and TMT-carbocysteinate systems, with very similar stability, confirming that carbocysteinate behaves as a dicarboxylic amino acid without involving the sulfur-bridge potential binding site in metal coordination.     

Multinuclear (P, Pt) magnetic resonance and electrospray mass spectrometric studies of the reactions between platinum bis(dithiolates) and two potentially tetradentate phosphine ligands

The reactions of platinum(II) bis(dithiolates) Pt(S---S)₂ ((S---S)=S₂P(OEt)₂ (dtp), S₂COⁿPr (xan), S₂CNEt₂ (dtc)) with two potentially tetradentate phosphine ligands have been investigated by multinuclear magnetic resonance spectroscopy and electrospray mass spectrometry (ESMS). The phosphines used were P(CH₂CH₂PPh₂)₃ (P₃P′) and Ph₂PCH₂CH₂P(Ph)CH₂CH₂P(Ph)CH₂CH₂PPh₂ (P₂P′₂). ³¹P and ¹⁹⁵Pt NMR spectroscopies show that P₃P′ reacts in dichloromethane solution with Pt(dtp)₂ and Pt(xan)₂ to give five-coordinate [(η⁴-P₃P′)Pt(η¹-S---S)]⁺ and with Pt(dtc)₂ to give a temperature dependent mixture of [(η⁴-P₃P′)Pt(η¹-dtc)]⁺ and [(η³-P₃P′)Pt(η²-dtc)]⁺. All these formulations were confirmed by observation of the intact ions in the ES mass spectra directly from the solutions. [(η⁴-P₃P′)Pt(η¹-xan)]⁺ slowly reacts with the free xan ion to give the dithiocarbonate complex (η³-P₃P′)Pt(η²-S₂CO). The pendant phosphine in [(η³-P₃P′)Pt(η²-dtc)]⁺ undergoes various chemical reactions such as methylation and reaction with sulfur, and the cation behaves as a monodentate phosphine towards Pt(dtp)₂ to give [(η¹-dtp)(η²-dtp)Pt(η¹-μ²-η³-P₃P′)Pt(η²-dtc)]⁺ which was fully characterised by multi-NMR spectroscopy and confirmed by observation of the intact ion by ESMS. P₂P′₂ reacts with Pt(dtp)₂ to give [(P₂P′₂)Pt]²⁺, but with Pt(xan)₂ and Pt(dtc)₂ the products are [(η⁴-P₂P′₂)Pt(η¹-S---S)]⁺, but the xanthate complex slowly de-alkylates to give (η³-P₂P′₂)Pt(η²-S₂CO). The identities of the cationic P₂P′₂ species in solution were confirmed by direct observation of the intact ion by ESMS.     

Genetically Engineering Bacillus subtilis with a Heat-Resistant Arsenite Methyltransferase for Bioremediation of Arsenic-Contaminated Organic Waste

Organic manures may contain high levels of arsenic (As) due to the use of As-containing growth-promoting substances in animal feed. To develop a bioremediation strategy to remove As from organic waste, Bacillus subtilis 168, a bacterial strain which can grow at high temperature but is unable to methylate and volatilize As, was genetically engineered to express the arsenite S-adenosylmethionine methyltransferase gene (CmarsM) from the thermophilic alga Cyanidioschyzon merolae. The genetically engineered B. subtilis 168 converted most of the inorganic As in the medium into dimethylarsenate and trimethylarsine oxide within 48 h and volatized substantial amounts of dimethylarsine and trimethylarsine. The rate of As methylation and volatilization increased with temperature from 37 to 50°C. When inoculated into an As-contaminated organic manure composted at 50°C, the modified strain significantly enhanced As volatilization. This study provides a proof of concept of using genetically engineered microorganisms for bioremediation of As-contaminated organic waste during composting.     

Toxicological properties of the thiolated inorganic arsenic and arsenosugar metabolite thio-dimethylarsinic acid in human bladder cells

Thio-dimethylarsinic acid (thio-DMA^V) has recently been identified as human metabolite after exposure toward both the human carcinogen inorganic arsenic and arsenosugars, which are the major arsenical constituents of marine algae. This study aims to get further insight in the toxic modes of action of thio-DMA^V in cultured human urothelial cells. Among others effects of thio-DMA^V on eight cell death related endpoints, cell cycle distribution, genotoxicity, cellular bioavailability as well as for the first time its impact on DNA damage induced poly(ADP-ribosyl)ation were investigated and compared to effects induced by arsenite. The data indicate that thio-DMA^V exerts its cellular toxicity in a similar or even lower concentration range, however most likely via different mechanisms, than arsenite. Most interestingly, thio-DMA^V decreased damage-induced cellular poly(ADP-ribosyl)ation by 35,000-fold lower concentrations than arsenite. The inhibition of this essential DNA-damage induced and DNA-repair related signaling reaction might contribute to inorganic arsenic induced toxicity, at least in the bladder. Therefore, and also because thio-DMA^V is to date by far the most toxic human metabolite identified after arsenosugar intake, thio-DMA^V should contemporary be fully (also in vivo) toxicologically characterized, to assess risks to human health related to inorganic arsenic but especially arsenosugar dietary intake.     

Biotransformation of arsenobetaine by microorganisms from the human gastrointestinal tract

Abstract

The consumption of fish and shellfish is a major route of human exposure to arsenic (As), because they contain relatively large concentrations of organoarsenicals, in particular arsenobetaine (AB). AB is considered non-toxic because of its rapid excretion from the human body. However, previous studies on human metabolism and excretion of AB have used the compound in solution rather than considering the effects that occur during the digestion of food in the gastrointestinal tract. In this preliminary study, we used microcosms inoculated with human faecal matter to investigate the aerobic and anaerobic degradation of AB by microorganisms associated with the large intestine. Samples were recovered over 30 days, centrifuged, filtered and the supernatant analysed for total As content and As speciation, using ICP–MS and HPLC–ICP–MS respectively. After 7 days the total As in the supernatants from the aerobic experiment fell to a minimum of 65% of the total added, recovering to 15% less than added after 30 days. By using anion and cation exchange chromatography coupled to ICP–MS detection, arsenobetaine (AB), dimethylarsinic acid (DMA), dimethylarsinoylacetic acid (DMAA) and trimethylarsine oxide (TMAO) were identified as degradation products. Results from the aerobic system showed that after 7 days incubation the AB had been degraded to DMA, DMAA and TMAO and after 30 days the degraded AB reappeared in the samples. The results for the anaerobic system showed no degradation of AB over the 30 day course of the experiment. These findings demonstrate for the first time that biocatalytic capability for AB degradation exists within the human gastrointestinal tract.     

Tris(triazolyl)borate ligands of intermediate steric bulk for the synthesis of biomimetic structures with hydrogen bonding and solubility in hydrophilic solvents

Tris(triazolyl)borate ligands (Ttz) of intermediate steric bulk were synthesized to investigate their potential for hydrogen bonding and improved solubility in hydrophilic solvents as applied to biomimetic chemistry. The crystal structure of 3-phenyl-5-methyl-1,2,4-triazole (Htz^Ph,Me) revealed hydrogen bonding and π stacking interactions. The new ligand salt, potassium tris(3-phenyl-5-methyl-1,2,4-triazolyl)borate (KTtz^Ph,Me) was synthesized as the first example of a Ttz ligand of intermediate steric bulk. Metathesis between KTtz^Ph,Me and NaCl followed by recrystallization produced [NaTtz^Ph,Me] · 6CH₃OH in which the geometry around the sodium is octahedral with an unusual N₃O₃ donor set; this structure also shows that a hydrogen bonding network is formed by methanol molecules and triazole nitrogens. (Ttz^Ph,Me)ZnCl was synthesized and characterized crystallographically as [(Ttz^Ph,Me)ZnCl] · 0.5CH₃OH in which the zinc is tetrahedral and the triazole rings are within hydrogen bonding distance of CH₃OH. All of these new compounds are methanol soluble to varying degrees and Htz^Ph,Me and KTtz^Ph,Me are soluble in methanol/water mixtures.     

Arsenic accumulation in three species of sea turtles

Arsenic in the liver, kidney and muscle of three species of sea turtles, e.g., green turtles (Chelonia mydas), loggerhead turtles (Caretta caretta) and hawksbill turtles (Eretmochelys imbricata), were determined using HG-AAS, followed by arsenic speciation analysis using HPLC-ICP-MS. The order of arsenic concentration in tissues was muscle > kidney > liver. Unexpectedly, the arsenic concentrations in the hawksbill turtles feeding mainly on sponges were higher than the two other turtles primarily eating algae and mollusk which accumulate a large amount of arsenic. Especially, the muscles of the hawksbill turtles contained remarkably high arsenic concentrations averaging 153 mg kg^–1 dry weight with the range of 23.1–205 mg kg^–1 (n=4), even in comparison with the data from other organisms. The arsenic concentrations in the tissues of the green turtles were significantly decreased with standard carapace length as an indicator of growth. In arsenic compounds, arsenobetaine was mostly detected in the tissues of all the turtles. Besides arsenobetaine, a small amount of dimethylarsinic acid was also observed in the hawksbill turtles.     

Syntheses and structures of the heterometallic clusters [(Ph3PAu)3Re(CO)4], [(Ph3PAu)4Re(CO)4], [(Ph3PAu)6AuRe2(CO)8], and [(Ph3PAu)6Re(CO)3]

The reaction of [HRe₃(CO)₁₂]²⁻ with an excess of Ph₃PAuCl in CH₂Cl₂ yields [(Ph₃PAu)₄Re(CO)₄]⁺ as the main product, which crystallizes as [(Ph₃PAu)₄Re(CO)₄]PF₆ · CH₂Cl₂ (1 · CH₂Cl₂) after the addition of KPF₆.The crystal structure determination reveals a trigonal bipyramidal Au₄Re cluster with the Re atom in equatorial position.If [(Ph₃PAu)₄Re(CO)₄]⁺ is reacted with PPh₄Cl, a cation [Ph₃PAu]⁺ is eliminated as Ph₃PAuCl, and the neutral cluster [(Ph₃PAu)₃Re(CO)₄] (2) is formed.It combines with excess [(Ph₃PAu)₄Re(CO)₄]⁺ to afford the cluster cation, [(Ph₃PAu)₆AuRe₂(CO)₈]⁺. It crystallizes from CH₂Cl₂ as[(Ph₃PAu)₆AuRe₂(CO)₈]PF₆ · 4CH₂Cl₂ (3 · 4CH₂Cl₂). In [(Ph₃PAu)₃Re(CO)₄] the metal atoms are arranged in form of a lozenge while in [(Ph₃PAu)₆AuRe₂(CO)₈]⁺ two Au₄Re trigonal bipyramids are connected by a common axial Au atom.The treatment of [(Ph₃PAu)₄Re(CO)₄]⁺ with KOH and Ph₃PAuCl in methanol yields the cluster cation [(Ph₃PAu)₆Re(CO)₃]⁺, which crystallizes with from CH₂Cl₂ as [(Ph₃PAu)₆Re(CO)₃]PF₆ · CH₂Cl₂ (4 · CH₂Cl₂). The metal atoms in this cluster form a pentagonal bipyramid with the Re atom in the axial position.     

Synthesis and characterization of thiolato-bridged cadmium(II) complexes with NNS-chelating thiolic ligands

Cadmium(II) complexes with 2-[(2-aminoethyl)amino]ethanethiol (HL¹), 2-[(3-aminopropyl)amino]ethanethiol (HL²), 2-[(2-pyridylmethyl)amino]ethanethiol (HL³), and 2-[[2-(2-pyridyl)ethyl]amino]ethanethiol (HL⁴), [Cd(L¹)](ClO₄) (1), [Cd(L²)](ClO₄)·1/2CH₃OH (2), [Cd{Cd(L²)₂}₂](ClO₄)₂·CH₃CON(CH₃)₂ (3a·CH₃CON(CH₃)₂), [Cd{Cd(L²)₂}₂]Cl₂·2CH₃OH (3b·2CH₃OH), [Cd{Cd(L³)₂}₂](ClO₄)₂ (4), [Cd(L⁴)](ClO₄) (5), have been synthesized and characterized by measurements of the infrared and electronic spectra. The X-ray crystal structures show that 3a and 3b have a thiolato-bridged trinuclear core with a linear arrangement of three metal atoms.     

An assessment of DFT methods for predicting the thermochemistry of ion-molecule reactions of group 14 elements (Si, Ge, Sn)

Experimental mass-spectrometry data on thermochemistry of methide transfer reactions (CH₃)₃M⁺ + M'(CH₃)₄ ? M(CH₃)₄?+?(CH₃)₃M'⁺ (M, M'?=?Si, Ge or Sn) and the formation energy of the [(CH₃)₃Si-CH₃-Si(CH₃)₃]⁺ complex are used as benchmarks for DFT methods (B3LYP, BMK, M06L, and ωB97XD). G2 and G3 theory methods are also used for the prediction of thermochemical data. BMK, M06L, and ωB97XD methods give the best fit to experimental data (close to chemical accuracy) as well as to G2 and G3 results, while B3LYP demonstrates poor performance. From the first three methods M06L gives the best overall result. Structures and formation energies of intermediate “mixed” [(CH₃)₃M-CH₃- M′(CH₃)₃] complexes not observed in experiment are predicted. Their structures, better described as M(CH₃)₄?[M′(CH₃)₃]⁺ complexes, explain their fast decompositions.

Structural and magnetic characteristics of tetramethylammonium tetrahalogenoferrates(III)

A series of tetramethylammonium tetrahalogenoferrates(III), [FeBr_4−nCl_n]⁻ (n = 0, 1, 3, 4), of general formula [(CH₃)₄N][FeBr_4−nCl_n], have been synthesized. The crystal and molecular structures of [(CH₃)₄N][FeCl₄] were determined. The compound is isostructural with its [FeBr_4−nCl_n]⁻ (n = 0, 1, 3, 4) analogues. Magnetic measurements of the powdered samples of [(CH₃)₄N][FeBr_4−nCl_n] gave negative values of the Weiss constant, which suggest antiferromagnetic coupling. The strength of the antiferromagnetic interactions strongly depends on the kind of halide ligands in the coordination sphere of iron(III) and increases with an increasing number of the bromide anions.     

Arsenic in the human food chain,biotransformation and toxicology – Review focusing on seafood arsenic

Fish and seafood are main contributors of arsenic (As) in the diet. The dominating arsenical is the organoarsenical arsenobetaine (AB), found particularly in finfish. Algae, blue mussels and other filter feeders contain less AB, but more arsenosugars and relatively more inorganic arsenic (iAs), whereas fatty fish contain more arsenolipids. Other compounds present in smaller amounts in seafood include trimethylarsine oxide (TMAO), trimethylarsoniopropionate (TMAP), dimethylarsenate (DMA), methylarsenate (MA) and sulfur-containing arsenicals. The toxic and carcinogenic arsenical iAs is biotransformed in humans and excreted in urine as the carcinogens dimethylarsinate (DMA) and methylarsonate (MA), producing reactive intermediates in the process. Less is known about the biotransformation of organoarsenicals, but new insight indicates that bioconversion of arsenosugars and arsenolipids in seafood results in urinary excretion of DMA, possibly also producing reactive trivalent arsenic intermediates. Recent findings also indicate that the pre-systematic metabolism by colon microbiota play an important role for human metabolism of arsenicals. Processing of seafood may also result in transformation of arsenicals.     

Tin and Tin-Resistant Microorganisms in Chesapeake Bay

Sediment and water samples from nine stations in Chesapeake Bay were examined for tin content and for microbial populations resistant to inorganic tin (75 mg of Sn liter⁻¹ as SnCl₄·5H₂O) or to the organotin compound dimethyltin chloride [15 mg of Sn liter⁻¹ as (CH₃)₂SnCl₂]. Tin concentrations in sediments were higher (3.0 to 7.9 mg kg⁻¹) at sites impacted by human activity than at open water sites (0.8 to 0.9 mg kg⁻¹), and they were very high (239.6 mg kg⁻¹) in Baltimore Harbor, which is impacted by both shipping and heavy industry. Inorganic tin (75 mg Sn liter⁻¹) in agar medium significantly decreased viable counts, but its toxicity was markedly reduced in liquid medium; it was not toxic in medium solidified with silica gel. Addition of SnCl₄·5H₂O to these media produced a tin precipitate which was not involved in the metal's toxicity. The data suggest that a soluble tin-agar complex which is toxic to cells is formed in agar medium. Thus, the toxicity of tin depends more on the chemical species than on the metal concentration in the medium. All sites in Chesapeake Bay contained organisms resistant to tin. The microbial flora was more sensitive to (CH₃)₂SnCl₂ than to SnCl₄·5H₂O. The elevated level of tin-resistant microorganisms in some aeas not containing unusually high tin concentrations suggests that factors other than tin may participate in the selection for a tin-tolerant microbial flora.