Application of response-surface methodology to evaluate the optimum medium components for the enhanced production of lichenysin by Bacillus licheniformis R2

Bacillus subtilis as a host for natural product discovery and engineering of biosynthetic gene clusters

Covering: up to October 2023Many bioactive natural products are synthesized by microorganisms that are either difficult or impossible to cultivate under laboratory conditions, or that produce only small amounts of the desired compound. By transferring biosynthetic gene clusters (BGCs) into alternative host organisms that are more easily cultured and engineered, larger quantities can be obtained and new analogues with potentially improved biological activity or other desirable properties can be generated. Moreover, expression of cryptic BGCs in a suitable host can facilitate the identification and characterization of novel natural products. Heterologous expression therefore represents a valuable tool for natural product discovery and engineering as it allows the study and manipulation of their biosynthetic pathways in a controlled setting, enabling innovative applications. Bacillus is a genus of Gram-positive bacteria that is widely used in industrial biotechnology as a host for the production of proteins from diverse origins, including enzymes and vaccines. However, despite numerous successful examples, Bacillus species remain underexploited as heterologous hosts for the expression of natural product BGCs. Here, we review important advantages that Bacillus species offer as expression hosts, such as high secretion capacity, natural competence for DNA uptake, and the increasing availability of a wide range of genetic tools for gene expression and strain engineering. We evaluate different strain optimization strategies and other critical factors that have improved the success and efficiency of heterologous natural product biosynthesis in B. subtilis. Finally, future perspectives for using B. subtilis as a heterologous host are discussed, identifying research gaps and promising areas that require further exploration.

A comprehensive review on production of bio-surfactants by bio-degradation of waste carbohydrate feedstocks: an approach towards sustainable development

The advancement of science and technology demands chemistry which is safer, smarter and green by nature. The sustainability of science thus requires well-behaved alternates that best suit the demand. Bio-surfactants are surface active compounds, established to affect surface chemistry. In general, microbial bio-surfactants are a group of structurally diverse molecules produced by different microbes. A large number of bio-surfactants are produced during hydrocarbon degradation by hydrocarbonoclistic microorganisms during their own growth on carbohydrates and the production rate is influenced by the rate of degradation of carbohydrates. The production of such biological surfactants is thus of greater importance. This write up is a dedicated review to update the existing knowledge of inexpensive carbohydrate sources as substrates, microorganisms and technologies of biosurfactant production. This is an economy friendly as well as sustainable approach which will facilitate achieving some sustainable development goals. The production is dependent on the fermentation strategies, different factors of the microbial culture broth and downstream processing; these all have been elaborately presented in this article.

Construct a synthetic Entner-Doudoroff pathway in Bacillus licheniformis for enhancing lichenysin production

Lichenysin, a cyclic lipopeptide biosurfactant produced by Bacillus licheniformis, is composed of aspartate, glutamine, valine, leucine, isoleucine, and branched chain fatty acids. The synthesis of these amino acids and fatty acids requires pyruvate and NADPH as the primary precursor and cofactor. Therefore, a sufficient supply of pyruvate and NADPH is crucial for lichenysin production. This study aimed to increase lichenysin production by constructing a synthetic ED pathway in B. licheniformis WX02 through introducing phosphogluconate dehydratase (encoded by gene edd) and 2-keto-3-deoxygluconate 6-phosphate aldolase (encoded by gene eda) from Escherichia coli. Additionally, the NADP⁺-dependent glucose-6-phosphate dehydrogenase (encoded by gene zwf) was overexpressed, resulting in an engineered strain WX02/pHY-edda(Ec)-zwf. Analysis of the fermentation process revealed that the concentrations of pyruvate, aspartate, glutamine, valine, leucine, branched-chain fatty acids (iC15:0, aC15:0, iC16:0, iC17:0), and NADPH in WX02/pHY-edda(Ec)-zwf were increased by 77.21%, 80.41%, 85.31%, 141.64%, 44.94%, 35.08%, 38.08%, 19.33%, 21.16%, and 425%, respectively, compared to the control strain WX02/pHY300, which resulted in a 45.43% increase of lichenysin titer. This work took advantage of the ED pathway to increase lichenysin production for the first time, and provides a promising strategy for boosting the productivity of biochemicals that require pyruvate and NADPH as precursor and cofactor.

A comprehensive study on microbial-surfactants from bioproduction scale-up toward electrokinetics remediation of environmental pollutants: Challenges and perspectives

Currently, researchers have focused on electrokinetic (EK) bioremediation due to its potential to remove a wide-range of pollutants. Further, to improve their performance, synthetic surfactants are employed as effective additives because of their excellent solubility and mobility. Synthetic surfactants have an excessive position in industries since they are well-established, cheap, and easily available. Nevertheless, these surfactants have adverse environmental effects and could be detrimental to aquatic and terrestrial life. Owing to social and environmental awareness, there is a rising demand for bio-based surfactants in the global market, from environmental sustainability to public health, because of their excellent surface and interfacial activity, higher and stable emulsifying property, biodegradability, non- or low toxicity, better selectivity and specificity at extreme environmental conditions. Unfortunately, challenges to biosurfactants, like expensive raw materials, low yields, and purification processes, hinder their applicability to large-scale. To date, extensive research has already been conducted for production scale-up using multidisciplinary approaches. However, it is still essential to research and develop high-yielding bacteria for bioproduction through traditional and biotechnological advances to reduce production costs. Herein, this review evaluates the recent progress made on microbial-surfactants for bioproduction scale-up and provides detailed information on traditional and advanced genetic engineering approaches for cost-effective bioproduction. Furthermore, this study emphasized the role of electrokinetic (EK) bioremediation and discussed the application of BioS-mediated EK for various pollutants remediation.

Optimization of Medium Components for Fed-Batch Fermentation Using Central Composite Design to Enhance Lichenysin Production by Bacillus licheniformis Ali5

Lichenysin, an amphiphilic biosurfactant with structural and physicochemical properties similar to surfactin, is produced by Bacillus licheniformis. Its low toxicity, good environmental compatibility, solubilization, foaming, emulsification and detergent activities have led to a wide range of applications in agricultural biocontrol, enhanced oil recovery, foaming agents for cosmetics and detergents for household cleaning products. However, despite the extraordinary surface-active properties and potential applications of lichenysin, the number of wild bacteria found so far is relatively low. Low titers and high costs are the main limiting factors for widespread industrial applications. In this study, a factorial design was used to optimize the composition of the medium for the production of lichenysin by Bacillus licheniformis Ali5. Firstly, the solutions of carbon, nitrogen, amino acids, inorganic salts and trace elements in the medium were evaluated in flasks using a single-factor optimization method. Meanwhile, the operating conditions were optimized in the same way. Afterwards, a partial factorial design was used to investigate the effect of six variables (five medium compositions and inoculum size) on lichenysin production. Based on the results obtained, the concentrations of sucrose and ammonium nitrate and the inoculum size were considered to be important for lichenysin production. Subsequently, a full factorial design was used to optimize these three variables. The optimized medium composition were sucrose 19.8 g/L, NH4NO3 3.9 g/L, K2HPO4·3H2O 4.0 g/L, MgSO4·7H2O 0.6 g/L, FeSO4·7H2O 0.1 g/L, CaCl2 0.01 g/L, NaCl 3.0, trace elements 1.2 mL/L. Finally, the titer of lichenysin after fed-batch fermentation reached 1425.85 mg/L, which was approximately 5.5 times higher than the titer of lichenysin from the original medium. Consequently, the method was further demonstrated to be suitable for lichenysin production.

Bacillus licheniformis: The unexplored alternative for the anaerobic production of lipopeptide biosurfactants?

Microbial biosurfactants have attracted the attention of researchers and companies for the last decades, as they are considered promising candidates to replace chemical surfactants in numerous applications. Although in the last years, considerable advances were performed regarding strain engineering and the use of low-cost substrates in order to reduce their production costs, one of the main bottlenecks is their production at industrial scale. Conventional aerobic biosurfactant production processes result in excessive foaming, due to the use of high agitation and aeration rates necessary to increase dissolved oxygen concentration to allow microbial growth and biosurfactant production. Different approaches have been studied to overcome this problem, although with limited success. A not widely explored alternative is the development of foam-free processes through the anaerobic growth of biosurfactant-producing microorganisms. Surfactin, produced by Bacillus subtilis, is the most widely studied lipopeptide biosurfactant, and the most powerful biosurfactant known so far. Bacillus licheniformis strains produce lichenysin, a lipopeptide biosurfactant which structure is similar to surfactin. However, despite its extraordinary surface-active properties and potential applications, lichenysin has been scarcely studied. According to previous studies, B. licheniformis is better adapted to anaerobic growth than B. subtilis, and could be a good alternative for the anaerobic production of lipopeptide biosurfactants. In this review, the potential and limitations of surfactin and lichenysin production under anaerobic conditions will be analyzed, and the possibility of implementing foam-free processes for lichenysin production, in order to expand the market and applications of biosurfactants in different fields, will be discussed.

Lichenysin Production by Bacillus licheniformis Food Isolates and Toxicity to Human Cells

Bacillus licheniformis can cause foodborne intoxication due to the production of the surfactant lichenysin. The aim of this study was to measure the production of lichenysin by food isolates of B. licheniformis in LB medium and skimmed milk and its cytotoxicity for intestinal cells. Out of 11 B. licheniformis isolates tested, most showed robust growth in high salt (1M NaCl), 4% ethanol, at 37 or 55°C, and aerobic and anaerobic conditions. All strains produced lichenysin (in varying amounts), but not all strains were hemolytic. Production of this stable compound by selected strains (high producers B4094 and B4123, and type strain DSM13^T) was subsequently determined using LB medium and milk, at 37 and 55°C. Lichenysin production in LB broth and milk was not detected at cell densities < 5 log₁₀ CFU/ml. The highest concentrations were found in the stationary phase of growth. Total production of lichenysin was 4–20 times lower in milk than in LB broth (maximum 36 μg/ml), and ∼10 times lower in the biomass obtained from milk agar than LB agar. Under all conditions tested, strain B4094 consistently yielded the highest amounts. Besides strain variation and medium composition, temperature also had an effect on lichenysin production, with twofold lower amounts of lichenysin produced at 55°C than at 37°C. All three strains produced lichenysin A with varying acyl chain lengths (C11–C18). The relative abundance of the C14 variant was highest in milk and the C15 variant highest in LB. The concentration of lichenysin needed to reduce cell viability by 50% (IC₅₀) was 16.6 μg/ml for Caco-2 human intestinal epithelial cells and 16.8 μg/ml for pig ileum organoids. Taken together, the presence of low levels (<5 log₁₀ CFU/ml) of B. licheniformis in foods is unlikely to pose a foodborne hazard related to lichenysin production. However, depending on the strain present, the composition, and storage condition of the food, a risk of foodborne intoxication may arise if growth to high levels is supported and such product is ingested.

OVAT Analysis and Response Surface Methodology Based on Nutrient Sources for Optimization of Pigment Production in the Marine-Derived Fungus Talaromyces albobiverticillius 30548 Submerged Fermentation

Pigment production from filamentous fungi is gaining interest due to the diversity of fungal species, the variety of compounds synthesized, and the possibility of controlled massive productions. The Talaromyces species produce a large panel of metabolites, including Monascus-like azaphilone pigments, with potential use as natural colorants in industrial applications. Optimizing pigment production from fungal strains grown on different carbon and nitrogen sources, using statistical methods, is widespread nowadays. The present work is the first in an attempt to optimize pigments production in a culture of the marine-derived T. albobiverticillius 30548, under the influence of several nutrients sources. Nutrient combinations were screened through the one-variable-at-a-time (OVAT) analysis. Sucrose combined with yeast extract provided a maximum yield of orange pigments (OPY) and red pigments (RPY) (respectively, 1.39 g/L quinizarin equivalent and 2.44 g/L Red Yeast pigment equivalent), as well as higher dry biomass (DBW) (6.60 g/L). Significant medium components (yeast extract, K₂HPO₄ and MgSO₄·7H₂O) were also identified from one-variable-at-a-time (OVAT) analysis for pigment and biomass production. A five-level central composite design (CCD) and a response surface methodology (RSM) were applied to evaluate the optimal concentrations and interactive effects between selected nutrients. The experimental results were well fitted with the chosen statistical model. The predicted maximum response for OPY (1.43 g/L), RPY (2.59 g/L), and DBW (15.98 g/L) were obtained at 3 g/L yeast extract, 1 g/L K₂HPO₄, and 0.2 g/L MgSO₄·7H₂O. Such optimization is of great significance for the selection of key nutrients and their concentrations in order to increase the pigment production at a pilot or industrial scale.

Enhanced Oil Removal by a Non-Toxic Biosurfactant Formulation

In this study, a new formulation of low-cost, biodegradable, and non-toxic biosurfactant by Candida sphaerica UCP 0995 was investigated. The study was conducted in a bioreactor on an industrial waste-based medium, and a central composite rotatable design was used for optimization. The best results, namely a 25.22 mN/m reduction in surface tension, a biosurfactant yield of 10.0 g/L, and a critical micelle concentration of 0.2 g/L, were achieved in 132 h at an agitation speed of 175 rpm and an aeration rate of 1.5 vvm. Compositional and spectroscopic analyses of the purified biosurfactant by chemical methods, Fourier transform infrared spectroscopy, and nuclear magnetic resonance suggested that it is a glycolipid-type biosurfactant, and it showed no cytotoxicity in the MTT assay. The biosurfactant, submitted to different formulation methods as a commercial additive, remained stable for 120 days at room temperature. Tensioactive properties and stability were evaluated at different pH values, temperatures, and salt concentrations. The biosurfactant obtained with all formulation methods demonstrated good stability, with tolerance to wide ranges of pH, temperature and salinity, enabling application under extreme environmental conditions. Bioremediation tests were performed to check the efficacy of the isolated biosurfactant and the selected microbial species in removing oil from soil. The results demonstrated that the biosurfactant produced has promising properties as an agent for the bioremediation of contaminated soil.

Improved Production of Two Anti-Candida Lipopeptide Homologues Co- Produced by the Wild-Type Bacillus subtilis RLID 12.1 under Optimized Conditions

BACKGROUND

Antifungal cyclic lipopeptides, bioactive metabolites produced by many species of the genus Bacillus, are promising alternatives to synthetic fungicides and antibiotics for the biocontrol of human pathogenic fungi. In a previous study, the co- production of five antifungal lipopeptides homologues (designated as AF1, AF2, AF3, AF4 and AF5) by the producer strain Bacillus subtilis RLID 12.1 using unoptimized medium was reported; though the two homologues AF3 and AF5 differed by 14 Da and in fatty acid chain length were found effective in antifungal action, the production/ yield rate of these two lipopeptides determined by High-Performance Liquid Chromatography was less in the unoptimized media.

METHODS

In this study, the production/yield enhancement of the two compounds AF3 and AF5 was specifically targeted. Following the statistical optimization (Plackett-Burman and Box-Behnken designs) of media formulation, temperature and growth conditions, the production of AF3 and AF5 was improved by about 25.8- and 7.4-folds, respectively under static conditions.

RESULTS

To boost the production of these two homologous lipopeptides in the optimized media, heat-inactivated Candida albicans cells were used as a supplement resulting in 34- and 14-fold increase of AF3 and AF5, respectively. Four clinical Candida auris isolates had AF3 and AF5 MICs (100 % inhibition) ranging between 4 and 16 μg/ml indicating the lipopeptide's clinical potential. To determine the in vitro pharmacodynamic potential of AF3 and AF5, time-kill assays were conducted which showed that AF3 (at 4X and 8X concentrations) at 48h exhibited mean log reductions of 2.31 and 3.14 CFU/ml of C. albicans SC 5314, respectively whereas AF5 at 8X concentration showed a mean log reduction of 2.14 CFU/ml.

CONCLUSION

With the increasing threat of multidrug-resistant yeasts and fungi, these antifungal lipopeptides produced by optimized method promise to aid in the development of novel antifungal that targets disease-causing fungi with improved efficacy.

Stimulation of biosurfactant production by Lactobacillus plantarum using ultrasound

Due to their nonpathogenic status, biosurfactants produced by Lactobacillus strains have been shown to have potential applicability in several industrial sectors, particularly food and pharmaceutical industries. However, products with high efficiency are needed to fulfill the demand for these biosurfactants. Therefore, the present study investigated kinetic parameters, biomass and biosurfactant production of Lactobacillus plantarum ATCC 8014 applying standard MRS and modified MRS (supplemented standard MRS by nitrogen and carbon sources) culture medium under various ultrasonic frequencies of 20, 25, 35, 45, 130 and 950 kHz to obtain more efficient conditions. The optimum conditions were found when using the modified MRS treated by the frequency of 25 kHz (the power of 7.4 W) for 30 min, which led to a significant effect on the growth rate (µ_max, h^-1) rather than control. Furthermore, this condition caused the highest population (10.07 ± 0.1 log CFU/mL) and biomass concentration (4.33 ± 0.06 g/L), and lowest surface tension (39.26 ± 0.5 mN/m), leading to higher biosurfactant production. Hence, given the results of the present study, it can be established that controlled ultrasound exposure and supplementation of culture media using the main growth factors can intensify the microbial activity and the productivity of biological processes.

Optimization of biosurfactant production by Bacillus Subtilis N3-1P using the brewery waste as the carbon source

Biosurfactants are biologically produced by microorganisms and therefore biodegradable, making ideal substitutes to chemical surfactants for various applications. Large scale production of biosurfactants is limited because of the high cost. The production cost could be reduced by optimizing cultural conditions and using wastes as substrates. In this work, the response surface methodology (RSM) was used to optimize biosurfactant production by Bacillus subtilis N3-1P strain using brewery waste as the sole carbon source. Five independent variables were varied; carbon and nitrogen concentration, agitation speed, temperature and initial pH. Surface tension and emulsification index were used to measure biosurfactant production. Results indicated that the 'best' surface tension and emulsification index were 27.31 mN m^-1 and 63.11%, respectively, under optimized cultural conditions (7% (v v^-1) brewery waste, 6.22 g L^-1 ammonium nitrate, initial pH of 6.41, 150 rpm, and 27°C). The predicted responses were validated experimentally under the 'optimum' conditions, and 657 mg L^-1 of biosurfactant was produced with a critical micelle concentration of 107 mg L^-1.

Production, Characterization, and Application of Bacillus licheniformis W16 Biosurfactant in Enhancing Oil Recovery

The biosurfactant production by Bacillus licheniformis W16 and evaluation of biosurfactant based enhanced oil recovery (EOR) using core-flood under reservoir conditions were investigated. Previously reported nine different production media were screened for biosurfactant production, and two were further optimized with different carbon sources (glucose, sucrose, starch, cane molasses, or date molasses), as well as the strain was screened for biosurfactant production during the growth in different media. The biosurfactant reduced the surface tension and interfacial tension to 24.33 ± 0.57 mN m-1 and 2.47 ± 0.32 mN m-1 respectively within 72 h, at 40°C, and also altered the wettability of a hydrophobic surface by changing the contact angle from 55.67 ± 1.6 to 19.54°± 0.96°. The critical micelle dilution values of 4X were observed. The biosurfactants were characterized by different analytical techniques and identified as lipopeptide, similar to lichenysin-A. The biosurfactant was stable over wide range of extreme environmental conditions. The core flood experiments showed that the biosurfactant was able to enhance the oil recovery by 24-26% over residual oil saturation (Sor). The results highlight the potential application of lipopeptide biosurfactant in wettability alteration and microbial EOR processes.

Screening concepts, characterization and structural analysis of microbial-derived bioactive lipopeptides: a review

Lipopeptide biosurfactants are surface active biomolecules that are produced by a variety of microorganisms. Microbial lipopeptides have gained the interest of microbiologists, chemists and biochemists for their high biodiversity as well as efficient action, low toxicity and good biodegradability in comparison to synthetic counterparts. In this report, we review methods for the production, isolation and screening, purification and structural characterization of microbial lipopeptides. Several techniques are currently available for each step, and we describe the most commonly utilized and recently developed techniques in this review. Investigations on lipopeptide biosurfactants in natural products require efficient isolation techniques for the characterization and evaluation of chemical and biological properties. A combination of chromatographic and spectroscopic techniques offer opportunities for a better characterization of lipopeptide structures, which in turn can lead to the application of lipopeptides in food, pharmaceutical, cosmetics, agricultural and bioremediation industries.

Characterization and Application of Biosurfactant Produced by Bacillus licheniformis R2

The biosurfactant produced by Bacillus licheniformis R2 was characterized and studied for enhancing the heavy crude oil recovery at 80 °C in coreflood experiments. The strain was found to be nonpathogenic and produced biosurfactant, reducing the surface tension of medium from 70 to 28 mN/m with 1.1 g/l yield. The biosurfactant was quite stable during exposure to elevated temperatures (85 °C for 90 days), high salinity (10 % NaCl), and a wide range of pH (5-12) for 10 days. It was characterized as lipopeptide similar to lichenysin-A, with a critical micelle concentration of about 19.4 mg/l. The efficiency of crude biosurfactant for enhanced oil recovery by core flood studies revealed it to recovering additional 37.1 % oil from Berea sandstone cores at 80 °C. The results are indicative of the potential for the development of lipopeptide biosurfactant-based ex situ microbial enhanced heavy oil recovery from depleting oil fields with extreme temperatures.

Transcriptional characteristics associated with lichenysin biosynthesis in Bacillus licheniformis from Chinese Maotai-flavor liquor making

This work investigated the biosynthetic mechanism of lichenysin, the newly identified nonvolatile matrix component in Chinese liquors. Transcriptomes were analyzed in three producers, Bacillus licheniformis CGMCC 3961, 3962, and 3963, which were isolated from Maotai-flavor liquor-making process and produced 386.3, 553.5, and 795.2 μg/L lichenysin in a simulative liquor fermentation process. Lichenysin synthetase genes lchAA-AD in these three producers were expressed much more highly than those of the nonproducer B. licheniformis ATCC 14580 (>18.4-fold). In addition, ABC transporters were the most significant responsive metabolic pathway, and the expression levels of peptide transporter genes dppABCDE all increased more than 19.2-fold. When B. licheniformis CGMCC 3963 was cultured in synthetic medium, the expression of dppABCDE and lichenysin both increased with the addition of casein hydrolysate (containing various peptides). This indicated that peptide would act as a substrate for lichenysin synthesis. This work sheds new light on the mechanism for lichenysin biosynthesis.

Improvement of lichenysin production in Bacillus licheniformis by replacement of native promoter of lichenysin biosynthesis operon and medium optimization

Lichenysin is a biodegradable surfactant with huge potential for recovering crude oil from the oil reservoir. The current production of lichenysin is made through fermentation from wild strain of Bacillus licheniformis, which is limited by low yield. The aim of this work was to improve lichenysin-producing capability of a wide strain B. licheniformis WX-02. Lichenysin produced from WX-02 was first extracted, purified, and identified. Through the substitution of the promoter of lichenysin biosynthesis operon, the mutants B. licheniformis WX02-P43lch, WX02-Pxyllch, and WX02-Psrflch were constructed with the constitutive promoter (P43), the xylose-inducible promoter (P xyl ), and the surfactin operon promoter (P srf ), respectively. A consistent change trend was observed between lichenysin production and lchAA gene transcription, confirming the strength of the promoters as an important factor for lichenysin synthesis. Among the three mutants, WX02-Psrflch produced the highest lichenysin yield. The production by the mutant WX02-Psrflch was further improved with the optimization of the major medium components including glucose, NH4NO3, and Na2HPO4/KH2PO4. Under 30 g/L glucose, 5 g/L NH4NO3, and 80 mM/60 mM Na2HPO4/KH2PO4, the strain WX02-Psrflch produced 2,149 mg/L lichenysin, a 16.8-fold improvement compared to that of wild strain WX-02.

Biosurfactant production by Bacillus subtilis B30 and its application in enhancing oil recovery

The fermentative production of biosurfactants by Bacillus subtilis strain B30 and the evaluation of biosurfactant based enhanced oil recovery using core-flood were investigated. Different carbon sources (glucose, sucrose, starch, date molasses, cane molasses) were tested to determine the optimal biosurfactant production. The isolate B30 produced a biosurfactant that could reduce the surface tension and interfacial tension to 26.63±0.45 mN/m and 3.79±0.27 mN/m, respectively in less than 12h in both glucose or date molasses based media. A crude biosurfactant concentration of 0.3-0.5 g/l and critical micelle dilution (CMD) values of 1:8 were observed. The biosurfactants gave stable emulsions with wide range of hydrocarbons including light and heavy crude oil. The biosurfactants were partially purified and identified as a mixture of lipopeptides similar to surfactin, using high performance thin layer chromatography and Fourier transform infrared spectroscopy. The biosurfactants were stable over wide range of pH, salinity and temperatures. The crude biosurfactant preparation enhanced light oil recovery by 17-26% and heavy oil recovery by 31% in core-flood studies. The results are indicative of the potential of the strain for the development of ex situ microbial enhanced oil recovery processes using glucose or date molasses based minimal media.

Lichenysin is produced by most Bacillus licheniformis strains

AIMS

The aim of this study was to elucidate the prevalence of lichenysin production in Bacillus licheniformis and to see whether this feature was restricted to certain genotypes. Secondly, we wanted to see whether cytotoxicity reflected the measured levels of lichenysin.

METHODS AND RESULTS

Fifty-three genotyped strains of B. licheniformis, representing a wide variety of sources, were included. lchAA gene fragments were detected in all strains by polymerase chain reaction (PCR). All 53 strains produced lichenysins with four molecular masses as confirmed by LC-MS/MS (liquid chromatography-tandem mass spectrometry) analysis. The amounts of lichenysin varied more than two orders of magnitude between strains and were irrespective of genotype. Finally, there was a strong association between lichenysin concentrations and toxicity towards boar spermatozoa, erythrocytes and Vero cells.

CONCLUSIONS

Lichenysin synthesis was universal among the 53 B. licheniformis strains examined. The quantities varied considerably between strains, but were not specifically associated with genotype. Cytotoxicity was evident at lichenysin concentrations above 10 μg ml(-1) , which is in accordance with previous studies.

SIGNIFICANCE AND IMPACT OF STUDY

This study might be of interest to those working on B. licheniformis for commercial use as well as for authorities who make risk assessments of B. licheniformis when used as a food and feed additive.

Optimization of the Nutritional Parameters for Enhanced Production of B. subtilis SPB1 Biosurfactant in Submerged Culture Using Response Surface Methodology

Nutritional requirements can contribute considerably to the production cost and the bioprocess economics. Media optimisation using response surface methodology is one of the used methods to ameliorate the bioprocess economics. In the present study, biosurfactant production by Bacillus subtilis SPB1 was effectively enhanced by response surface methodology. A Plackett-Burman-based statistical screening procedure was adopted to determine the most important factor affecting lipopeptide production. Eleven variables are screened and results show that glucose, K₂HPO₄, and urea concentrations influence the most biosurfactant production. A Central Composite Design was conducted to optimize the three selected factors. Statistical analyses of the data of model fitting were done by using NemrodW. Results show a maximum predicted biosurfactant concentration of 2.93 (±0.32) g/L when using 15 g/L glucose, 6 g/L urea, and 1 g/L K₂HPO₄. The predicted value is approximately 1.65 much higher than the original production determined by the conventional one-factor-at-a-time optimization method.

Biosurfactant's role in bioremediation of NAPL and fermentative production

Surfactants and biosurfactants are amphipathic molecules with both hydrophilic and hydrophobic moieties that partition preferentially at the interface between fluid phases that have different degrees of polarity and hydrogen bonding which confers excellent detergency, emulsifying, foaming and dispersing traits, making them most versatile process chemicals. One of the major applications of (bio)surfactants is in environmental bioremediation field. Most synthetic organic compounds present in contaminated soils are only weakly soluble or completely insoluble in water, so they exist in the subsurface as separate liquid phase, often referred as a non-aqueous phase liquids (NAPL), which poses as threat to environment. Several studies have revealed the use of surfactants for remediation; however, several factors limit the use of surfactants in environmental remediation, mainly persistence of surfactants or their metabolites and thus potentially pose an environmental concern. Biosurfactants may provide a more cost-effective approach for subsurface remediation when used alone or in combination with synthetic surfactants. There are several advantages of biosurfactants when compared to chemical surfactants, mainly biodegradability, low toxicity, biocompatibility and ability to be synthesized from renewable feedstock. Despite having many commercially attractive properties and clear advantages compared with their synthetic counterparts, biosurfactants have not yet been employed extensively in industry because of their low yields and relatively high production and recovery costs. However, the use of mutants and recombinant hyperproducing microorganisms along with the use of cheaper raw materials and optimal growth and production conditions and more efficient recovery processes, the production of biosurfactant can be made economically feasible. Therefore, future research aiming for high-level production of biosurfactants must be focused towards the development of appropriate combinations of hyperproducing microbial strains, optimized cheaper production media and optimized process conditions, which will lead to economical commercial level biosurfactant production.