Rhamnolipid Research Articles

Rhamnolipids Induced by Glycerol Enhance Dibenzothiophene Biodegradation in Burkholderia sp. C3

Abstract In highly urbanized areas, pollution from anthropogenic activities has compromised the integrity of the land, decreasing soil availability for agricultural practices. Dibenzothiophene (DBT) is a heterocyclic aromatic hydrocarbon frequently found in urbanized areas, and is often used as a model chemical to study the microbial transformation of pollutants. The potential for human exposure and its health risk makes DBT a chemical of concern; thus, it needs to be environmentally managed. We utilized glycerol to stimulate Burkholderia sp. C3 in order to degrade DBT in respect to ① DBT biodegradation kinetics, ② bacterial growth, ③ rhamnolipid (RL) biosynthesis, and ④ RL secretion. Under an optimum glycerol-to-DBT molar ratio, the DBT biodegradation rate constants increased up to 18-fold and enhanced DBT biodegradation by 25%–30% at day 1 relative to cultivation with DBT alone. This enhancement was correlated with an increase in bacterial growth and RL biosynthesis. Proteomics studies revealed the enzymes involved in the upper and main steps of RL biosynthesis. The RL congeners Rha-C10-C10, Rha-Rha-C10-C10, Rha-Rha-C10-C12, and Rha-Rha-C12-C12 were identified in the medium supplemented with glycerol and DBT, whereas only Rha-C12-C12 was identified in cultures without glycerol or with RL inhibitors. The studies indicated that glycerol enhances DBT biodegradation via increased RL synthesis and bacterial growth. The results warrant further studies of environmental biostimulation with glycerol to advance bioremediation technologies and increase soil availability for agricultural purposes.

DNA-based stable isotope probing identifies triclosan degraders in nitrification systems under different surfactants

Three widely-used surfactants, rhamnolipid (RL), sophorolipid (SL) and sodium dodecyl benzene sulfonate (SDBS), were chosen to investigate their effects on the nitrification systems treating step-wised triclosan (TCS). Surfactants had little effects on nitrification. Surfactants could promote the desorption of TCS and enhance the TCS biodegradation in nitrification systems. And TCS biodegradation efficiencies obtained with RL, SL and SDBS were 1.25, 1.23 and 1.14 times higher than the control with 9.0 mg/L TCS, respectively. Illumina MiSeq sequencing showed that Amaricoccus could be resistant to TCS. And Amaricoccus, detected with RL, SL and SDBS, were more abundant than the control. DNA-based stable isotope probing assays revealed Amaricoccus was the major TCS degrader. And the addition of surfactants could obviously increase the diversity of active TCS degraders, especially for biosurfactants. It seems that the addition of surfactants showed positive effects for the nitrification systems treating TCS wastewater.

Exploring the Pharmacological Potentials of Biosurfactant Derived from Planococcus maritimus SAMP MCC 3013.

Therapeutic potential of biosurfactant (BS) has been improved in recent years. Our present study deals with production of BS from Planococcus maritimus SAMP MCC 3013 in a mineral salt medium (MSM) supplemented with glucose (1.5%w/v). Further, BS has been purified and partially characterized as glycolipid type through our previous publication. Current research article aimed to evaluate biological potential of BS against Mycobacterium tuberculosis, Plasmodium falciparum and cancerous cell lines. Planococcus derived glycolipid BS was found to be a promising inhibitor of M. tuberculosis (MTB) H37Ra at IC50 64.11 ± 1.64μg/mL and MIC at 160.8 ± 1.64μg/mL. BS also showed growth inhibition of P. falciparum at EC50 34.56 ± 0.26µM. Additionally, BS also displayed the cytotoxicity against HeLa (IC50 41.41 ± 4.21μg/mL), MCF-7 (IC50 42.79 ± 6.07μg/mL) and HCT (IC50 31.233 ± 5.08μg/mL) cell lines. Molecular docking analysis was carried for the most popular glycolipid type BS namely Rhamnolipid (RHL) aiming to interpret the possible binding interaction for anti-tubercular and anti-cancer activity. This analysis revealed the involvement of RHL binding with enoyl reductase (InhA) of M. tuberculosis. Docking studies of RHL with tubulin directed several hydrophobic and Vander Waal interactions to exhibit anti-cancer potential. The present study will be helpful for further development of marine bioactive molecules for therapeutic applications. Their anti-tubercular, anti-plasmodial and cytotoxic activities make BS molecules as a noteworthy candidate to combat several diseases. To the best of our knowledge, this is the first report on projecting the pharmacological potential of Planococcus derived BS.

Evaluation of Anti-oxidant and Anti-biofilm Activities of Biogenic Surfactants Derived from Bacillus amyloliquefaciens and Pseudomonas aeruginosa.

Biosurfactants, the microbial originated surface active agents, can modify the physicochemical properties of surfaces and reduce the bacterial adhesion via changing bacterial adhesion interactions on surfaces. They were also able to block oxidative chain reactions and might show antioxidant properties. The goal of this study was to evaluate the antioxidant and antibiofilm activities of biosurfactants which were derived from two autochthonous biosurfactant-producing strains, Bacillus amyloliquefaciens NS6 (surfactin), and Pseudomonas aeruginosa MN1 (rhamnolipids). Their antioxidant activities were determined by ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) methods. Ferric thiocyanate (FTC) assay was used for determination of their lipid peroxidation inhibition capacity. Their effect to reduce the adhesion of Streptococcus mutans on polystyrene surfaces and disruption of its pre-formed biofilms were also investigated. Our results indicated that surfactin showed higher antioxidant activity than rhamnolipids and showed relatively similar efficiency to BHA that suggests it as a good alternative for synthetic antioxidants. In other hand, rhamnolipid conditioned surfaces showed higher antiadhesive and antibiofilm activity in comparison with surfactin treated surfaces.

Recent advancements in the production of rhamnolipid biosurfactants by Pseudomonas aeruginosa.

Rhamnolipid (RL) biosurfactant which is produced by Pseudomonas species is one of the most effective surface-active agents investigated in the literature. Over the years, many efforts have been made and an array of techniques has been developed for the isolation of RL produced strains as well as RL homolog characterization. Reports show that RL productivity by the best-known producer, Pseudomonas aeruginosa, is very diverse, from less than 1 gr/l to more than 200 g L−1. There are some major parameters that can affect RL productivity. These are culture conditions, medium composition, the mode of operation (batch, fed-batch and continuous), bioengineering/gene manipulation and finally extraction methods. The present paper seeks to provide a comprehensive overview on the production of rhamnolipid biosurfactant by different species of Pseudomonas bacteria. In addition, we have extensively reviewed their potential for possible future applications.

Disperser coupled rhamnolipid disintegration of pulp and paper mill waste biosolid: Characterisation, methane production, energy assessment and cost analysis

In this study, the disintegration potential of disperser coupled rhamnolipid (RLD) was investigated on pulp and paper mill secondary sedimentation tank (PPST) sludge. Initially, RLD dosage and pH were optimized for liquefied organic content release. Maximal of liquefied organic content release of 2158 mg/L was attained at an optimized RLD dosage (0.009 g/g TS (Total solids), pH 10). To augment liquefaction of PPST sludge further, disperser and disperser coupled RLD methods were carried out. Disperser coupled RLD method has achieved maximal liquefaction rate (27%) and total suspended solids (TSS) reduction (20%) at 5128 kJ/kg TS when compared to disperser method. Subsequently, methane assay was performed in which disperser coupled RLD method yielded higher methane production of 295 mL/g VS (Volatile solids). Then, cost analysis was performed in which disperser coupled RLD method achieved a net profit of 134 $/ ton of PPST sludge.

Analysis of flux decline during rhamnolipid based micellar-enhanced ultrafiltration for simultaneous removal of Cd+2 and crystal violet from aqueous solution

Micellar enhanced ultrafiltration (MEUF) experiments were carried out with rhamnolipid (RHL) biosurfactant in a stirred cell for removal of Cd+2 and crystal violet (CV), simultaneously from aqueous solution. The influence of various operating conditions on the transient profiles of permeate flux and observed rejections were investigated. Experimental results revealed that for the treatment of aqueous feed under optimal conditions (RHL: 1730 × 10−3 kg. m−3; Cd+2: 30 × 10−3 kg. m−3; CV: 15 × 10−3 kg. m−3; NaCl: 5 kg.m−3; pH:7.8), the process condition (414 kPa, 600 rpm and 40 °C) was found to be the most suitable to achieve the permeate flux of (75 ± 1.5) L.m-2. h-1 at volume concentration ratio of 2 with more than (98 ± 0.1)% rejections of both the pollutants (Cd+2 and CV) and minimum surfactant loss (<3 %) to the permeate. The rapid decline in permeate flux at the earlier stage of filtration was attributed to adsorption-pore blocking followed by gradual decline at the later stage due to the growth of a cake layer of RHL-pollutant aggregates on the membrane surface. The transition of fouling mechanism occurred in the range of 200−390 s depending on the operating conditions. A combined model based on resistance-in-series theory coupled with Hermia’s constant pressure cake-filtration model was developed to analyze the profiles of flux decline and observed rejections of Cd+2, CV and RHL. The predicted results showed a good agreement with the experimental data. The developed model was successfully tested to other MEUF studies. The estimated model parameters in this study would help in design and scaling up of such MEUF process.

A novel approach for the production of green biosurfactant from Pseudomonas aeruginosa using renewable forest biomass

The rising demand for surfactants by the pharmaceuticals and cosmetic industries has generated vast amounts of petroleum-based synthetic surfactants, which are often toxic and non-degradable. Owing to their low toxicity, stability in extreme conditions, and biodegradability, biosurfactants could represent a sustainable alternative. The present study aimed to maximize the production of rhamnolipids (RL) from Pseudomonas aeruginosa by optimizing glucose concentration, temperature, and C/N and C/P ratios. After 96 h of cultivation at 37 °C, the final RL concentration was 4.18 ± 0.19 g/L with a final yield of 0.214 ± 0.010 g/gglucose when pure glucose was used as a carbon source. At present, the main obstacle towards commercialization of RL production is economic sustainability, due to the high cost of downstream processes and media components. For this reason, a renewable source such as wood hydrolysates (from birch and spruce woodchips) was examined here as a possible source of glucose for RL production. Both hydrolysates proved to be adequate, resulting in 2.34 ± 0.17 and 2.31 ± 0.10 g/L of RL, respectively, and corresponding yields of 0.081 ± 0.006 and 0.089 ± 0.004 g/gsugar after 96 h. These results demonstrate the potential of using renewable biomass for the production of biosurfactants and, to the best of our knowledge, they constitute the first report on the use of wood hydrolysates for RL production.

Rapid and solitary production of mono-rhamnolipid biosurfactant and biofilm inhibiting pyocyanin by a taxonomic outlier Pseudomonas aeruginosa strain CR1

Biosurfactant - Rhamnolipids (RLs) and antibacterial toxin - pyocyanin (PYO) produced by Pseudomonas aeruginosa strains have great potential for biotechnological applications. Generally, RLs are produced as a mixture of di-rhamnolipids (di-RLs) and mono-rhamnolipids (mono-RLs). Mono-RLs possess superior emulsification and antimicrobial properties and are costlier than di-RLs. In this study, a taxonomic outlier P. aeruginosa strain CR1 isolated from rhizosphere soil was explored for mono-RLs and PYO production. Phylogenetically strain CR1 resembles avirulent outlier P. aeruginosa strain ATCC9027, lacks archetypical virulence genes and harbors unique pathways for the synthesis of solely mono-RLs and PYO. Strain CR1 produced RL biosurfactant which efficiently emulsified hydrocarbons, showed hemolysis and inhibited Bacillus subtilis. At 37 °C, strain CR1 exclusively produced 21.77 g L−1 and 19.22 g L−1 rhamnolipid in glycerol amended Luria Bertani (LB) medium and basal medium amended with rice bran oil, respectively after 54 h growth. Besides RL production was unaffected under varying nitrogen sources. Structural characterization using FTIR, TLC, and LC–MS confirmed that strain CR1 exclusively produced mono-RLs, majorly dominated by Rha-C10-C10, Rha-C10-C8, and CH3-Rha-C12:2-C10:1. The compound was stable over a wide pH range (4–12), salinity (25%) and 100 °C indicating its applicability under harsh environmental conditions. In addition, strain CR1 produced 4.5 μg mL−1 PYO, which could efficiently inhibit biofilm formation by Bacillus species. The environmental outlier strain CR1 can be used for the industrial production of biotechnologically important mono-RLs and PYO.

Screening of Rhamnolipid Produced by Marine Bacterium for Heavy Metal Removal in Mangrove Soil

Mangrove located near urban area is exposed to various industrial discharge including heavy metals. Mangrove soil is capable of accumulating and storing these heavy metals. Heavy metals are toxic and non-biodegradable, so their accumulations affect water quality, while bioaccumulation and bio-assimilation of heavy metals in mangrove organisms negatively impact the food chain. Bacteria-derived biosurfactants are compounds capable of removing heavy metals from soil and sediment. Furthermore, environmentally friendly properties, such as biodegradability and low toxicity, exhibited by biosurfactants make them a suitable replacement for chemical surfactants for remediation efforts. This study was conducted to investigate the lead- (Pb) and zinc- (Zn) removing capability of rhamnolipid (RL), a type of biosurfactant produced by marine bacterium, Pseudomonas aeruginosa UMTKB-5. Rhamnolipid solutions of three different concentrations (25 mg/L, 50 mg/L and 75 mg/L) were added to mangrove soil and incubated for 7 days. The removal of Pb from soils was up to 18.3% using 25 mg/L RL solution, while 50 mg/L RL solution removed 48.3%, and 75 mg/L RL solution removed 75.9% Pb over time. Meanwhile, zinc removal of 25 mg/L RL solution was up to 24.9%, while 50 mg/L removed 16.5%, and 75 mg/L RL removed 30.5% of Zn. The results showed that RL from P. aeruginosa UMTKB-5 could be a potential biomaterial to use to remediate heavy metals in sediment.

High Di-rhamnolipid Production Using Pseudomonas aeruginosa KT1115, Separation of Mono/Di-rhamnolipids, and Evaluation of Their Properties.

Rhamnolipids (RLs) are important bioproducts that are regarded as promising biosurfactant for applications in oil exploitation, cosmetics, and food industry. In this study, the newly isolated Pseudomonas aeruginosa KT1115 showed high production of di-RLs. The highest yield of RLs by P. aeruginosa KT1115, reaching 44.39 g/L after 8 days of fermentation in a 5 L bioreactor, was obtained from rapeseed oil-nitrate medium after process optimization. Furthermore, we established a new separation process that achieved up to 91.82% RLs recovery with a purity of 89% and further obtained mono/di-rhamnolipids. Finally, ESI-MS analysis showed that the RLs produced by strain KT1115 have a high proportion of di-RLs (mono-RLs: di-RLs = 11.47: 88.53), which have a lower critical micelle-forming concentration (8 mN/m) and better emulsification ability with kerosene (52.1% EI24) than mono-RLs (167 mN/m and 41.4% EI24, respectively). These results demonstrated that P. aeruginosa KT1115 is a potential industrial producer of di-RLs, which have improved applicability and offer significant commercial benefits.

Effect of molecular structure of eco-friendly glycolipid biosurfactants on the adsorption of hair-care conditioning polymers

Pseudo-binary mixtures of different glycolipids, four different rhamnolipids (RL) and an alkyl polyglucoside (APG), with poly(diallyl-dimethylammonium chloride) (PDADMAC) have been studied in relation to their adsorption onto negatively charged surfaces to shed light on the impact of the molecular structure of surfactants from natural sources (instead of synthetic surfactant, such as sodium laureth sulfate) on the adsorption of hair-conditioning polymers. For this purpose, the self-assembly of such mixtures in aqueous solution and their adsorption onto negatively charged surfaces mimicking the negative charge of damaged hair fibres have been studied combining experiments and self-consistent field (SCF) calculations. The results show that the specific physico-chemical properties of the surfactants (charge, number of sugar rings present in surfactant structure and length of the hydrocarbon length) play a main role in the control of the adsorption process, with the adsorption efficiency and hydration being improved in relation to conventional sulfate-based systems for mixtures of PDADMAC and glycolipids with the shortest alkyl chains. SCF calculations and Energy Dispersive X-Ray Spectroscopy (EDS) analysis on real hair confirmed such observations. The results allow one to assume that the characteristic of the surfactants, especially rhamnolipids, conditions positively the adsorption potential of polyelectrolytes in these model systems. This study provides important insights on the mechanisms underlying the performance of more complex but eco-friendly washing formulations.

Rhamnolipids as an eco-friendly corrosion inhibitor of rebars in simulated concrete pore solution: evaluation of conditioning and addition methods

ABSTRACTThe objective of this study was to evaluate the use of rhamnolipids (RLs) extracted from Pseudomonas aeruginosa as a possible eco-friendly inhibitor for the corrosion protection of rebars in concrete. Two application methods were tested: application of RLs as a coating on the steel (conditioning method) and addition of the RLs directly to the aggressive environment (addition method). Both methods were evaluated for their ability to protect steel in simulated concrete pore solution containing 0.5 M NaCl. The results highlight a delay in the initiation of local corrosion followed by a rapid propagation rate of corrosion for conditioning method. This evolution is in relation with the heterogeneity of the formed RLs layers. The addition method provides a different film formation and better protection against corrosion. Using a 1 g·L concentration, the inhibition effect was observed at least for 24 h of immersion.

Simultaneous Multi-metal Removal from Soil with Washing Agents of Waste, Plant and Microbial Origin

ABSTRACT In this study, batch washings of soil highly contaminated with Cd, Cu, Ni, Pb and Zn were performed with three washing agents (WAs) of different origin, i.e., humic-like substances (HLS) extracted from municipal sewage sludge, a plant polyphenol (tannic acid, TA) and microbial rhamnolipids (RAM). At optimum concentration and pH, i.e., 5 g C/L and pH 4 (HLS), 21 g C/L and pH 4 (TA), and 3 g C/L and pH 5 (RAM), the efficiencies of HM removal were 50% (Pb) to 89% (Cd) for HLS, 61% (Zn) to 89% (Cd) for TA, and 24% (Cu) to 62% (Cd) for RAM. HLS was competitive with commercially available TA, especially for the removal of Cd, which had the highest toxic-response factor. Although single washing with HLS and TA decreased total Cd, Cu, Ni and Zn concentrations below quality standards for agricultural soil and washing with RAM decreased the Zn concentration below the standard, most HMs did not have a low potential ecological risk index after washing (Er > 40). Thus, sequential soil washing with HLS followed by HLS or with TA followed by HLS should achieve low ecological risk from HMs in soil.

Antimicrobial and antibiofilm potential of bacteriocin loaded nano-vesicles functionalized with rhamnolipids against foodborne pathogens

Synthetic lipid membranes are considered as promising food-grade nano vesicles (NVs), but their functionalization is required to empower them as active-nano vesicle systems. In this study, rhamnosomes (RS) were developed by engineering the membrane of nano-liposomes with antimicrobial surfactant i.e. rhamnolipids (RL). Intrinsically active rhamnosome nano-vesicles (RSNVs) were loaded with bacteriocin (nisin Z) to acquire broad-spectrum antimicrobial activity. Addition of rhamnolipids into the lipid bilayer exhibited an increase in the encapsulation efficiency of nisin from 47 ± 4% to 88 ± 7%. Scanning electron microscope (SEM) and Zeta-sizer revealed that the surface functionalization with RL increased the size of vesicles from 145 ± 2 nm to 209 ± 4 nm. Whereas, the zeta potential of nisin-loaded RSNVs was −20 ± 0.25 mV as compared to −3.47 ± 0.13 mV for loaded nano-liposomes, indicating higher physical stability of RSNVs. RSNVs not only demonstrated higher antimicrobial activity than liposomes but also enhanced the activity of nisin against Gram-positive and Gram-negative resistant foodborne pathogens including L. monocytogenes, S. aureus, E. coli and P. aeruginosa. Almost 80% reduction in biofilm biomass was observed when treated with nisin-loaded RSNVs due to its improved binding with bacterial surface. Thus, surface-active nanoliposomes (intrinsically active) with higher stability can provide an innovative strategy to control the biofilm-forming food associated pathogens.

INDUCTION OF RHAMNOLIPID PRODUCTION BY PSEUDOMONAS AERUGINOSA A3 USING CHEMICAL AND PHYSICAL MUTAGENIC FACTORS

This study was depend to select Pseudomonas aeruginosa A3 as a good producer of rhamnolipid (RL) biosurfactant after screening on agar plate where it was able to biosynthesize 4.3 g/L with emulsification index 52% and reducing the surface tension of water to 33.2 mN/m. Therefore, this study was aimed to increase the production of biosurfactant from selected isolate by exposure to several physical and chemical mutagenic factors like gamma radiation, nitrosoguanidine, ethyl methane sulfonate and lithium chloride. The results were shown that 0.2 g/L of nitrosoguanidine was the best mutant for increasing the production to about 2 folds (9.4 g/L) after 15 mins exposure to this material, as well as the emulsification index and surface tension of water were reached to 62% and 26.1 mN/m, respectively, comparing with non-mutant isolate. Also, the critical micelle concentration (CMC) and critical micelle dilution (CMD) of produced rhamnolipid were reached to 120 mg/L and 100 fold, respectively. The optimum conditions of RL production from mutant isolate were determined as 34ºC a best temperature, 6.5 optimum pH and incubation period of 108 h where the production was reached to 10.6 g/L and emulsification index 64% with surface tension of water 26 mN/m. characterization study of purified RL by using thin layer chromatography (TLC) analysis indicated that it was composed of a mixture of mono and di-rhamnolipid.

Chemical Induction of Aminoglycoside Uptake Overcomes Antibiotic Tolerance and Resistance in Staphylococcus aureus

Aminoglycoside antibiotics require proton motive force (PMF) for bacterial internalization. In non-respiring populations, PMF drops below the level required for drug influx, limiting the utility of aminoglycosides against strict and facultative anaerobes. We recently demonstrated that rhamnolipids (RLs), biosurfactant molecules produced by Pseudomonas aeruginosa, potentiate aminoglycoside activity against Staphylococcus aureus. Here, we demonstrate that RLs induce PMF-independent aminoglycoside uptake to restore sensitivity to otherwise tolerant persister, biofilm, small colony variant, and anaerobic populations of S. aureus. Furthermore, we show that this approach represses the rise of resistance, restores sensitivity to highly resistant clinical isolates, and is effective against other Gram-positive pathogens. Finally, while other membrane-acting agents can synergize with aminoglycosides, induction of PMF-independent uptake is uncommon, and distinct to RLs among several compounds tested. In all, small-molecule induction of PMF-independent aminoglycoside uptake circumvents phenotypic tolerance, overcomes genotypic resistance, and expands the utility of aminoglycosides against intrinsically recalcitrant bacterial populations.

Determination and comparison of the activation energies of biodiesel microemulsion and biodiesel blends

ABSTRACT Ignition delay is commonly used to evaluate biodiesel ignition quality and it is positively correlated to the activation energy of biodiesel. This study compared the effect of microemulsification and biodiesel/diesel blending on activation energies using thermogravimetric analysis. Water-in-biodiesel microemulsion was formed by the assistant of surfactant rhamnolipid (RL), with activation energies of water-in-biodiesel microemulsion and biodiesel/diesel blends being calculated for assessing thermal oxidation and ignition properties of these biodiesel hybrid fuels. Tmax values (the temperature at maximum decomposition rate) of biodiesel hybrid fuels were shifted to higher temperatures and DTGmax (the maximum decomposition rate) decreased upon the formation of microemulsion. Biodiesel microemulsification had the same effect on reduction of activation energy of biodiesel as blending diesel into biodiesel (50/50, V/V). The activation energy at lower conversion rate (α) was reduced significantly, demonstrating the great potential of using microemulsification to improve the ignition properties of the biodiesel.

Weakened adhesion force between extracellular polymeric substances of waste activated sludge caused by rhamnolipid leading to more efficient carbon release.

Rhamnolipid (RL), a biosurfactant produced by bacteria, is investigated to alter the physical characteristics of extracellular polymeric substance (EPS) of waste-activated sludge (WAS), and subsequently promotes hydrolysis and acidogenesis during anaerobic digestion for short chain fatty acids (SCFAs) production. The results revealed that RL could decrease the adhesion force of EPS from 13.46 nN to 1.08 nN, resulting in EPS disintegration layer by layer, decreasing the median particle size by 31.57 μm and releasing abundant soluble organic matter. The cell number of living bacteria remained stable after RL pretreatment (2.59 × 109 vs. 2.66 × 109), indicating that RL has a minimal impact on microbial cells (only ~2% bacterial lysis was observed). The kinetic studies of ammonia nitrogen release and SCFA production suggested that, in the RL-pretreated WAS, the reaction rate constants for hydrolysis and acidogenesis were respectively 2-fold and 1.5-fold higher than those of the control group.

Rice based distillers dried grains with solubles as a low cost substrate for the production of a novel rhamnolipid biosurfactant having anti-biofilm activity against Candida tropicalis

In this study, rhamnolipid (RL) production by Pseudomonas aeruginosa SS14 utilizing rice based Distillers Dried Grains with Solubles (rDDGS) as the sole carbon source was evaluated and the production parameters were optimized using response surface methodology. Highest RL (RL-rDDGS) yield was 14.87 g/L in a culture medium containing 12% (w/v) rDDGS and 11% (v/v) inoculum concentration after 48 h of fermentation at 35 °C. RL-rDDGS was produced as a mixture of mono and di-RL congeners with four novel homologues Rha-C18:2, Rha-C19, Rha-C9, and Rha-Rha-C19. The RL reduced the surface tension of water to 34.8 mN/m at a critical micelle concentration (CMC) value of 100 mg/L, exhibited high stability at a wide range of pH (6–12), heating time (0–120 min), and salinity (2–12% NaCl). Furthermore, RL-rDDGS demonstrated appreciable biofilm disruptive property against Candida tropicalis. This is the first report on the usage of rDDGS for sustainable and low cost production of RL.