Identification and characterisation of short chain rhamnolipid production in a previously uninvestigated, non-pathogenic marine pseudomonad

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.

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.

Sustainable rhamnolipids production in the next decade - Advancing with Burkholderia thailandensis as a potent biocatalytic strain

Rhamnolipids are one of the most promising eco-friendly green glycolipids for bio-replacements of commercially available fossil fuel-based surfactants. However, the current industrial biotechnology practices cannot meet the required standards due to the low production yields, expensive biomass feedstocks, complicated processing, and opportunistic pathogenic nature of the conventional rhamnolipid producer strains. To overcome these problems, it has become important to realize non-pathogenic producer substitutes and high-yielding strategies supporting biomass-based production. We hereby review the inherent characteristics of Burkholderia thailandensis E264 which favor its competence towards such sustainable rhamnolipid biosynthesis. The underlying biosynthetic networks of this species have unveiled unique substrate specificity, carbon flux control and rhamnolipid congener profile. Acknowledging such desirable traits, the present review provides critical insights towards metabolism, regulation, upscaling, and applications of B. thailandensis rhamnolipids. Identification of their unique and naturally inducible physiology has proved to be beneficial for achieving previously unmet redox balance and metabolic flux requirements in rhamnolipids production. These developments in part are targeted by the strategic optimization of B. thailandensis valorizing low-cost substrates ranging from agro-industrial byproducts to next generation (waste) fractions. Accordingly, safer bioconversions can propel the industrial rhamnolipids in advanced biorefinery domains to promote circular economy, reduce carbon footprint and increased applicability as both social and environment friendly bioproducts.

Biosurfactants: Forthcomings and Regulatory Affairs in Food-Based Industries

The terms discussed in this review-biosurfactants (BSs) and bioemulsifiers (BEs)-describe surface-active molecules of microbial origin which are popular chemical entities for many industries, including food. BSs are generally low-molecular-weight compounds with the ability to reduce surface tension noticeably, whereas BEs are high-molecular-weight molecules with efficient emulsifying abilities. Some other biomolecules, such as lecithin and egg yolk, are useful as natural BEs in food products. The high toxicity and severe ecological impact of many chemical-based surfactants have directed interest towards BSs/BEs. Interest in food surfactant formulations and consumer anticipation of "green label" additives over synthetic or chemical-based surfactants have been steadily increasing. BSs have an undeniable prospective for replacing chemical surfactants with vast significance to food formulations. However, the commercialization of BSs/BEs production has often been limited by several challenges, such as the optimization of fermentation parameters, high downstream costs, and low yields, which had an immense impact on their broader adoptions in different industries, including food. The foremost restriction regarding the access of BSs/BEs is not their lack of cost-effective industrial production methods, but a reluctance regarding their potential safety, as well as the probable microbial hazards that may be associated with them. Most research on BSs/BEs in food production has been restricted to demonstrations and lacks a comprehensive assessment of safety and risk analysis, which has limited their adoption for varied food-related applications. Furthermore, regulatory agencies require extensive exploration and analysis to secure endorsements for the inclusion of BSs/BEs as potential food additives. This review emphasizes the promising properties of BSs/BEs, trailed by an overview of their current use in food formulations, as well as risk and toxicity assessment. Finally, we assess their potential challenges and upcoming future in substituting chemical-based surfactants.

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.

Mono-Rhamnolipid Biosurfactants Synthesized by Pseudomonas aeruginosa Detrimentally Affect Colorectal Cancer Cells

Over the past 15 years, glycolipid-type biosurfactant compounds have been postulated as novel, naturally synthesized anticancer agents. This study utilized a recombinant strain of Pseudomonas aeruginosa to biosynthesize a preparation of mono-rhamnolipids that were purified via both liquid and solid-phase extraction, characterized by HPLC-MS, and utilized to treat two colorectal cancer cell lines (HCT-116 and Caco2) and a healthy colonic epithelial cell line CCD-841-CoN. Additionally, the anticancer activity of these mono-rhamnolipids was compared to an alternative naturally derived anticancer agent, Piceatannol. XTT cell viability assays showed that treatment with mono-rhamnolipid significantly reduced the viability of both colorectal cancer cell lines whilst having little effect on the healthy colonic epithelial cell line. At the concentrations tested mono-rhamnolipids were also shown to be more cytotoxic to the colorectal cancer cells than Piceatannol. Staining of mono-rhamnolipid-treated cells with propidium iodine and acridine orange appeared to show that these compounds induced necrosis in both colorectal cancer cell lines. These data provide an early in vitro proof-of-principle for utilizing these compounds either as active pharmaceutical ingredient for the treatment of colorectal cancer or incorporations into nutraceutical formulations to potentially prevent gastrointestinal tract cancer.

A Systematic Review on Biosurfactants Contribution to the Transition to a Circular Economy

Since they are more environmentally acceptable than their chemically synthesized counterparts, biosurfactants are used in a wide range of environmental applications. However, less research has been done on biosurfactants within the context of the circular economy, despite their theoretical potential to fulfill a number of circular economy ambitions, including closing the consumption loop, regenerating natural systems, and maintaining resource value within the system. Hence, the main objective of this review is to identify and analyze the contributions of biosurfactants to the implementation of the circular economy. A final sample of 30 papers from the Web of Science database was examined. We identified five broad categories of contributions: waste stream-derived production, combating food waste, strengthening soil health, and improving the efficiency of water resources. We concluded that, while manufacturing biosurfactants from waste streams can reduce production costs, optimizing yield remains a contentious issue that complicates the adoption of biosurfactants into the circular economy framework.

Biogenic propane production by a marine Photobacterium strain isolated from the Western English Channel

Propane is a major component of liquefied petroleum gas, a major energy source for off-grid communities and industry. The replacement of fossil fuel-derived propane with more sustainably derived propane is of industrial interest. One potential production route is through microbial fermentation. Here we report, for the first time, the isolation of a marine bacterium from sediment capable of natural propane biosynthesis. Propane production, both in mixed microbial cultures generated from marine sediment and in bacterial monocultures was detected and quantified by gas chromatography–flame ionization detection. Using DNA sequencing of multiple reference genes, the bacterium was shown to belong to the genus Photobacterium. We postulate that propane biosynthesis is achieved through inorganic carbonate assimilation systems. The discovery of this strain may facilitate synthetic biology routes for industrial scale production of propane via microbial fermentation.

Bioreactor-scale production of rhamnolipids from food waste digestate and its recirculation into anaerobic digestion for enhanced process performance: Creating closed-loop integrated biorefinery framework

Reaching industrially relevant productivities in bioprocesses and their efficient integration in the existing industrial infrastructure remain as important challenges in the circular economy to create closed loop sustainability framework. Using anaerobic digestion (AD) biorefinery as a model, the present work addressed these problems via integration of next-generation rhamnolipids production with AD. A high rhamnolipids concentration of 10.25 ± 1.34 g/L was obtained by fed-batch fermentation using food waste digestate as medium. Digestate-derived rhamnolipids contained Rha-C₁₀-C₁₀ and Rha-Rha-C₁₀-C₁₀ as the predominant congeners. These were used back in single-phase AD to demonstrate their effect on sludge solubilization and digestion efficiency. A dosage of 0.02 g rhamnolipids/g total suspended solids was found to be optimal which enhanced the hydrolysis-acidogenesis reactions to up to 27% over control. It however retarded methane production which could be overcome by the prolongation of digestion time. Finally, the value chain appreciation by the proposed process was demonstrated by a feasibility analysis.

Evaluation of di-rhamnolipid biosurfactants production by a novel Pseudomonas sp. S1WB: Optimization, characterization and effect on petroleum-hydrocarbon degradation

Rhamnolipid biosurfactants are multifunctional compounds that can play an indispensable role in biotechnological, biomedical, and environmental bioremediation-related fields, and have attracted significant attention in recent years. Herein, a novel strain Pseudomonas sp. S1WB was isolated from an oil-contaminated water sample. The biosurfactants produced by this strain have capabilities to reduce surface tension (SFT) at 32.75 ± 1.63 mN/m and emulsified 50.2 ± 1.13 % in liquid media containing 1 % used engine oil (UEO) as the sole carbon source. However, the lowest SFT reduction (28.25 ± 0.21), highest emulsification index (60.15 ± 0.07), and the maximum yields (900 mg/L) were achieved under optimized conditions; where, the glucose/urea and glycerol/urea combinations were found efficient carbon and nitrogen substrates for improved biosurfactants production. Biosurfactants product was characterized using ultra-high performance liquid chromatography-mass spectrometry (UHPLC- MS) and detected various di- rhamnolipids congeners. In addition, the di-rhamnolipids produced by S1WB strain was found highly stable in terms of surface activity and EI indices at different environmental factors i.e. temperature, pH and various NaCl concentrations, where, emulsifying property was found high stable till 30 days of incubation. Moreover, the stain was capable to degrade hydrocarbon at 42.2 ± 0.04 %, and the Gas chromatography- mass spectrometry (GC-MS) profile showed the majority of peak intensities of hydrocarbons have been completely degraded compared to control.

Isolation and Identification of Bacteria with Surface and Antibacterial Activity from the Gut of Mediterranean Grey Mullets

Fish gut represents a peculiar ecological niche where bacteria can transit and reside to play vital roles by producing bio-compounds with nutritional, immunomodulatory and other functions. This complex microbial ecosystem reflects several factors (environment, feeding regimen, fish species, etc.). The objective of the present study was the identification of intestinal microbial strains able to produce molecules called biosurfactants (BSs), which were tested for surface and antibacterial activity in order to select a group of probiotic bacteria for aquaculture use. Forty-two bacterial isolates from the digestive tracts of twenty Mediterranean grey mullets were screened for testing emulsifying (E-24), surface and antibiotic activities. Fifty percent of bacteria, ascribed to Pseudomonas aeruginosa, Pseudomonas sp., P. putida and P. anguilliseptica, P. stutzeri, P. protegens and Enterobacter ludwigii were found to be surfactant producers. Of the tested strains, 26.6% exhibited an antibacterial activity against Staphylococcus aureus (10.0 ± 0.0–14.5 ± 0.7 mm inhibition zone), and among them, 23.3% of isolates also showed inhibitory activity vs. Proteus mirabilis (10.0 ± 0.0–18.5 ± 0.7 mm inhibition zone) and 6.6% vs. Klebsiella pneumoniae (11.5 ± 0.7–17.5 ± 0.7 mm inhibition zone). According to preliminary chemical analysis, the bioactive compounds are suggested to be ascribed to the class of glycolipids. This works indicated that fish gut is a source of bioactive compounds which deserves to be explored.

Response and oil degradation activities of a northeast Atlantic bacterial community to biogenic and synthetic surfactants

BACKGROUND

Biosurfactants are naturally derived products that play a similar role to synthetic dispersants in oil spill response but are easily biodegradable and less toxic. Using a combination of analytical chemistry, 16S rRNA amplicon sequencing and simulation-based approaches, this study investigated the microbial community dynamics, ecological drivers, functional diversity and robustness, and oil biodegradation potential of a northeast Atlantic marine microbial community to crude oil when exposed to rhamnolipid or synthetic dispersant Finasol OSR52.

RESULTS

Psychrophilic Colwellia and Oleispira dominated the community in both the rhamnolipid and Finasol OSR52 treatments initially but later community structure across treatments diverged significantly: Rhodobacteraceae and Vibrio dominated the Finasol-amended treatment, whereas Colwellia, Oleispira, and later Cycloclasticus and Alcanivorax, dominated the rhamnolipid-amended treatment. Key aromatic hydrocarbon-degrading bacteria, like Cycloclasticus, was not observed in the Finasol treatment but it was abundant in the oil-only and rhamnolipid-amended treatments. Overall, Finasol had a significant negative impact on the community diversity, weakened the taxa-functional robustness of the community, and caused a stronger environmental filtering, more so than oil-only and rhamnolipid-amended oil treatments. Rhamnolipid-amended and oil-only treatments had the highest functional diversity, however, the overall oil biodegradation was greater in the Finasol treatment, but aromatic biodegradation was highest in the rhamnolipid treatment.

CONCLUSION

Overall, the natural marine microbial community in the northeast Atlantic responded differently to crude oil dispersed with either synthetic or biogenic surfactants over time, but oil degradation was more enhanced by the synthetic dispersant. Collectively, our results advance the understanding of how rhamnolipid biosurfactants and synthetic dispersant Finasol affect the natural marine microbial community in the FSC, supporting their potential application in oil spills. Video abstract.

Crude oil biodegradation potential of biosurfactant-producing Pseudomonas aeruginosa and Meyerozyma sp

This study investigates the potential of crude oil degrading capabilities of biosurfactant-producing strains of Pseudomonas aeruginosa MF069166 and Meyerozyma sp. MF138126. P. aeruginosa produced mono-/di-rhamnolipids congeners whereas, Meyerozyma sp. produced acidic and lactonic forms of sophorolipids with crude oil. The values of critical micelle concentrations of rhamnolipids and sophorolipids were 40 mg/L and 50 mg/L with reductions in surface tension of water to 29 mN/m and 33 mN/m. Dynamic light scattering revealed that the average diameter of micellar aggregates of rhamnolipids ranged between 300 and 350 nm and the average size of sophorolipids micelles was 309 nm and 380 nm. Biosurfactants from P. aeruginosa and Meyerozyma sp. exhibited emulsification activities of 87% and 84% in crude oil. Cell surface hydrophobicity of both strains was higher in the presence of hydrophobic contaminants. The biosurfactants showed stability under varying pH, NaCl concentrations and temperatures. Gravimetric and GC-MS analyses demonstrated that P. aeruginosa degraded 91% of the petroleum hydrocarbons while Meyerozyma sp. showed 87% biodegradation efficiency. P. aeruginosa and Meyerozyma sp. have also been found to degrade halogen-containing compounds and showed excellent crude oil degradation efficiency. It is concluded that both strains have high potential of applications in the bioremediation of hydrocarbons-contaminated sites.

Biotechnological applications of marine bacteria in bioremediation of environments polluted with hydrocarbons and plastics

Marine ecosystems are some of the most adverse environments on Earth and contain a considerable portion of the global bacterial population, and some of these bacterial species play pivotal roles in several biogeochemical cycles. Marine bacteria have developed different molecular mechanisms to address fluctuating environmental conditions, such as changes in nutrient availability, salinity, temperature, pH, and pressure, making them attractive for use in diverse biotechnology applications. Although more than 99% of marine bacteria cannot be cultivated with traditional microbiological techniques, several species have been successfully isolated and grown in the laboratory, facilitating investigations of their biotechnological potential. Some of these applications may contribute to addressing some current global problems, such as environmental contamination by hydrocarbons and synthetic plastics. In this review, we first summarize and analyze recently published information about marine bacterial diversity. Then, we discuss new literature regarding the isolation and characterization of marine bacterial strains able to degrade hydrocarbons and petroleum-based plastics, and species able to produce biosurfactants. We also describe some current limitations for the implementation of these biotechnological tools, but also we suggest some strategies that may contribute to overcoming them. KEY POINTS: • Marine bacteria have a great metabolic capacity to degrade hydrocarbons in harsh conditions. • Marine environments are an important source of new bacterial plastic-degrading enzymes. • Secondary metabolites from marine bacteria have diverse potential applications in biotechnology.

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.

Toxicity Profiling of Biosurfactants Produced by Novel Marine Bacterial Strains

Surface active agents (SAAs), currently used in modern industry, are synthetic chemicals produced from non-renewable sources, with potential toxic impacts on humans and the environment. Thus, there is an increased interest for the identification and utilization of natural derived SAAs. As such, the marine environment is considered a promising source of biosurfactants with low toxicity, environmental compatibility, and biodegradation compared to their synthetic counterparts. MARISURF is a Horizon 2020 EU-funded project aiming to identify and functionally characterize SAAs, derived from a unique marine bacterial collection, towards commercial exploitation. Specifically, rhamnolipids produced by Marinobacter MCTG107b and Pseudomonas MCTG214(3b1) strains were previously identified and characterized while currently their toxicity profile was assessed by utilizing well-established methodologies. Our results showed a lack of cytotoxicity in in vitro models of human skin and liver as indicated by alamar blue and propidium iodide assays. Additionally, the use of the single gel electrophoresis assay, under oxidative stress conditions, revealed absence of any significant mutagenic/anti-mutagenic potential. Finally, both 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonicacid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) cell-free assays, revealed no significant anti-oxidant capacity for neither of the tested compounds. Consequently, the absence of significant cytotoxicity and/or mutagenicity justifies their commercial exploitation and potential development into industrial end-user applications as natural and environmentally friendly biosurfactants.

Application of Environment-Friendly Rhamnolipids against Transmission of Enveloped Viruses Like SARS-CoV2

In the face of new emerging respiratory viruses, such as SARS-CoV2, vaccines and drug therapies are not immediately available to curb the spread of infection. Non-pharmaceutical interventions, such as mask-wearing and social distance, can slow the transmission. However, both mask and social distance have not prevented the spread of respiratory viruses SARS-CoV2 within the US. There is an urgent need to develop an intervention that could reduce the spread of respiratory viruses. The key to preventing transmission is to eliminate the emission of SARS-CoV2 from an infected person and stop the virus from propagating in the human population. Rhamnolipids are environmentally friendly surfactants that are less toxic than the synthetic surfactants. In this study, rhamnolipid products, 222B, were investigated as disinfectants against enveloped viruses, such as bovine coronavirus and herpes simplex virus 1 (HSV-1). The 222B at 0.009% and 0.0045% completely inactivated 6 and 4 log PFU/mL of HSV-1 in 5–10 min, respectively. 222B at or below 0.005% is also biologically safe. Moreover, 50 μL of 222B at 0.005% on ~1 cm² mask fabrics or plastic surface can inactivate ~10³ PFU HSV-1 in 3–5 min. These results suggest that 222B coated on masks or plastic surface can reduce the emission of SARS-CoV2 from an infected person and stop the spread of SARS-CoV2.

Biosurfactants and Their Applications in the Oil and Gas Industry: Current State of Knowledge and Future Perspectives

Surfactants are a group of amphiphilic chemical compounds (i.e., having both hydrophobic and hydrophilic domains) that form an indispensable component in almost every sector of modern industry. Their significance is evidenced from the enormous volumes that are used and wide diversity of applications they are used in, ranging from food and beverage, agriculture, public health, healthcare/medicine, textiles, and bioremediation. A major drive in recent decades has been toward the discovery of surfactants from biological/natural sources-namely bio-surfactants-as most surfactants that are used today for industrial applications are synthetically-manufactured via organo-chemical synthesis using petrochemicals as precursors. This is problematic, not only because they are derived from non-renewable resources, but also because of their environmental incompatibility and potential toxicological effects to humans and other organisms. This is timely as one of today's key challenges is to reduce our reliance on fossil fuels (oil, coal, gas) and to move toward using renewable and sustainable sources. Considering the enormous genetic diversity that microorganisms possess, they offer considerable promise in producing novel types of biosurfactants for replacing those that are produced from organo-chemical synthesis, and the marine environment offers enormous potential in this respect. In this review, we begin with an overview of the different types of microbial-produced biosurfactants and their applications. The remainder of this review discusses the current state of knowledge and trends in the usage of biosurfactants by the Oil and Gas industry for enhancing oil recovery from exhausted oil fields and as dispersants for combatting oil spills.

Characterization of Enterobacter cloacae BAGM01 Producing a Thermostable and Alkaline-Tolerant Rhamnolipid Biosurfactant from the Gulf of Mexico

The search for novel biosurfactants (Bs) requires the isolation of microorganisms from different environments. The Gulf of Mexico (GoM) is a geographical area active in the exploration and exploitation of hydrocarbons. Recent metagenomic and microbiologic studies in this area suggested a potential richness for novel Bs microbial producers. In this work, nineteen bacterial consortia from the GoM were isolated at different depths of the water column and marine sediments. Bs production from four bacterial consortia was detected by the CTAB test and their capacity to reduce surface tension (ST), emulsion index (EI₂₄), and hemolytic activity. These bacterial consortia produced Bs in media supplemented with kerosene, diesel, or sucrose. Cultivable bacteria from these consortia were isolated and identified by bacterial polyphasic characterization. In some consortia, Enterobacter cloacae was the predominant specie. E. cloacae BAGM01 presented Bs activity in minimal medium and was selected to improve its Bs production using a Taguchi and Box-Behnken experimental design; this strain was able to grow and presented Bs activity at 35 g L^-1 of NaCl. This Bs decreased ST to around 34.5 ± 0.56 mNm^-1 and presented an EI₂₄ of 71 ± 1.27%. Other properties of this Bs were thermal stability, stability in alkaline conditions, and stability at high salinity, conferring important and desirable characteristics in multiple industries. The analysis of the genome of E. cloacae BAGM01 showed the presence of rhlAB genes that have been reported in the synthesis of rhamnolipids, and alkAB genes that are related to the degradation of alkanes. The bioactive molecule was identified as a rhamnolipid after HPLC derivatization, ¹H NMR, and UPLC-QTOF-MS analysis.

Towards Rational Biosurfactant Design-Predicting Solubilization in Rhamnolipid Solutions

The efficiency of micellar solubilization is dictated inter alia by the properties of the solubilizate, the type of surfactant, and environmental conditions of the process. We, therefore, hypothesized that using the descriptors of the aforementioned features we can predict the solubilization efficiency, expressed as molar solubilization ratio (MSR). In other words, we aimed at creating a model to find the optimal surfactant and environmental conditions in order to solubilize the substance of interest (oil, drug, etc.). We focused specifically on the solubilization in biosurfactant solutions. We collected data from literature covering the last 38 years and supplemented them with our experimental data for different biosurfactant preparations. Evolutionary algorithm (EA) and kernel support vector machines (KSVM) were used to create predictive relationships. The descriptors of biosurfactant (logP_BS, measure of purity), solubilizate (logP_sol, molecular volume), and descriptors of conditions of the measurement (T and pH) were used for modelling. We have shown that the MSR can be successfully predicted using EAs, with a mean R² _val of 0.773 ± 0.052. The parameters influencing the solubilization efficiency were ranked upon their significance. This represents the first attempt in literature to predict the MSR with the MSR calculator delivered as a result of our research.

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.

Optimization of Process Parameters of Rhamnolipid Treatment of Oily Sludge Based on Response Surface Methodology

Oily sludge is a hazardous waste. If not handled properly, it can not only pollute the environment but also endanger human health. This study is the first to use a response surface method to optimize the main parameters of rhamnolipid-based recovery of oil from oily sludge. Using rhamnolipids as the cleaning agent and the oil recovery fraction as the evaluation index, the factors affecting the cleaning efficiency of oily sludge were optimized. The aforementioned sludge was obtained from the Tarim Oilfield. A single-factor experiment was conducted to determine the optimal range of the dosage, liquid-solid ratio, pH value, and time. The Box-Behnken response surface method was used to investigate the influence of each variable on the residual oil fraction of the oily sludge, and the dosage, pH value, and time were found to have a significant impact. The model optimization results show that the best process conditions for rhamnolipid-based recovery of oil are as follows: rhamnolipid dosage = 167.785 mg/L; liquid-solid ratio = 4.589:1; pH = 9.618; time = 1.627 h. Under optimal conditions, the model-predicted oil recovery fraction and the actual oil recovery fraction were 85.15 and 82.56%, respectively; the relative error between the predicted and the actual values was 2.59%. These results indicate that the model results are reliable. The solid residue after the cleaning was also analyzed to gain an in-depth understanding of the cleaning process. This study determined the feasibility of a rhamnolipid-based solution for the treatment of oily sludge and oil-contaminated soil.

Structural and Physicochemical Characterization of Rhamnolipids produced by Pseudomonas aeruginosa P6

Rhamnolipids are important biosurfactants for application in bioremediation, enhanced oil recovery, pharmaceutical, and detergent industry. In this study, rhamnolipids extracted from P. aeruginosa P6 were characterized to determine their potential fields of application. Thin-layer chromatographic analysis of the produced rhamnolipids indicated the production of two homologues: mono- and di-rhamnolipids, whose structures were verified by 1H and 13C nuclear magnetic resonance spectroscopy. Additionally, high performance liquid chromatography-mass spectrometry identified seven different rhamnolipid congeners, of which a significantly high proportion was di-rhamnolipids reaching 80.16%. Rha-Rha-C10-C10 was confirmed as the principal compound of the rhamnolipid mixture (24.30%). The rhamnolipids were capable of lowering surface tension of water to 36 mN/m at a critical micelle concentration of 0.2 g/L, and exhibited a great emulsifying activity (E24 = 63%). In addition, they showed excellent stability at pH ranges 4-8, NaCl concentrations up to 9% (w/v) and temperatures ranging from 20 to 100 °C and even after autoclaving. These results suggest that rhamnolipids, produced by P. aeruginosa P6 using the cheap substrate glycerol, are propitious for biotechnology use in extreme and complex environments, like oil reservoirs and hydrocarbon contaminated soil. Moreover, P. aeruginosa P6 may be considered, in its wild type form, as a promising industrial producer of di-RLs, which have superior characteristics for potential applications and offer outstanding commercial benefits.

Pseudomonas aeruginosa RTE4: A Tea Rhizobacterium With Potential for Plant Growth Promotion and Biosurfactant Production

Tea is an ancient non-alcoholic beverage plantation crop cultivated in the most part of Assam, India. Being a long-term monoculture, tea plants are prone to both biotic and abiotic stresses, and requires massive amounts of chemicals as fertilizers and pesticides to achieve worthy crop productivity. The rhizosphere bacteria with the abilities to produce phytohormone, secreting hydrolytic enzyme, biofilm formation, bio-control activity provides induced systemic resistance to plants against pathogens. Thus, plant growth promoting (PGP) rhizobacteria represents as an alternative candidate to chemical inputs for agriculture sector. Further, deciphering the secondary metabolites, including biosurfactant (BS) allow developing a better understanding of rhizobacterial strains. The acidic nature of tea rhizosphere is predominated by Bacillus followed by Pseudomonas that enhances crop biomass and yield through accelerating uptake of nutrients. In the present study, a strain Pseudomonas aeruginosa RTE4 isolated from tea rhizosphere soil collected from Rosekandy Tea Garden, Cachar, Assam was evaluated for various plant-growth promoting attributes. The strain RTE4 produces indole acetic acid (74.54 μg/ml), hydrolytic enzymes, and solubilize tri-calcium phosphate (46 μg/ml). Bio-control activity of RTE4 was recorded against two foliar fungal pathogens of tea (Corticium invisium and Fusarium solani) and a bacterial plant pathogen (Xanthomonas campestris). The strain RTE4 was positive for BS production in the preliminary screening. Detailed analytical characterization through TLC, FTIR, NMR, and LCMS techniques revealed that the strain RTE4 grown in M9 medium with glucose (2% w/v) produce di-rhamnolipid BS. This BS reduced surface tension of phosphate buffer saline from 71 to 31 mN/m with a critical micelle concentration of 80 mg/L. Purified BS of RTE4 showed minimum inhibitory concentration of 5, 10, and 20 mg/ml against X. campestris, F. solani and C. invisium, respectively. Capability of RTE4 BS to be employed as a biofungicide as compared to Carbendazim - commercially available fungicide is also tested. The strain RTE4 exhibits multiple PGP attributes along with production of di-rhamnolipid BS. This gives a possibility to produce di-rhamnolipid BS from RTE4 in large scale and explore its applications in fields as a biological alternative to chemical fertilizer.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

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.

Marine derived biosurfactants: a vast potential future resource

Surfactants and emulsifiers are surface-active compounds (SACs) which play an important role in various industrial processes and products due to their interfacial properties. Many of the chemical surfactants in use today are produced from non-renewable petrochemical feedstocks, while biosurfactants (BS) produced by microorganisms from renewable feedstocks are considered viable alternatives to petroleum based surfactants, due to their biodegradability and eco-friendly nature. However, some well-characterised BS producers are pathogenic and therefore, not appropriate for scaled-up production. Marine-derived BS have been found to be produced by non-pathogenic organisms making them attractive possibilities for exploitation in commercial products. Additionally, BS produced from marine bacteria may show excellent activity at extreme conditions (temperature, pH and salinity). Despite being non-pathogenic, marine-derived BS have not been exploited commercially due to their low yields, insufficient structural elucidation and uncharacterised genes. Therefore, optimization of BS production conditions in marine bacteria, characterization of the compounds produced as well as the genes involved in the biosynthesis are necessary to improve cost-efficiency and realise the industrial demands of SACs.