Novel insights into biosynthesis and uptake of rhamnolipids and their precursors

Metabolic insights from mass spectrometry imaging of biofilms: A perspective from model microorganisms

Biofilms are dense aggregates of bacterial colonies embedded inside a self-produced polymeric matrix. Biofilms have received increasing attention in medical, industrial, and environmental settings due to their enhanced survival. Their characterization using microscopy techniques has revealed the presence of structural and cellular heterogeneity in many bacterial systems. However, these techniques provide limited chemical detail and lack information about the molecules important for bacterial communication and virulence. Mass spectrometry imaging (MSI) bridges the gap by generating spatial chemical information with unmatched chemical detail, making it an irreplaceable analytical platform in the multi-modal imaging of biofilms. In the last two decades, over 30 species of biofilm-forming bacteria have been studied using MSI in different environments. The literature conveys both analytical advancements and an improved understanding of the effects of environmental variables such as host surface characteristics, antibiotics, and other species of microorganisms on biofilms. This review summarizes the insights from frequently studied model microorganisms. We share a detailed list of organism-wide metabolites, commonly observed mass spectral adducts, culture conditions, strains of bacteria, substrate, broad problem definition, and details of the MS instrumentation, such as ionization sources and matrix, to facilitate future studies. We also compared the spatial characteristics of the secretome under different study designs to highlight changes because of various environmental influences. In addition, we highlight the current limitations of MSI in relation to biofilm characterization to enable cross-comparison between experiments. Overall, MSI has emerged to become an important approach for the spatial/chemical characterization of bacterial biofilms and its use will continue to grow as MSI becomes more accessible.

A review of chemical signaling pathways in the quorum sensing circuit of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an increasingly common competitive and biofilm organism in healthcare infection with sophisticated, interlinked and hierarchic quorum systems (Las, Rhl, PQS, and IQS), creates the greatest threats to the medical industry and has rendered prevailing chemotherapy medications ineffective. The rise of multidrug resistance has evolved into a concerning and potentially fatal occurrence for human life. P. aeruginosa biofilm development is assisted by exopolysaccharides, extracellular DNA, proteins, macromolecules, cellular signaling and interaction. Quorum sensing is a communication process between cells that involves autonomous inducers and regulators. Quorum-induced infectious agent biofilms and the synthesis of virulence factors have increased disease transmission, medication resistance, infection episodes, hospitalizations and mortality. Hence, quorum sensing may be a potential therapeutical target for bacterial illness, and developing quorum inhibitors as an anti-virulent tool could be a promising treatment strategy for existing antibiotics. Quorum quenching is a prevalent technique for treating infections caused by microbes because it diminishes microbial pathogenesis and increases microbe biofilm sensitivity to antibiotics, making it a potential candidate for drug development. This paper examines P. aeruginosa quorum sensing, the hierarchy of quorum sensing mechanism, quorum sensing inhibition and quorum sensing inhibitory agents as a drug development strategy to supplement traditional antibiotic strategies.

Available strategies for improving the biosynthesis of surfactin: a review

Surfactin is an excellent biosurfactant with a wide range of application prospects in many industrial fields. However, its low productivity and high cost have largely limited its commercial applications. In this review, the pathways for surfactin synthesis in Bacillus strains are summarized and discussed. Further, the latest strategies for improving surfactin production, including: medium optimization, genome engineering methods (rational genetic engineering, genome reduction, and genome shuffling), heterologous synthesis, and the use of synthetic biology combined with metabolic engineering approaches to construct high-quality artificial cells for surfactin production using xylose, are described. Finally, the prospects for improving surfactin synthesis are discussed in detail.

Biotechnological potential of microbial bio-surfactants, their significance, and diverse applications

Globally, there is a huge demand for chemically available surfactants in many industries, irrespective of their detrimental impact on the environment. Naturally occurring green sustainable substances have been proven to be the best alternative for reducing reliance on chemical surfactants and promoting long-lasting sustainable development. The most frequently utilized green active biosurfactants, which are made by bacteria, yeast, and fungi, are discussed in this review. These biosurfactants are commonly originated from contaminated sites, the marine ecosystem, and the natural environment, and it holds great potential for environmental sustainability. In this review, we described the importance of biosurfactants for the environment, including their biodegradability, low toxicity, environmental compatibility, and stability at a wide pH range. In this review, we have also described the various techniques that have been utilized to characterize and screen the generation of microbial biosurfactants. Also, we reviewed the potential of biosurfactants and its emerging applications in the foods, cosmetics, pharmaceuticals, and agricultural industries. In addition, we also discussed the ways to overcome problems with expensive costs such as low-cost substrate media formulation, gravitational techniques, and solvent-free foam fractionation for extraction that could be employed during biosurfactant production on a larger scale.

Biosynthesis and Gene Regulation of Rhamnolipid Congeners

Rhamnolipid congeners have been widely used in agriculture and biomedicine as potent surfactants. They have recently attracted attention due to their diverse and versatile biological functions, which include an important bacterial virulence factor that makes them attractive targets for research into biosynthetic pathways and gene regulation. The intricate gene expression and regulation network controlling their biosynthesis remain to be completely understood. This article summarizes current knowledge about the biosynthesis pathways and regulatory mechanisms of rhamnolipid congeners, that meet the pharmacological needs of human health and agriculture.

Improving rhamnolipids production using fermentation-foam fractionation coupling system: cell immobilization and waste frying oil emulsion

This work focused on the development of an inexpensive carbon source and the improvement of the fermentation-foam fractionation coupling system. The rhamnolipids production capacity of waste frying oil (WFO) was evaluated. The suitable bacterial cultivation of seed liquid and the addition amount of WFO was 16 h and 2% (v/v), respectively. A combined strategy of cell immobilization and oil emulsion avoid cell entrainment inside foam and improves the oil mass transfer rate. The immobilization conditions of bacterial cells into alginate-chitosan-alginate (ACA) microcapsules were optimized using the response surface method (RSM). Under the optimal conditions, rhamnolipids production using batch fermentation with immobilized strain reached 7.18 ± 0.23% g/L. WFO was emulsified into a fermentation medium using rhamnolipids as emulsifier (0.5 g/L). By monitoring dissolved oxygen, 30 mL/min was selected as a suitable air volumetric flow rate for fermentation-foam fractionation coupling operation. The total production and recovery percentage of rhamnolipids were 11.29 ± 0.36 g/L and 95.62 ± 0.38%, respectively.

Glycolipid Biosurfactants in Skincare Applications: Challenges and Recommendations for Future Exploitation

The 21st century has seen a substantial increase in the industrial applications of glycolipid biosurfactant technology. The market value of the glycolipid class of molecules, sophorolipids, was estimated to be USD 409.84 million in 2021, with that of rhamnolipid molecules projected to reach USD 2.7 billion by 2026. In the skincare industry, sophorolipid and rhamnolipid biosurfactants have demonstrated the potential to offer a natural, sustainable, and skin-compatible alternative to synthetically derived surfactant compounds. However, there are still many barriers to the wide-scale market adoption of glycolipid technology. These barriers include low product yield (particularly for rhamnolipids) and potential pathogenicity of some native glycolipid-producing microorganisms. Additionally, the use of impure preparations and/or poorly characterised congeners as well as low-throughput methodologies in the safety and bioactivity assessment of sophorolipids and rhamnolipids challenges their increased utilisation in both academic research and skincare applications. This review considers the current trend towards the utilisation of sophorolipid and rhamnolipid biosurfactants as substitutes to synthetically derived surfactant molecules in skincare applications, the challenges associated with their application, and relevant solutions proposed by the biotechnology industry. In addition, we recommend experimental techniques/methodologies, which, if employed, could contribute significantly to increasing the acceptance of glycolipid biosurfactants for use in skincare applications while maintaining consistency in biosurfactant research outputs.

Potential of Indigenous Strains Isolated from the Wastewater Treatment Plant of a Crude Oil Refinery

Contamination of the environment with crude oil or other fuels is an enormous disaster for all organisms. The microbial communities for bioremediation have been an effective tool for eliminating pollution. This study aimed to determine individual cultures’ and a strain mixture’s ability to utilize alkanes (single alkanes and crude oil). The proper study of pure cultures is necessary to design synergistically working consortia. The Acinetobacter venetianus ICP1 and Pseudomonas oleovorans ICTN13 strains isolated from a wastewater treatment plant of a crude oil refinery can grow in media containing various aromatic and aliphatic hydrocarbons. The genome of the strain ICP1 contains four genes encoding alkane hydroxylases, whose transcription depended on the length of the alkane in the media. We observed that the hydrophobic cells of the strain ICP1 adhered to hydrophobic substrates, and their biofilm formation increased the bioavailability and biodegradation of the hydrocarbons. Although strain ICTN13 also has one alkane hydroxylase-encoding gene, the growth of the strain in a minimal medium containing alkanes was weak. Importantly, the growth of the mixture of strains in the crude oil-containing medium was enhanced compared with that of the single strains, probably due to the specialization in the degradation of different hydrocarbon classes and co-production of biosurfactants.

Rhamnolipid Self-Aggregation in Aqueous Media: A Long Journey toward the Definition of Structure–Property Relationships

The need to protect human and environmental health and avoid the widespread use of substances obtained from nonrenewable sources is steering research toward the discovery and development of new molecules characterized by high biocompatibility and biodegradability. Due to their very widespread use, a class of substances for which this need is particularly urgent is that of surfactants. In this respect, an attractive and promising alternative to commonly used synthetic surfactants is represented by so-called biosurfactants, amphiphiles naturally derived from microorganisms. One of the best-known families of biosurfactants is that of rhamnolipids, which are glycolipids with a headgroup formed by one or two rhamnose units. Great scientific and technological effort has been devoted to optimization of their production processes, as well as their physicochemical characterization. However, a conclusive structure–function relationship is far from being defined. In this review, we aim to move a step forward in this direction, by presenting a comprehensive and unified discussion of physicochemical properties of rhamnolipids as a function of solution conditions and rhamnolipid structure. We also discuss still unresolved issues that deserve further investigation in the future, to allow the replacement of conventional surfactants with rhamnolipids.

Antibiofilm properties of cathelicidin LL-37: an in-depth review

Notwithstanding ceaseless endeavors toward developing effective antibiofilm chemotherapeutics, biofilm-associated infections continue to be one of the most perplexing challenges confronting medicine today. Endogenous host defense peptides, such as the human cathelicidin LL-37, are being propounded as promising options for treating such infectious diseases. Over the past decennium, LL-37 has duly received tremendous research attention by virtue of its broad-spectrum antimicrobial activity and immunomodulatory properties. No attempt has hitherto been made, as far as we are aware, to comprehensively review the antibiofilm effects of LL-37. Accordingly, the intent in this paper is to provide a fairly all-embracing review of the literature available on the subject. Accumulating evidence suggests that LL-37 is able to prevent biofilm establishment by different bacterial pathogens such as Acinetobacter baumannii, Aggregatibacter actinomycetemcomitans, Bacteroides fragilis, Burkholderia thailandensis, Cutibacterium acnes, Escherichia coli, Francisella tularensis, Helicobacter pylori, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes. Inhibition of bacterial adhesion, downregulation of biofilm-associated genes, suppression of quorum-sensing pathways, degradation of biofilm matrix, and eradication of biofilm-residing cells are the major mechanisms responsible for antibiofilm properties of LL-37. In terms of its efficacy and safety in vivo, there are still many questions to be answered. Undoubtedly, LL-37 can open up new windows of opportunity to prevent and treat obstinate biofilm-mediated infections.

Guava Seed Oil: Potential Waste for the Rhamnolipids Production

Guava is consumed in natura and is also of considerable importance to the food industry. The seeds and peel of this fruit are discarded, however, guava seeds yield oil (~13%) that can be used for the bioproducts synthesis. The use of a by-product as a carbon source is advantageous, as it reduces the environmental impact of possible harmful materials to nature, while adding value to products. In addition, the use of untested substrates can bring new yield and characterization results. Thus, this research sought to study rhamnolipids (RLs) production from guava seed oil, a by-product of the fructorefinery. The experiments were carried out using Pseudomonas aeruginosa LBI 2A1 and experimental design was used to optimize the variables Carbon and Nitrogen concentration. Characterization of RLs produced occurred by LC-MS. In this study, variables in the quadratic forms and the interaction between them influenced the response (p < 0.05). The most significant variable was N concentration. Maximum RLs yield achieved 39.97 g/L, predominantly of mono-RL. Characterization analysis revealed 9 homologues including the presence of RhaC10C14:2 (m/z 555) whose structure has not previously been observed. This research showed that guava seed oil is an alternative potential carbon source for rhamnolipid production with rare rhamnolipid homologues.

Microbial surfactants: A journey from fundamentals to recent advances

Microbial surfactants are amphiphilic surface-active substances aid to reduce surface and interfacial tensions by accumulating between two fluid phases. They can be generically classified as low or high molecular weight biosurfactants based on their molecular weight, whilst overall chemical makeup determines whether they are neutral or anionic molecules. They demonstrate a variety of fundamental characteristics, including the lowering of surface tension, emulsification, adsorption, micelle formation, etc. Microbial genera like Bacillus spp., Pseudomonas spp., Candida spp., and Pseudozyma spp. are studied extensively for their production. The type of biosurfactant produced is reliant on the substrate utilized and the pathway pursued by the generating microorganisms. Some advantages of biosurfactants over synthetic surfactants comprise biodegradability, low toxicity, bioavailability, specificity of action, structural diversity, and effectiveness in harsh environments. Biosurfactants are physiologically crucial molecules for producing microorganisms which help the cells to grasp substrates in adverse conditions and also have antimicrobial, anti-adhesive, and antioxidant properties. Biosurfactants are in high demand as a potential product in industries like petroleum, cosmetics, detergents, agriculture, medicine, and food due to their beneficial properties. Biosurfactants are the significant natural biodegradable substances employed to replace the chemical surfactants on a global scale in order to make a cleaner and more sustainable environment.

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.

Production and Characterization of Rhamnolipids Produced by Pseudomonas aeruginosa DBM 3774: Response Surface Methodology Approach

Rhamnolipids are extensively studied biosurfactants due to their potential in many industrial applications, eco-friendly production and properties. However, their availability for broader application is severely limited by their production costs, therefore the optimization of efficacy of their cultivation gains significance as well as the information regarding the physio-chemical properties of rhamnolipids resulting from various cultivation strategies. In this work, the bioprocess design focused on optimization of the rhamnolipid yield of Pseudomonas aeruginosa DBM 3774 utilizing the response surface methodology (RSM). Six carbon sources were investigated for their effect on the rhamnolipid production. The RSM prediction improved the total rhamnolipid yield from 2.2 to 13.5 g/L and the rhamnolipid productivity from 11.6 to 45.3 mg/L/h. A significant effect of the carbon source type, concentration and the C/N ratio on the composition of the rhamnolipid congeners has been demonstrated for cultivation of P. aeruginosa DBM 3774 in batch cultivation. Especially, changes in presence of saturated fatty acid in the rhamnolipid congeners, ranging from 18.8% of unsaturated fatty acids (carbon source glycerol; 40 g/L) to 0% (sodium citrate 20 g/L) were observed. This demonstrates possibilities of model based systems as basis in cultivation of industrially important compounds like biosurfactants rhamnolipids and the importance of detailed study of interconnection between cultivation conditions and rhamnolipid mixture composition and properties.

Transcription-Associated Fluorescence-Activated Droplet Sorting for Di-rhamnolipid Hyperproducers

Rhamnolipids (RLs) are biosurfactants with great economic significance that have been used extensively in multiple industries. Pseudomonas aeruginosa is a promising microorganism for sustainable RL production. However, current CTAB-MB based screening of RL-producing strains is time-consuming, labor-intensive, and unable to distinguish mono- and di-RL. In this study, we developed a novel transcription-associated fluorescence-activated droplet sorting (FADS) method to specifically target the di-RL hyperproducers. We first investigated critical factors associated with this method, including the specificity and sensitivity for discriminating di-RL overproducers from other communities. Validation of genotype-phenotype linkage between the GFP intensity, rhlC transcription, and di-RL production showed that rhlC transcription is closely correlated with di-RL production, and the GFP intensity is responsive to rhlC transcription, respectively. Using this platform, we screened out ten higher di-RL producing microorganisms, which produced 54-208% more di-RL than the model P. aeruginosa PAO1. In summary, the droplet-based microfluidic platform not only facilitates a more specific, reliable, and rapid screening of P. aeruginosa colonies with desired phenotypes, but also shows that intracellular transcription-associated GFP intensity can be used to measure the yield of di-RL between populations of droplets containing different environmental colonies. This method also can be integrated with transposon mutation libraries to target P. aeruginosa mutants.

Structural, mechanistic and physiological insights into phospholipase A-mediated membrane phospholipid degradation in Pseudomonas aeruginosa

Cells steadily adapt their membrane glycerophospholipid (GPL) composition to changing environmental and developmental conditions. While the regulation of membrane homeostasis via GPL synthesis in bacteria has been studied in detail, the mechanisms underlying the controlled degradation of endogenous GPLs remain unknown. Thus far, the function of intracellular phospholipases A (PLAs) in GPL remodeling (Lands cycle) in bacteria is not clearly established. Here, we identified the first cytoplasmic membrane-bound phospholipase A₁ (PlaF) from Pseudomonas aeruginosa, which might be involved in the Lands cycle. PlaF is an important virulence factor, as the P. aeruginosa ΔplaF mutant showed strongly attenuated virulence in Galleria mellonella and macrophages. We present a 2.0-Å-resolution crystal structure of PlaF, the first structure that reveals homodimerization of a single-pass transmembrane (TM) full-length protein. PlaF dimerization, mediated solely through the intermolecular interactions of TM and juxtamembrane regions, inhibits its activity. The dimerization site and the catalytic sites are linked by an intricate ligand-mediated interaction network, which might explain the product (fatty acid) feedback inhibition observed with the purified PlaF protein. We used molecular dynamics simulations and configurational free energy computations to suggest a model of PlaF activation through a coupled monomerization and tilting of the monomer in the membrane, which constrains the active site cavity into contact with the GPL substrates. Thus, these data show the importance of the PlaF-mediated GPL remodeling pathway for virulence and could pave the way for the development of novel therapeutics targeting PlaF.

Isolation and chemical characterization of the biosurfactant produced by Gordonia sp. IITR100

Biosurfactants are amphipathic molecules produced from microorganisms. There are relatively few species known where the detailed chemical characterization of biosurfactant has been reported. Here, we report isolation and chemical characterization of the biosurfactant produced by a biodesulfurizing bacterium Gordonia sp. IITR100. Biosurfactant production was determined by performing oil spreading, drop-collapse, Emulsion index (E24), and Bacterial adhesion to hydrocarbons (BATH) assay. The biosurfactant was identified as a glycolipid by LCMS and GCMS analysis. The chemical structure was further confirmed by performing FTIR and NMR of the extracted biosurfactant. The emulsion formed by the biosurfactant was found to be stable between temperatures of 4°C to 30°C, pH of 6 to 10 and salt concentrations up to 2%. It was successful in reducing the surface tension of the aqueous media from 61.06 mN/m to 36.82 mN/m. The biosurfactant produced can be used in petroleum, detergents, soaps, the food and beverage industry and the healthcare industry.

The beauty of biocatalysis: sustainable synthesis of ingredients in cosmetics

Covering: 2015 up to July 2021The market for cosmetics is consumer driven and the desire for green, sustainable and natural ingredients is increasing. The use of isolated enzymes and whole-cell organisms to synthesise these products is congruent with these values, especially when combined with the use of renewable, recyclable or waste feedstocks. The literature of biocatalysis for the synthesis of ingredients in cosmetics in the past five years is herein reviewed.

Production of rhamnolipids by the Thermoanaerobacter sp. CM-CNRG TB177 strain isolated from an oil well in Mexico

This study aimed to produce and characterize biosurfactants using the Thermoanaerobacter sp. CM-CNRG TB177 strain isolated from an oil field in Mexico, as well as assessing the influence of different carbon and nitrogen sources on the capacity of the produced surfactant to reduce the surface tension of water. The thin-layer chromatography (TLC) revealed that the obtained extract corresponds to a mono-rhamnolipid; the results of the ultra-performance-liquid chromatography/mass spectrometry (UPLC/MS) analysis revealed that the Thermoanaerobacter sp. CM-CNRG TB177 strain produces a mixture of three rhamnolipids, whose masses correspond to mono-rhamnolipid. The rhamnolipids mixture obtained using 2.5% molasses as carbon source diminished the surface tension of water to 29.67 mNm^-1, indicating that the concentration of molasses influenced the capacity of the produced surfactant to reduce the surface tension of water. Also, the microorganism was not capable of growing in the absence of yeast extract as nitrogen source. To the best of our knowledge, the presented results describe for the first time the nature of the biosurfactant produced by a bacterium of the Thermoanaerobacter genus.Key points• Thermoanaerobacter sp. CM-CNRG TB177 produces biosurfactants, and its glycolipid nature is described for the first time.• The HPLC analysis revealed a mixture of three rhamnolipid congeners, and UPLC/MS analysis determined that two of the congeners are the rhamnolipids Rha-C8-C10 and Rha-C12-C10.• The lowest surface tension of 29.67 mNm^-1 was obtained with molasses as source of carbon at a 2.5% concentration.

Glycolipid Biosurfactant Production from Waste Cooking Oils by Yeast: Review of Substrates, Producers and Products

Biosurfactants are a microbially synthesized alternative to synthetic surfactants, one of the most important bulk chemicals. Some yeast species are proven to be exceptional biosurfactant producers, while others are emerging producers. A set of factors affects the type, amount, and properties of the biosurfactant produced, as well as the environmental impact and costs of biosurfactant’s production. Exploring waste cooking oil as a substrate for biosurfactants’ production serves as an effective cost-cutting strategy, yet it has some limitations. This review explores the existing knowledge on utilizing waste cooking oil as a feedstock to produce glycolipid biosurfactants by yeast. The review focuses specifically on the differences created by using raw cooking oil or waste cooking oil as the substrate on the ability of various yeast species to synthesize sophorolipids, rhamnolipids, mannosylerythritol lipids, and other glycolipids and the substrate’s impact on the composition, properties, and limitations in the application of biosurfactants.

A Complex of LaoA and LaoB Acts as a Tat-Dependent Dehydrogenase for Long-Chain Alcohols in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa can utilize unusual carbon sources, like sodium dodecyl sulfate (SDS) and alkanes. Whereas the initiating enzymatic steps of the corresponding degradation pathways have been characterized in detail, the oxidation of the emerging long-chain alcohols has received little attention. Recently, the genes for the Lao (long-chain-alcohol/aldehyde oxidation) system were discovered to be involved in the oxidation of long-chain alcohols derived from SDS and alkane degradation. In the Lao system, LaoA is predicted to be an alcohol dehydrogenase/oxidase; however, according to genetic studies, efficient long-chain-alcohol oxidation additionally required the Tat-dependent protein LaoB. In the present study, the Lao system was further characterized. In vivo analysis revealed that the Lao system complements the substrate spectrum of the well-described Exa system, which is required for growth with ethanol and other short-chain alcohols. Mutational analysis revealed that the Tat site of LaoB was required for long-chain-alcohol oxidation activity, strongly suggesting a periplasmic localization of the complex. Purified LaoA was fully active only when copurified with LaoB. Interestingly, in vitro activity of the purified LaoAB complex also depended on the presence of the Tat site. The copurified LaoAB complex contained a flavin cofactor and preferentially oxidized a range of saturated, unbranched primary alcohols. Furthermore, the LaoAB complex could reduce cytochrome c₅₅₀-type redox carriers like ExaB, a subunit of the Exa alcohol dehydrogenase system. LaoAB complex activity was stimulated by rhamnolipids in vitro. In summary, LaoAB constitutes an unprecedented protein complex with specific properties apparently required for oxidizing long-chain alcohols. IMPORTANCE Pseudomonas aeruginosa is a major threat to public health. Its ability to thrive in clinical settings, water distribution systems, or even jet fuel tanks is linked to detoxification and degradation of diverse hydrophobic substrates that are metabolized via alcohol intermediates. Our study illustrates a novel flavoprotein long-chain-alcohol dehydrogenase consisting of a facultative two-subunit complex, which is unique among related enzymes, while the homologs of the corresponding genes are found in numerous bacterial genomes. Understanding the catalytic and compartmentalization processes involved is of great interest for biotechnological and hygiene research, as it may be a potential starting point for rationally designing novel antibacterial substances with high specificity against this opportunistic pathogen.

Heavy Vacuum Gas Oil Upregulates the Rhamnosyltransferases and Quorum Sensing Cascades of Rhamnolipids Biosynthesis in Pseudomonas sp. AK6U

We followed a comparative approach to investigate how heavy vacuum gas oil (HVGO) affects the expression of genes involved in biosurfactants biosynthesis and the composition of the rhamnolipid congeners in Pseudomonas sp. AK6U. HVGO stimulated biosurfactants production as indicated by the lower surface tension (26 mN/m) and higher yield (7.8 g/L) compared to a glucose culture (49.7 mN/m, 0.305 g/L). Quantitative real-time PCR showed that the biosurfactants production genes rhlA and rhlB were strongly upregulated in the HVGO culture during the early and late exponential growth phases. To the contrary, the rhamnose biosynthesis genes algC, rmlA and rmlC were downregulated in the HVGO culture. Genes of the quorum sensing systems which regulate biosurfactants biosynthesis exhibited a hierarchical expression profile. The lasI gene was strongly upregulated (20-fold) in the HVGO culture during the early log phase, whereas both rhlI and pqsE were upregulated during the late log phase. Rhamnolipid congener analysis using high-performance liquid chromatography-mass spectrometry revealed a much higher proportion (up to 69%) of the high-molecularweight homologue Rha–Rha–C₁₀–C₁₀ in the HVGO culture. The results shed light on the temporal and carbon source-mediated shifts in rhamonlipids’ composition and regulation of biosynthesis which can be potentially exploited to produce different rhamnolipid formulations tailored for specific applications.

Biosurfactant based formulation of Pseudomonas guariconensis LE3 with multifarious plant growth promoting traits controls charcoal rot disease in Helianthus annus

Biosurfactants are environment compatible surface-active biomolecules with multifunctional properties which can be utilized in various industries. In this study a biosurfactant producing novel plant growth promoting isolate Pseudomonas guariconensis LE3 from the rhizosphere of Lycopersicon esculentum is presented as biostimulant and biocontrol agent. Biosurfactant extracted from culture was characterized to be mixture of various mono- and di-rhamnolipids with antagonistic activity against Macrophomina phaseolina, causal agent of charcoal rot in diverse crops. Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (¹H NMR) analysis confirmed the rhamnolipid nature of biosurfactant. PCR analysis established the presence of genes involved in synthesis of antibiotics diacetylphloroglucinol, phenazine 1-carboxylic acid and pyocyanin, and lytic enzymes chitinase and endoglucanase suggesting biocontrol potential of the isolate. Plant growth promoting activities shown by LE3 were phosphate solubilization and production of siderophores, indole acetic acid (IAA), ammonia and 1-aminocyclopropane-1-carboxylate deaminase (ACCD). To assemble all the characteristics of LE3 various bioformuations were developed. Amendment of biosurfactant in bioformulation of LE3 cells improved the shelf life. Biosurfactant amended formulation of LE3 cells was most effective in biocontrol of charcoal rot disease of sunflower and growth promotion in field conditions. The root adhered soil mass of plantlets inoculated with LE3 plus biosurfactant was significantly higher over control. Biosurfactant amended formulation of LE3 cells caused maximum yield enhancement (80.80%) and biocontrol activity (75.45%), indicating that addition of biosurfactant improves the plant-bacterial interaction and soil properties leading to better control of disease and overall improvement of plant health and yield.

The role of transport proteins in the production of microbial glycolipid biosurfactants

Several microorganisms are currently being used as production platform for glycolipid biosurfactants, providing a greener alternative to chemical biosurfactants. One of the reasons why these processes are commercially competitive is the fact that microbial producers can efficiently export their product to the extracellular environment, reaching high product titers. Glycolipid biosynthetic genes are often found in a dedicated cluster, amidst which genes encoding a dedicated transporter committed to shuttle the glycolipid to the extracellular environment are often found, as is the case for many other secondary metabolites. Knowing this, one can rely on gene clustering features to screen for novel putative transporters, as described and performed in this review. The above strategy proves to be very powerful to identify glycolipid transporters in fungi but is less valid for bacterial systems. Indeed, the genetics of these export systems are currently largely unknown, but some hints are given. Apart from the direct export of the glycolipid, several other transport systems have an indirect effect on glycolipid production. Specific importers dictate which hydrophilic and hydrophobic substrates can be used for production and influence the final yields. In eukaryotes, cellular compartmentalization allows the assembly of glycolipid building blocks in a highly specialized and efficient way. Yet, this requires controlled transport across intracellular membranes. Next to the direct export of glycolipids, the current state of the art regarding this indirect involvement of transporter systems in microbial glycolipid synthesis is summarized in this review. KEY POINTS: • Transporters are directly and indirectly involved in microbial glycolipid synthesis. • Yeast glycolipid transporters are found in their biosynthetic gene cluster. • Hydrophilic and hydrophobic substrate uptake influence microbial glycolipid synthesis.

Rhamnolipid the Glycolipid Biosurfactant: Emerging trends and promising strategies in the field of biotechnology and biomedicine

Rhamnolipids (RLs) are surface-active compounds and belong to the class of glycolipid biosurfactants, mainly produced from Pseudomonas aeruginosa. Due to their non-toxicity, high biodegradability, low surface tension and minimum inhibitory concentration values, they have gained attention in various sectors like food, healthcare, pharmaceutical and petrochemicals. The ecofriendly biological properties of rhamnolipids make them potent materials to be used in therapeutic applications. RLs are also known to induce apoptosis and thus, able to inhibit proliferation of cancer cells. RLs can also act as immunomodulators to regulate the humoral and cellular immune systems. Regarding their antimicrobial property, they lower the surface hydrophobicity, destruct the cytoplasmic membrane and lower the critical micelle concentration to kill the bacterial cells either alone or in combination with nisin possibly due to their role in modulating outer membrane protein. RLs are also involved in the synthesis of nanoparticles for in vivo drug delivery. In relation to economic benefits, the post-harvest decay of food can be decreased by RLs because they prevent the mycelium growth, spore germination of fungi and inhibit the emergence of biofilm formation on food. The present review focuses on the potential uses of RLs in cosmetic, pharmaceutical, food and health-care industries as the potent therapeutic agents.

Rhamnolipids produced by Pseudomonas: from molecular genetics to the market

Rhamnolipids are biosurfactants with a wide range of industrial applications that entered into the market a decade ago. They are naturally produced by Pseudomonas aeruginosa and some Burkholderia species. Occasionally, some strains of different bacterial species, like Pseudomonas chlororaphis NRRL B-30761, which have acquired RL-producing ability by horizontal gene transfer, have been described. P. aeruginosa, the ubiquitous opportunistic pathogenic bacterium, is the best rhamnolipids producer, but Pseudomonas putida has been used as heterologous host for the production of this biosurfactant with relatively good yields. The molecular genetics of rhamnolipids production by P. aeruginosa has been widely studied not only due to the interest in developing overproducing strains, but because it is coordinately regulated with the expression of different virulence-related traits by the quorum-sensing response. Here, we highlight how the research of the molecular mechanisms involved in rhamnolipid production have impacted the development of strains that are suitable for industrial production of this biosurfactant, as well as some perspectives to improve these industrial useful strains.

Microbial biosurfactant research: time to improve the rigour in the reporting of synthesis, functional characterization and process development

The demand for microbially produced surface-active compounds for use in industrial processes and products is increasing. As such, there has been a comparable increase in the number of publications relating to the characterization of novel surface-active compounds: novel producers of already characterized surface-active compounds and production processes for the generation of these compounds. Leading researchers in the field have identified that many of these studies utilize techniques are not precise and accurate enough, so some published conclusions might not be justified. Such studies lacking robust experimental evidence generated by validated techniques and standard operating procedures are detrimental to the field of microbially produced surface-active compound research. In this publication, we have critically reviewed a wide range of techniques utilized in the characterization of surface-active compounds from microbial sources: identification of surface-active compound producing microorganisms and functional testing of resultant surface-active compounds. We have also reviewed the experimental evidence required for process development to take these compounds out of the laboratory and into industrial application. We devised this review as a guide to both researchers and the peer-reviewed process to improve the stringency of future studies and publications within this field of science.

Characterization and application of rhamnolipid from Pseudomonas plecoglossicida BP03

The production of rhamnolipid (glycolipid) biosurfactant was achieved under optimized conditions from newly isolated bacteria (Pseudomonas plecoglossicida BP03) from rice mill effluent. The isolated biosurfactant was structurally characterized using FTIR and NMR spectroscopic studies. The obtained biosurfactant (1·39 g l^-1 ) showed a variety of applications including larvicidal and pupicidal activity against malarial vector (Anopheles sunadicus). It also exhibited antimicrobial activity against human pathogens, and possessed potent anti-biofilm activity against Staphylococcus aureus, Bacillus subtilis and Aeromonas hydrophila. The obtained biosurfactant showed a dose-dependent inhibition of exopolymeric substance (EPS) and growth curve in S. aureus. Furthermore, the cytotoxicity assays revealed that the biosurfactant exhibit a cytotoxic potency against the human fibroblastic sarcoma cells Ht-1080. An in silco analysis was also performed using Schrodinger maestro 9.3 against surface protein (SasG) of S. aureus, and the resultant analysis revealed an interactive docking score of -3·4 kcal mol^-1 . The obtained result indicates that the synthesized economically viable biosurfactant ensures excellent applications towards various fields.

Heterologous Rhamnolipid Biosynthesis: Advantages, Challenges, and the Opportunity to Produce Tailor-Made Rhamnolipids

The first heterologous expression of genes responsible for the production of rhamnolipids was already implemented in the mid-1990s during the functional identification of the rhlAB operon. This was the starting shot for multiple approaches to establish the rhamnolipid biosynthesis in different host organisms. Since most of the native rhamnolipid producing organisms are human or plant pathogens, the intention for these ventures was the establishment of non-pathogenic organisms as heterologous host for the production of rhamnolipids. The pathogenicity of producing organisms is one of the bottlenecks for applications of rhamnolipids in many industrial products especially foods and cosmetics. The further advantage of heterologous rhamnolipid production is the circumvention of the complex regulatory network, which regulates the rhamnolipid biosynthesis in wild type production strains. Furthermore, a suitable host with an optimal genetic background to provide sufficient amounts of educts allows the production of tailor-made rhamnolipids each with its specific physico-chemical properties depending on the contained numbers of rhamnose sugar residues and the numbers, chain length and saturation degree of 3-hydroxyfatty acids. The heterologous expression of rhl genes can also enable the utilization of unusual carbon sources for the production of rhamnolipids depending on the host organism.

Large Enrichment of Anthropogenic Organic Matter Degrading Bacteria in the Sea-Surface Microlayer at Coastal Livingston Island (Antarctica)

The composition of bacteria inhabiting the sea-surface microlayer (SML) is poorly characterized globally and yet undescribed for the Southern Ocean, despite their relevance for the biogeochemistry of the surface ocean. We report the abundances and diversity of bacteria inhabiting the SML and the subsurface waters (SSL) determined from a unique sample set from a polar coastal ecosystem (Livingston Island, Antarctica). From early to late austral summer (January–March 2018), we consistently found a higher abundance of bacteria in the SML than in the SSL. The SML was enriched in some Gammaproteobacteria genus such as Pseudoalteromonas, Pseudomonas, and Colwellia, known to degrade a wide range of semivolatile, hydrophobic, and surfactant-like organic pollutants. Hydrocarbons and other synthetic chemicals including surfactants, such as perfluoroalkyl substances (PFAS), reach remote marine environments by atmospheric transport and deposition and by oceanic currents, and are known to accumulate in the SML. Relative abundances of specific SML-enriched bacterial groups were significantly correlated to concentrations of PFASs, taken as a proxy of hydrophobic anthropogenic pollutants present in the SML and its stability. Our observations provide evidence for an important pollutant-bacteria interaction in the marine SML. Given that pollutant emissions have increased during the Anthropocene, our results point to the need to assess chemical pollution as a factor modulating marine microbiomes in the contemporaneous and future oceans.

Integration of Genetic and Process Engineering for Optimized Rhamnolipid Production Using Pseudomonas putida

Rhamnolipids are biosurfactants produced by microorganisms with the potential to replace synthetic compounds with petrochemical origin. To promote industrial use of rhamnolipids, recombinant rhamnolipid production from sugars needs to be intensified. Since this remains challenging, the aim of the presented research is to utilize a multidisciplinary approach to take a step toward developing a sustainable rhamnolipid production process. Here, we developed expression cassettes for stable integration of the rhamnolipid biosynthesis genes into the genome outperformed plasmid-based expression systems. Furthermore, the genetic stability of the production strain was improved by using an inducible promoter. To enhance rhamnolipid synthesis, energy- and/or carbon-consuming traits were removed: mutants negative for the synthesis of the flagellar machinery or the storage polymer PHA showed increased production by 50%. Variation of time of induction resulted in an 18% increase in titers. A scale-up from shake flasks was carried out using a 1-L bioreactor. By recycling of the foam, biomass loss could be minimized and a rhamnolipid titer of up to 1.5 g/L was achieved without using mechanical foam destroyers or antifoaming agents. Subsequent liquid-liquid extraction was optimized by using a suitable minimal medium during fermentation to reduce undesired interphase formation. A technical-scale production process was designed and evaluated by a life-cycle assessment (LCA). Different process chains and their specific environmental impact were examined. It was found that next to biomass supply, the fermentation had the biggest environmental impact. The present work underlines the need for multidisciplinary approaches to address the challenges associated with achieving sustainable production of microbial secondary metabolites. The results are discussed in the context of the challenges of microbial biosurfactant production using hydrophilic substrates on an industrial scale.

Rhamnolipid enhances Burkholderia pseudomallei biofilm susceptibility, disassembly and production of virulence factors

Aim: This study evaluated the effect of the biosurfactant rhamnolipid on the antimicrobial susceptibility, biofilm growth dynamics and production of virulence factors by Burkholderia pseudomallei. Materials & methods: The effects of rhamnolipid on planktonic and biofilm growth and its interaction with antibacterial drugs were evaluated. Then, its effects on growing and mature biofilms and on protease and siderophore production were assessed. Results: Rhamnolipid did not inhibit B. pseudomallei growth, but significantly enhanced the activity of meropenem and amoxicillin-clavulanate against mature biofilms. Rhamnolipid significantly reduced the biomass of mature biofilms, significantly increased protease production by growing and mature biofilms and siderophore release by growing biofilms. Conclusion: Rhamnolipid enhances the antimicrobial activity against B. pseudomallei, assists biofilm disassembly and alters protease and siderophore production by bacterial biofilms.

Environmentally friendly rhamnolipid production for petroleum remediation

Biosurfactants have potential applications in the remediation of petroleum-contaminated sites. Several strategies can be used to reduce the production costs of these surfactants and make the process more environmentally friendly. In this study, we combined some of these strategies to produce the rhamnolipid-type biosurfactant, including the use of the genetically modified strain Pseudomonas aeruginosa-estA, an industrial coproduct as a carbon source, a simple and low-cost medium, and a simple downstream process. The process resulted in a high yield (17.6 g L^-1), even using crude glycerin as the carbon source, with substrate in product conversion factor (Y_RML/s) of 0.444. The cell-free supernatant (CFS) was not toxic to Artemia salina and selected mammalian cell lineages, suggesting that it can be used directly in the environment without further purification steps. Qualitative analysis showed that CFS has excellent dispersion in the oil-displacement test, emulsifying (IE₂₄ = 65.5%), and tensoactive properties. When salinity, temperature and pressure were set to seawater conditions, the values for interfacial tension between crude oil and water were below 1.0 mN m^-1. Taken together, these results demonstrate that it is possible to obtain a nontoxic crude rhamnolipid product, with high productivity, to replace petroleum-based surfactants in oil spill cleanups and other environmental applications.

Transcriptome analysis of crude oil degrading Pseudomonas aeruginosa strains for identification of potential genes involved in crude oil degradation

In the microbial world, bacteria are the most effective agents in petroleum hydrocarbons (PHs) degradation, utilization/mineralization and they serve as essential degraders of crude oil contaminated environment. Some genes and traits are involved in the hydrocarbon utilization process for which transcriptome analyses are important to identify differentially expressed genes (DEGs) among different conditions, leading to a new understanding of genes or pathways associated with crude oil degradation. In this work, three crude oil utilizing Pseudomonas aeruginosa strains designated as N002, TP16 and J001 subjected to transcriptome analyses revealed a total of 81, 269 and 137 significant DEGs. Among them are 80 up-regulated genes and one downregulated gene of N002, 121 up- regulated and 148 down-regulated genes of TP16, 97 up-regulated and 40 down-regulated genes of J001 which are involved in various metabolic pathways. TP16 strain has shown more number of DEGs upon crude oil treatment in comparison to the other two strains. Through quantitative real time polymerase chain reaction (qRT-PCR), the selected DEGs of each strain from transcriptome data were substantiated. The results have shown that the up- regulated and down-regulated genes observed by qRT-PCR were consistent with transcriptome data. Taken together, our transcriptome results have revealed that TP16 is a potential P. aeruginosa strain for functional analysis of identified potential DEGs involved in crude oil degradation.

Comparison of Three Xylose Pathways in Pseudomonas putida KT2440 for the Synthesis of Valuable Products

Pseudomonas putida KT2440 is a well-established chassis in industrial biotechnology. To increase the substrate spectrum, we implemented three alternative xylose utilization pathways, namely the Isomerase, Weimberg, and Dahms pathways. The synthetic operons contain genes from Escherichia coli and Pseudomonas taiwanensis. For isolating the Dahms pathway in P. putida KT2440 two genes (PP_2836 and PP_4283), encoding an endogenous enzyme of the Weimberg pathway and a regulator for glycolaldehyde degradation, were deleted. Before and after adaptive laboratory evolution, these strains were characterized in terms of growth and synthesis of mono-rhamnolipids and pyocyanin. The engineered strain using the Weimberg pathway reached the highest maximal growth rate of 0.30 h-1. After adaptive laboratory evolution the lag phase was reduced significantly. The highest titers of 720 mg L-1 mono-rhamnolipids and 30 mg L-1 pyocyanin were reached by the evolved strain using the Weimberg or an engineered strain using the Isomerase pathway, respectively. The different stoichiometries of the three xylose utilization pathways may allow engineering of tailored chassis for valuable bioproduct synthesis.

Simultaneous Application of Biosurfactant and Bioaugmentation with Rhamnolipid-Producing Shewanella for Enhanced Bioremediation of Oil-Polluted Soil

In the present study, a combined treatment strategy involving the addition of rhamnolipid, rhamnolipid-producing bacteria (Shewanella sp. BS4) and a native soil microbial community for the remediation of hydrocarbon-contaminated soil under pilot-scale conditions was adopted. The isolate BS4 (rhl+), demonstrating the highest emulsification activity and surface tension reduction efficiency, was identified based on 16 S rDNA sequencing as Shewanella sp. strain. Growth conditions for rhamnolipid production were optimized based on Central Composite Design (CCD) as 2.9% crude oil, a 54 × 106 CFU g−1 inoculation load of soil, a temperature of 30.5 °C, and a pH of 6.7. In situ bioremediation experiments, conducted using hydrocarbon-contaminated soil treated with the combination of rhamnolipid and rhamnolipid-producing bacteria, showed that the inoculated Shewanella sp. BS4, along with the indigenous soil microbial community, supported the highest hydrocarbon-degrading bacterial population and soil respiration activity, and this treatment resulted in 75.8% hydrocarbon removal efficiency, which was higher compared to contaminated soil devoid of any treatment.

Marine Biosurfactants: Biosynthesis, Structural Diversity and Biotechnological Applications

Biosurfactants are amphiphilic secondary metabolites produced by microorganisms. Marine bacteria have recently emerged as a rich source for these natural products which exhibit surface-active properties, making them useful for diverse applications such as detergents, wetting and foaming agents, solubilisers, emulsifiers and dispersants. Although precise structural data are often lacking, the already available information deduced from biochemical analyses and genome sequences of marine microbes indicates a high structural diversity including a broad spectrum of fatty acid derivatives, lipoamino acids, lipopeptides and glycolipids. This review aims to summarise biosyntheses and structures with an emphasis on low molecular weight biosurfactants produced by marine microorganisms and describes various biotechnological applications with special emphasis on their role in the bioremediation of oil-contaminated environments. Furthermore, novel exploitation strategies are suggested in an attempt to extend the existing biosurfactant portfolio.

Heterologous rhamnolipid biosynthesis by P. putida KT2440 on bio-oil derived small organic acids and fractions

In many cases in industrial biotechnology, substrate costs make up a major part of the overall production costs. One strategy to achieve more cost-efficient processes in general is to exploit cheaper sources of substrate. Small organic acids derived from fast pyrolysis of lignocellulosic biomass represent a significant proportion of microbially accessible carbon in bio-oil. However, using bio-oil for microbial cultivation is a highly challenging task due to its strong adverse effects on microbial growth as well as its complex composition. In this study, the suitability of bio-oil as a substrate for industrial biotechnology was investigated with special focus on organic acids. For this purpose, using the example of the genetically engineered, non-pathogenic bacterium Pseudomonas putida KT2440 producing mono-rhamnolipids, cultivation on small organic acids derived from fast pyrolysis of lignocellulosic biomass, as well as on bio-oil fractions, was investigated and evaluated. As biosurfactants, rhamnolipids represent a potential bulk product of industrial biotechnology where substitution of traditional carbon sources is of conceivable interest. Results suggest that maximum achievable productivities as well as substrate-to-biomass yields are in a comparable range for glucose, acetate, as well as the mixture of acetate, formate and propionate. Similar yields were obtained for a pretreated bio-oil fraction, which was used as reference real raw material, although with significantly lower titers. As such, the reported process constitutes a proof-of-principle for using bio-oil as a potential cost-effective alternative carbon source in a future bio-based economy.

Role of β-oxidation and de novo fatty acid synthesis in the production of rhamnolipids and polyhydroxyalkanoates by Pseudomonas aeruginosa

Pseudomonas aeruginosa are ubiquitous γ-proteobacteria capable of producing the biosurfactant rhamnolipids (RL) and the polymer polyhydroxyalkanoate (PHA). RL are glycolipids with high biotechnological potential, whereas PHA is used for the production of biodegradable plastics. It has been proposed that the β-oxidation pathway provides intermediates for RL biosynthesis, even when using a non-fatty acid carbon source for growth, while an intermediate of de novo fatty acid biosynthesis (FASII) pathway [(R)-3-hydroxyacyl-ACP] is used for PHA biosynthesis. The aim of this work is to study the inter-relationship of the RL and PHA biosynthetic pathways in a culture medium with a non-fatty acid carbon source, focusing on the role of FASII and β-oxidation in supplying the substrates for the first step in RL and PHA synthesis, carried out by the RhlA and PhaG enzymes, respectively. The PHA synthases (PhaC1 and PhaC2) are only able to use CoA-linked 3-hydroxy acids and the PhaG enzyme catalyzes the conversion of (R)-3-hydroxyacyl-ACP to (R)-3-hydroxyacyl-CoA, the substrate of PhaC1 and PhaC2. RhlA in turn catalyzes the synthesis of the RL precursor 3-(3-hydroxyalkanoyloxy) alkanoic acids (HAA) by the dimerization of two 3-hydroxyalkanoic acid molecules (that have been shown to be also (R)-3-hydroxyacyl-ACP). In this work, we show that RhlA can produce both RL and PHA precursors (presumably CoA-linked HAA), that the blockage of carbon flux through β-oxidation pathway does not decrease RL titer, and that the enoyl-CoA hydratase RhlY and enoyl-CoA hydratase/isomerase RhlZ produce the main fatty acids precursor of RL using as substrate also a FASII intermediate (presumably (S)-3-hydroxyacyl-CoA).

Rhamnolipids from Pseudomonas aeruginosa disperse the biofilms of sulfate-reducing bacteria

Biofilm formation is an important problem for many industries. Desulfovibrio vulgaris is the representative sulfate-reducing bacterium (SRB) which causes metal corrosion in oil wells and drilling equipment, and the corrosion is related to its biofilm formation. Biofilms are extremely difficult to remove since the cells are cemented in a polymer matrix. In an effort to eliminate SRB biofilms, we examined the ability of supernatants from Pseudomonas aeruginosa PA14 to disperse SRB biofilms. We found that the P. aeruginosa supernatants dispersed more than 98% of the biofilm. To determine the biochemical basis of this SRB biofilm dispersal, we examined a series of P. aeruginosa mutants and found that mutants rhlA, rhlB, rhlI, and rhlR, defective in rhamnolipids production, had significantly reduced levels of SRB biofilm dispersal. Corroborating these results, purified rhamnolipids dispersed SRB biofilms, and rhamnolipids were detected in the P. aeruginosa supernatants. Hence, P. aeruginosa supernatants disperse SRB biofilms via rhamnolipids. To determine the genetic basis of how the P. aeruginosa supernatants disperse SRB biofilms, a whole transcriptomic analysis was conducted (RNA-seq); based on this analysis, we identified four proteins (DVUA0018, DVUA0034, DVUA0066, and DVUA0084) of the D. vulgaris megaplasmid that influence biofilm formation, with production of DVUA0066 (a putative phospholipase) reducing biofilm formation 5.6-fold. In addition, the supernatants of P. aeruginosa dispersed the SRB biofilms more readily than protease in M9 glucose minimum medium and were also effective against biofilms of Escherichia coli and Staphylococcus aureus.

A subclass of glycolipids produced by the bacterium Pseudomonas aeruginosa breaks down a corrosive bacterial biofilm that afflicts industries such as petroleum extraction. The P. aeruginosa molecules, known as rhamnolipids, have been previously used to break down other bacterial biofilms. Now, a team from the United States, led by Pennsylvania State University’s Thomas Wood, showed that extracts from P. aeruginosa dispersed 98% of Desulfovibrio vulgaris biofilm, which is problematic for many industries, and also dispersed Escherichia coli and Staphylococcus aureus biofilms. Genetic investigations showed rhamnolipids were responsible for the majority of the biofilm inhibition. Further analyses also revealed four D. vulgaris proteins that significantly affect biofilm formation. This research highlights a mechanism that may be used to reduce the impact of industry-affecting biofilms and deepens the understandings of the mechanisms of biofilm formation.