Production, functional stability, and effect of rhamnolipid biosurfactant from Klebsiella sp. on phenanthrene degradation in various medium systems

Microbe cultivation guidelines to optimize rhamnolipid applications

In the growing landscape of interest in natural surfactants, selecting the appropriate one for specific applications remains challenging. The extensive, yet often unsystematized, knowledge of microbial surfactants, predominantly represented by rhamnolipids (RLs), typically does not translate beyond the conditions presented in scientific publications. This limitation stems from the numerous variables and their interdependencies that characterize microbial surfactant production. We hypothesized that a computational recipe for biosynthesizing RLs with targeted applicational properties could be developed from existing literature and experimental data. We amassed literature data on RL biosynthesis and micellar solubilization and augmented it with our experimental results on the solubilization of triglycerides (TGs), a topic underrepresented in current literature. Utilizing this data, we constructed mathematical models that can predict RL characteristics and solubilization efficiency, represented as logPRL = f(carbon and nitrogen source, parameters of biosynthesis) and logMSR = f(solubilizate, rhamnolipid (e.g. logPRL), parameters of solubilization), respectively. The models, characterized by robust R2 values of respectively 0.581-0.997 and 0.804, enabled the ranking of descriptors based on their significance and impact-positive or negative-on the predicted values. These models have been translated into ready-to-use calculators, tools designed to streamline the selection process for identifying a biosurfactant optimally suited for intended applications.

Performance evaluation of rhamnolipid biosurfactant produced by Pseudomonas aeruginosa and its effect on marine oil-spill remediation

This study aimed to reveal that the effect of biosurfactant on the dispersion and degradation of crude oil. Whole genome analysis showed that Pseudomonas aeruginosa GB-3 contained abundant genes involved in biosurfactant synthesis and metabolic processes and had the potential to degrade oil. The biosurfactant produced by strain GB-3 was screened by various methods. The results showed that the surface tension reduction activity was 28.6 mN·m-1 and emulsification stability was exhibited at different pH, salinity and temperature. The biosurfactant was identified as rhamnolipid by LC-MS and FTIR. The fermentation conditions of strain GB-3 were optimized by response surface methodology, finally the optimal system (carbon source: glucose, nitrogen source: ammonium sulfate, C/N ratio:16:1, pH: 7, temperature: 30-35 °C) was determined. Compared with the initial fermentation, the yield of biosurfactant increased by 4.4 times after optimization. In addition, rhamnolipid biosurfactant as a dispersant could make the dispersion of crude oil reach 38% within seven days, which enhanced the bioavailability of crude oil. As a biostimulant, it could also improve the activity of indigenous microorganism and increase the degradation rate of crude oil by 10-15%. This study suggested that rhamnolipid biosurfactant had application prospect in bioremediation of marine oil-spill.

Biosurfactants-based mixed polycyclic aromatic hydrocarbon degradation: From microbial community structure toward non-targeted metabolomic profile determination

Biosurfactants-based bioremediation is considered an efficient technology to eliminate environmental pollutants including polycyclic aromatic hydrocarbons (PAHs). However, the precise role of rhamnolipids or lipopeptide-biosurfactants in mixed PAH dissipation, shaping microbial community structure, and influencing metabolomic profile remained unclear. In this study, results showed that the maximum PAH degradation was achieved in lipopeptide-assisted treatment (SPS), where the pyrene and phenanthrene were substantially degraded up to 74.28 % and 63.05 % respectively, as compared to rhamnolipids (SPR) and un-aided biosurfactants (SP). Furthermore, the high throughput sequencing analysis revealed a significant change in the PAH-degrading microbial community, with Proteobacteria being the predominant phylum (>98 %) followed by Bacteroidota and Firmicutes in all the treatments. Moreover, Pseudomonas and Pannonibacter were found as highly potent bacterial genera for mixed PAH degradation in SPR, SPS, and SP treatments, nevertheless, the abundance of the genus Pseudomonas was significantly enhanced (>97 %) in SPR treatment groups. On the other hand, the non-targeted metabolomic profile through UHPLC-MS/MS exhibited a remarkable change in the metabolites of amino acids, carbohydrates, and lipid metabolisms by the input of rhamnolipids or lipopeptide-biosurfactants whereas, the maximum intensities of metabolites (more than two-fold) were observed in SPR treatment. The findings of this study suggested that the aforementioned biosurfactants can play an indispensable role in mixed PAH degradation as well as seek to offer new insights into shifts in PAH-degrading microbial communities and their metabolic function, which can guide the development of more efficient and targeted strategies for complete removal of organic pollutants such as PAH from the contaminated environment.

Exploring the bioremediation capability of petroleum-contaminated soils for enhanced environmental sustainability and minimization of ecotoxicological concerns

The bioremediation of soils contaminated with petroleum hydrocarbons (PHCs) has emerged as a promising approach, with its effectiveness contingent upon various types of PHCs, i.e., crude oil, diesel, gasoline, and other petroleum products. Strategies like genetically modified microorganisms, nanotechnology, and bioaugmentation hold potential for enhancing remediation of polycyclic aromatic hydrocarbon (PAH) contamination. The effectiveness of bioremediation relies on factors such as metabolite toxicity, microbial competition, and environmental conditions. Aerobic degradation involves enzymatic oxidative reactions, while bacterial anaerobic degradation employs reductive reactions with alternative electron acceptors. Algae employ monooxygenase and dioxygenase enzymes, breaking down PAHs through biodegradation and bioaccumulation, yielding hydroxylated and dihydroxylated intermediates. Fungi contribute via mycoremediation, using co-metabolism and monooxygenase enzymes to produce CO2 and oxidized products. Ligninolytic fungi transform PAHs into water-soluble compounds, while non-ligninolytic fungi oxidize PAHs into arene oxides and phenols. Certain fungi produce biosurfactants enhancing degradation of less soluble, high molecular-weight PAHs. Successful bioremediation offers sustainable solutions to mitigate petroleum spills and environmental impacts. Monitoring and assessing strategy effectiveness are vital for optimizing biodegradation in petroleum-contaminated soils. This review presents insights and challenges in bioremediation, focusing on arable land safety and ecotoxicological concerns.

Enhanced remediation of oil-contaminated intertidal sediment by bacterial consortium of petroleum degraders and biosurfactant producers

Oil pollution in intertidal zones is an important environmental issue that has serious adverse effects on coastal ecosystems. This study investigated the efficacy of a bacterial consortium constructed from petroleum degraders and biosurfactant producers in the bioremediation of oil-polluted sediment. Inoculation of the constructed consortium significantly enhanced the removal of C₈-C₄₀n-alkanes (80.2 ± 2.8% removal efficiency) and aromatic compounds (34.4 ± 10.8% removal efficiency) within 10 weeks. The consortium played dual functions of petroleum degradation and biosurfactant production, greatly improving microbial growth and metabolic activities. Real-time quantitative polymerase chain reaction (PCR) showed that the consortium markedly increased the proportions of indigenous alkane-degrading populations (up to 3.88-times higher than that of the control treatment). Microbial community analysis demonstrated that the exogenous consortium activated the degradation functions of indigenous microflora and promoted synergistic cooperation among microorganisms. Our findings indicated that supplementation of a bacterial consortium of petroleum degraders and biosurfactant producers is a promising bioremediation strategy for oil-polluted sediments.

Role of extremophilic Bacillus cereus KH1 and its lipopeptide in treatment of organic pollutant in wastewater

An effective biosurfactant producer and extremophiles bacteria, Bacillus cereus KH1, was isolated from textile effluent and the biosurfactant was produced using molasses as the sole carbon source. Growth parameters such as pH, temperature, salinity and concentration of molasses were optimised for decolourising the textile effluent with 24-h incubation. The biosurfactant property of B. cereus KH1 was evaluated based on haemolytic activity, oil displacement technique, drop-collapsing test and emulsification index. The results of the produced biosurfactant showed a positive reaction in haemolytic activity, oil displacement technique, drop-collapsing test and exhibiting a 67% emulsification index. The cell-free broth was stable in 40 °C pH 7, 7% salinity and 7% molasses. Thin-Layer Chromatography and Fourier Transform Infrared Spectroscopy analysis revealed that the biosurfactant was a lipopeptide with a yield 2.98 g L^-1. These findings proved the synergistic action of B. cereus KH1 with lipopeptide biosurfactant may accelerated the decolourisation efficiency to 87%.

Rapid effective treatment of waxy oily sludge using a method of dispersion combined with biodegradation in a semi-fluid state

Waxy oily sludge (WOS) from petrochemical enterprises has complex components and difficult treatment. Long-term large-scale stacking has seriously threatened human health and the ecological environment. In this paper, a new rapid and effective treatment method combining dispersion and biodegradation in a semi-fluid state was developed for the WOS. The degradation mechanism of the WOS in the bioreactor was preliminarily discussed. The component analysis results showed that the compounds with large molecular weight (M ≥ 282) in the WOS accounted for more than 50%. Among all microbial consortiums, the treatment effect of the consortium FF: NY3 = 9: 1 was the best for treating the crude oil in WOS, which was significantly different from that of a single strain (p < 0.05). Under the optimal nitrogen source NH₄NO₃ and the concentration of rhamnolipid, the developed high-efficiency microbial consortium (FF: NY3 = 9:1) could remove 85% of the total hydrocarbon pollutants in the 20 L semi-fluid bioreactor within 9 days. The degradation characteristics of WOS components in the bioreactor showed that the developed consortium has good degradation ability for n-alkanes (about 90%), middle- (77.35%)/long-chain (72.66%) isomeric alkanes, alkenes (79.12%), alicyclic hydrocarbons (78.9%) and aromatic hydrocarbons (62.78%). The kinetic analysis results indicated that, in comparison, the middle-chain n-alkanes, middle-chain isomeric saturated alkanes, alkenes, and alicyclic hydrocarbons were most easily removed. The removal rates of long-chain n-alkanes, long-chain isomeric saturated alkanes, and aromatic hydrocarbons were relatively low. The biological toxicity test showed that the germination rate of wheat seeds in treated waxy sludge was Significantly higher than that in untreated waxy sludge (p < 0.01). These results suggest that the new method developed in this paper can treat refractory WOS quickly and effectively. This method lays the foundation for the pilot-scale treatment of the semi-fluid bioreactor.

Microbial conversion of agro-processing waste (peanut meal) to rhamnolipid by Pseudomonas aeruginosa: solid-state fermentation, water extraction, medium optimization and potential applications

The high cost and severe foam in rhamnolipid fermentation are still bottlenecks for its industrial production and application. Non-foaming production of rhamnolipid by Pseudomonas aeruginosa FA1 was explored in solid-state fermentation using the agro-processing waste (peanut meal) as low-cost substrate. An environmental-friendly extraction method was developed to harvest rhamnolipid from solid-state culture. Strain FA1 produced 265.4 ± 8.2 mg rhamnolipid using 10 g peanut meal. HPLC-MS results revealed that 7 rhamnolipid homologues were produced, mainly including Rha-C₈-C₁₀ and Rha-Rha-C₁₀-C₁₀. Nitrate was the optimal nitrogen source. Peanut meal, MgSO₄ and CaCl₂ were significant factors for rhamnolipid production in solid-state fermentation. Rhamnolipid production was enhanced 31 % using the solid-state medium optimized by response surface method. The produced rhamnolipid reduced water surface tension to 28.1 ± 0.2 mN/m with a critical micelle concentration of 70 mg/L. The crude oil was emulsified with an emulsification index of 75.56 ± 1.29 %. The growth of tested bacteria and fungi was inhibited.

Sustainable production of biosurfactants via valorisation of industrial wastes as alternate feedstocks

Globally, the rapid increase in the human population has given rise to a variety of industries, which have produced a variety of wastes. Due to their detrimental effects on both human and environmental health, pollutants from industry have taken centre stage among the various types of waste produced. The amount of waste produced has therefore increased the demand for effective waste management. In order to create valuable chemicals for sustainable waste management, trash must be viewed as valuable addition. One of the most environmentally beneficial and sustainable choices is to use garbage to make biosurfactants. The utilization of waste in the production of biosurfactant provides lower processing costs, higher availability of feedstock and environmental friendly product along with its characteristics. The current review focuses on the use of industrial wastes in the creation of sustainable biosurfactants and discusses how biosurfactants are categorized. Waste generation in the fruit industry, agro-based industries, as well as sugar-industry and dairy-based industries is documented. Each waste and wastewater are listed along with its benefits and drawbacks. This review places a strong emphasis on waste management, which has important implications for the bioeconomy. It also offers the most recent scientific literature on industrial waste, including information on the role of renewable feedstock for the production of biosurfactants, as well as the difficulties and unmet research needs in this area.

Novel production of biodispersant by Serratia marcescens UCP 1549 in solid-state fermentation and application for oil spill bioremediation

Oil spills in aquatic ecosystems cause irreparable damage to marine life and the coastal populations of affected areas. In recent years, chemical dispersants have been extensively used to remedy these impacted ecosystems, although these agents have been increasingly restricted due to their toxic potential. In this context, biosurfactants are emerging as a promising alternative to chemical dispersants, which have some advantages including low toxicity, high biodegradability and good ecological acceptability. Thus, this study aimed to the production of biosurfactant by the bacteria Serratia marcescens UCP 1549 for application as biodispersant. The experiment was carried out using wheat bran as substrate in solid-state fermentation (SSF) as low-cost technology. Biosurfactant production was verified by the reduction of surface tension (28.4 mN/m) and interfacial tension (4.1 mN/m) with n-hexadecane. Also, promising result of emulsification (94%) with burned motor oil was obtained. Acid precipitation yielded 52.0 g/kg dry substrate of biosurfactant, that was identified as an anionic compound of a lipopeptide nature by the Zeta potential and FTIR spectrum, respectively. The biomolecule showed stability under extreme conditions of temperature, pH and salinity, as well as low toxicity against the microcrustacean Artemia salina. In addition, the biosurfactant demonstrated excellent properties to dispersing burned motor oil in water (ODA = 50.24 cm²) and to washing of marine stones (100% removal of burned motor oil). Therefore, these results confirm SSF as a sustainable technology for the production of biodispersant by S. marcescens UCP 1549, promising in the bioremediation of marine ecosystems impacted by petroderivatives.

Microbial originated surfactants with multiple applications: a comprehensive review

Microbial synthesized surfactants are used in contaminated soil bioremediation processes and have multiple applications in various industries. These compounds minimize the negative influences in soil via absorption by detoxifying the toxic metals or compounds. Further, applications of biosurfactants are detected in treating chronic diseases or synthetic drugs alternatives in current periods. Various surfactant molecules can provide many benefits due to their diversities in structural and functional groups. These compounds showed a wide array of applications in multiple sectors such as biomedical or pharmaceutical fields. Agricultural, food processing, laundry, or other sectors. Many microbial systems or plant cells are utilized in biosurfactant production as confirmed by biochemical analysis of genome sequencing tools. Biosurfactant compounds can alter drug transport across the cell membrane. Different nature of biosurfactant compounds exhibited their antifungal, antibacterial, antiviral activities, or antiadhesive coating agents used in reduction of many hospital infections. These distinct properties of biosurfactants pushed their broad spectrum applications in biomedical, agriculture sectors and bioremediation tasks. Additionally, many strains of fungi or bacteria are utilized for biosurfactant synthesis involved in the detoxification of soil/other components of the environment. In these reviews, authors explained various biosurfactants molecules and their mode of actions. Also, applications of microbial originated biosurfactants along with their process technologies are described. Future perspectives of biosurfactants and their scope are also critically explained so that this review paper can be used as a showcase for production and application of biosurfactants.

Efficient biodegradation of phenanthrene using Pseudomonas stutzeri LSH-PAH1 with the addition of sophorolipids: Alleviation of biotoxicity and cometabolism studies

Phenanthrene (PHE) is widely distributed, and it can cause genotoxicity in humans by interacting with enzymes in the body. A current challenge for PHE bioremediation is the inhibitory effect of biotoxic intermediates on bacterial growth. Notably, the aerobic biotransformation processes for PHE in the presence of sophorolipids have been poorly studied. Here, a PHE-degrading strain was isolated from sediments and identified as Pseudomonas stutzeri and named LSH-PAH1. It was observed that 1-naphthol (a biotoxic substance that can inhibit strain growth) was produced during the PHE metabolism process of LSH-PAH1. The biodegradation ratio increased from 21.4% to 91.7% within 48 h after the addition of sophorolipids. Unexpectedly, this addition accelerated the metabolic process for 1-naphthol rather than causing its accumulation. The cometabolism of 1-naphthol and sophorolipids alleviated the biotoxic effects for the strain, which was verified by gene expression analysis. We identified a new PHE-degrading strain and provided a mechanism for PHE biodegradation using LSH-PAH1 with the addition of sophorolipids, which provides a reference for practical applications of the bioremediation of PHE and study of the cometabolism of biotoxic intermediates.

Interactive analysis of biosurfactants in fruit-waste fermentation samples using BioSurfDB and MEGAN

Agroindustrial waste, such as fruit residues, are a renewable, abundant, low-cost, commonly-used carbon source. Biosurfactants are molecules of increasing interest due to their multifunctional properties, biodegradable nature and low toxicity, in comparison to synthetic surfactants. A better understanding of the associated microbial communities will aid prospecting for biosurfactant-producing microorganisms. In this study, six samples of fruit waste, from oranges, mangoes and mixed fruits, were subjected to autochthonous fermentation, so as to promote the growth of their associated microbiota, followed by short-read metagenomic sequencing. Using the DIAMOND+MEGAN analysis pipeline, taxonomic analysis shows that all six samples are dominated by Proteobacteria, in particular, a common core consisting of the genera Klebsiella, Enterobacter, Stenotrophomonas, Acinetobacter and Escherichia. Functional analysis indicates high similarity among samples and a significant number of reads map to genes that are involved in the biosynthesis of lipopeptide-class biosurfactants. Gene-centric analysis reveals Klebsiella as the main assignment for genes related to putisolvins biosynthesis. To simplify the interactive visualization and exploration of the surfactant-related genes in such samples, we have integrated the BiosurfDB classification into MEGAN and make this available. These results indicate that microbiota obtained from autochthonous fermentation have the genetic potential for biosynthesis of biosurfactants, suggesting that fruit wastes may provide a source of biosurfactant-producing microorganisms, with applications in the agricultural, chemical, food and pharmaceutical industries.

Applying hybrid genetic and artificial bee colony algorithms to simulate a bio-treatment of synthetic dye-polluted wastewater using a rhamnolipid biosurfactant

The present work aims at optimization and advanced simulation of removal efficiency of dye material from a synthetic wastewater using a locally generated rhamnolipid (RL) biosurfactant. For this purpose, bio-treatment of dye polluted synthetic wastewater was experimentally, kinetically, and statistically investigated by the ion flotation process in the presence of the RL. The removal rate of methylene blue (MB) as the dye material was assessed by the ultraviolet (UV)-visible absorbance measurements. The impact of operating variables including RL concentration (as a dye collector, 5-50 ppm), methyl isobutyl carbinol (MIBC) dosage (as a frother, 10-70 ppm), solution pH (2-12) and aeration rate (1-5 l/min) were assessed through one-way analysis of variance (ANOVA) and Anderson-Darling as the normality analysis strategy. The process was simulated using two artificial neural network (ANN) optimization algorithms, i.e., genetic algorithm (GA) and artificial bee colony (ABC) as a novel approach. The statistical results indicated that the dye removal process was significantly influenced by all operating variables (p_value<0.05) while their relative intensity followed the order of aeration rate > solution pH > RL concentration > MIBC dosage. Anderson-Darling approach disclosed that the all factors were perfectly followed the normal trend with A² less than unity and p-value of greater than 0.05 at 95% confidence level. Main effect plots revealed that except MIBC dosage with nonlinear trend, the rest of factors had an ascending influence on the removal efficiency. The process was optimized by interpreting the interaction effect among various variables to reach the maximum dye bioflotation. The maximum removal of 97 ± 0.13% was achieved at pH 12, airflow rate of 5 l/min, MIBC and rhamnolipid concentrations of 30 and 40 ppm, respectively with a flotation kinetic rate of 0.015 sec^-1. Finally, the intelligent simulation results showed that the process could be modelled using an artificial bee colony algorithm of 4-7-1 structure with 99% and 98.8% accuracies in the training and testing steps, respectively. Further, we found that the artificial bee colony algorithm was superior to the genetic algorithm in terms of complexity analysis.

Mathematical Modelling of Canola Oil Biodegradation and Optimisation of Biosurfactant Production by an Antarctic Bacterial Consortium Using Response Surface Methodology

An Antarctic soil bacterial consortium (reference BS14) was confirmed to biodegrade canola oil, and kinetic studies on this biodegradation were carried out. The purpose of this study was to examine the ability of BS14 to produce biosurfactants during the biodegradation of canola oil. Secondary mathematical equations were chosen for kinetic analyses (Monod, Haldane, Teissier-Edwards, Aiba and Yano models). At the same time, biosurfactant production was confirmed through a preliminary screening test and further optimised using response surface methodology (RSM). Mathematical modelling demonstrated that the best-fitting model was the Haldane model for both waste (WCO) and pure canola oil (PCO) degradation. Kinetic parameters including the maximum degradation rate (μmax) and maximum concentration of substrate tolerated (Sm) were obtained. For WCO degradation these were 0.365 min-1 and 0.308%, respectively, while for PCO they were 0.307 min-1 and 0.591%, respectively. The results of all preliminary screenings for biosurfactants were positive. BS14 was able to produce biosurfactant concentrations of up to 13.44 and 14.06 mg/mL in the presence of WCO and PCO, respectively, after optimisation. The optimum values for each factor were determined using a three-dimensional contour plot generated in a central composite design, where a combination of 0.06% salinity, pH 7.30 and 1.55% initial substrate concentration led to the highest biosurfactant production when using WCO. Using PCO, the highest biosurfactant yield was obtained at 0.13% salinity, pH 7.30 and 1.25% initial substrate concentration. This study could help inform the development of large-scale bioremediation applications, not only for the degradation of canola oil but also of other hydrocarbons in the Antarctic by utilising the biosurfactants produced by BS14.

Biodegradation of waste cooking oil and simultaneous production of rhamnolipid biosurfactant by Pseudomonas aeruginosa P7815 in batch and fed-batch bioreactor

Biosurfactants are non-toxic, surface-active biomolecules capable of reducing surface tension (ST) and emulsifying interface at a comparably lower concentration than commercial surfactants. Yet, poor yield, costlier substrates, and complex cultivation processes limit their commercial applications. This study focuses on producing biosurfactants by Pseudomonas aeruginosa P7815 in batch and fed-batch bioreactor systems using waste cooking oil (WCO) as the sole carbon source. The batch study showed a 92% of WCO biodegradation ability of P. aeruginosa producing 11 g L^-1 of biosurfactant. To enhance this biosurfactant production, a fed-batch oil feeding strategy was opted to extend the stationary phase of the bacterium and minimize the effects of substrate deprivation. An enhanced biosurfactant production of 16 g L^-1 (i.e. 1.5 times of batch study) was achieved at a feed rate of 5.7 g L^-1d^-1 with almost 94% of WCO biodegradation activity. The biosurfactant was characterized as rhamnolipid using Fourier transform infrared spectroscopy (FTIR), and its interfacial characterization showed ST reduction to 29 ± 1 mN m^-1 and effective emulsification stability at pH value of 4, temperature up to 40 °C and salinity up to 40 g L^-1. The biosurfactant exhibited antibacterial activity with minimum inhibitory concentration (MIC) values of 100 µg mL^-1 and 150 µg mL^-1 for pathogenic E. hirae and E. coli, respectively. These findings suggest that biodegradation of WCO by P. aeruginosa in a fed-batch cultivation strategy is a potential alternative for the economical production of biosurfactants, which can be further explored for biomedical, cosmetics, and oil washing/recovery applications.

Enhanced biodegradation and valorization of drilling wastewater via simultaneous production of biosurfactants and polyhydroxyalkanoates by Pseudomonas citronellolis SJTE-3

Pseudomonas citronellolis SJTE-3 was isolated as a highly efficient microorganism for biodegradation and valorization of drilling fluids (DF) wastewater. The strain metabolised DF and oily mud exhibiting up to 93%, 86%, 85% and 88% of chemical oxygen demand (COD), n-dodecane, n-tetradecane and naphthalene removal efficiency respectively. Enhanced bioconversion was enabled through production of biosurfactants that reduced the surface tension of water by 53% and resulted in 43.3% emulsification index (E24), while synthesizing 24% of dry cell weight (DCW) as medium-chain-length polyhydroxyalkanoates (PHA). Expression from the main pathways for alkanes and naphthalene biodegradation as well as biosurfactants and PHA biosynthesis revealed that although the alkanes and naphthalene biodegradation routes were actively expressed even at stationary phase, PHA production was stimulated at late stationary phase and putisolvin could comprise the biosurfactant synthesized. The bioconversion of toxic petrochemical residues to added-value thermoelastomers and biosurfactants indicate the high industrial significance of P. citronellolis SJTE-3.

Genomic characterization of Enterobacter xiangfangensis STP-3: Application to real time petroleum oil sludge bioremediation

Sustainable treatment of petroleum oil sludge still remains as a major challenge to petroleum refineries. Bioremediation is the promising technology involving bacteria for simultaneous production of biosurfactant and followed by degradation of petroleum compounds. Complete genomic knowledge on such potential microbes could accentuate its successful exploitation. The present study discusses the genomic characteristics of novel biosurfactant producing petrophilic/ petroleum hydrocarbon degrading strain, Enterobacter xiangfangensis STP-3, isolated from petroleum refinery oil sludge contaminated soil. The genome has 4,584,462 bp and 4372 protein coding sequences. Functional analysis using the RAST and KEGG databases revealed the presence of biosynthetic gene clusters linked to glycolipid and lipopeptide production and multiple key candidate genes linked with the degradation pathway of petroleum hydrocarbons. Orthology study revealed diversity in gene clusters associated to membrane transport, carbohydrate, amino acid metabolism, virulence and defence mechanisms, and nucleoside and nucleotide synthesis. The comparative analysis with 27 other genomes predicted that the core genome contributes to its inherent bioremediation potential, whereas the accessory genome influences its environmental adaptability in unconventional environmental conditions. Further, experimental results showed that E. xiangfangensis STP-3 was able to degrade PHCs by 82 % in 14 days during the bioremediation of real time petroleum oil sludge with the concomitant production of biosurfactant and metabolic enzymes, To the best of our knowledge, no comprehensive genomic study has been previously reported on the biotechnological prospective of this species.

Isolation, screening and molecular characterization of biosurfactant producing bacteria from soil samples of auto repair shops

A total of 107 bacterial strains were isolated from used motor oil contaminated soil samples from auto-repair shops. The isolates were evaluated for their biosurfactant production abilities by employing a series of screening techniques, including hemolytic assay, oil displacement assay, drop-collapse assay, and parafilm M test. The potential biosurfactant producers were characterized by 16S rDNA-based molecular tools and were identified as Proteus mirabilis, Klebsiella pneumoniae, Enterobacter cloacae, Micrococcus sp., Citrobacter sp., and Bacillus sp. The widest clearing zone with a diameter of 6.5 cm was observed upon the addition of cell-free supernatant (CFS) from P. mirabilis SLM-B52 as assayed by the oil displacement test. Remarkable emulsification indexes, equivalent to 42% (against kerosene), 53% (against xylenes), and 50% (against benzene and toluene), were recorded by the CFSs of Micrococcus sp. SLM-B28, P. mirabilis SLM-B85, and K. pneumoniae SLM-B46, respectively. Du Noüy tensiometer analysis showed that biosurfactant produced by P. mirabilis SLM-B52 has the highest surface tension reduction capacity with a value of 30.5 mN m^-1. The emulsifying activity of a CFS from P. mirabilis was also described in this study for the first time. Taking together, biosurfactants from promising bacterial strains have potential application in microorganism-based biodegradation processes of hydrocarbons which cause detrimental effects on the environment.

Advanced Simulation of Removing Chromium from a Synthetic Wastewater by Rhamnolipidic Bioflotation Using Hybrid Neural Networks with Metaheuristic Algorithms

This work aims at presenting an advanced simulation approach for a novel rhamnolipidic-based bioflotation process to remove chromium from wastewater. For this purpose, the significance of key influential operating variables including initial solution pH (2, 4, 6, 8, 10 and 12), rhamnolipid to chromium ratio (RL:Cr = 0.010, 0.025, 0.050, 0.075 and 0.100), reductant (Fe) to chromium ratio (Fe:Cr of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0), and air flowrate (50, 100, 150, 200 and 250 mL/min) were investigated and evaluated using Analysis of Variance (ANOVA) method. The RL as both collector and frother was produced using a pure strain of Pseudomonas aeruginosa MA01 under specific conditions. The bioflotation tests were carried out within a bubbly regimed column cell with the dimensions of 60 × 5.70 × 0.1 cm. Four optimization techniques based on Artificial Neural Network (ANN) including Cuckoo, genetic, firefly and biogeography-based optimization algorithms were applied to 113 experiments to identify the optimum values of studied factors. The ANOVA results revealed that all four variables influence the bioflotation performance through a non-linear trend. Their influences, except for aeration rate, were found statistically significant (p-value < 0.05), and all parameters followed the normal distribution according to Anderson-Darlin (AD) criterion. Maximum chromium removal of about 98% was achieved at pH of 6, rhamnolipid to chromium ratio of 0.05, air flowrate of 150 mL/min, and Fe to Cr ratio of 1.0. Flotation kinetics study indicated that chromium bioflotation follows the first-order kinetic model with a rate of 0.023 sec-1. According to the statistical assessment of the model accuracy, the firefly algorithm (FFA) with a structure of 4-9-1 yielded the highest level of reliability with the mean squared, root mean squared, percentage errors and correlation coefficient values of test-data of 0.0038, 0.0617, 3.08% and 96.92%, respectively. These values were evidences of the consistency of the well-structured ANN method to simulate the process.

Investigation on spectral and biomedical characterization of rhamnolipid from a marine associated bacterium Pseudomonas aeruginosa (DKB1)

Bio-surfactants are a principal group of significant molecules obtained from the microbial sources expressed with distinctive characteristics like biodegradation of hydrocarbons and also have different biomedical properties. The present investigation aims to assess the biomedical properties of synthesized bio-surfactant, rhamnolipid from Pseudomonas aeruginosa (DKB1) under in vitro conditions. The candidate bacterium P. aeruginosa (DKB1) was isolated from oil-polluted fishing harbors of Kanyakumari coast. Initially, the bio-surfactant production by this candidate strain was confirmed by oil displacement assay, hemolytic assay, drop collapse assay and emulsification index. Further, the production of bio-surfactant was achieved through submerged fermentation process using Bushnell-Haas mineral salts medium supplemented with 2% olive oil. The yield of the bio-surfactant was attained as 2.4 g/l and confirmed as rhamnolipid through blue agar plate assay; further, the extracted rhamnolipid was purified and characterized through standard procedures. In stability studies, the rhamnolipid could withstand up to pH 12, temperature 100 °C and 15% of NaCl concentration. The biomedical application of rhamnolipid (30 μg ml^-1) was determined by antibacterial, antioxidant and cytotoxic studies. It exhibited a maximum growth inhibition against Bacillus subtilis (26 mm) with the MIC value of 8 μg ml^-1. In antioxidant test, rhamnolipid expressed significant (P < 0.0001) inhibition of total reducing power (44.11%), DPPH activity (61.60%), hydroxyl radical (83.30%) and nitric oxide (51.86%) scavenging ability at 100 μg ml^-1with the respective IC50 values of 130.50, 77.18, 52.08 and 95.43 μg ml^-1. The anticancer activity of the rhamnolipid was assessed with the help of MTT test against MCF-7, HT-29 and E-143 cancer cell lines individually, and the viability of the cells was observed, respectively, as 10.24, 17.66 and 13.50% at 250 μg ml^-1concentration with the respective IC50 values of 140.2, 81.02 and 138.9 μg ml^-1. From the results, it could be concluded that the rhamnolipid produced by P. aeruginosa (DKB1) isolated from oil-polluted area has effective biomedical properties.