Microbial surfactants of marine origin: potentials and prospects

Isolation and screening of antimicrobial biosurfactants obtained from mangrove plant root-associated bacteria

The unique properties of biosurfactants obtained from microbes, including their activity at extreme temperatures, make them more attractive than synthetic alternatives. Henceforth, the principle objective is to isolate and detect the antibacterial and antifungal activities of the biosurfactants produced from bacteria of the economically competitive mangrove ecosystem. Using the serial dilution method, 53 bacterial strains were recovered from the Manakudy mangrove forest in Kanyakumari, India, for the investigation. Different biosurfactant screening methods and morphological and biochemical tests were opted to select the potential biosurfactant producer. After the initial screening, two strains were discovered by 16S rRNA gene sequencing followed by extraction using chloroform: methanol (2:1) by the precipitation method. The partially purified biosurfactants were then screened for antimicrobial properties against pathogens including Mucor sp., Trichoderma sp. Morphological, biochemical, and 16S rRNA gene sequencing identified the two strains to be gram-positive, rod-shaped bacteria namely Virgibacillus halodentrificans CMST-ZI (GenBank Accession No.: OL336402.1) and Pseudomonas pseudoalcaligenes CMST-ZI (GenBank Accession No (10 K): OL308085.1). The two extracted biosurfactants viz., 1,2-benzenedicarboxylic acid, mono (2-ethylhexyl) ester, as well as cycloheptane efficiently inhibited human pathogens, including Enterococcus faecalis, and fungi, including Mucor sp., Trichoderma sp., indicated by the formation of a zone of inhibition in pharmacological screening. Thus, there is a growing interest in the prospective application of these biosurfactants isolated from marine microbes, exhibiting antimicrobial properties which can be further studied as a potential candidate in biomedical studies and eco-friendly novel drug development.

Microbial biosurfactants: Multifarious applications in sustainable agriculture

Agriculture in the 21st century faces grave challenges to meet the unprecedented food demand of the burgeoning population as well as reduce the ecological footprint for achieving sustainable development goals. The extensive use of harsh synthetic surfactants in pesticides and the agrochemical industry has substantial adverse impacts on the soil and environment due to their toxic and non-biodegradable nature. Biosurfactants derived from plant, animal, and microbial sources can be an eco-friendly alternative to chemical surfactants. Microbes producing biosurfactants play a noteworthy role in biofilm formation, plant pathogen elimination, biodegradation, bioremediation, improving nutrient bioavailability, and can thrive well under stressful environments. Microbial biosurfactants are well suited for heavy metal and organic contaminants remediation in agricultural soil due to their low toxicity, high activity at fluctuating temperatures, biodegradability, and stability over a wide array of environmental conditions. This green technology will improve the agricultural soil quality by increasing the soil flushing efficiency, mobilization, and solubilization of nutrients by forming metal-biosurfactant complexes, and through the dissemination of complex nutrients. Such characteristics help it to play a pivotal role in environmental sustainability in the foreseeable future, which is required to increase the viability of biosurfactants for extensive commercial uses, making them accessible, affordable, and economically sustainable.

Cold-adapted bacterial extracts as a source of anti-infective and antimicrobial compounds against Staphylococcus aureus

Aim: The dramatic emergence of antibiotic resistance has directed the interest of research toward the discovery of novel antimicrobial molecules. In this context, cold-adapted marine bacteria living in polar regions represent an untapped reservoir of biodiversity endowed with an interesting chemical repertoire. The aim of this work was to identify new antimicrobials and/or antibiofilm molecules produced by cold-adapted bacteria. Materials & methods: Organic extracts obtained from polar marine bacteria were tested against Staphylococcus aureus. Most promising samples were subjected to suitable purification strategies. Results: Results obtained led to the identification of a novel lipopeptide able to effectively inhibit the biofilm formation of S. aureus. Conclusion: New lipopeptide may be potentially useful in a wide variety of biotechnological and medical applications.

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.

Characterization of Drug-like Chemical Space for Cytotoxic Marine Metabolites Using Multivariate Methods

In the last few decades, marine metabolites have been exploited to find commercially viable products in several areas. In this article, molecular descriptors [log P, mass, total polar surface area (TPSA), H-bond donor, H-bond acceptor, and the number of rotatable bonds] for the marine-derived cytotoxic metabolites were calculated and compared with marketed anticancer drugs to understand their position in the drug-like space. Marine-based cytotoxic metabolites are divided into highly toxic (HT) and moderately toxic (MT) classes. The marketed anticancer drugs complied well with Lipinski's rule of five for all molecular descriptors. The majority of HT and MT metabolites complied solely with H-bond donors and a number of rotatable bonds with the Lipinski cutoff values. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were also performed using 73 molecular descriptors on an ensemble of highly cytotoxic or moderately cytotoxic marine metabolites and the marketed reference drugs. The HCA results showed that 12% of marine metabolites clustered with the marketed anticancer drugs and many of them had structural scaffold homology. The PCA results revealed the presence of a clear distinction between the cytotoxic marine metabolites and the marketed anticancer drugs. Results indicate that mass, TPSA, and log P are the vital parameters and the careful optimization of these parameters for marine cytotoxic metabolites may generate more meaningful anticancer candidates in the future.

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.

High-throughput optimization of medium components and culture conditions for the efficient production of a lipopeptide pseudofactin by Pseudomonas fluorescens BD5

Background

Lipopeptides are a promising group of surface-active compounds of microbial origin (biosurfactants). These diverse molecules are produced mainly by Bacillus and Pseudomonas strains. Because of their attractive physiochemical and biological properties, biosurfactants are considered to be “green and versatile molecules of the future”. The main obstacles in widespread use of biosurfactants are mainly their low yields and high production costs. Pseudofactin (PF) is a lipopeptide produced by Pseudomonas fluorescens BD5. Recently, we identified two analogues, PF1 (C₁₆-Val) and PF2 (C₁₆-Leu), and reported that PF2 has good emulsification and foaming activities, as well as antibacterial, antifungal, anticancer, and antiadhesive properties. Reported production of PF in a mineral salt medium was approximately 10 mg/L.

Results

Here, we report successful high-throughput optimization of culture medium and conditions for efficient PF production using P. fluorescens BD5. Compared with production in minimal medium, PF yield increased almost 120-fold, up to 1187 ± 13.0 mg/L. Using Plackett–Burman and central composite design methodologies we identified critical factors that are important for efficient PF production, mainly high glycerol concentration, supplementation with amino acids (leucine or valine) and complex additives (e.g. tryptone), as well as high culture aeration. We also detected the shift in a ratio of produced PF analogues in response to supplementation with different amino acids. Leucine strongly induces PF2 production, while valine addition supports PF1 production. We also reported the identification of two new PF analogues: PF3 (C₁₈-Val) and PF4 (C₁₈-Leu).

Conclusions

Identification of critical culture parameters that are important for lipopeptide production and their high yields can result in reduction of the production costs of these molecules. This may lead to the industrial-scale production of biosurfactants and their widespread use. Moreover, we produced new lipopeptide pure analogues that can be used to investigate the relationship between the structure and biological activity of lipopeptides.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0968-x) contains supplementary material, which is available to authorized users.

Direct quantification of lipopeptide biosurfactants in biological samples via HPLC and UPLC-MS requires sample modification with an organic solvent

The rapid and accurate quantification of biosurfactants in biological samples is challenging. In contrast to the orcinol method for rhamnolipids, no simple biochemical method is available for the rapid quantification of lipopeptides. Various liquid chromatography (LC) methods are promising tools for relatively fast and exact quantification of lipopeptides. Here, we report strategies for the quantification of the lipopeptides pseudofactin and surfactin in bacterial cultures using different high- (HPLC) and ultra-performance liquid chromatography (UPLC) systems. We tested three strategies for sample pretreatment prior to LC analysis. In direct analysis (DA), bacterial cultures were injected directly and analyzed via LC. As a modification, we diluted the samples with methanol and detected an increase in lipopeptide recovery in the presence of methanol. Therefore, we suggest this simple modification as a tool for increasing the accuracy of LC methods. We also tested freeze-drying followed by solvent extraction (FDSE) as an alternative for the analysis of “heavy” samples. In FDSE, the bacterial cultures were freeze-dried, and the resulting powder was extracted with different solvents. Then, the organic extracts were analyzed via LC. Here, we determined the influence of the extracting solvent on lipopeptide recovery. HPLC methods allowed us to quantify pseudofactin and surfactin with run times of 15 and 20 min per sample, respectively, whereas UPLC quantification was as fast as 4 and 5.5 min per sample, respectively. Our methods provide highly accurate measurements and high recovery levels for lipopeptides. At the same time, UPLC-MS provides the possibility to identify lipopeptides and their structural isoforms.

Aneurinifactin, a new lipopeptide biosurfactant produced by a marine Aneurinibacillus aneurinilyticus SBP-11 isolated from Gulf of Mannar: Purification, characterization and its biological evaluation

Biosurfactants are microbial-derived amphiphilic molecules having hydrophobic and hydrophilic moieties produced by bacteria, fungi, yeasts and algae and are extracellular or cell wall-associated compounds. In an ongoing survey for bioactive microbial metabolites from microbes isolated from diverse ecological niches, a new lipopeptide biosurfactant was identified from a marine bacterium; Aneurinibacillus aneurinilyticus strain SBP-11, which was isolated from a marine diversity hotspot, Gulf of Mannar, India. A new lipopeptide biosurfactant was purified and characterized based on TLC, FT-IR, NMR, GC-MS, HPLC, MALDI-TOF-MS and tandem MS analysis as Stearic acid-Thr-Tyr-Val-Ser-Tyr-Thr (named as Aneurinifactin). The critical micelle concentration of Aneurinifactin was 26mgL^-1 at a surface tension of 26mNm^-1. Further, the biosurfactant showed stable emulsification at a wide range of pH (2-9) and temperature up to 80°C. Aneurinifactin showed promising antimicrobial activity and concentration dependent efficient oil recovery. This is the first report on Aneurinifactin, a lipopeptide biosurfactant produced by a marine A. aneurinilyticus SBP-11, which could be explored as a promising candidate for use in various biomedical and industrial applications.

Biosurfactants in agriculture

Agricultural productivity to meet growing demands of human population is a matter of great concern for all countries. Use of green compounds to achieve the sustainable agriculture is the present necessity. This review highlights the enormous use of harsh surfactants in agricultural soil and agrochemical industries. Biosurfactants which are reported to be produced by bacteria, yeasts, and fungi can serve as green surfactants. Biosurfactants are considered to be less toxic and eco-friendly and thus several types of biosurfactants have the potential to be commercially produced for extensive applications in pharmaceutical, cosmetics, and food industries. The biosurfactants synthesized by environmental isolates also has promising role in the agricultural industry. Many rhizosphere and plant associated microbes produce biosurfactant; these biomolecules play vital role in motility, signaling, and biofilm formation, indicating that biosurfactant governs plant–microbe interaction. In agriculture, biosurfactants can be used for plant pathogen elimination and for increasing the bioavailability of nutrient for beneficial plant associated microbes. Biosurfactants can widely be applied for improving the agricultural soil quality by soil remediation. These biomolecules can replace the harsh surfactant presently being used in million dollar pesticide industries. Thus, exploring biosurfactants from environmental isolates for investigating their potential role in plant growth promotion and other related agricultural applications warrants details research. Conventional methods are followed for screening the microbial population for production of biosurfactant. However, molecular methods are fewer in reaching biosurfactants from diverse microbial population and there is need to explore novel biosurfactant from uncultured microbes in soil biosphere by using advanced methodologies like functional metagenomics.

Antibacterial activity and cytotoxicity analysis of halistanol trisulphate from marine sponge Petromica citrina

OBJECTIVES

An aqueous extract and fraction from the marine sponge Petromica citrina have antibacterial activity. We performed a chemical and biological characterization of the antibiotic substance from P. citrina and investigated its mode of action on Staphylococcus aureus cells.

METHODS

The inhibitory activity of the aqueous extract of P. citrina was determined against 14 bacteria belonging to type strains and clinical antibiotic-resistant strains. The aqueous extract was fractionated under bioassay guidance and the bioactive substance was identified by its (1)H-NMR, (13)C-NMR and mass spectra. The MIC and the MBC of this substance were determined. This substance was also subjected to cytotoxic bioassays. The mode of action on S. aureus cells was investigated by light and transmission electron microscopy analysis.

RESULTS

P. citrina showed a large spectrum of activity against type strains and resistant-bacteria such as S. aureus, Staphylococcus epidermidis, Enterococcus faecalis, Mycobacterium fortuitum and Neisseria gonorrhoeae. The aqueous extract was fractionated and halistanol trisulphate (24ε,25-dimethylcholestane-2β,3α,6α-triol trisodium sulphate) was isolated for the first time from P. citrina. Halistanol trisulphate had a bactericidal effect on exponentially growing S. aureus cells at the MIC (512 mg/L). Cytotoxicity biossays showed moderate toxicity against cancer cell line L929 (fibrosarcoma). This substance apparently acts by damaging the cell membrane, with subsequent cell lysis.

CONCLUSIONS

Halistanol trisulphate is a broad-spectrum antibiotic isolated from P. citrina with a mode of action involving disruption of the cytoplasmic membrane. It is a new candidate for research on antibacterial substances.

Enzyme-assisted extraction of lipids directly from the culture of the oleaginous yeast Rhodosporidium toruloides

Lipids produced by oleaginous microorganisms are a potential feedstock for biodiesel production and chemical synthesis. Yet, the costs of microbial lipids remain high, partially because the lipid recovery process is tedious and costly. In the present study, enzyme-assisted extraction of lipids from the culture of the yeast Rhodosporidium toruloides was carried out. With a heat pre-treatment with microwave, enzymatic treatment with the recombinant β-1,3-glucomannanase, plMAN5C, and extraction with ethyl acetate, 96.6% of the total lipids were extracted from R. toruloides cells at room temperature and atmospheric pressure directly from the culture without dewatering. Therefore, this process could significantly reduce energy consumption and costs for lipids extraction from the yeast.

Functional metagenomic strategies for the discovery of novel enzymes and biosurfactants with biotechnological applications from marine ecosystems

Marine ecosystems are home to bacteria which are exposed to a wide variety of environmental conditions, such as extremes in temperature, salinity, nutrient availability and pressure. Survival under these conditions must have necessitated the adaptation and the development of unique cellular biochemistry and metabolism by these microbes. Thus, enzymes isolated from these microbes have the potential to possess quite unique physiological and biochemical properties. This review outlines a number of function-based metagenomic approaches which are available to screen metagenomic libraries constructed from marine ecosystems to facilitate the exploitation of some of these potentially novel biocatalysts. Functional screens to isolate novel cellulases, lipases and esterases, proteases, laccases, oxidoreductases and biosurfactants are described, together with approaches which can be employed to help overcome some of the typical problems encountered with functional metagenomic-based screens.