Biodegradation of Tributyltin (TBT) by Extremophile Bacteria from Atacama Desert and Speciation of Tin By-products

Tributyltin degrading microbial enzymes: A promising remediation approach

Brazil is one of the countries most impacted along the entire coastline by the presence of tributyltin (TBT), a biocide used in antifouling paints. Despite being banned since 2008, its use is still registered in the country, and it is possible to find recent inputs of this substance in places under the influence of shipyards, marinas, and fishing ports. In this study, a bacterium isolated from TBT-contaminated sediment from Santos and São Vicente Estuarine System (SESS) in Brazil, identified as Achromobacter sp., proved to be resistant to this compound. Furthermore, its crude enzymatic extract presented the ability to reduce up to 25 % of the initial TBT concentration in the liquid phase in 1 h, demonstrating to be a simple, fast, effective procedure and a potential tool for the environmental attenuation of TBT.

iChip increases the success of cultivation of TBT-resistant and TBT-degrading bacteria from estuarine sediment

Standard methods of microbial cultivation only enable the isolation of a fraction of the total environmental bacteria. Numerous techniques have been developed to increase the success of isolation and cultivation in the laboratory, some of which derive from diffusion chambers. In a diffusion chamber, environmental bacteria in agar medium are put back in the environment to grow as close to their natural conditions as possible, only separated from the environment by semi-permeable membranes. In this study, the iChip, a device that possesses hundreds of mini diffusion chambers, was used to isolate tributyltin (TBT) resistant and degrading bacteria. IChip was shown to be efficient at increasing the number of cultivable bacteria compared to standard methods. TBT-resistant strains belonging to Oceanisphaera sp., Pseudomonas sp., Bacillus sp. and Shewanella sp. were identified from Liverpool Dock sediment. Among the isolates in the present study, only members of Pseudomonas sp. were able to use TBT as a sole carbon source. It is the first time that members of the genus Oceanisphaera have been shown to be TBT-resistant. Although iChip has been used in the search for molecules of biomedical interest here we demonstrate its promising application in bioremediation.

Insights into the Restoration of Tributyltin Contaminated Environments Using Marine Bacteria from Portuguese Fishing Ports

Tributyltin (TBT) is an organotin chemical mainly used as biocide in marine antifouling paints. Despite the restrictions and prohibitions on its use, TBT is still an environmental problem due to its extensive application and subsequent release into the environment, being regarded as one of the most toxic chemicals released into the marine ecosystems. Microorganisms inhabiting impacted sites are crucial for their restoration since they have developed mechanisms to tolerate and break down pollutants. Nonetheless, transformation products resulting from the degradation process may still be toxic or, sometimes, even more toxic than the parent compound. The determination of the parent and degradation products by analytical methods, although necessary, may not be ecologically relevant since no information is provided regarding their ecotoxicity. In this study, marine bacteria collected from seven Portuguese fishing ports were isolated and grown in the presence of TBT. Bacteria that exhibited higher growth were used to bioremediate TBT-contaminated waters. The potential of these bacteria as bioremediation agents was evaluated through ecotoxicological assays using the sea snail Gibbula umbilicalis as model organism. Data suggested that some TBT-tolerant bacteria, such as Pseudomonas putida, can reduce the toxicity of TBT contaminated environments. This work contributes to the knowledge of TBT-degrading bacteria.

Assessing the Efficacy of a Sediment Remediation Program Using Benthic and Pelagic Copepod Bioassays

Tributyltin is an organotin chemical that has been commonly used in ship antifouling paints. Despite the global total prohibition of tributyltin-based paint in 2008, tributyltin continues to be found at toxic levels in areas of high maritime traffic such as ports and harbors. A remediation program was conducted at a New Zealand port to reduce tributyltin and copper concentrations to acceptable values. The present study assessed the efficacy of the program using a combination of chemical analyses and copepod bioassays. Sediment and water samples were collected at 3 locations along a spatial gradient within the port, and concentrations of various organotin compounds and trace metal levels were measured pre- and postremediation. The toxicity of sediment and elutriate samples was estimated by benthic and pelagic copepod bioassays. Although acute toxicity in sediment samples was reduced following remediation, reproductive success was still affected for the benthic copepod. This approach combining chemical analysis and bioassays is promising for assessing the efficacy of remediation processes at contaminated marine sites. Environ Toxicol Chem 2020;39:492-499. © 2019 SETAC.

Monitoring the degradation capability of novel haloalkaliphilic tributyltin chloride (TBTCl) resistant bacteria from butyltin-polluted site

Tributyltin (TBT) is recognized as a major environmental problem at a global scale. Haloalkaliphilic tributyltin (TBT)-degrading bacteria may be a key factor in the remediation of TBT polluted sites. In this work, three haloalkaliphilic bacteria strains were isolated from a TBT-contaminated site in the Mediterranean Sea. After analysis of the 16S rRNA gene sequences the isolates were identified as Sphingobium sp. HS1, Stenotrophomonas chelatiphaga HS2 and Rhizobium borbori HS5. The optimal growth conditions for biodegradation of TBT by the three strains were pH 9 and 7% (w/v) salt concentration. S. chelatiphaga HS2 was the most effective TBT degrader and has the ability to transform most TBT into dibutyltin and monobutyltin (DBT and MBT). A gene was amplified from strain HS2 and identified as TBTB-permease-like, that encodes an ArsB-permease. A reverse transcription polymerase chain reaction analysis in the HS2 strain confirmed that the TBTB-permease-like gene contributes to TBT resistance. The three novel haloalkaliphilic TBT degraders have never been reported previously.

SugE belongs to the small multidrug resistance (SMR) protein family involved in tributyltin (TBT) biodegradation and bioremediation by alkaliphilic Stenotrophomonas chelatiphaga HS2

Tributyltin (TBT) used in a variety of industrial processes, subsequent discharge into the environment, its fate, toxicity and human exposure are topics of current concern. TBT degradation by alkaliphilic bacteria may be a key factor in the remediation of TBT in high pH contaminated sites. In this study, Stenotrophomonas chelatiphaga HS2 were isolated and identified from TBT contaminated site in Mediterranean Sea. S. chelatiphaga HS2 has vigor capability to transform TBT into dibutyltin and monobutyltin (DBT and MBT) at pH 9 and 7% NaCl (w/v). A gene was amplified and characterized from strain HS2 as SugE protein belongs to SMR protein family, a reverse transcription polymerase chain reaction analysis confirmed that SugE protein involved in the TBT degradation by HS2 strain. TBT bioremediation was investigated in stimulated TBT contaminated sediment samples (pH 9) using S chelatiphaga HS2 in association with E. coli BL21 (DE3)-pET28a(+)-sugE instead of S chelatiphaga HS2 alone reduced significantly the TBT half-life from 12d to 5d, although no TBT degradation appeared using E. coli BL21 (DE3)-pET28a(+)-sugE alone. This finding indicated that SugE gene increased the rate and degraded amount of TBT and is necessary in enhancing TBT bioremediation.

Efficient dibutyltin (DBT) elimination by the microscopic fungus Metarhizium robertsii under conditions of intensive aeration and ascorbic acid supplementation

Dibutyltin (DBT) is an environmental pollutant characterized by immunotoxic, neurotoxic, and pro-oxidant properties. In this study, an attempt was made to enhance DBT elimination by the Metarhizium robertsii strain. We observed enhanced fungal growth in the bioreactor (pO₂ ≥ 20%) compared to flask cultures (μ _max increased from 0.061 to 0.086 h^-1). Moreover, under aerated conditions, M. robertsii mycelium with "hairy" morphology biodegraded DBT (20 mg l^-1) 10-fold faster in the bioreactor than in the flask cultures. Monobutyltin (MBT) and a hydroxylated derivative of MBT (OHBuSnH₂) were detected as by-products of dibutyltin debutylation. Simultaneous usage of glucose and butyltins indicates the comatabolic nature of monobutyltin and dibutyltin removal. In order to protect fungal cells from oxidative stress caused by DBT presence, vitamin C (20 mg l^-1) was applied. Supplementation with ascorbic acid (AA) resulted in a 3-fold acceleration of MBT removal during the first 7 h of incubation. Using the HPLC-MS/MS technique, a quantitative analysis of malondialdehyde (MDA), a marker of oxidative stress, was performed. In the AA presence, a decrease in the MDA amount (about 45%) was observed compared to the case with fungal cells exposed to DBT alone.