Metal binding properties of the EPS produced by Halomonas sp. TG39 and its potential in enhancing trace element bioavailability to eukaryotic phytoplankton

Genetic Adaptations and Mechanistic Insights Into Bacterial Bioremediation in Ecosystems

Metal pollution poses significant threats to the ecosystem and human health, demanding effective remediation strategies. Bioremediation, which leverages the unique metal-resistant genes found in bacteria, offers a cost-effective and efficient solution to heavy metal contamination. Genes such as Cad, Chr, Cop, and others provide pathways to improve the detoxification of the ecosystem. Through multiple techniques, genetic engineering makes bacterial genomes more capable of improving metal detoxification; nonetheless, there are still unanswered questions regarding the nature of new metal-resistant genes. This article examines bacteria's complex processes to detoxify toxic metals, including biosorption, bioaccumulation, bio-precipitation, and bioleaching. It also explores essential genes, proteins, signaling mechanisms, and bacterial biomarkers involved in breaking toxic metals.

Mechanism and application of bacterial exopolysaccharides: An advanced approach for sustainable heavy metal abolition from soil

The escalation of heavy metal pollutants in soils and effluents, driven by industrialization and human activities, poses significant environmental and health risks. Conventional remediation methods are often costly and ineffective, prompting a shift towards sustainable alternatives such as biological treatments. Natural biosorbents, including microbial cells and their byproducts, have emerged as promising solutions. One such approach involves leveraging exopolysaccharides (EPS), complex high-molecular-weight biopolymers synthesized by microbes under environmental stress conditions. EPS are intricate organic macromolecules comprising proteins, polysaccharides, uronic acids, humic compounds, and lipids, either located within microbial cells or secreted into their surroundings. Their anionic functional groups enable efficient electrostatic binding of cationic heavy metals, making EPS effective biosorbents for soil remediation. This review thoroughly explores the pivotal role of bacterial EPS in the removal of heavy metals, focusing on EPS biosynthesis mechanisms, the dynamics of interaction with heavy metals, and case studies that illustrate their effectiveness in practical remediation strategies. By highlighting these aspects, the review underscores the innovation and practical implications of EPS-based bioremediation technologies, demonstrating their potential to address critical environmental challenges effectively while paving the way for sustainable environmental management practices. Key findings reveal that EPS exhibit robust metal-binding capacities, facilitated by their anionic functional groups, thereby offering a promising solution for mitigating metal pollution in diverse environmental matrices.

Production of exopolysaccharide from Klebsiella oxytoca: Rheological, emulsifying, biotechnological properties, and bioremediation applications

Bacteria can synthesize a broad spectrum of multifunctional polysaccharides including extracellular polysaccharides (EPS). Bacterial EPS can be utilized in the food, pharmaceutical, and biomedical areas owing to their physical and rheological properties in addition to generally presenting low toxicity. From an ecological viewpoint, EPS are biodegradable and environment compatible, offering several advantages over synthetic compounds. This study investigated the EPS produced by Klebsiella oxytoca (KO-EPS) by chemically characterizing and evaluating its properties. The monosaccharide components of the KO-EPS were determined by HPLC coupled with a refractive index detector and GC-MS. The KO-EPS was then analyzed by methylation analysis, FT-IR and NMR spectroscopy to give a potential primary structure. KO-EPS demonstrated the ability to stabilize hydrophilic emulsions with various hydrophobic compounds, including hydrocarbons and vegetable and mineral oils. In terms of iron chelation capacity, the KO-EPS could sequester 41.9 % and 34.1 % of the most common iron states, Fe2+ and Fe3+, respectively. Moreover, KO-EPS exhibited an improvement in the viscosity of aqueous dispersion, being proportional to the increase in its concentration and presenting a non-Newtonian pseudoplastic flow behavior. KO-EPS also did not present a cytotoxic effect indicating that the KO-EPS could have potential applications as a natural thickener, bioemulsifier, and bioremediation agent.

Comprehensive review on recent trends and perspectives of natural exo-polysaccharides: Pioneering nano-biotechnological tools

Exopolysaccharides (EPSs), originating from various microbes, and mushrooms, excel in their conventional role in bioremediation to showcase diverse applications emphasizing nanobiotechnology including nano-drug carriers, nano-excipients, medication and/or cell encapsulation, gene delivery, tissue engineering, diagnostics, and associated treatments. Acknowledged for contributions to adsorption, nutrition, and biomedicine, EPSs are emerging as appealing alternatives to traditional polymers, for biodegradability and biocompatibility. This article shifts away from the conventional utility to delve deeply into the expansive landscape of EPS applications, particularly highlighting their integration into cutting-edge nanobiotechnological methods. Exploring EPS synthesis, extraction, composition, and properties, the discussion emphasizes their structural diversity with molecular weight and heteropolymer compositions. Their role as raw materials for value-added products takes center stage, with critical insights into recent applications in nanobiotechnology. The multifaceted potential, biological relevance, and commercial applicability of EPSs in contemporary research and industry align with the nanotechnological advancements coupled with biotechnological nano-cleansing agents are highlighted. EPS-based nanostructures for biological applications have a bright future ahead of them. Providing crucial information for present and future practices, this review sheds light on how eco-friendly EPSs derived from microbial biomass of terrestrial and aquatic environments can be used to better understand contemporary nanobiotechnology for the benefit of society.

Acclimation of microbial communities to low and moderate salinities in anaerobic digestion

In recent years anaerobic digestion (AD) has been investigated as suitable biotechnology to treat wastewater at elevated salinities. However, when starting up AD reactors with inocula that are not adapted to salinity, low concentrations of sodium (Na+) in the influent can already cause disintegration of microbial aggregates and wash-out. This study investigated biomass acclimation to 5 g Na+/L of two different non-adapted inocula in two lab-scale hybrid expanded granular sludge bed (EGSB)-anaerobic filter (AF) reactors fed with synthetic wastewater. After an initial biomass disintegration, new aggregates were formed relatively fast (i.e., after 95 days of operation), indicating microbial community adaptation. The newly formed microbial aggregates accumulated Na+ at the expense of calcium (Ca2+), but this did not hamper biomass retention or process performance. The hybrid reactor configuration, including a pumice stone filter in the upper section, and the low up-flow velocities applied, were key features for retaining the biomass within the system. This reactor configuration can be easily applied and represents a low-cost alternative for acclimating biomass to saline effluents, even in existing digesters. When the acclimated biomass was transferred from EGSB to an up-flow anaerobic sludge blanket (UASB) reactor configuration also fed with saline synthetic wastewater, more dense aggregates in the form of granules were obtained. The performances of the UASB inoculated with the acclimated biomass were comparable to another reactor seeded with saline-adapted granular sludge from a full-scale plant. Regardless of the inoculum origin, a defined core microbiome of Bacteria (Thermovirga, Bacteroidetes vadinHA17, Blvii28 wastewater-sludge group, Mesotoga, and Synergistaceae) and Archaea (Methanosaeta and Methanobacterium) was detected, highlighting the importance of these microbial groups in developing halotolerance and maintaining AD process stability.

"AMP plus": Immunostimulant-Inspired Design Based on Chemotactic Motif-(PhHAhPH)n

Ability to stimulate antimicrobial immunity has proven to be a useful therapeutic strategy in treating infections, especially in the face of increasing antibiotic resistance. Natural antimicrobial peptides (AMPs) exhibiting immunomodulatory functions normally encompass complex activities, which make it difficult to optimize their therapeutic benefits. Here, a chemotactic motif was harnessed as a template to design a series of AMPs with immunostimulatory activities plus bacteria-killing activities ("AMP plus"). An amphipathic peptide ((PhHAhPH)n) was employed to improve the antimicrobial impact and expand the therapeutic potential of the chemotactic motif that lacked obvious bacteria-killing properties. A total of 18 peptides were designed and evaluated for their structure-activity relationships. Among the designed, KWH2 (1) potently killed bacteria and exhibited a narrow antimicrobial spectrum against Gram-negative bacteria and (2) activated macrophages (i.e., inducing Ca2+ influx, cell migration, and reactive oxygen species production) as a macrophage chemoattractant. Membrane permeabilization is the major antimicrobial mechanism of KWH2. Furthermore, the mouse subcutaneous abscess model supported the dual immunomodulatory and antimicrobial potential of KWH2 in vivo. The above results confirmed the efficiency of KWH2 in treating bacterial infection and provided a viable approach to develop immunomodulatory antimicrobial materials with desired properties.

Sustainable production of bioemulsifiers, a critical overview from microorganisms to promising applications

Microbial bioemulsifiers are molecules of amphiphilic nature and high molecular weight that are efficient in emulsifying two immiscible phases such as water and oil. These molecules are less effective in reducing surface tension and are synthesized by bacteria, yeast and filamentous fungi. Unlike synthetic emulsifiers, microbial bioemulsifiers have unique advantages such as biocompatibility, non-toxicity, biodegradability, efficiency at low concentrations and high selectivity under different conditions of pH, temperature and salinity. The adoption of microbial bioemulsifiers as alternatives to their synthetic counterparts has been growing in ongoing research. This article analyzes the production of microbial-based emulsifiers, the raw materials and fermentation processes used, as well as the scale-up and commercial applications of some of these biomolecules. The current trend of incorporating natural compounds into industrial formulations indicates that the search for new bioemulsifiers will continue to increase, with emphasis on performance improvement and economically viable processes.

Potential functions and applications of diverse microbial exopolysaccharides in marine environments

Exopolysaccharides (EPSs) from microorganisms are essential harmless natural biopolymers used in applications including medications, nutraceuticals and functional foods, cosmetics, and insecticides. Several microbes can synthesize and excrete EPSs with chemical properties and structures that make them suitable for several important applications. Microbes secrete EPSs outside their cell walls, as slime or as a "jelly" into the extracellular medium. These EPS-producing microbes are ubiquitous and can be isolated from aquatic and terrestrial environments, such as freshwater, marine water, wastewater, and soils. They have also been isolated from extreme niches like hot springs, cold waters, halophilic environments, and salt marshes. Recently, microbial EPSs have attracted interest for their applications such as environmental bio-flocculants because they are degradable and nontoxic. However, further efforts are required for the cost-effective and industrial-scale commercial production of microbial EPSs. This review focuses on the exopolysaccharides obtained from several extremophilic microorganisms, their synthesis, and manufacturing optimization for better cost and productivity. We also explored their role and applications in interactions between several organisms.

Biotechnological impacts of Halomonas: a promising cell factory for industrially relevant biomolecules

Extremophiles are the most fascinating life forms for their special adaptations and ability to offer unique extremozymes or bioactive molecules. Halophiles, the natural inhabitants of hypersaline environments, are one among them. Halomonas are the common genus of halophilic bacteria. To support growth in unusual environments, Halomonas produces various hydrolytic enzymes, compatible solutes, biopolymers like extracellular polysaccharides (EPS) and polyhydroxy alkaloates (PHA), antibiotics, biosurfactants, pigments, etc. Many of such molecules are being produced in large-scale bioreactors for commercial use. However, the prospect of the remaining bioactive molecules with industrial relevance is far from their application. Furthermore, the genetic engineering of the respective gene clusters could open up a new path to bio-prospect these molecules by overproducing their products through heterologous expression. The present survey on Halomonas highlights their ecological diversity, application potential of the their various industrially relevant biomolecules and impact of these biomolecules on respective fields.

Microwave-Assisted Enzymatic Extraction, Partial Characterization, and Antioxidant Potential of Polysaccharides from Sagittaria trifolia Tuber

Sagittaria trifolia tuber is an aquatic vegetable. In this work, microwave-assisted enzymatic extraction (MEE) was used to extract S. trifolia tuber polysaccharides (STTPs). Optimum conditions were complex enzyme of 2 %, liquid-to-solid ratio of 43 : 1 mL g^-1 , microwave power of 506 W, and time of 8 min, under which STTPs yield was 36.22±0.69 %, higher than those of other methods. STTPs were sulfated polysaccharides with sulfur valence of S⁶⁺ . STTPs comprised mannose, glucose, galactose, and arabinose at a mole ratio of 3.69 : 19.33 : 6.21 : 1.00, molecular weights of 3606 kDa and 149.6 kDa, particle size of 220 nm, and zeta potential of -5.02 mV. The surface of STTPs was full of bumps and holes, and abundant in O1s and non-functionalized C1s. STTPs would scavenge reactive oxygen species with advantage. It would provide an efficient MEE method to obtain antioxidant STTPs, also a clue for extracting polysaccharides from starch-rich crops.

Proteomic response of the marine ammonia-oxidising archaeon Nitrosopumilus maritimus to iron limitation reveals strategies to compensate for nutrient scarcity

Dissolved iron (Fe) is vanishingly low in the oceans, with ecological success conferred to microorganisms that can restructure their biochemistry to maintain high growth rates during Fe scarcity. Chemolithoautotrophic ammonia-oxidising archaea (AOA) are highly abundant in the oceans, constituting ~30% of cells below the photic zone. Here we examine the proteomic response of the AOA isolate Nitrosopumilus maritimus to growth-limiting Fe concentrations. Under Fe limitation, we observed a significant reduction in the intensity of Fe-dense ferredoxins associated with respiratory complex I whilst complex III and IV proteins with more central roles in the electron transport chain remain unchanged. We concomitantly observed an increase in the intensity of Fe-free functional alternatives such as flavodoxin and plastocyanin, thioredoxin and alkyl hydroperoxide which are known to mediate electron transport and reactive oxygen species detoxification, respectively. Under Fe limitation, we found a marked increase in the intensity of the ABC phosphonate transport system (Phn), highlighting an intriguing link between Fe and P cycling in N. maritimus. We hypothesise that an elevated uptake of exogenous phosphonates under Fe limitation may either supplement N. maritimus' endogenous methylphosphonate biosynthesis pathway - which requires Fe - or enhance the production of phosphonate-containing exopolysaccharides known to efficiently bind environmental Fe.

Genome analysis of a halophilic bacterium Halomonas malpeensis YU-PRIM-29T reveals its exopolysaccharide and pigment producing capabilities

Halomonas malpeensis strain YU-PRIM-29T is a yellow pigmented, exopolysaccharide (EPS) producing halophilic bacterium isolated from the coastal region. To understand the biosynthesis pathways involved in the EPS and pigment production, whole genome analysis was performed. The complete genome sequencing and the de novo assembly were carried out using Illumina sequencing and SPAdes genome assembler (ver 3.11.1) respectively followed by detailed genome annotation. The genome consists of 3,607,821 bp distributed in 18 contigs with 3337 protein coding genes and 53% of the annotated CDS are having putative functions. Gene annotation disclosed the presence of genes involved in ABC transporter-dependent pathway of EPS biosynthesis. As the ABC transporter-dependent pathway is also implicated in the capsular polysaccharide (CPS) biosynthesis, we employed extraction protocols for both EPS (from the culture supernatants) and CPS (from the cells) and found that the secreted polysaccharide i.e., EPS was predominant. The EPS showed good emulsifying activities against the petroleum hydrocarbons and its production was dependent on the carbon source supplied. The genome analysis also revealed genes involved in industrially important metabolites such as zeaxanthin pigment, ectoine and polyhydroxyalkanoate (PHA) biosynthesis. To confirm the genome data, we extracted these metabolites from the cultures and successfully identified them. The pigment extracted from the cells showed the distinct UV-Vis spectra having characteristic absorption peak of zeaxanthin (λmax 448 nm) with potent antioxidant activities. The ability of H. malpeensis strain YU-PRIM-29T to produce important biomolecules makes it an industrially important bacterium.

Cation exchange membrane behaviour of extracellular polymeric substances (EPS) in salt adapted granular sludge

This paper aims to elucidate the role of extracellular polymeric substances (EPS) in regulating anion and cation concentrations and toxicity towards microorganisms in anaerobic granular sludges adapted to low (0.22 M of Na⁺) and high salinity (0.87 M of Na⁺). The ion exchange properties of EPS were studied with a novel approach, where EPS were entangled with an inert binder (PVDF-HFP) to form a membrane and characterized in an electrodialysis cell. With a mixture of NaCl and KCl salts the EPS membrane was shown to act as a cation exchange membrane (CEM) with a current efficiency of ∼80%, meaning that EPS do not behave as ideal CEM. Surprisingly, the membrane had selectivity for transport of K⁺ compared to Na⁺ with a separation factor ( [Formula: see text] ) of 1.3. These properties were compared to a layer prepared from a model compound of EPS (alginate) and a commercial CEM. The alginate layer had a similar current efficiency (∼80%.), but even higher [Formula: see text] of 1.9, while the commercial CEM did not show selectivity towards K⁺ or Na⁺, but exhibited the highest current efficiency of 92%. The selectivity of EPS and alginate towards K⁺ transport has interesting potential applications for ion separation from water streams and should be further investigated. The anion repelling and cation binding properties of EPS in hydrated and dehydrated granules were further confirmed with microscopy (SEM-EDX, epifluorescence) and ion chromatography (ICP-OES, IC) techniques. Results of specific methanogenic activity (SMA) tests conducted with 0.22 and 0.87 M Na⁺ adapted granular sludges and with various monovalent salts suggested that ions which are preferentially transported by EPS are also more toxic towards methanogenic cells.

Biosynthesis of rhamnolipid by a Marinobacter species expands the paradigm of biosurfactant synthesis to a new genus of the marine microflora

BACKGROUND

In comparison to synthetically derived surfactants, biosurfactants produced from microbial culture are generally regarded by industry as being more sustainable and possess lower toxicity. One major class of biosurfactants are rhamnolipids primarily produced by Pseudomonas aeruginosa. Due to its pathogenicity rhamnolipid synthesis by this species is viewed as being commercially nonviable, as such there is a significant focus to identify alternative producers of rhamnolipids.

RESULTS

To achieve this, we phenotypically screened marine bacteria for biosurfactant production resulting in the identification of rhamnolipid biosynthesis in a species belonging to the Marinobacter genus. Preliminary screening showed the strain to reduce surface tension of cell-free supernatant to 31.0 mN m^-1. A full-factorial design was carried out to assess the effects of pH and sea salt concentration for optimising biosurfactant production. When cultured in optimised media Marinobacter sp. MCTG107b produced 740 ± 28.3 mg L^-1 of biosurfactant after 96 h of growth. Characterisation of this biosurfactant using both HPLC-MS and tandem MS showed it to be a mixture of different rhamnolipids, with di-rhamnolipid, Rha-Rha-C₁₀-C₁₀ being the most predominant congener. The strain exhibited no pathogenicity when tested using the Galleria mellonella infection model.

CONCLUSIONS

This study expands the paradigm of rhamnolipid biosynthesis to a new genus of bacterium from the marine environment. Rhamnolipids produced from Marinobacter have prospects for industrial application due to their potential to be synthesised from cheap, renewable feed stocks and significantly reduced pathogenicity compared to P. aeruginosa strains.

Magnesium and calcium ions: roles in bacterial cell attachment and biofilm structure maturation

The ubiquitous divalent cations magnesium and calcium are important nutrients required by bacteria for growth and cell maintenance. Multi-faceted roles are shown both in bacterial initial attachment and biofilm maturation. The effects of calcium and magnesium can be highlighted in physio-chemical interactions, gene regulation and bio-macromolecular structural modification, which lead to either promotion or inhibition of biofilms. This review outlines recent research addressing phenotypic changes and mechanisms undertaken by calcium and magnesium in affecting bacterial biofilm formation.

Characterization and mechanism of copper biosorption by a highly copper-resistant fungal strain isolated from copper-polluted acidic orchard soil

In this paper, a highly copper-resistant fungal strain NT-1 was characterized by morphological, physiological, biochemical, and molecular biological techniques. Physiological response to Cu(II) stress, effects of environmental factors on Cu(II) biosorption, as well as mechanisms of Cu(II) biosorption by strain NT-1 were also investigated in this study. The results showed that NT-1 belonged to the genus Gibberella, which exhibited high tolerance to both acidic conditions and Cu(II) contamination in the environment. High concentrations of copper stress inhibited the growth of NT-1 to various degrees, leading to the decreases in mycelial biomass and colony diameter, as well as changes in morphology. Under optimal conditions (initial copper concentration: 200 mg L^-1, temperature 28 °C, pH 5.0, and inoculum dose 10%), the maximum copper removal percentage from solution through culture of strain NT-1 within 5 days reached up to 45.5%. The biosorption of Cu(II) by NT-1 conformed to quasi-second-order kinetics and Langmuir isothermal adsorption model and was confirmed to be a monolayer adsorption process dominated by surface adsorption. The binding of NT-1 to Cu(II) was mainly achieved by forming polydentate complexes with carboxylate and amide group through covalent interactions and forming Cu-nitrogen-containing heterocyclic complexes via Cu(II)-π interaction. The results of this study provide a new fungal resource and key parameters influencing growth and copper removal capacity of the strain for developing an effective bioremediation strategy for copper-contaminated acidic orchard soils.

Growth and Toxin Production of Gambierdiscus spp. Can Be Regulated by Quorum-Sensing Bacteria

Gambierdiscus spp. are the major culprit responsible for global ciguatera fish poisoning (CFP). At present, the effects of microbiological factors on algal proliferation and toxin production are poorly understood. To evaluate the regulatory roles of quorum-sensing (QS) bacteria in the physiology of Gambierdiscus, co-culture experiments with screened QS strains were conducted in this study. Except for the growth-inhibiting effect from the strain Marinobacter hydrocarbonoclasticus, the algal host generally displayed much higher growth potential and toxin production ability with the existence of QS strains. In addition, Bacillus anthracis particularly exhibited a broad-spectrum growth enhancement effect on various Gambierdiscus types, as well as a remarkable influence on algal toxicity. The variations of algal physiological status, including growth rate, chlorophyll content, and responsive behaviors, are potential reasons for the observed positive or negative affection. This study suggests that QS bacteria regulate the algal growth and toxin production. Based on the evidence, we further speculate that QS bacteria may contribute to the site-specific distribution of CFP risk through regulating the algal host biomass and toxicity.

Exploiting Microbial Polysaccharides for Biosorption of Trace Elements in Aqueous Environments-Scope for Expansion via Nanomaterial Intervention

With pollution sounding high alarms all around us, there is an immediate necessity for remediation. In most cases, the remediation measures require further remediation-the anti-pollutants themselves cause pollution. In this correspondence, the search deepens towards natural biogenic components that can be used for bioremediation. Polysaccharide and biosorption have been themes in discussion for quite some time, where a slow decline in the enthusiasm in this area has been observed. This review revisits the importance of using polysaccharide based materials for biosorption. The need for polysaccharide-based nanocomposites, which hold better promise for greater deliverables, is emphasized as a means of rejuvenating the future perspectives in this area of application.

Microbial Extracellular Polymeric Substances (EPSs) in Ocean Systems

Microbial cells (i.e., bacteria, archaea, microeukaryotes) in oceans secrete a diverse array of large molecules, collectively called extracellular polymeric substances (EPSs) or simply exopolymers. These secretions facilitate attachment to surfaces that lead to the formation of structured 'biofilm' communities. In open-water environments, they also lead to formation of organic colloids, and larger aggregations of cells, called 'marine snow.' Secretion of EPS is now recognized as a fundamental microbial adaptation, occurring under many environmental conditions, and one that influences many ocean processes. This relatively recent realization has revolutionized our understanding of microbial impacts on ocean systems. EPS occur in a range of molecular sizes, conformations and physical/chemical properties, and polysaccharides, proteins, lipids, and even nucleic acids are actively secreted components. Interestingly, however, the physical ultrastructure of how individual EPS interact with each other is poorly understood. Together, the EPS matrix molecules form a three-dimensional architecture from which cells may localize extracellular activities and conduct cooperative/antagonistic interactions that cannot be accomplished efficiently by free-living cells. EPS alter optical signatures of sediments and seawater, and are involved in biogeomineral precipitation and the construction of microbial macrostructures, and horizontal-transfers of genetic information. In the water-column, they contribute to the formation of marine snow, transparent exopolymer particles (TEPs), sea-surface microlayer biofilm, and marine oil snow. Excessive production of EPS occurs during later-stages of phytoplankton blooms as an excess metabolic by product and releases a carbon pool that transitions among dissolved-, colloidal-, and gel-states. Some EPS are highly labile carbon forms, while other forms appear quite refractory to degradation. Emerging studies suggest that EPS contribute to efficient trophic-transfer of environmental contaminants, and may provide a protective refugia for pathogenic cells within marine systems; one that enhances their survival/persistence. Finally, these secretions are prominent in 'extreme' environments ranging from sea-ice communities to hypersaline systems to the high-temperatures/pressures of hydrothermal-vent systems. This overview summarizes some of the roles of exopolymer in oceans.

Bacterial Exopolysaccharide mediated heavy metal removal: A Review on biosynthesis, mechanism and remediation strategies

Heavy metal contamination has been recognized as a major public health risk, particularly in developing countries and their toxicological manifestations are well known. Conventional remediation strategies are either expensive or they generate toxic by-products, which adversely affect the environment. Therefore, necessity for an environmentally safe strategy motivates interest towards biological techniques. One of such most profoundly driven approach in recent times is biosorption through microbial biomass and their products. Extracellular polymeric substances are such complex blend of high molecular weight microbial (prokaryotic and eukaryotic) biopolymers. They are mainly composed of proteins, polysaccharides, uronic acids, humic substances, lipids etc. One of its essential constituent is the exopolysaccharide (EPS) released out of self defense against harsh conditions of starvation, pH and temperature, hence it displays exemplary physiological, rheological and physio-chemical properties. Its net anionic makeup allows the biopolymer to effectively sequester positively charged heavy metal ions. The polysaccharide has been expounded deeply in this article with reference to its biosynthesis and emphasizes heavy metal sorption abilities of polymer in terms of mechanism of action and remediation. It reports current investigation and strategic advancements in dealing bacterial cells and their EPS in diverse forms - mixed culture EPS, single cell EPS, live, dead or immobilized EPS. A significant scrutiny is also involved highlighting the existing challenges that still lie in the path of commercialization. The article enlightens the potential of EPS to bring about bio-detoxification of heavy metal contaminated terrestrial and aquatic systems in highly sustainable, economic and eco-friendly manner.

Effects of iron on growth, antioxidant enzyme activity, bound extracellular polymeric substances and microcystin production of Microcystis aeruginosa FACHB-905

Toxic cyanobacterial blooms have occurred in various water bodies during recent decades and made serious health hazards to plants, animals and humans. Iron is an important micronutrient for algal growth and recently, the concentration of which has increased remarkably in freshwaters. In this paper, the cyanobacterium Microcystis aeruginosa FACHB-905 was cultivated under non-iron (0μM), iron-limited (10μM) and iron-replete (100μM) conditions to investigate the effects of iron on growth, antioxidant enzyme activity, EPS and microcystin production. The results showed that algal cell density and chlorophyll-a content were maximal at the highest iron concentration. Antioxidant enzymes activity increased notably under all three conditions in the early stage of experiment, of which the SOD activity recovered soon from oxidative stress in 10μM group. The productions of some protein-like substances and humic acid-like substances of bound EPS were inhibited in iron-containing groups in the early stage of experiment while promoted after the adaptation period of Microcystis aeruginosa. Iron addition is a factor affecting the formation of cyanobacterial blooms through its impact on the content of LB-EPS and the composition of TB-EPS. The intracellular MC-LR concentration and the productivity potential of MC-LR were the lowest in 0μM group and highest in 10μM group. No obvious extracellular release of MC-LR was observed during the cultivation time. Therefore, iron addition can promote the physiological activities of M. aeruginosa, but a greater harm could be brought into environment under iron-limited (10μM) condition than under iron-replete (100μM) condition.

Sulfhydryl Binding Sites within Bacterial Extracellular Polymeric Substances

In this study, the concentration of sulfhydryl sites on bacterial biomass samples with and without extracellular polymeric substances (EPS) was measured in order to determine the distribution of sulfhydryl sites on bacteria. Three different approaches were employed for EPS removal from Pseudomonas putida, and the measured sulfhydryl concentrations on bacterial EPS molecules are independent of the EPS removal protocols used. Prior to EPS removal, the measured sulfhydryl sites within P. putida samples was 34.9 ± 9.5 μmol/g, and no sulfhydryl sites were detected after EPS removal, indicating that virtually all of the sulfhydryl sites are located on the EPS molecules produced by P. putida. In contrast, the sulfhydryl sites within the S. oneidensis samples increased from 32.6 ± 3.6 μmol/g to 51.9 ± 7.2 μmol/g after EPS removal, indicating that the EPS produced by S. oneidensis contained fewer sulfhydryl sites than those present on the untreated cells. This study suggests that the sulfhydryl concentrations on EPS molecules may vary significantly from one bacterial species to another, thus it is crucial to quantify the concentration of sulfhydryl sites on EPS molecules of other bacterial species in order to determine the effect of bacterial EPS on metal cycling in the environment.

Biosequestration of lead using Bacillus strains isolated from seleniferous soils and sediments of Punjab

The present study was conducted to isolate and explore bacterial strains with a potential to sequester lead (Pb) and tolerate other heavy metals from industrial effluents and sediments. Out of the six bacterial strains isolated from seleniferous sites of Punjab, three isolates (RS-1, RS-2, and RS-3) were screened out for further growth-associated lead sequestration and molecular characterization on the basis of their tolerance toward lead and other heavy metals. Biomass and cell-free supernatant were analyzed for lead contents using ICP-MS after growth-associated lead sequestration studies in tryptone soya broth (pH = 7.2 ± 0.2) under aerobic conditions at 37 °C temperature. Almost 82 % and 70 % divalent lead was sequestered in cell pellets of RS-1 and RS-3, respectively while only 45 % of lead was found in cell pellet of RS-2 in the first 24 h. However, significant biosequestration of lead was observed in RS-2 after 48 h of incubation with concomitant increase in biomass. Simultaneously, morphological, biochemical, and physiological characterization of selected strains was carried out. 16S rRNA gene sequence of these isolates revealed their phylogenetic relationship with class Bacillaceae, a low G + C firmicutes showing 98 % homology with Bacillus sp.