Optimization and characterization of biosurfactant production from kitchen waste oil using Pseudomonas aeruginosa

Biological machinery for the production of biosurfactant and their potential applications

The growing biotechnology industry has focused a lot of attention on biosurfactants because of several advantages over synthetic surfactants. These benefits include worldwide public health, environmental sustainability, and the increasing demand from sectors for environmentally friendly products. Replacement with biosurfactants can reduce upto 8% lifetime CO2 emissions avoiding about 1.5 million tons of greenhouse gas released into the atmosphere. Therefore, the demand for biosurfactants has risen sharply occupying about 10% (∼10 million tons/year) of the world production of surfactants. Biosurfactants' distinct amphipathic structure, which is made up of both hydrophilic and hydrophobic components, enables these molecules to perform essential functions in emulsification, foam formation, detergency, and oil dispersion-all of which are highly valued characteristic in a variety of sectors. Today, a variety of biosurfactants are manufactured on a commercial scale for use in the food, petroleum, and agricultural industries, as well as the pharmaceutical and cosmetic industries. We provide a thorough analysis of the body of knowledge on microbial biosurfactants that has been gained over time in this research. We also discuss the benefits and obstacles that need to be overcome for the effective development and use of biosurfactants, as well as their present and future industrial uses.

Glycolipids biosurfactants production using low-cost substrates for environmental remediation: progress, challenges, and future prospects

The production of renewable materials from alternative sources is becoming increasingly important to reduce the detrimental environmental effects of their non-renewable counterparts and natural resources, while making them more economical and sustainable. Chemical surfactants, which are highly toxic and non-biodegradable, are used in a wide range of industrial and environmental applications harming humans, animals, plants, and other entities. Chemical surfactants can be substituted with biosurfactants (BS), which are produced by microorganisms like bacteria, fungi, and yeast. They have excellent emulsifying, foaming, and dispersing properties, as well as excellent biodegradability, lower toxicity, and the ability to remain stable under severe conditions, making them useful for a variety of industrial and environmental applications. Despite these advantages, BS derived from conventional resources and precursors (such as edible oils and carbohydrates) are expensive, limiting large-scale production of BS. In addition, the use of unconventional substrates such as agro-industrial wastes lowers the BS productivity and drives up production costs. However, overcoming the barriers to commercial-scale production is critical to the widespread adoption of these products. Overcoming these challenges would not only promote the use of environmentally friendly surfactants but also contribute to sustainable waste management and reduce dependence on non-renewable resources. This study explores the efficient use of wastes and other low-cost substrates to produce glycolipids BS, identifies efficient substrates for commercial production, and recommends strategies to improve productivity and use BS in environmental remediation.

Transcriptomics aids in uncovering the metabolic shifts and molecular machinery of Schizochytrium limacinum during biotransformation of hydrophobic substrates to docosahexaenoic acid

BACKGROUND

Biotransformation of waste oil into value-added nutraceuticals provides a sustainable strategy. Thraustochytrids are heterotrophic marine protists and promising producers of omega (ω) fatty acids. Although the metabolic routes for the assimilation of hydrophilic carbon substrates such as glucose are known for these microbes, the mechanisms employed for the conversion of hydrophobic substrates are not well established. Here, thraustochytrid Schizochytrium limacinum SR21 was investigated for its ability to convert oils (commercial oils with varying fatty acid composition and waste cooking oil) into ω-3 fatty acid; docosahexaenoic acid (DHA).

RESULTS

Within 72 h SR21 consumed ~ 90% of the oils resulting in enhanced biomass (7.5 g L- 1) which was 2-fold higher as compared to glucose. Statistical analysis highlights C16 fatty acids as important precursors of DHA biosynthesis. Transcriptomic data indicated the upregulation of multiple lipases, predicted to possess signal peptides for secretory, membrane-anchored and cytoplasmic localization. Additionally, transcripts encoding for mitochondrial and peroxisomal β-oxidation along with acyl-carnitine transporters were abundant for oil substrates that allowed complete degradation of fatty acids to acetyl CoA. Further, low levels of oxidative biomarkers (H2O2, malondialdehyde) and antioxidants were determined for hydrophobic substrates, suggesting that SR21 efficiently mitigates the metabolic load and diverts the acetyl CoA towards energy generation and DHA accumulation.

CONCLUSIONS

The findings of this study contribute to uncovering the route of assimilation of oil substrates by SR21. The thraustochytrid employs an intricate crosstalk among the extracellular and intracellular molecular machinery favoring energy generation. The conversion of hydrophobic substrates to DHA can be further improved using synthetic biology tools, thereby providing a unique platform for the sustainable recycling of waste oil substrates.

High mono-rhamnolipids production by a novel isolate Pseudomonas aeruginosa LP20 from oily sludge: characterization, optimization, and potential application

This study aims to isolate microbial strains for producing mono-rhamnolipids with high proportion. Oily sludge is rich in petroleum and contains diverse biosurfactant-producing strains. A biosurfactant-producing strain LP20 was isolated from oily sludge, identified as Pseudomonas aeruginosa based on phylogenetic analysis of 16S rRNA. High-performance liquid chromatography-mass spectrometry results indicated that biosurfactants produced from LP20 were rhamnolipids, mainly containing Rha-C8-C10, Rha-C10-C10, Rha-Rha-C8-C10, Rha-Rha-C10-C10, Rha-C10-C12:1, and Rha-C10-C12. Interestingly, more mono-rhamnolipids were produced by strain LP20 with a relative abundance of 64.5%. Pseudomonas aeruginosa LP20 optimally produced rhamnolipids at a pH of 7.0 and a salinity of 0.1% using glycerol and nitrate. The culture medium for rhamnolipids by strain LP20 was optimized by response surface methodology. LP20 produced rhamnolipids up to 6.9 g L-1, increased by 116%. Rhamnolipids produced from LP20 decreased the water surface tension to 28.1 mN m-1 with a critical micelle concentration of 60 mg L-1. The produced rhamnolipids emulsified many hydrocarbons with EI24 values higher than 56% and showed antimicrobial activity against Staphylococcus aureus and Cladosporium sp. with inhibition rates 48.5% and 17.9%, respectively. Pseudomonas aeruginosa LP20 produced more proportion of mono-rhamnolipids, and the LP20 rhamnolipids exhibited favorable activities and promising potential in microbial-enhanced oil recovery, bioremediation, and agricultural biocontrol.

Chemical and biological evaluation of biosurfactant fractions from Wickerhamomyces anomalus CCMA 0358

Biosurfactants (BS) are becoming a solution for today's world since they are considered a reasonable and eco-friendly option for use in products that require surfactants. This study aimed to evaluate the antibacterial activity of purified fractions containing biosurfactants produced by the yeast Wickerhamomyces anomalus CCMA 0358 using waste cooking oil (WCO) as substrate. Mixed fractions were separated and characterized by TLC, MPLC, GC-MS, LC-OMS, LC-SQMS, FTIR, 1H, 13C, DEPT 135, COSY, HSQC, and HMBC. The results confirmed the presence of palmitic acid and oleic acid fatty acids, derived from the core biosurfactant structure; however, the core could not be identified. The crude biosurfactant and its purified fractions were evaluated against pathogenic bacteria, and the purified fractions of the biosurfactant are more efficient at inhibitory and bactericidal activities than the crude biosurfactant. To the best of our knowledge, this is the first study that evaluated the antimicrobial activity of purified fractions of biosurfactants produced by the species Wickerhamomyces anomalus. Therefore, the purification of biosurfactants can emerge as an interesting alternative to increase the bioactivity of the compounds and ensure greater efficiency and biotechnological employability. KEY POINTS: • Successful production of a biosurfactant using a renewed carbon source. • Evaluation of the antimicrobial activity of purified fractions of BS. • Separated fractions of the BS are more efficient against bacteria than the crude BS.

Novel Perspectives on Food-Based Natural Antimicrobials: A Review of Recent Findings Published since 2020

Various fruit and vegetable wastes, particularly peels, seeds, pulp, and unprocessed residues from the food industry, are abundant sources of antioxidants and essential antimicrobial agents. These valuable bioactive compounds recovered from the food industry have a great application in food, agriculture, medicine, and pharmacology. Food-derived natural antimicrobials offer advantages such as diminishing microbial loads and prolonging the shelf life of food products particularly prone to microbial spoilage. They not only enrich the foods with antioxidants but also help prevent microbial contamination, thereby prolonging their shelf life. Similarly, incorporating these natural antimicrobials into food packaging products extends the shelf life of meat products. Moreover, in agricultural practices, these natural antimicrobials act as eco-friendly pesticides, eliminating phytopathogenic microbes responsible for causing plant diseases. In medicine and pharmacology, they are being explored as potential therapeutic agents. This review article is based on current studies conducted in the last four years, evaluating the effectiveness of food-based natural antimicrobials in food, agriculture, medicine, and pharmacology.

Valorization of Food Waste to Produce Value-Added Products Based on Its Bioactive Compounds

The rapid growth of the global population and changes in lifestyle have led to a significant increase in food waste from various industrial, agricultural, and household sources. Nearly one-third of the food produced annually is wasted, resulting in severe resource depletion. Food waste contains rich organic matter, which, if not managed properly, can pose a serious threat to the environment and human health, making the proper disposal of food waste an urgent global issue. However, various types of food waste, such as waste from fruit, vegetables, grains, and other food production and processing, contain important bioactive compounds, such as polyphenols, dietary fiber, proteins, lipids, vitamins, organic acids, and minerals, some of which are found in greater quantities in the discarded parts than in the parts accepted by the market. These bioactive compounds offer the potential to convert food waste into value-added products, and fields including nutritional foods, bioplastics, bioenergy, biosurfactants, biofertilizers, and single cell proteins have welcomed food waste as a novel source. This review reveals the latest insights into the various sources of food waste and the potential of utilizing bioactive compounds to convert it into value-added products, thus enhancing people’s confidence in better utilizing and managing food waste.

Enhanced bioremediation of oil-contaminated soil in a slurry bioreactor by H2O2-stimulation of oil-degrading/biosurfactant-generating bacteria: performance optimization and bacterial metagenomics

Oil-contaminated soil is the main challenge for oil-rich countries, and this study aimed to investigate the performance of the H₂O₂-stimulated slurry bioreactor for the bioremediation of real oil-contaminated soil. The effect of biomass concentration, soil to water (S/W) ratio, slurry temperature, pH, and H₂O₂ concentration were optimized for the removal of total petroleum hydrocarbons (TPH) from oil-contaminated soil. TPH removal efficiency, biosurfactants production, and peroxidase and dehydrogenase activities were measured. The optimum conditions for the complete biodegradation of 32 [Formula: see text] in the slurry bioreactor during 6 days were biomass of 2250 mg/L, S/W ratio of 20%, the temperature of 30 °C, pH of 7, and an H₂O₂ concentration of 120 mg/L. The highest peroxidase, dehydrogenase, surfactin, and rhamnolipid formation were also obtained under optimum conditions. The results pointed out that complete biodegradation of 32 g/kg of TPH in oil-contaminated soil at a short reaction time of 6 days is achievable in the developed process operated under optimum conditions. The GC/FID analysis of solid and liquid phases showed that the bioprocess completely biodegraded the different TPH fractions. H₂O₂ efficiently stimulated the biosurfactant-generating bacteria to produce peroxidase and thereby accelerating the bioremediation rate. Accordingly, an H₂O₂-mediated slurry bioreactor inoculated with biosurfactant/peroxidase-generating bacteria is a promising technique for cleaning up oil-contaminated soils.

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

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

Optimization and characterization of rhamnolipids produced by Pseudomonas aeruginosa ATCC 9027 using molasses as a substrate

The present study aims to evaluate the growth potential of the P. aeruginosa ATCC9027 strain with molasses as the sole carbon source to produce rhamnolipids. The influence of the cultivation time and substrate concentration on biosurfactant production was investigated by using a complete 3-level factorial design, with the rhamnolipid concentration as the variable response. The strain was able to produce the biosurfactant in all design conditions tested, producing 758.04 mg/L rhamnolipids with 7% v/v substrate concentration in a cultivation time of 120 h. The substrate concentration used in the cultivation step directly influenced the biosurfactant production, and, even with the decrease in biomass growth, the biosurfactant production continued to increase. High Performance Liquid Chromatography (HPLC) revealed the presence of 62.3% mono- (RL1) and 37.6% di-rhamnolipids (RL3). The stability tests showed that the biosurfactant has good performance in extreme conditions of temperature, pH and saline concentration. The emulsification index was also evaluated for several oils and hydrocarbons, obtaining emulsification rates of up to 84.9% for the burnt motor oil. In addition, rhamnolipid showed a good ability to remove spilled oil from the sand, removing 58.51% of burnt motor oil and 70.09% of post-frying soybean oil. The results indicate that molasses, an agro-industrial residue abundant in Brazil, can be used as the only carbon source for quality rhamnolipid production when under optimized conditions, therefore presenting itself as a management option for this residue and, at the same time, providing the production product with high added value.

Interaction between indigenous hydrocarbon-degrading bacteria in reconstituted mixtures for remediation of weathered oil in soil

It has been demonstrated that biostimulation is necessary to investigate the interactions between indigenous bacteria and establish an approach for the bioremediation of soils contaminated with weathered oil. This was achieved by adjusting the carbon (C)/nitrogen (N)/phosphorus (P) ratio to 100/10/1 combined with the application of 0.8 mL/kg Tween-80. In addition, three indigenous bacteria isolated from the same soil were introduced solely or combined concomitantly with stimulation. Removal of n-alkanes and the ratios of n-heptadecane to pristane and n-octadecane to phytane were taken to indicate their biodegradation performance over a period of 16 weeks. One strain of Pseudomonas aeruginosa D7S1 improved the efficiency of the process of stimulation. However, another Pseudomonas aeruginosa, D5D1, inhibited the overall process when combined with other bacteria. One strain of Bacillus licheniformis D1D2 did not affect the process significantly. The Fourier transform infrared analysis of the residual hydrocarbons supported the conclusions pertaining to the biodegradation processes when probing the modifications in densities and stretching. The indigenous bacteria cannot mutually benefit from their metabolisms for bioremediation if augmented artificially. However, the strain Pseudomonas. aeruginosa D7S1 was able to perform better alone than in a consortium of indigenous bacteria.

Artificial consortia of Bacillus amyloliquefaciens HM618 and Bacillus subtilis for utilizing food waste to synthetize iturin A

Food waste is a cheap and abundant organic resource that can be used as a substrate for the production of the broad-spectrum antifungal compound iturin A. To increase the efficiency of food waste biotransformation, different artificial consortia incorporating the iturin A producer Bacillus amyloliquefaciens HM618 together with engineered Bacillus subtilis WB800N producing lipase or amylase were constructed. The results showed that recombinant B. subtilis WB-A13 had the highest amylase activity of 23406.4 U/mL, and that the lipase activity of recombinant B. subtilis WB-L01 was 57.5 U/mL. When strain HM618 was co-cultured with strain WB-A14, the higher yield of iturin A reached to 7.66 mg/L, representing a 32.9% increase compared to the pure culture of strain HM618. In the three-strain consortium comprising strains HM618, WB-L02, and WB-A14 with initial OD₆₀₀ values of 0.2, 0.15, and 0.15, respectively, the yield of iturin A reached 8.12 mg/L, which was 38.6% higher than the control. Taken together, artificial consortia of B. amyloliquefaciens and recombinant B. subtilis can produce an increased yield of iturin A, which provides a new strategy for the valorization of food waste.

Nitrogen dependence of rhamnolipid mediated degradation of petroleum crude oil by indigenous Pseudomonas sp. WD23 in seawater

Effect of oil spills on living forms demands for safe, ecofriendly and cost-effective methods to repair the damage. Pseudomonads have exceptional tolerance to xenobiotics and can grow at varied environmental conditions. This study aims at biosurfactant mediated degradation of petroleum crude oil by an indigenous Pseudomonas sp. WD23 in sea water. Pseudomonas sp. WD23 degraded 34% of petroleum crude oil (1.0% v/v) on supplementation of yeast extract (0.05 g/L) with glucose (1.0 g/L) in seawater. The strain produced a biosurfactant which was confirmed as a rhamnolipid (lipid: rhamnose 1:3.35) by FT-IR, LCMS and quantitative analysis. Produced rhamnolipid had low CMC (20.0 mg/L), emulsified petroleum oils (75-80%) and had high tolreance to varied conditions of pH, temperature and ionic strength. OFAT studies were performed to analyse the effect of petroleum crude oil, glucose, inoculum, yeast extract, pH, agitation speed and incubation time on degradation by Pseudomonas sp. WD23. Petroleum crude oil and glucose had significant effect on biodegradation, rhamnolipid production and growth, further optimized by central composite design. At optimum conditions of 3.414% v/v PCO and 6.53 g/L glucose, maximum degradation of 81.8 ± 0.67% was observed at pH 7.5, 100 RPM, 15.0% v/v inoculum in 28 days, with a 3-fold increase in biodegradation. GCMS analysis revealed degradation (86-100%) of all low and high molecular weight hydrocarbons present in petroleum crude oil. Hence, the strain Pseudomonas sp. WD23 can be effectively developed for management of oil spills in seas and oceans due to its excellent degradation abilities.

Kinetics and Production of Rhamnolipid from Pseudomonas sp. TMB2 in Shake-Flask and Fabricated Batch Reactor

Rhamnolipid producing Pseudomonas sp. TMB2 was selected for this investigation to optimize the metabolite production in fabricated batch reactor after studying yield kinetics in shake-flask and tried to reduce the overall production cost through In-situ recovery technology. Using various kinetic models, maximum specific growth rate (μmax) and half velocity constant (KS) of TMB2 were determined to be 0.185 ± 0.0025 h-1 and 0.124 ± 0.024 g/L in shake-flask, respectively. Further, a batch reactor was designed with integration of a foam fractionate column in the lid of the vessel and their performances were compared with shake-flask studies. The yields of rhamnolipids production on biomass (YP/X), rhamnolipids production on substrate (YP/S) and biomass production on substrate (YX/S) were found to be higher in reactor than that of shake-flask. The best conditions for maximum rhamnolipid production in reactor were observed to be 2 vvm and 300 rpm, giving YP/S = 0.152 g/g, YP/X = 0.542 g/g and YX/S = 0.280 g/g. Rhamnolipid production was increased by ≈ 10.18% in the reactor than that of shake-flask in optimized conditions. Rhamnolipid concentrations in the foamate were also found to be higher than that of reactor vessels. Further, the performance of foam fractionation was validated through enrichment and recovery, which were found in the range of 2.75-4.86 and 25.33-64.64%, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-022-01021-0.

Understanding the management of household food waste and its engineering for sustainable valorization- A state-of-the-art review

Increased urbanization and industrialization accelerated demand for energy, large-scale waste output, and negative environmental consequences. Therefore, the implementation of an effective solid-waste-management (SWM) policy for the handling of food waste is of great importance. The global food waste generation is estimated at about 1.6 gigatons/yr which attributes to an economic revenue of 750 billion USD. It can be converted into high-value enzymes, surfactants, Poly-hydroxybutyrate, biofuels, etc. However, the heterogeneous composition of food with high organic load and varying moisture content makes their transformation into value-added products difficult. This review aims to bring forth the possibilities and repercussions of food waste management. The socio-economic challenges related to SWM are comprehensively discussed particularly in terms of environmental concern. The engineering aspect in the collection, storage, and biotransformation of food waste into useful value-added products such as biofuels, advanced biomaterials, bioactive compounds, and platform chemicals are critically reviewed for efficient food waste management.

A review on the physicochemical and biological applications of biosurfactants in biotechnology and pharmaceuticals

Biosurfactants are the chemical compounds that are obtained from various micro-organisms and possess the ability to decrease the interfacial tension between two similar or different phases. The importance of biosurfactants in cosmetics, pharmaceuticals, biotechnology, agriculture, food and oil industries has made them an interesting choice in various physico-chemical and biological applications. With the aim of representing different properties of biosurfactants, this review article is focused on emphasizing their applications in various industries summarizing their importance in each field. Along with this, the production of recently developed chemically and biologically important biosurfactants has been outlined. The advantages of biosurfactants over the chemical surfactants have also been discussed with emphasis on the latest findings and research performed worldwide. Moreover, the chemical and physical properties of different biosurfactants have been presented and different characterization techniques have been discussed. Overall, the review article covers the latest developments in biosurfactants along with their physico-chemical properties and applications in different fields, especially in pharmaceuticals and biotechnology.

Oily Wastewater Treatment: Methods, Challenges, and Trends

The growing interest in innovations regarding the treatment of oily wastewater stems from the fact that the oil industry is the largest polluter of the environment. The harm caused by this industry is seen in all countries. Companies that produce such wastewater are responsible for its treatment prior to disposal or recycling into their production processes. As oil emulsions are difficult to manage and require different types of treatment or even combined methods, a range of environmental technologies have been proposed for oil-contaminated effluents, such as gravity separation, flotation, flocculation, biological treatment, advanced oxidation processes, and membranes. Natural materials, such as biopolymers, constitute a novel, sustainable solution with considerable potential for oily effluent separation. The present review offers an overview of the treatment of oily wastewater, describing current trends and the latest applications. This review also points to further research needs and major concerns, especially with regards to sustainability, and discusses potential biotechnological applications.

Improved the lipopeptide production of Bacillus amyloliquefaciens HM618 under co-culture with the recombinant Corynebacterium glutamicum producing high-level proline

The application of antibacterial lipopeptides is limited by high cost and low yield. Herein, the exogenous L-proline significantly improved lipopeptide production by Bacillus amyloliquefaciens HM618. A recombinant Corynebacterium glutamicum producing high levels of proline using genetically modifying proB and putA was used to establish consortium, to improve lipopeptide production of strain HM618. Compared to a pure culture, the levels of iturin A, fengycin, and surfactin in consortium reached 67.75, 39.32, and 37.25 mg L^-1, respectively, an increase of 3.19-, 2.05-, and 1.63-fold over that produced by co-cultures of B. amyloliquefaciens and recombinant C. glutamicum with normal medium. Commercial amylase and recombinant Pichia pastoris with a heterologous amylase gene were used to hydrolyze kitchen waste. A three-strain consortium with recombinant P. pastoris and C. glutamicum increased the lipopeptide production of strain HM618 in medium containing KW. This work provides new strategies to improve lipopeptide production by B. amyloliquefaciens.

Conversion of Waste Cooking Oil to Rhamnolipid by a Newly Oleophylic Pseudomonas aeruginosa WO2

The components of waste cooking oil (WCO) are complex and contain toxic substances, which are difficult to treat biologically. Pseudomonas aeruginosa WO2 was isolated from oily sludge by an anaerobic enrichment–aerobic screening method, which could efficiently utilize WCO and produce rhamnolipid. The effects of nutrients and culture conditions on bacterial growth and lipase activity were investigated to optimize the fermentation of WCO. The results showed that strain WO2 utilized 92.25% of WCO and produced 3.03 g/L of rhamnolipid at 120 h. Compared with inorganic sources, the organic nitrogen source stabilized the pH of fermentation medium, improved lipase activity (up to 19.98 U/mL), and promoted the utilization of WCO. Furthermore, the WO2 strain exhibited inferior utilization ability of the soluble starch contained in food waste, but superior salt stress up to 60 g/L. These unique characteristics demonstrate the potential of Pseudomonas aeruginosa WO2 for the utilization of high-salinity oily organic waste or wastewater.

Processes and prospects on valorizing solid waste for the production of valuable products employing bio-routes: A systematic review

Humanity is struggling against a major problem for a proper management of generated municipal solid waste. The collected waste causes natural issues like uncontrollable emission of greenhouse gases and others. Even though, escalation of waste results in minimizing the areas accessible for disposing the waste. Creating awareness in the society to use organic products like biofuels, biofertilizers and biogas is a need of an hour. Biochemical processes such as composting, vermicomposting, anaerobic digestion, and landfilling play important role in valorizing biomass and solid waste for production of biofuels, biosurfactants and biopolymer. This paper covers the details of biomass and solid waste characteristics and its composition. It is also focused to provide updated information about reutilization of biomass for value creation. Technologies and products obtained through bio-routes are discussed in current review paper together with the integrated system of solid waste management. It also covers challenges, innovations and perspectives in this field.

Exploiting Microbes in the Petroleum Field: Analyzing the Credibility of Microbial Enhanced Oil Recovery (MEOR)

Crude oil is a major energy source that is exploited globally to achieve economic growth. To meet the growing demands for oil, in an environment of stringent environmental regulations and economic and technical pressure, industries have been required to develop novel oil salvaging techniques. The remaining ~70% of the world’s conventional oil (one-third of the available total petroleum) is trapped in depleted and marginal reservoirs, and could thus be potentially recovered and used. The only means of extracting this oil is via microbial enhanced oil recovery (MEOR). This tertiary oil recovery method employs indigenous microorganisms and their metabolic products to enhance oil mobilization. Although a significant amount of research has been undertaken on MEOR, the absence of convincing evidence has contributed to the petroleum industry’s low interest, as evidenced by the issuance of 400+ patents on MEOR that have not been accepted by this sector. The majority of the world’s MEOR field trials are briefly described in this review. However, the presented research fails to provide valid verification that the microbial system has the potential to address the identified constraints. Rather than promising certainty, MEOR will persist as an unverified concept unless further research and investigations are carried out.

A critical review on various feedstocks as sustainable substrates for biosurfactants production: a way towards cleaner production

The quest for a chemical surfactant substitute has been fuelled by increased environmental awareness. The benefits that biosurfactants present like biodegradability, and biocompatibility over their chemical and synthetic counterparts has contributed immensely to their popularity and use in various industries such as petrochemicals, mining, metallurgy, agrochemicals, fertilizers, beverages, cosmetics, etc. With the growing demand for biosurfactants, researchers are looking for low-cost waste materials to use them as substrates, which will lower the manufacturing costs while providing waste management services as an add-on benefit. The use of low-cost substrates will significantly reduce the cost of producing biosurfactants. This paper discusses the use of various feedstocks in the production of biosurfactants, which not only reduces the cost of waste treatment but also provides an opportunity to profit from the sale of the biosurfactant. Furthermore, it includes state-of-the-art information about employing municipal solid waste as a sustainable feedstock for biosurfactant production, which has not been simultaneously covered in many published literatures on biosurfactant production from different feedstocks. It also addresses the myriad of other issues associated with the processing of biosurfactants, as well as the methods used to address these issues and perspectives, which will move society towards cleaner production.

Application of Random Mutagenesis and Synthetic FadR Promoter for de novo Production of ω-Hydroxy Fatty Acid in Yarrowia lipolytica

As a means to develop oleaginous biorefinery, Yarrowia lipolytica was utilized to produce ω-hydroxy palmitic acid from glucose using evolutionary metabolic engineering and synthetic FadR promoters for cytochrome P450 (CYP) expression. First, a base strain was constructed to produce free fatty acids (FFAs) from glucose using metabolic engineering strategies. Subsequently, through ethyl methanesulfonate (EMS)-induced random mutagenesis and fluorescence-activated cell sorting (FACS) screening, improved FFA overproducers were screened. Additionally, synthetic promoters containing bacterial FadR binding sequences for CYP expression were designed to respond to the surge of the concentration of FFAs to activate the ω-hydroxylating pathway, resulting in increased transcriptional activity by 14 times from the third day of culture compared to the first day. Then, endogenous alk5 was screened and expressed using the synthetic FadR promoter in the developed strain for the production of ω-hydroxy palmitic acid. By implementing the synthetic FadR promoter, cell growth and production phases could be efficiently decoupled. Finally, in batch fermentation, we demonstrated de novo production of 160 mg/L of ω-hydroxy palmitic acid using FmeN3-TR1-alk5 in nitrogen-limited media. This study presents an excellent example of the production of ω-hydroxy fatty acids using synthetic promoters with bacterial transcriptional regulator (i.e., FadR) binding sequences in oleaginous yeasts.

Study of bacterial interactions in reconstituted hydrocarbon-degrading bacterial consortia from a local collection, for the bioremediation of weathered oily-soils

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Reconstituted hydrocarbon-degrading bacteria consortia from the weathered sites interact positively and negatively in bioremediation processes.

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Bioaugmentation using endogenous bacteria should be based on selection of the appropriate strains, which can co-growth with inhibition.

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The reconstituted hydrocarbon-degrading bacteria consortia lead to reduction of the lag phases and increase of TPH removal at 10 times soil TPH concentrations.

To enhance the process of bacterial remediation of weathered hydrocarbons, the area of Dukhan, Qatar, was considered as a model for weathering processes. Self-purification by indigenous hydrocarbon-degrading bacteria showed low performance. Biostimulation/seeding using one or another of the indigenous bacteria improved the performance. Symbiosis between three strains dominating the soil; Bacillus sorensis D11, Bacillus cereus D12, and Pseudomonas stutzeri D13, was highly performant for removal of total petroleum hydrocarbons in the weathered soil. D11, the most sensitive, showed the highest performance when mixed with D12 or D13. D12, less performant than D11, was more active on diesel range organics (DRO: C10-C28), similar to D11. D13 showed a metabolic behavior close to commensal and co-metabolic ones. It was more active on hydrocarbons above C29. Combination of the three strains conducted to the removal of at least 80% of C10-C35 organics in the extract at concentrations of 31.1 mg/g TPH-DRO.

Bio-based rhamnolipids production and recovery from waste streams: Status and perspectives

Bio-based rhamnolipid production from waste streams is gaining momentum nowadays because of increasing market demand, huge range of applications and its economic and environment friendly nature. Rhamnolipid type biosurfactants are produced by microorganisms as secondary metabolites and have been used to reduce surface/interfacial tension between two different phases. Biosurfactants have been reported to be used as an alternative to chemical surfactants. Pseudomonas sp. has been frequently used for production of rhamnolipid. Various wastes can be used in production of rhamnolipid. Rhamnolipids are widely used in various industrial applications. The present review provides information about structure and nature of rhamnolipid, production using different waste materials and scale-up of rhamnolipid production. It also provides comprehensive literature on various industrial applications along with perspectives and challenges in this research area.

Remediation of oily sludge wastes using biosurfactant produced by bacterial isolate Pseudomonas balearica strain Z8

Biological treatment of oily sludge wastes was studied using an isolated halo-tolerant strain Pseudomonas balearica strain Z8. An oily sludge sample was obtained from oil fields of south waste of Iran and was fully characterized. The initial TPH content was 44,500 mg kg^-1. The ability of Pseudomonas balearica strain Z8 in production of biosurfactant was investigated using oil displacement method. Results demonstrated that isolated strain is a biosurfactant producing bacteria. The CMC and emulsification index [E₂₄] of produced biosurfactant were 90 mg L^-1 and 44% for crude oil. Effect of operational parameters including nitrogen source, sludge/water ratio and temperature were investigated against the time. The most TPH removal of 35% was observed for nitrogen source of NH₄Cl, sludge/ water ratio of 1:7 and temperature of 40 °C.

Potential for native hydrocarbon-degrading bacteria to remediate highly weathered oil-polluted soils in Qatar through self-purification and bioaugmentation in biopiles

Petroleum-derived contamination events constitute a unique environmental issue in the arid areas because of the weathering processes, accentuated due to harsh conditions and representing the main origin of failure of bioremediation applications. The industrial area of Dukhan and the AlZubara coast represent wethered oily-sites as an appropriate model due to the extreme weather, which characterizes Qatar. Indigenous bacteria would be highly adapted and when re-introduced or stimulated would conduct to the remediation of these sites. An appropriate approach to bioremediating-weathered oil was investigated in these two areas. Systematic soil sampling was performed, and the soil samples were analyzed. The results clearly showed the harsh chemical compositions (high salinity and contents of total petroleum components contents in the range of the oil organics). By implementation of a procedure of isolation of highly adapted bacteria, few hydrocarbon-degrading bacteria were isolated in the objective of selecting those for further application. Their identification by ribotyping showed dominance of Bacillus and Virgibacillus in AlZubara site, and Bacillus and Pseudomonas in Dukhan site. All bacterial strains were highly tolerant to 10 % diesel and showed potential of removal of 20 %-85 % of C 10 to C 36 hydrocarbons. This potential was confirmed by determination of the n-heptadecane/pristane and n-octadecane/phytane ratios, indicating in turn their potential to bioremediate oil. This was demonstrated by comparison of the self-remediation to bioaugmentation using two selected Bacillus and Pseudomonas strains using Dukhan soil in biopiles. These strains when biostimulted in such a soil increased the removal of total petroleum components to 53 % compared to 30 % with self-purification, after 90 d. The results indicated that highly adapted endogenous bacteria might be used to bioremediate highly weathered oil-contaminated soil under harsh conditions.

Metabolic Checkpoint Aldehyde Dehydrogenases Are Important for Diverting β-Oxidation into 1-Butanol Biosynthesis from Kitchen Waste Oil in Pseudomonas aeruginosa

1-Butanol (1-BD) is a promising fuel additive which can be biosynthesized via reversed β-oxidation pathway in bacteria. However, heterologous reversed β-oxidation pathway is a carbon chain prolongation process with several genes overexpressed in most of bacterial hosts, leading to low titer of 1-BD and high cost for production. Here we displayed a forward β-oxidation pathway for 1-BD production in a kitchen waste oil (KWO) degrading Pseudomonas aeruginosa PA-3, and we proved that aldehyde dehydrogenase (ALDH) is a checkpoint for diverting metabolic flux into 1-BD biosynthesis. With nitrogen source supplied, titer of 1-BD was increased accompanied with 12 ALDH coding genes transcriptionally promoted to different degrees. At the same time, binding energies of these ALDHs with different length of acyl-CoAs in β-oxidation were calculated to identify their specificities. Based on the above information, ALDH deletions were conducted. We certified that deletion of ALDH8 and ALDH9 led to significant decreased titers of 1-BD. Finally, these two ALDHs were separately overexpressed in PA-3, and titer of 1-BD was promoted to 1.36 g/L at 72 h in shake flask. Totally in this work, we provided a forward β-oxidation pathway for 1-BD production from KWO, and the roles of ALDHs were confirmed.

Eco-friendly biosurfactant from Wickerhamomyces anomalus CCMA 0358 as larvicidal and antimicrobial

Kitchen waste oil (KWO) was evaluated as a substrate for production of biosurfactant by Wickerhamomyces anomalus CCMA 0358 and was tested against Aedes aegypti larvae, the mosquito causing neglected diseases, such as dengue fever, Zika, and Chikungunya, achieving 100 % mortality in the lowest concentration (6.25 %) evaluated in 24 h. Furthermore, possible applications of this compound were evaluated as antibacterial, antiadhesive, and antifungal. At a concentration of 50 %, the biosurfactant was found to inhibit the growth of Bacillus cereus, showing high inhibitions levels against Salmonella Enteritidis, Staphylococcus aureus, and Escherichia coli. The antifungal activity was evaluated against Aspergillus, Cercospora, Colletotrichum, and Fusarium, obtaining results of up to 95 % inhibition. In addition to these promising results, the yeast W. anomalus produced the biosurfactant from an inexpensive substrate, which increases the possibility of its application in several industries owing to the low cost involved.

Characterization and properties of the biosurfactant produced by PAH-degrading bacteria isolated from contaminated oily sludge environment

The aim of the present study was to investigate biosurfactant production ability of five different polyaromatic hydrocarbon (PAH)-metabolizing bacteria, such as Ochrobactrum anthropi IITR07, Pseudomonas mendocina IITR46, Microbacterium esteraromaticum IITR47, Pseudomonas aeruginosa IITR48, and Stenotrophomonas maltophilia IITR87. These bacteria showed biosurfactant production using 2% glucose as rich substrate; strain IITR47 yielded the highest with 906 and 534 mg/L biosurfactant in the presence of naphthalene and crude oil as the unique carbon sources. P. aeruginosa IITR48 showed the least surface tension at 29 N/m and the highest emulsification index at 63%. The biosurfactants produced were identified as glycolipid and rhamnolipid based on Fourier transform infrared spectroscopy analysis. In particular, the biosurfactant produced by bacteria S. maltophilia IITR87 efficiently emulsified mustard oil with an E24 value of 56%. It was observed that, all five biosurfactants from these degrader strains removed 2.4-, 1.7-, 0.9-, 3.8-, and 8.3-fold, respectively, crude oil from contaminated cotton cloth. Rhamnolipid derived from IITR87 was most efficient, exhibiting highest desorption of crude oil. These biosurfactants exhibited good stability without significantly losing its emulsification ability under extreme conditions, thus can be employed for bioremediation of PAHs from diverse contaminated ecosystem. Graphical Abstract.

Investigation of fermentation conditions of biodiesel by-products for high production of β-farnesene by an engineered Escherichia coli

Recently, the research on conversion of biodiesel by-products to high value-added products has received much attention, due to the adverse effects of large accumulations of biodiesel by-products caused by the rapid increase in biodiesel production. Herein, this study investigated the utilization of by-products crude glycerol (CG-1 and CG-2) from two different industrial methods of biodiesel production and the favorable fermentation conditions for the high yield of β-farnesene by an engineered Escherichia coli F4, which harbored an optimized mevalonate pathway. Through analyzing by-products' components and fermentation performance, we found that CG-2 did not contain harmful impurities such as methanol and black solid impurities, and the β-farnesene production was up to 2.7 g/L from CG-2, which was similar to that from pure glycerol (2.5 g/L) and higher than that (2.21 g/L) from CG-1. Therefore, CG-2 was more suitable for β-farnesene production than CG-1, which might provide a reference for choosing a more suitable method on practical biodiesel production. Afterward, a variety of important fermentation conditions were explored using CG-2 as a substrate in shaken flasks. Under the optimal conditions (including induced cell density 1.0, initial cell density 0.25, temperature after induction 33 °C, initial medium pH 6.5), the yield of β-farnesene from CG-2 reached 10.31 g/L in a 5-L bioreactor, which was 2.8-fold higher than initial conditions in shake flasks and was the highest yield of β-farnesene produced from biodiesel by-products by fermentation as well. The recommended fermentation conditions in this work will provide a valuable reference for the industrial production of β-farnesene utilizing biodiesel by-products.

Characterization of Pseudomonas sp. TMB2 produced rhamnolipids for ex-situ microbial enhanced oil recovery

The present study describes the ex-situ production of a biosurfactant by Pseudomonas sp. TMB2 for its potential application in enhancing oil recovery. The physicochemical parameters such as temperature and pH were optimized as 30 °C and 7.2, respectively, for their maximum laboratory scale production in mineral salt medium containing glucose and sodium nitrate as best carbon and nitrogen sources. The surface activity of the resulting culture broth was declined from 71.9 to 33.4 mN/m having the highest emulsification activity against kerosene oil. The extracted biosurfactant was characterized chemically as glycolipid by Fourier-transform infrared spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy analyses. The presence of mono-rhamnolipids (Rha-C8:2, Rha-C10, Rha-C10-C10, and Rha-C10-C12:1) and di-rhamnolipids (Rha-Rha-C12-C10, Rha-Rha-C10-C10, and Rha-Rha-C10-C12:1) congeners were determined by liquid chromatography-mass spectroscopy analysis. The thermostability and degradation pattern of the candidate biosurfactant were tested by thermogravimetry assay and differential scanning calorimetry studies for its suitability in ex-situ oil recovery technology. The rhamnolipid based slug, prepared in 4000 ppm brine solution reduced the interfacial tension between liquid paraffin oil and aqueous solution to 0.8 mN/m from 39.1 mN/m at critical micelle concentration of 120 mg/L. The flooding test was performed using conventional core plugs belonging to oil producing horizons of Upper Assam Basin and recovered 16.7% of original oil in place after secondary brine flooding with microscopic displacement efficiency of 27.11%.

Microbial strategies for bio-transforming food waste into resources

With the changing life-style and rapid urbanization of global population, there is increased generation of food waste from various industrial, agricultural, and household sources. According to Food and Agriculture Organization (FAO), almost one-third of the total food produced annually is wasted. This poses serious concern as not only there is loss of rich resources; their disposal in environment causes concern too. Food waste is rich in organic, thus traditional approaches of land-filling and incineration could cause severe environmental and human health hazard by generating toxic gases. Thus, employing biological methods for the treatment of such waste offers a sustainable way for valorization. This review comprehensively discusses state-of-art knowledge about various sources of food waste generation, their utilization, and valorization by exploiting microorganisms. The use of microorganisms either aerobically or anaerobically could be a sustainable and eco-friendly solution for food waste management by generating biofuels, electrical energy, biosurfactants, bioplastics, biofertilizers, etc.

Bioconversion of kitchen wastes into bioflocculant and its pilot-scale application in treating iron mineral processing wastewater

In this study, the feasibility of converting kitchen waste into bioflocculant using Bacillus agaradhaerens C9 was analyzed. The result showed that strain C9 could secrete various degrading enzymes, including amylase, protease, lipase, cellulase, xylanase and pectinase, promoting the hydrolysis of kitchen waste. Strong alkaline fermentation condition was able to induce the bioflocculant production, and inhibit the growth of contaminated bacteria, which avoids the sterilization process of kitchen waste. The optimum fermentation condition for enzymatic hydrolysis and bioflocculant production was 40 g/L kitchen waste, 37 °C, pH 9.5, and the highest bioflocculant yield of 6.92 g/L was achieved. Furthermore, bioflocculant was applied to treat pilot-scale (30 L) of mineral processing wastewater for the first time, and the removal rate of 92.35% was observed when 9 mg/L bioflocculant was added into wastewater. Therefore, this study could promote the resource utilization of kitchen waste and recycling of mineral processing wastewater.

Production of a Biosurfactant by Cunninghamella echinulata Using Renewable Substrates and Its Applications in Enhanced Oil Spill Recovery

This study aimed to evaluate the production of a surfactant by Cunninghamella echinulata, using agro-industrial residues, corn steep liquor (CSL), and soybean oil waste (SOW). The study had a factorial design, using as a variable response to the reduction of surface tension. C. echinulata was able to produce biosurfactant in assay, CSL (8.82%) and SOW (2%). The results showed that the biosurfactant was successfully produced by C. echinulata and had attractive properties, such as a low surface tension (31.7 mN/m), a yield of 5.18 g/L at 120 h of cultivation, and an anionic profile. It also achieved a reduction in surface tension stability in a wide range of pH values, temperatures, and salinity values. The biosurfactant produced by C. echinulata showed an absence of toxicity to Artemia salina. The influence of the biosurfactant on the viscosity of engine oil, burnt engine oil, diesel, soybean oil post-frying, canola oil, and water was investigated. The results reveal a mechanism for the decrease of the viscosity using hydrophobic substrates and the new biosurfactant solution at 1.5% of the (CMC). This enables the formulation of a low-cost culture medium alternative, based on corn steep liquor and the reuse of soybean oil after frying to produce a biosurfactant. Additionally, performance of the biosurfactant isolated from C. echinulata showed an excellent ability to remove spilled oil, such as diesel (98.7%) and kerosene (92.3%) from marine sand.