Bromoform Toxicity to Marine Microalgae: Studies using the Diatom Chaetoceros lorenzianus as a Model Organism.

Bromoform is the most prominent, relatively long-lived chlorination by-product in condenser effluents from seawater-based power plant cooling systems. There are few reports on the potential toxicity of this trihalomethane to marine phytoplankton. We investigated this using a marine diatom, Chaetoceros lorenzianus as the model organism. The study was conducted by exposing the diatom to bromoform concentrations 0, 50, 100, 150, 250, 500 and 1000 µg/L for exposure time of 3 and 24 h. The mode of action of bromoform was examined using endpoints which include chlorophyll a fluorescence, cell viability by SYTOX® green stain and genotoxicity by comet assay. The relative fluorescence unit and percent viability changed significantly at all concentrations in duration of study. The 24-h IC50 for viability and chlorophyll was estimated to be 255.6 µg/L and 343.5 µg/L, respectively. The tail DNA of 5-20% observed by comet assay indicated low-level DNA damage. Bromoform manages to target cell membrane and internal machinery, DNA and chlorophyll molecule of cell, leading to cause damage at multiple physiological levels. Based on the present data, the current discharge levels of bromoform 50-250 µg/L cause significant impact on the phytoplankton under investigation. However, the impact can be limited under actual field conditions wherein mixing of cooling water with natural water bodies is considered. Nevertheless, more studies are required to understand the toxicological response of organisms to bromoform, so that discharge levels can be continued to be kept within safe levels.

An evaluation of arsenic contamination status and its potential health risk assessment in villages of Nadia and North 24 Parganas, West Bengal, India.

The present study was conducted to evaluate the arsenic (As) contamination and possible associated health hazards to exposed population in four villages of two districts (Nadia and North 24 Parganas) of West Bengal, India. The study included two villages each from Nadia (Jaguli and Kugacchi) and North 24 Parganas (Chamta and Byaspur) districts. Groundwater, surface water, soil, rice grains and rice-based food samples were collected from these villages. The results revealed the presence of As in high concentrations in groundwater (35.00 to 186.00 µg L-1), surface water (30.00 to 61.00 µg L-1), soil (46.17 to 66.00 mg kg-1), rice grains (0.017 to 1.27 µg g-1) and rice-based food products (0.012 to 0.40 µg g-1). The maximum As levels were recorded in all types of samples collected from Kugacchi village. The rice grain samples included high-yielding and local varieties, and the level of As in high-yielding varieties was found to be higher (0.72 to 1.27 µg g-1) than in local varieties (0.25 to 1.06 µg g-1). The data of As concentrations was used for understanding the hazard quotient (HQ) and incremental lifetime cancer risk (ILCR) to the As-exposed population, and significant non-carcinogenic and carcinogenic risks were revealed considering consumption of rice grains at 400 g per day. The study demonstrates the severity of As contamination in the surveyed villages, which may pose a hindrance to attainment of sustainable development goals (SDGs) by 2030 and proposes the implementation of requisite safety measures.

Response of green mussels (Perna viridis) subjected to chlorination: investigations by valve movement monitoring.

Perna viridis Linnaeus (1758) is a major foulant in the cooling water systems of electric power stations located on the East coast of India. Though chlorination is considered an effective fouling control measure, the strategy may fail in the case of bivalve mussels, due to the ability of the mussels to close their shells and still survive for extended periods of time. In a given power station, continuous low dose (exomotive) chlorination (0.2 ± 0.1 mg l-1) is practiced to control biofouling. Laboratory experiments were carried out to assess the mortality and valve movement response of Perna viridis exposed to chlorine, using a Mosselmonitor®. All size groups tested showed progressive reduction in valve opening upon chlorination. However, continuous dosing of chlorine concentration as high as 1.0 mg l-1 was required for sustained and complete valve closure response in this mussel. At lower concentration (0.7 mg l-1), the mussels were able to open their shells and feed. Sustained valve closure resulted in physiological stress to the mussels due to reduced feeding, subsequently leading to death. Time to 100% mortality was dependent on the size of the mussels. At 1.0 mg l-1 chlorine residual, smaller size group (30-50 mm) mussels showed 100% mortality in 79.3 h, while larger groups (50-70 mm and 70-90 mm) took 152 h and 243 h, respectively. Frequency of valve opening was high in smaller size group mussels (30-50 mm), compared with larger groups (70-90 mm). Even though the time taken for killing was size-dependent, frequency of valve opening and time period between successive openings were found to be characteristic of individual mussels. The observations provide new insight into the response of bivalve mussels to continuous chlorination in the context of biofouling control and point to the need to adopt pragmatic strategies to prevent mussel spat settlement rather than killing of adult mussels, thereby reducing environmental burden due to chlorine residuals. Usage of target-specific biocidal strategies (intermittent/pulse dosing) or alternative biocides (chlorine dioxide) may help mitigate green mussel fouling in tropical cooling water systems.

Multimarker study of the effects of antifouling biocide on benthic organisms: results using Perna viridis as candidate species.

Toxic effects of continuous low dose application of the antifouling biocide chlorine on marine benthic organisms were monitored using transplanted green mussels (Perna viridis) and a suite of biomarkers. Caged mussels were deployed in chlorinated and non-chlorinated sections of the cooling system of an operating electric power plant. Biomarkers indicative of general stress, oxidative stress (superoxide dismutase and catalase), and DNA integrity, along with expression of stress proteins, were studied to assess the effects. Deterioration in condition index with corresponding increase in DNA strand breaks was indicative of chlorine stress. Superoxide dismutase enzyme did not show any particular trend, but catalase activity was high during the initial days of exposure at the chlorinated site; later, it became almost equal to that at the control site. Similarly, expressions of stress proteins (HSP60, HSP70, HSP22, GSTS1, and CYP4) showed bell-shaped pattern during the period of study. Positive correlation among the endpoints indicated the utility of the multimarker approach to monitor the effects of continuous low dose chlorination on mussels.

Comparative toxicological effects of two antifouling biocides on the marine diatom Chaetoceros lorenzianus: Damage and post-exposure recovery.

Antifouling biocides are commonly used in coastal electric power stations to prevent biofouling in their condenser cooling systems. However, the environmental impact of the chemical biocides is less understood than the thermal stress effects caused by the condenser effluents. In this study, Chaetoceros lorenzianus, a representative marine diatom, was used to analyse the toxicity of two antifouling biocides, chlorine and chlorine dioxide. The diatom cells were subjected to a range of concentrations of the biocides (from 0.05 to 2mg/L, as total residual oxidants, TRO) for contact time of 30min. They were analysed for viability, genotoxicity, chlorophyll a and cell density endpoints. The cells were affected at all concentrations of the biocides (0.05-2mg/L), showing dose-dependent decrease in viability and increase in DNA damage. The treated cells were later incubated in filtered seawater devoid of biocide to check for recovery. The cells were able to recover in terms of overall viability and DNA damage, when they had been initially treated with low concentrations of the biocides (0.5mg/L of Cl2 or 0.2mg/L of ClO2). Chlorophyll a analysis showed irreparable damage at all concentrations, while cell density showed increasing trend of reduction, if treated above 0.5mg/L of Cl2 and 0.2mg/L of ClO2. The data indicated that in C. lorenzianus, cumulative toxic effects and recovery potential of ClO2 up to 0.2mg/L were comparable with those of Cl2, up to 0.5mg/L concentration in terms of the studied endpoints. The results indicate that at the biocide levels currently being used at power stations, recovery of the organism is feasible upon return to ambient environment. Similar studies should be carried out on other planktonic and benthic organisms, which will be helpful in the formulation of future guidelines for discharge of upcoming antifouling biocides such as chlorine dioxide.

Chlorine dioxide as an alternative antifouling biocide for cooling water systems: Toxicity to larval barnacle Amphibalanus reticulatus (Utinomi).

Chlorine dioxide (ClO2) is seen as an effective alternative to chlorine, which is widely used as an antifouling biocide. However, data on its efficacy against marine macrofoulants is scanty. In this study, acute toxicity of ClO2 to larval forms of the fouling barnacle Amphibalanus reticulatus was investigated. ClO2 treatment at 0.1mg/L for 20min elicited 45-63% reduction in naupliar metamorphosis, 70% inhibition of cyprid settlement and 80% inhibition of metamorphosis to juveniles. Increase in concentration to 0.2mg/L did not result in any significant difference in the settlement inhibition or metamorphosis. Treatment with 0.2mg/L of ClO2 elicited substantial reduction in the settlement of barnacle larvae compared to control. The study indicates the possibility of using ClO2 as an alternative antifouling biocide in power plant cooling water systems. However, more work needs to be done on the environmental effects of such switchover, which we are currently undertaking.

Chlorination induced damage and recovery in marine diatoms: Assay by SYTOX® Green staining.

Phytoplankton entrained into cooling water systems of coastal power stations are subjected to acute chemical stress due to biocides (chlorine) used for biofouling control. They are subsequently released into the environment, where they may survive/recover or succumb. Experiments were conducted to evaluate the susceptibility of a centric (Chaetoceros lorenzianus) and pennate (Navicula sp.) diatom to in-plant administered concentrations of chlorine (0.2-0.5mg/L, TRO). Viability of cells exposed to chlorine was assessed by SYTOX® Green fluorimetry and was compared with other conventional end points like total cell counts, chlorophyll a content and cellular autofluorescence. Results showed a concentration-dependant reduction in viability, chlorophyll a and autofluorescence. C. lorenzianus cells were more susceptible to chlorine compared to Navicula sp. SYTOX® Green staining appears to be a sensitive method to assess chlorine-induced damages. The data show that in-use levels of chlorination can potentially impact entrained organisms; however, they can recover when returned to coastal waters.

A fence that eats the weed: Alginate lyase immobilization on ultrafiltration membrane for fouling mitigation and flux recovery.

Polysaccharide fouling poses a significant challenge in the widespread application of membrane filtration for water purification. In order to mitigate the problem, a polysaccharide-degrading enzyme alginate lyase (Alg L; EC 4.2.2.3) was successfully immobilized on cellulose acetate ultrafiltration membrane using a dead-end filtration unit. Attenuated total reflectance Fourier transform infrared microscopy confirmed covalent linkage of the Alg L to the membrane. HPLC and Alg L activity studies confirmed that Alg L in immobilized form was enzymatically active. Even after 21 d, Alg L in immobilized form retained 80% of its original activity, compared to its free counterpart, which retained only 20% of its original activity. In fouling experiments using tap water containing 50 mg L-1 alginate, a simple backwash could remove the fouling on Alg L immobilized membrane, but not that on the control membrane. Atomic force microscopic analysis and bright field microscopic images of the fouled test membrane after backwash showed significant removal of fouling, while fouling on the control membrane remained largely intact. The immobilized Alg L remained active even after 10 runs of fouling-backwash cycle. The present antifouling technology using immobilized enzyme is suitable for keeping ultrafiltration membranes clean without the use of toxic chemical biocides.

Chlorination-induced genotoxicity in the mussel Perna viridis: assessment by single cell gel electrophoresis (comet) assay.

Mussels are important fouling organisms in the cooling water systems of coastal power plants. Continuous low-dose chlorination (CLDC) is being practiced as an effective method to control mussel biofouling in power plant cooling water systems. CLDC effectively controls mussel fouling by discouraging larval settlement rather than by killing the larvae or adults. Mussels are an integral part of the natural benthic community in the receiving water body where the coolant water is discharged. Hence, from a toxicological point of view, they can serve as both target and non-target organisms. Previous researchers have indicated that chlorine residual, rather than elevated temperature, can be the major stress factor in the effluents released from coastal power plants. However, very little data are available on the sub-lethal effects of low level chlorination on representative benthic fauna. In this study, we used native and transplanted mussels (Perna viridis) to study lethal and sub-lethal effects of chlorination in the cooling water circuit of an operating power plant. Experiments involving comet assay suggested that CLDC can cause DNA damage in treated mussels. However, activation of DNA repair appeared to get initiated after the accrued damage reached a threshold. The results indicate that, at chlorine residual levels observed at the discharge point, exposure to chlorinated effluents is unlikely to cause significant genetic damage to mussels in the recipient water body.

Protein as chemical cue: non-nutritional growth enhancement by exogenous protein in Pseudomonas putida KT2440.

Research pertaining to microbe-microbe and microbe-plant interactions has been largely limited to small molecules like quorum sensing chemicals. However, a few recent reports have indicated the role of complex molecules like proteins and polysaccharides in microbial communication. Here we demonstrate that exogenous proteins present in culture media can considerably accelerate the growth of Pseudomonas putida KT2440, even when such proteins are not internalized by the cells. The growth enhancement is observed when the exogenous protein is not used as a source of carbon or nitrogen. The data show non-specific nature of the protein inducing growth; growth enhancement was observed irrespective of the protein type. It is shown that growth enhancement is mediated via increased siderophore secretion in response to the exogenous protein, leading to better iron uptake. We highlight the ecological significance of the observation and hypothesize that exogenous proteins serve as chemical cues in the case of P.putida and are perceived as indicator of the presence of competitors in the environment. It is argued that enhanced siderophore secretion in response to exogenous protein helps P.putida establish numerical superiority over competitors by way of enhanced iron assimilation and quicker utilization of aromatic substrates.

Endogenously triggered electrospun fibres for tailored and controlled antibiotic release.

The study was aimed at assessing the potential of enzyme-embedded antibiotic-releasing polycaprolactone (PCL)-based electrospun fibres for tunable drug delivery. This was attempted by incorporation of gentamicin sulphate (GS) in the biocompatible polymer (PCL) matrix, with the degradation of the matrix being ensured by co-impregnating a polymer-degrading enzyme (lipase). Single phase solutions were obtained by hydrophobic ion pairing of GS and surfactant coating of lipase with an anionic surfactant, docusate sodium salt Aerosol OT (AOT). By electrospinning the solution, we could produce PCL fibres containing 11% (w/w) GS-AOT and 28 U (w/w) lipase-AOT. However, sustained release of GS was not obtained. FESEM analysis showed that the fibres did not undergo the expected degradation. Subsequent experiments with unmodified lipase gave satisfactory results; the polymer underwent degradation displaying characteristic perforations in the fibres, suggestive of 'endo-attack'. By modulating the concentrations of lipase (1 to 28 U, w/w), we could obtain GS release rates that varied from 0.53 to 32 mg/ml/d. Accordingly, the lifetime of the fibres could be tuned (10 h to 25 days). The fibres showed excellent antibacterial activity against Staphylococcus aureus throughout their lifetime.

Disruption of microbial biofilms by an extracellular protein isolated from epibiotic tropical marine strain of Bacillus licheniformis.

BACKGROUND: Marine epibiotic bacteria produce bioactive compounds effective against microbial biofilms. The study examines antibiofilm ability of a protein obtained from a tropical marine strain of Bacillus licheniformis D1. METHODOLOGY/PRINCIPAL FINDINGS: B. licheniformis strain D1 isolated from the surface of green mussel, Perna viridis showed antimicrobial activity against pathogenic Candida albicans BH, Pseudomonas aeruginosa PAO1 and biofouling Bacillus pumilus TiO1 cultures. The antimicrobial activity was lost after treatment with trypsin and proteinase K. The protein was purified by ultrafiltration and size-exclusion chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis revealed the antimicrobial agent to be a 14 kDa protein designated as BL-DZ1. The protein was stable at 75°C for 30 min and over a pH range of 3.0 to 11.0. The sequence alignment of the MALDI-fingerprint showed homology with the NCBI entry for a hypothetical protein (BL00275) derived from B. licheniformis ATCC 14580 with the accession number gi52082584. The protein showed minimum inhibitory concentration (MIC) value of 1.6 µg/ml against C. albicans. Against both P. aeruginosa and B. pumilus the MIC was 3.12 µg/ml. The protein inhibited microbial growth, decreased biofilm formation and dispersed pre-formed biofilms of the representative cultures in polystyrene microtiter plates and on glass surfaces. CONCLUSION/SIGNIFICANCE: We isolated a protein from a tropical marine strain of B. licheniformis, assigned a function to the hypothetical protein entry in the NCBI database and described its application as a potential antibiofilm agent.

Biomedical evaluation of a novel nitrogen oxides releasing wound dressing.

Chronic wounds are a major cause for both suffering and economical losses. Management of chronic non-healing wounds requires multipronged approach. They are polymicrobial and agonizing for the patient due to associated pain. Moist dressing providing antimicrobial action is a highly desirable chronic wound management option. Here we report a hydrogel based dressing that possesses the antimicrobial properties of acidified sodium nitrite and the homeostatic property of a hydrogel. The dressing was developed by combining citric acid cross-linked cotton gauze and sodium nitrite loaded gelatin. The cotton gauze was cross-linked with citric acid by pad-dry-curing in presence of nano-titania catalyst. The cotton gauze-gelatin hydrogel combination was gamma-irradiated and freeze-dried. At the time of application, the freeze-dried dressing is wetted by sodium nitrite solution. The dressing has a fluid uptake ability of 90 % (w/v) and the water vapour evaporation rate was estimated to be 2,809 ± 20 g/m(2)/day. The dressing showed significant antimicrobial activity against both planktonic and biofilm forms and was effective during consecutive re-uses. Cytotoxicity study showed inhibition of fibroblasts, but to a lesser extent than clinically administered concentrations of antiseptic like povidone iodine. Storage at 37 °C over a 3 month period resulted in no significant loss of its antimicrobial activity.

Disruption of Yarrowia lipolytica biofilms by rhamnolipid biosurfactant.

BACKGROUND: Yarrowia lipolytica is an ascomycetous dimorphic fungus that exhibits biofilm mode of growth. Earlier work has shown that biosurfactants such as rhamnolipids are efficient dispersants of bacterial biofilms. However, their effectiveness against fungal biofilms (particularly Y. lipolytica) has not been investigated. The aim of this study was to determine the effect of rhamnolipid on a biofilm forming strain of Y. lipolytica. Two chemical surfactants, cetyl-trimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) were used as controls for comparison. RESULTS: The methylene blue dye exclusion assay indicated an increase in fungal cell permeability after rhamnolipid treatment. Microtiter plate assay showed that the surfactant coating decreased Y. lipolytica biofilm formation by 50%. Rhamnolipid treatment disrupted pre-formed biofilms in a more effective manner than the other two surfactants. Confocal laser scanning microscopic studies showed that biofilm formation onto glass surfaces was decreased by 67% after sub-minimum inhibitory concentration (sub-MIC) treatment with rhamnolipids. The disruption of biofilms after rhamnolipid treatment was significant (P<0.05) when compared to SDS and CTAB. CONCLUSION: The results indicate a potential application of the biological surfactant to disrupt Y. lipolytica biofilms.

P-nitrophenol biodegradation by aerobic microbial granules.

Mixed microbial consortia in the form of aerobic microbial granules (AMG) capable of xenobiotic degradation can be developed from activated sludge or by adaptation of microbial granules pre-grown on labile carbon sources. Both of these approaches were investigated for the cultivation of AMG capable of p-nitrophenol (PNP) biodegradation. Attempts to cultivate AMG from activated sludge using PNP as the sole carbon source were not successful due to poor microbial growth and washout of the inoculated activated sludge. As part of the second approach, parallel sequencing batch reactors (SBRs) were inoculated with pre-grown AMG and operated by feeding both acetate and PNP together (RA), PNP alone (RB) or acetate alone (RC). Acetate/PNP mineralization and nitrification were monitored in the three SBRs. PNP biodegradation was quickly established in both RA and RB. PNP removal rates were found to be 47 and 55 mg g VSS(-1) h(-1) in RA and RB, respectively. PNP biodegradation during the SBR cycle consisted of distinct lag, exponential and deceleration phases. However, with higher concentrations of PNP (>50 mg l(-1)), disintegration of granules was observed in RA and RB. When PNP was the sole carbon source, it inhibited the development of aerobic granules from activated sludge and caused disintegration of pre-cultivated aerobic granules. When PNP was the co-substrate along with acetate, the structural and functional integrity (including nitrification) of the granular sludge was maintained. This report highlights the importance of a labile co-substrate for maintaining the physical and functional integrity of granular sludge, when used for toxic waste degradation.

Denitrification of synthetic concentrated nitrate wastes by aerobic granular sludge under anoxic conditions.

The aim of the present work was to determine the denitrification potential of aerobic granular sludge for concentrated nitrate wastes. We cultivated mixed microbial granules in a sequencing batch reactor operated at a superficial air velocity of 0.8 cm s(-1). The denitrification experiments were performed under anoxic conditions using serum bottles containing synthetic media with 225-2250 mg L(-1) NO3-N. Time required for complete denitrification varied with the initial nitrate concentration and acetate to nitrate-N mass ratio. Complete denitrification of 2250 mg L(-1) NO3-N under anoxic conditions was accomplished in 120 h. Nitrite accumulation was not significant (<5 mg N L(-1)) at initial NO3-N concentrations below 677 mg L(-1). However, denitrification of higher concentrations of nitrate (≥900 mg N L(-1)) resulted in buildup of nitrite. Nevertheless, nitrite buildups observed in present study were relatively lower compared to that reported in previous studies using flocculent activated sludge. The experimental results suggest that acetate-fed aerobic granular sludge can be quickly adapted to treat high strength nitrate waste and can thus be used as seed biomass for developing high-rate bioreactors for efficient treatment of concentrated nitrate-bearing wastes.

Novel biocatalytic polymer-based antimicrobial coatings as potential ureteral biomaterial: preparation and in vitro performance evaluation.

Catheters and other indwelling devices placed inside human body are prone to bacterial infection, causing serious risk to patients. Infections associated with implants are difficult to resolve, and hence the prevention of bacterial colonization of such surfaces is quite appropriate. In this context, the development of novel antimicrobial biomaterials is currently gaining momentum. We describe here the preparation and antibacterial properties of an enzyme-embedded polycaprolactone (PCL)-based coating, coimpregnated with the antibiotic gentamicin sulfate (GS). The enzyme uses PCL itself as substrate; as a result, the antibiotic gets released at a rate controlled by the degradation of the PCL base. In vitro drug release studies demonstrated sustained release of GS from the PCL film throughout its lifetime. By modulating the enzyme concentration in the PCL film, we were able to vary the lifetime of the coating from 33 h to 16 days. In the end, the polymer is completely degraded, delivering the entire load of the antibiotic. The polymer exhibited antibacterial properties against three test isolates: Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Foley urinary catheters coated with the modified polymer exhibited sustained in vitro release of GS over a 60-h period. The results suggest that the antibiotic-plus-enzyme-loaded polymer can be used as tunable self-degrading antimicrobial biomaterial coating on catheters.

Rhamnolipid mediated disruption of marine Bacillus pumilus biofilms.

Removal of detrimental biofilms from surfaces exposed in the marine environment remains a challenge. A strain of Bacillus pumilus was isolated from the surface of titanium coupons immersed in seawater in the vicinity of Madras Atomic Power Station (MAPS) on the East coast of India. The bacterium formed extensive biofilms when compared to species such as Bacillus licheniformis, Pseudomonas aeruginosa PAO1 and Pseudomonas aureofaciens. A commercially available rhamnolipid was assessed for its ability to inhibit adhesion and disrupt pre-formed B. pumilus biofilms. The planktonic growth of B. pumilus cells was inhibited by concentrations >1.6mM. We studied the effect of various concentrations (0.05-100mM) of the rhamnolipid on adhesion of B. pumilus cells to polystyrene microtitre plates, wherein the effectiveness varied from 46 to 99%. Biofilms of B. pumilus were dislodged efficiently at sub-MIC concentrations, suggesting the role of surfactant activity in removing pre-formed biofilms. Scanning electron microscopy (SEM) confirmed the removal of biofilm-matrix components and disruption of biofilms by treatment with the rhamnolipid. The results suggest the possible use of rhamnolipids as efficient anti-adhesive and biofilm-disrupting agents with potential applications in controlling biofilms on surfaces.

Quorum sensing: implications on rhamnolipid biosurfactant production.

Quorum sensing (QS) has received significant attention in the past few decades. QS describes population density dependent cell to cell communication in bacteria using diffusible signal molecules. These signal molecules produced by bacterial cells, regulate various physiological processes important for social behavior and pathogenesis. One such process regulated by quorum sensing molecules is the production of a biosurfactant, rhamnolipid. Rhamnolipids are important microbially derived surface active agents produced by Pseudomonas spp. under the control of two interrelated quorum sensing systems; namely las and rhl. Rhamnolipids possess antibacterial, antifungal and antiviral properties. They are important in motility, cell to cell interactions, cellular differentiation and formation of water channels that are characteristics of Pseudomonas biofilms. Rhamnolipids have biotechnological applications in the uptake of hydrophobic substrates, bioremediation of contaminated soils and polluted waters. Rhamnolipid biosurfactants are biodegradable as compared to chemical surfactants and hence are more preferred in environmental applications. In this review, we examine the biochemical and genetic mechanism of rhamnolipid production by P. aeruginosa and propose the application of QS signal molecules in enhancing the rhamnolipid production.

Competition triggers plasmid-mediated enhancement of substrate utilisation in Pseudomonas putida.

Competition between species plays a central role in the activity and structure of communities. Stable co-existence of diverse organisms in communities is thought to be fostered by individual tradeoffs and optimization of competitive strategies along resource gradients. Outside the laboratory, microbes exist as multispecies consortia, continuously interacting with one another and the environment. Survival and proliferation of a particular species is governed by its competitive fitness. Therefore, bacteria must be able to continuously sense their immediate environs for presence of competitors and prevailing conditions. Here we present results of our investigations on a novel competition sensing mechanism in the rhizosphere-inhabiting Pseudomonas putida KT2440, harbouring gfpmut3b-modified Kan(R) TOL plasmid. We monitored benzyl alcohol (BA) degradation rate, along with GFP expression profiling in mono species and dual species cultures. Interestingly, enhanced plasmid expression (monitored using GFP expression) and consequent BA degradation were observed in dual species consortia, irrespective of whether the competitor was a BA degrader (Pseudomonas aeruginosa) or a non-degrader (E. coli). Attempts at elucidation of the mechanistic aspects of induction indicated the role of physical interaction, but not of any diffusible compounds emanating from the competitors. This contention is supported by the observation that greater induction took place in presence of increasing number of competitors. Inert microspheres mimicking competitor cell size and concentration did not elicit any significant induction, further suggesting the role of physical cell-cell interaction. Furthermore, it was also established that cell wall compromised competitor had minimal induction capability. We conclude that P. putida harbouring pWW0 experience a competitive stress when grown as dual-species consortium, irrespective of the counterpart being BA degrader or not. The immediate effect of this stress is a marked increase in expression of TOL, leading to rapid utilization of the available carbon source and massive increase in its population density. The plausible mechanisms behind the phenomenon are hypothesised and practical implications are indicated and discussed.