Isolation and identification of Aeromonas caviae strain KS-1 as TBTC- and lead-resistant estuarine bacteria

Simultaneous removal of ternary heavy metal ions by a newly isolated Microbacterium paraoxydans strain VSVM IIT(BHU) from coal washery effluent

In the present work, the removal of Cr (VI), Cd (II) and Pb (II) at 50 mg/L of each metal ion concentration was investigated by Microbacterium paraoxydans strain VSVM IIT(BHU). The heavy metal binding on the bacterial cell surface was confirmed through X-ray photoelectron spectroscopy and energy dispersive X-ray. X-ray photoelectron spectroscopy analysis also confirmed the reduction of Cr (VI) to Cr (III). Heavy metal removal dynamics was investigated by evaluating dimensionless, and the value of N_k (9.49 × 10^-3, 9.92 × 10^-3 and 1.23 × 10^-2 for Cr (VI), Cd (II) and Pb (II) ions) indicated that the removal of heavy metals by bacterial isolate was mixed diffusion and transfer controlled. It was found that both the experimental and predicted values for isolated bacterial strain coincided with each other with a good R² value in the L-M Algorithm range of 0.94-0.98 for the ternary metal ion system. The bacterial isolate presented a maximum heavy metal ion removal efficiency of 91.62% Cr (VI), 89.29% Pb (II), and 83.29% Cd (II) at 50 mg/L.

Bacterial tolerance strategies against lead toxicity and their relevance in bioremediation application

Among heavy metals, lead (Pb) is a non-essential metal having a higher toxicity and without any crucial known biological functions. Being widespread, non-biodegradable and persistent in every sphere of soil, air and water, Pb is responsible for severe health and environmental issues, which need appropriate remediation measures. However, microbes inhabiting Pb-contaminated area are found to have evolved distinctive mechanisms to successfully thrive in the Pb-contaminated environment without exhibiting any negative effects on their growth and metabolism. The defensive strategies used by bacteria to ameliorate the toxic effects of lead comprise biosorption, efflux, production of metal chelators like siderophores and metallothioneins and synthesis of exopolysaccharides, extracellular sequestration and intracellular bioaccumulation. Lead remediation technologies by employing microbes may appear as potential advantageous alternatives to the conventional physical and chemical means due to specificity, suitability for applying in situ condition and feasibility to upgrade by genetic engineering. Developing strategies by designing transgenic bacterial strain having specific metal binding properties and metal chelating proteins or higher metal adsorption ability and using bacterial activity such as incorporating plant growth-promoting rhizobacteria for improved Pb resistance, exopolysaccharide and siderophores and metallothionein-mediated immobilization may prove highly effective for formulating bioremediation vis-a-vis phytoremediation strategies.

A comparative analysis of heavy metal bioaccumulation and functional gene annotation towards multiple metal resistant potential by Ochrobactrum intermedium BPS-20 and Ochrobactrum ciceri BPS-26

The present study describes the heavy metal bioaccumulation potential of Ochrobactrum intermedium BPS-20 and Ochrobactrum ciceri BPS-26. A total of 27 isolates were retrieved from the soils of industrial areas and these two were selected based on their maximum metal tolerance. They can resist up to 2400 mg/L and 2000 mg/L of Lead and 850 mg/L and 1200 mg/L of Nickel respectively. The atomic absorption spectroscopic analysis showed considerably good bioaccumulation by O. intermedium BPS-20 (85.34% and 74.87%) and O. ciceri BPS-26 (71.20% and 88.48%) for Lead and Nickel respectively. The growth rate studies also demonstrated no inhibitory effects of heavy metals in the medium. Further the SEM analysis showed the presence of extracellular polymeric substances around bacterial cells. Moreover, the functional gene annotation confirmed the presence of ATPase, ABC, and HoxN/HupN/NixA families of transporters. Thus, both the isolates provide a better solution for the removal of metal pollutants.

Bacterial resistance to lead: Chemical basis and environmental relevance

Natural bacterial isolates from heavily contaminated sites may evolve diverse tolerance strategies, including biosorption, efflux mechanism, and intracellular precipitation under the continually increased stress of toxic lead (Pb) from anthropogenic activities. These strategies utilize a large variety of functional groups in biological macromolecules (e.g., exopolysaccharides (EPSs) and metalloproteins) and inorganic ligands, including carboxyl, phosphate and amide groups, for capturing Pb. The amount and type of binding sites carried by biologically originated materials essentially determines their performance and potential for Pb removal and remediation. Many factors, e.g., metal ion radius, electronegativity, the shape of the cell surface sheath, temperature and pH, are thought to exert significant influences on the abovementioned interactions with Pb. Conclusively, understanding the chemical basis of Pb-binding in these bacteria can allow for the development of effective microbial Pb remediation technologies and further elucidation of Pb cycling in the environment.

Chromate detoxification potential of Staphylococcus sp. isolates from an estuary

Chromium (Cr) pollution is an emerging environmental problem. The present study was carried out to isolate Cr-resistant bacteria and characterize their Cr detoxification and resistance ability. Bacteria screened by exposure to chromate (Cr⁶⁺) were isolated from Mandovi estuary Goa, India. Two isolates expressed high resistance to Cr⁶⁺ (MIC ≥ 300 µg mL^-1), Cr³⁺ (MIC ≥ 900 µg mL^-1), other toxic heavy metals and displayed a pattern of resistance to cephalosporins and ß-lactams. Biochemical and 16 S rRNA gene sequence analysis indicated that both isolates tested belonged to the Staphylococcus genus and were closely related to S. saprophyticus and S. arlettae. Designated as strains NIOER176 and NIOER324, batch experiments demonstrated that both removed 100% of 20 and 50 µg mL^-1 Cr⁶⁺ within 4 and 10 days, respectively. The rate of reduction in both peaked at 0.260 µg mL^-1 h^-1. ATP-binding cassette (ABC) transporter gene involved in transport of a variety of substrates including efflux of toxicants was present in strain NIOER176. Through SDS-PAGE analysis, whole-cell proteins extracted from both strains indicated chromium-induced specific induction and up-regulation of 24 and 40 kDa proteins. Since bacterial ability to ameliorate Cr⁶⁺ is of practical significance, these findings demonstrate strong potential of some estuarine bacteria to detoxify Cr⁶⁺ even when its concentrations far exceed the concentrations reported from many hazardous effluents and chromium contaminated natural habitats. Such potential of salt tolerant bacteria would help in Cr⁶⁺ bioremediation efforts.

Co-selection of multi-antibiotic resistance in bacterial pathogens in metal and microplastic contaminated environments: An emerging health threat

Misuse/over use of antibiotics increases the threats to human health since this is a main reason behind evolution of antibiotic resistant bacterial pathogens. However, metals such as mercury, lead, zinc, copper and cadmium are accumulating to critical concentration in the environment and triggering co-selection of antibiotic resistance in bacteria. The co-selection of metal driven antibiotic resistance in bacteria is achieved through co-resistance or cross resistance. Metal driven antibiotic resistant determinants evolved in bacteria and present on same mobile genetic elements are horizontally transferred to distantly related bacterial human pathogens. Additionally, in marine environment persistent pollutants like microplastics is recognized as a vector for the proliferation of metal/antibiotics and human pathogens. Recently published research confirmed that horizontal gene transfer between phylogenetically distinct microbes present on microplastics is much faster than free living microbes. Therefore, microplastics act as an emerging hotspot for metal driven co-selection of multidrug resistant human pathogens and pose serious threat to humans which do recreational activities in marine environment and ingest marine derived foods. Therefore, marine environment co-polluted with metal, antibiotics, human pathogens and microplastics pose an emerging health threat globally.

A facile approach for surface alteration of Pseudomonas putida I3 by supplying K2SO4 into growth medium: Enhanced removal of Pb(II) from aqueous solution

A new sight of obtaining a high efficient biosorbent by supplying specific salts into bacterial growth medium was investigated in this study for Pb(II). Among a series of salts including Na₂SO₄, Na₂S₂O₃, KCl, and K₂SO₄, the highest Pb(II) removal efficiency was observed by psychrotrophilic Pseudomonas putida I3 grown in the presence of 30g/L K₂SO₄ (KSI3-30) with biosorption capacity of 62.89mg/g under cold condition (15°C), which was increased by 42.35% as compared to control (without any additive, RI3). This stimulation effect was ascribed to the increase of potassium and sulfur containing groups on KSI3-30 surface via metabolic dependent ways. The probable mechanism for Pb(II) adsorption was ion-exchange and chemical complexation. The thermal and kinetic data well fitted to Langmuir adsorption model and pseudo-second order and intraparticle diffusion kinetic model. Good recyclability and effectively dealing with real wastewater suggested KSI3-30 was a promising biosorbent for Pb-contaminated wastewater treatment.

Metallothionein assisted periplasmic lead sequestration as lead sulfite by Providencia vermicola strain SJ2A

Lead resistant Providencia vermicola strain SJ2A was isolated from the waste of a battery manufacturing industry which could tolerate upto 3.0mM lead nitrate in the minimal medium. Interestingly, this isolate showed presence of a plasmid borne metallothionein gene, bmtA that matched significantly (96%) with that of Pseudomonas aeruginosa. Scanning electron micrographs of bacterial cells exposed to lead revealed a unique alteration in the cell morphology from rods to long inter-connected filaments. On the other hand, electron dispersive X-ray spectroscopy (EDX) clearly indicated no significant lead adsorption therefore, we speculated intracellular sequestration in this bacterial strain. Transmission electron micrographs of the bacterial cells exposed to lead evidently demonstrated periplasmic sequestration of lead which was also supported by Fourier transformed infrared spectroscopic (FTIR) analysis. The bacterium internalised 155.12mg Pb²⁺/g biomass as determined by atomic absorption spectroscopy. Subsequently, the accumulated lead was identified as lead sulfite by X-ray diffraction studies. Therefore P. vermicola strain SJ2A has potential to bioremediate lead contaminated environmental sites.

A Bacillus sp. isolated from sediments of the Sarno River mouth, Gulf of Naples (Italy) produces a biofilm biosorbing Pb(II)

A Pb-resistant bacterial strain (named hereinafter Pb15) has been isolated from highly polluted marine sediments at the Sarno River mouth, Italy, using an enrichment culture to which Pb(II) 0.48mmoll(-1) were added. 16S rRNA gene sequencing (Sanger) allowed assignment of the isolate to the genus Bacillus, with Bacillus pumilus as the closest species. The isolate is resistant to Pb(II) with a minimum inhibitory concentration (MIC) of 4.8mmoll(-1) and is also resistant to Cd(II) and Mn(II) with MIC of 2.22mmoll(-1) and 18.20mmoll(-1), respectively. Inductively coupled plasma atomic emission spectrometry (ICP-AES) showed that Pb inoculated in the growth medium is absorbed by the bacterial cells at removal efficiencies of 31.02% and 28.21% in the presence of 0.48mmoll(-1) or 1.20mmoll(-1) Pb(II), respectively. Strain Pb15 forms a brown and compact biofilm when grown in presence of Pb(II). Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS) confirm that the biofilm contains Pb, suggesting an active biosorption of this metal by the bacterial cells, sequestering 14% of inoculated Pb as evidenced by microscopic analyses. Altogether, these observations support evidence that strain Pb15 has potentials for being used in bioremediation of its native polluted sediments, with engineering solutions to be found in order to eliminate the adsorbed Pb before replacement of sediments in situ.

Tributyltin chloride (TBTCl)-enhanced exopolysaccharide and siderophore production in an estuarine Alcaligenes faecalis strain

Tributyltin chloride (TBTCl) has been used extensively as an antifouling agent in ship paints, which results in the contamination of aquatic sites. These contaminated sites serve as enrichment areas for TBTCl-resistant bacterial strains. One TBTCl-resistant bacterial strain was isolated from the sediments of Zuari estuary, Goa, India, which is a major hub of various ship-building activities. Based on biochemical characteristics and 16S rDNA sequence analysis, this bacterial strain was identified as Alcaligenes faecalis and designated as strain SD5. It could degrade ≥3 mM TBTCl by using it as a sole carbon source and transform it into the less toxic dibutyltin chloride, which was confirmed by nuclear magnetic resonance and mass spectroscopy. Interestingly, this bacterial strain also showed enhanced exopolysaccharide and siderophore production when cells were exposed to toxic levels of TBTCl, suggesting their involvement in conferring resistance to this antifouling biocide as well as degradative capability respectively.

Biotransformation of Tributyltin chloride by Pseudomonas stutzeri strain DN2

A bacterial isolate capable of utilizing tributyltin chloride (TBTCl) as sole carbon source was isolated from estuarine sediments of west coast of India and identified as Pseudomonas stutzeri based on biochemical tests and Fatty acid methyl ester (FAME) analysis. This isolate was designated as strain DN2. Although this bacterial isolate could resist up to 3 mM TBTCl level, it showed maximum growth at 2 mM TBTCl in mineral salt medium (MSM). Pseudomonas stutzeri DN2 exposed to 2 mM TBTCl revealed significant alteration in cell morphology as elongation and shrinkage in cell size along with roughness of cell surface. FTIR and NMR analysis of TBTCl degradation product extracted using chloroform and purified using column chromatography clearly revealed biotransformation of TBTCl into Dibutyltin dichloride (DBTCl₂) through debutylation process. Therefore, Pseudomonas stutzeri strain DN2 may be used as a potential bacterial strain for bioremediation of TBTCl contaminated aquatic environmental sites.