Natural biocide cocktails: Combinatorial antibiotic effects of prodigiosin and biosurfactants

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

Transcriptomic analysis of cell envelope inhibition by prodigiosin in methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading threat to public health as it is resistant to most currently available antibiotics. Prodigiosin is a secondary metabolite of microorganisms with broad-spectrum antibacterial activity. This study identified a significant antibacterial effect of prodigiosin against MRSA with a minimum inhibitory concentration as low as 2.5 mg/L. The results of scanning electron microscopy, crystal violet staining, and confocal laser scanning microscopy indicated that prodigiosin inhibited biofilm formation in S. aureus USA300, while also destroying the structure of the cell wall and cell membrane, which was confirmed by transmission electron microscopy. At a prodigiosin concentration of 1.25 mg/L, biofilm formation was inhibited by 76.24%, while 2.5 mg/L prodigiosin significantly reduced the vitality of MRSA cells in the biofilm. Furthermore, the transcriptomic results obtained at 1/8 MIC of prodigiosin indicated that 235and 387 genes of S. aureus USA300 were significantly up- and downregulated, respectively. The downregulated genes were related to two-component systems, including the transcriptional regulator LytS, quorum sensing histidine kinases SrrB, NreA and NreB, peptidoglycan biosynthesis enzymes (MurQ and GlmU), iron-sulfur cluster repair protein ScdA, microbial surface components recognizing adaptive matrix molecules, as well as the key arginine synthesis enzymes ArcC and ArgF. The upregulated genes were mainly related to cell wall biosynthesis, as well as two-component systems including vancomycin resistance-associated regulator, lipoteichoic acid biosynthesis related proteins DltD and DltB, as well as the 9 capsular polysaccharide biosynthesis proteins. This study elucidated the molecular mechanisms through which prodigiosin affects the cell envelope of MRSA from the perspectives of cell wall synthesis, cell membrane and biofilm formation, providing new potential targets for the development of antimicrobials for the treatment of MRSA.

Isolation, Identification, and Antibacterial Properties of Prodigiosin, a Bioactive Product Produced by a New Serratia marcescens JSSCPM1 Strain: Exploring the Biosynthetic Gene Clusters of Serratia Species for Biological Applications

Prodigiosin pigment has high medicinal value, so exploring this compound is a top priority. This report presents a prodigiosin bioactive compound isolated from Serratia marcescens JSSCPM1, a new strain. The purification process of this compound involves the application of different chromatographic methods, including UV-visible spectroscopy, high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC/MS). Subsequent analysis was performed using nuclear magnetic resonance (NMR) to achieve a deeper understanding of the compound's structure. Finally, through a comprehensive review of the existing literature, the structural composition of the isolated bioactive compound was found to correspond to that of the well-known compound prodigiosin. The isolated prodigiosin compound was screened for antibacterial activity against both Gram-positive and Gram-negative bacteria. The compound inhibited the growth of Gram-negative bacterial strains compared with Gram-positive bacterial strains. It showed a maximum minimum inhibitory concentration against Escherichia coli NCIM 2065 at a 15.9 ± 0.31 μg/mL concentration. The potential binding capabilities between prodigiosin and the OmpF porin proteins (4GCS, 4GCP, and 4GCQ) were determined using in silico studies, which are generally the primary targets of different antibiotics. Comparative molecular docking analysis indicated that prodigiosin exhibits a good binding affinity toward these selected drug targets.

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

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

Production of tailored hydroxylated prodiginine showing combinatorial activity with rhamnolipids against plant-parasitic nematodes

Bacterial secondary metabolites exhibit diverse remarkable bioactivities and are thus the subject of study for different applications. Recently, the individual effectiveness of tripyrrolic prodiginines and rhamnolipids against the plant-parasitic nematode Heterodera schachtii, which causes tremendous losses in crop plants, was described. Notably, rhamnolipid production in engineered Pseudomonas putida strains has already reached industrial implementation. However, the non-natural hydroxyl-decorated prodiginines, which are of particular interest in this study due to a previously described particularly good plant compatibility and low toxicity, are not as readily accessible. In the present study, a new effective hybrid synthetic route was established. This included the engineering of a novel P. putida strain to provide enhanced levels of a bipyrrole precursor and an optimization of mutasynthesis, i.e., the conversion of chemically synthesized and supplemented monopyrroles to tripyrrolic compounds. Subsequent semisynthesis provided the hydroxylated prodiginine. The prodiginines caused reduced infectiousness of H. schachtii for Arabidopsis thaliana plants resulting from impaired motility and stylet thrusting, providing the first insights on the mode of action in this context. Furthermore, the combined application with rhamnolipids was assessed for the first time and found to be more effective against nematode parasitism than the individual compounds. To obtain, for instance, 50% nematode control, it was sufficient to apply 7.8 μM hydroxylated prodiginine together with 0.7 μg/ml (~ 1.1 μM) di-rhamnolipids, which corresponded to ca. ¼ of the individual EC₅₀ values. In summary, a hybrid synthetic route toward a hydroxylated prodiginine was established and its effects and combinatorial activity with rhamnolipids on plant-parasitic nematode H. schachtii are presented, demonstrating potential application as antinematodal agents. Graphical Abstract.

Recent Advances in Prodigiosin as a Bioactive Compound in Nanocomposite Applications

Bionanocomposites based on natural bioactive entities have gained importance due to their abundance; renewable and environmentally benign nature; and outstanding properties with applied perspective. Additionally, their formulation with biological molecules with antimicrobial, antioxidant, and anticancer activities has been produced nowadays. The present review details the state of the art and the importance of this pyrrolic compound produced by microorganisms, with interest towards Serratia marcescens, including production strategies at a laboratory level and scale-up to bioreactors. Promising results of its biological activity have been reported to date, and the advances and applications in bionanocomposites are the most recent strategy to potentiate and to obtain new carriers for the transport and controlled release of prodigiosin. Prodigiosin, a bioactive secondary metabolite, produced by Serratia marcescens, is an effective proapoptotic agent against bacterial and fungal strains as well as cancer cell lines. Furthermore, this molecule presents antioxidant activity, which makes it ideal for treating wounds and promoting the general improvement of the immune system. Likewise, some of the characteristics of prodigiosin, such as hydrophobicity, limit its use for medical and biotechnological applications; however, this can be overcome by using it as a component of a bionanocomposite. This review focuses on the chemistry and the structure of the bionanocomposites currently developed using biorenewable resources. Moreover, the work illuminates recent developments in pyrrole-based bionanocomposites, with special insight to its application in the medical area.

Metabolomics and Genomics Approach for the Discovery of Serrawettin W2 Lipopeptides from Serratia marcescens NP2

A metabolomics/peptidomics and genomics approach, using UPLC-MS^E, molecular networking, and genome mining, was used to describe the serrawettin W2 lipopeptide family produced by Serratia marcescens NP2. Seven known serrawettin W2 analogues were structurally elucidated along with 17 new analogues, which varied based on the first (fatty acyl length of C₈, C₁₀, C₁₂, or C_12:1), fifth (Phe, Tyr, Trp, or Leu/Ile), and sixth (Leu, Ile, or Val) residues. Tandem MS results suggested that the previously classified serrawettin W3 may be an analogue of serrawettin W2, with a putative structure of cyclo(C₁₀H₁₈O₂-Leu-Ser-Thr-Leu/Ile-Val). Chiral phase amino acid analysis enabled the distinction between l/d-Leu and l-Ile residues within nine purified compounds. ¹H and ¹³C NMR analyses confirmed the structures of four purified new analogues. Additionally, genome mining was conducted using Serratia genome sequences available on the NCBI database to identify the swrA gene using the antiSMASH software. NRPSpredictor2 predicted the specificity score of the adenylation-domain within swrA with 100% for the first, second, and third modules (Leu-Ser-Thr), 60-70% for the fourth module (Phe/Trp/Tyr/Val), and 70% for the fifth module (Val/Leu/Ile), confirming MS^E data. Finally, antibacterial activity was observed for compounds 6 and 11 against a clinical Enterococcus faecium strain.

Trichoderma citrinoviride: Anti-Fungal Biosurfactants Production Characteristics

The mechanism of direct impact of Trichoderma fungi on other organisms is a multilayer process. The level of limiting the growth of other microorganisms is determined by the strain and often by the environment. Confirmation of the presence of extracellular biosurfactants in certain strains of Trichoderma considered as biocontrol agents was regarded as a crucial topic complementing the characterization of their interactive mechanisms. Selected strains of T. citrinoviride were cultured in media stimulating biosurfactant biosynthesis, optionally supplemented with lytic enzyme inducers. Results confirmed the anti-fungal properties of surface-active compounds in the tested culture fluids. Preparations that displayed high fungal growth inhibition presented marginal enzymatic activities of both chitinases and laminarinases, implying the inhibitory role of biosurfactants. Fractions from the foam of the culture fluid of the C1 strain, cultured on Saunders medium, and HL strain on MGP medium, without an additional carbon source, exhibited the most prominent ability to inhibit the growth of phytopathogens. Filamentous fungi capable of producing fungicidal compounds, including surfactants, may find applications in protecting the plants against agri-food pathogenic molds.

In vitro Test for Inhibition of Plasmodium falciparum 3D7 Parasites using Streptomyces hygroscopicus subsp. hygroscopicus Strain i18, Isolated from a Pineapple Farm in Lampung

Increasing natural ingredient awareness and utilization has created an increased demand for sources of natural medicinal ingredients, including sources of compound used to treat malaria. Streptomyces is a genus of prokaryote well recognized for its production of antibiotics and other pharmaceutically useful compound. This study aimed to assess the ability of unpurified fermentation metabolites to inhibit Plasmodium parasites. A strain of bacteria identified as Streptomyces hygroscopicus subsp. hygroscopicus strain i18 were isolated from pineapple fields in Lampung province, and was cultured and fermented on liquid synthetic Gause medium for 10 days. The supernatant was separated from the cells and extracted with ethyl acetate-methanol (1:1). Plasmodium falciparum 3D7 was used for antiplasmodial testing. Metabolites were tested qualitatively using a phytochemical approach. Saponins and triterpenoids were found to be present in the extract. Parasite inhibition as measured using probit analysis and yielded an IC50 value of 11.07 g.m/L. These findings suggest further examinations of this extract (e.g. assessment of off-target effects) are warranted.

Natural Pigments of Bacterial Origin and Their Possible Biomedical Applications

Microorganisms are considered one of the most promising niches for prospecting, production, and application of bioactive compounds of biotechnological interest. Among them, bacteria offer certain distinctive advantages due to their short life cycle, their low sensitivity to seasonal and climatic changes, their easy scaling as well as their ability to produce pigments of various colors and shades. Natural pigments have attracted the attention of industry due to an increasing interest in the generation of new products harmless to humans and nature. This is because pigments of artificial origin used in industry can have various deleterious effects. On this basis, bacterial pigments promise to be an attractive niche of new biotechnological applications, from functional food production to the generation of new drugs and biomedical therapies. This review endeavors to establish the beneficial properties of several relevant pigments of bacterial origin and their relation to applications in the biomedical area.

A Metabolomics and Molecular Networking Approach to Elucidate the Structures of Secondary Metabolites Produced by Serratia marcescens Strains

An integrated approach that combines reverse-phase high-performance liquid chromatography (RP-HPLC), electrospray ionization mass spectrometry, untargeted ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MSE) and molecular networking (using the Global Natural Products Social molecular network platform) was used to elucidate the metabolic profiles and chemical structures of the secondary metabolites produced by pigmented (P1) and non-pigmented (NP1) Serratia marcescens (S. marcescens) strains. Tandem mass spectrometry-based molecular networking guided the structural elucidation of 18 compounds for the P1 strain (including 6 serratamolides, 10 glucosamine derivatives, prodigiosin and serratiochelin A) and 15 compounds for the NP1 strain (including 8 serratamolides, 6 glucosamine derivatives and serratiochelin A) using the MSE fragmentation profiles. The serratamolide homologues were comprised of a peptide moiety of two L-serine residues (cyclic or open-ring) linked to two fatty acid chains (lengths of C10, C12, or C12:1). Moreover, the putative structure of a novel open-ring serratamolide homologue was described. The glucosamine derivative homologues (i.e., N-butylglucosamine ester derivatives) consisted of four residues, including glucose/hexose, valine, a fatty acid chain (lengths of C13 - C17 and varying from saturated to unsaturated) and butyric acid. The putative structures of seven novel glucosamine derivative homologues and one glucosamine derivative congener (containing an oxo-hexanoic acid residue instead of a butyric acid residue) were described. Moreover, seven fractions collected during RP-HPLC, with major molecular ions corresponding to prodigiosin, serratamolides (A, B, and C), and glucosamine derivatives (A, C, and E), displayed antimicrobial activity against a clinical Enterococcus faecalis S1 strain using the disc diffusion assay. The minimum inhibitory and bactericidal concentration assays however, revealed that prodigiosin exhibited the greatest antimicrobial potency, followed by glucosamine derivative A and then the serratamolides (A, B, and C). These results provide crucial insight into the secondary metabolic profiles of pigmented and non-pigmented S. marcescens strains and confirms that S. marcescens strains are a promising natural source of novel antimicrobial metabolites.

Seed treatment with prodigiosin controls damping-off of cucumber caused by Pythium ultimum

Ethanol extract of cell mass of Serratia marcescens strain N4-5, when applied as a treatment to cucumber seed, has been shown to provide control of the oomycete soil-borne plant pathogen Pythium ultimum equivalent to that provided by a seed-treatment chemical pesticide in some soils. Two dominant compounds in this extract, prodigiosin and the serratamolide serrawetin W1, were identified based on mass and collision induced dissociation mass fragmentation spectra. An additional four compounds with M+H⁺ masses (487, 541, 543, and 571) consistent with serratamolides reported in the literature were also detected. Several other compounds with M+H⁺ masses of 488, 536, 684, 834, 906, and 908 m/z were detected in this ethanol extract inconsistently over multiple liquid chromatography coupled with tandem mass spectrometry (LC/MS–MS) runs. A purified preparation of prodigiosin provided control of damping-off of cucumber caused by P. ultimum when applied as a seed treatment while ethanol extract of cell mass of strain Tn246, a transposon-mutant-derivative of strain N4-5, did not. Strain Tn246 contained a mini-Tn5 Km insertion in a prodigiosin biosynthetic gene and was deficient in production of prodigiosin. All other compounds detected in N4-5 extract were detected in the Tn246 extract. This is the first report demonstrating that prodigiosin can control a plant disease. Other compounds in ethanol extract of strain N4-5 may contribute to disease control.

Antifungal Activity of Polyoxometalate-Ionic Liquids on Historical Brick

Moulds inhabiting mineral-based materials may cause their biodeterioration, contributing to inestimable losses, especially in the case of cultural heritage objects and architectures. Fungi in mouldy buildings may also pose a threat to human health and constitute the main etiological factor in building related illnesses. In this context, research into novel compounds with antifungal activity is of high importance. The aim of this study was to evaluate the antifungal activity of polyoxometalate-ionic liquids (POM-ILs) and their use in the eradication of moulds from historical brick. In the disc diffusion assay, all the tested POM-ILs inhibited growth of a mixed culture of moulds including Engyodontium album, Cladosporium cladosporioides, Alternaria alternata and Aspergillus fumigatus. These were isolated from the surfaces of historical brick barracks at the Auschwitz II-Birkenau State Museum in Oświęcim, Poland. POM-IL coatings on historical brick samples, under model conditions, showed that two compounds demonstrated very high antifungal activity, completely limiting mould growth and development. The antifungal activity of the POM-ILs appeared to stem from their toxic effects on conidia, as evidenced by environmental scanning transmission electron microscopy observations. The results herein indicated that POM-ILs are promising disinfectant materials for use not only on historical objects, but probably also on other mineral-based materials.

Tetracycline Water Soluble Formulations with Enhanced Antimicrobial Activity

The negligible water solubility of tetracycline (TC), a well-known antibiotic of clinical use, is the major disadvantage for its oral administration. With the aim to improve the water solubility of TC, the micelles of formulae SLS@TC and CTAB@TC (SLS = sodium lauryl sulphate and CTAB = cetrimonium bromide) were synthesized. The micelles SLS@TC and CTAB@TC were characterized by melting point (m.p.), thermogravimetric differential thermal analysis (TG-DTA), differential scanning calorimetry (DTG/DSC), attenuated total reflection spectroscopy (FT-IR-ATR), ultra-violet visible (UV/vis) spectroscopy, proton nucleus magnetic resonance (1H-NMR) spectroscopy, and the ultrasonically-induced biregringence technique. The antimicrobial activity of SLS@TC and CTAB@TC was evaluated, by means of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and inhibition zone (IZ), against the Gram negative bacterial strains Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) and the Gram positive ones of the genus of Staphylococcus epidermidis (S. epidermidis) and Staphylococcus aureus (S. aureus). Generally, both micelles show better activity than that of TC against the microbial strains tested. Thus, the MIC value of CTAB@TC is 550-fold higher than that of free TC against S. epidermidis. Despite the stronger activity of CTAB@TC than SLS@TC against both Gram negative and Gram positive microbes, SLS@TC is classified as a bactericidal agent (in that it eliminates 99.9% of the microbes), in contrast to CTAB@TC, which is bacteriostatic one (inhibits, but does not kill the organisms). The toxicity of SLS@TC and CTAB@TC was evaluated against human corneal eukaryotic cells (HCECs). Moreover, SLS@TC and CTAB@TC exhibit low in vivo toxicity against Artemia salina, even at concentrations up to threefold higher than those of their MICmax. Therefore, SLS@TC and CTAB@TC can be candidates for the development of new antibiotics.

Microfluidics for Biotechnology: Bridging Gaps to Foster Microfluidic Applications

Microfluidics and novel lab-on-a-chip applications have the potential to boost biotechnological research in ways that are not possible using traditional methods. Although microfluidic tools were increasingly used for different applications within biotechnology in recent years, a systematic and routine use in academic and industrial labs is still not established. For many years, absent innovative, ground-breaking and “out-of-the-box” applications have been made responsible for the missing drive to integrate microfluidic technologies into fundamental and applied biotechnological research. In this review, we highlight microfluidics’ offers and compare them to the most important demands of the biotechnologists. Furthermore, a detailed analysis in the state-of-the-art use of microfluidics within biotechnology was conducted exemplarily for four emerging biotechnological fields that can substantially benefit from the application of microfluidic systems, namely the phenotypic screening of cells, the analysis of microbial population heterogeneity, organ-on-a-chip approaches and the characterisation of synthetic co-cultures. The analysis resulted in a discussion of potential “gaps” that can be responsible for the rare integration of microfluidics into biotechnological studies. Our analysis revealed six major gaps, concerning the lack of interdisciplinary communication, mutual knowledge and motivation, methodological compatibility, technological readiness and missing commercialisation, which need to be bridged in the future. We conclude that connecting microfluidics and biotechnology is not an impossible challenge and made seven suggestions to bridge the gaps between those disciplines. This lays the foundation for routine integration of microfluidic systems into biotechnology research procedures.

Screening an Established Natural Product Library Identifies Secondary Metabolites That Potentiate Conventional Antibiotics

Health organizations worldwide have warned that we are on the cusp of a "post-antibiotic era," necessitating new approaches to combat antibiotic resistant infections. One such approach is the development of antibiotic adjuvants, which have little or no inherent antibiotic activity at their active concentrations but instead potentiate the activity of antibiotics against antibiotic-resistant bacteria. Recently, we demonstrated that meridianin D, a natural product originally reported to have activity against Staphylococcus aureus and Mycobacterium tuberculosis, possesses the ability to reverse colistin resistance in colistin resistant bacteria. As most natural product screens typically involve screening for only certain activities (anticancer, antiviral, and antimicrobial are typical), we posited that the meridianin D discovery was not unique and there are potentially many natural products that have adjuvant activity. To explore this, the National Cancer Institute (NCI) Natural Product Library Set IV was screened for adjuvant activity using four classes of antibiotics (β-lactams, aminoglycosides, macrolides, and polymyxins) against three bacterial pathogens (methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii, and Klebsiella pneumoniae). Sixteen compounds suppressed β-lactam resistance in MRSA, five of which effected a 16-fold reduction in the oxacillin minimum inhibitory concentration (MIC). Two natural products effectively suppressed aminoglycoside resistance in both of the Gram-negative species tested, and no hits were observed with macrolides. In contrast, a larger number of natural product adjuvants were identified when screening against colistin-resistant strains of A. baumannii and K. pneumoniae. Nine compounds reduced the colistin MIC to its breakpoint or lower (up to a 1024-fold reduction). Clorobiocin, novobiocin, and prodigiosin were most effective, reducing the colistin MIC in K. pneumoniae strain B9 to 2 μg/mL at concentrations as low as 0.625, 2.5, and 1.25 μM, respectively. Restored sensitivity to colistin with these compounds does not appear to coincide with known mechanisms of colistin resistance.

Synergistic bactericidal profiling of prodigiosin extracted from Serratia marcescens in combination with antibiotics against pathogenic bacteria

The emergence of multidrug-resistant (MDR) bacteria is on the rise and the situation has been worsening with each passing day, which is evident from the outpouring number of reports about how more and more pathogens are becoming resistant to even the third and fourth generations of antibiotics. Lately, combination therapies or drug synergy have been giving promising results in curbing infections since it delineates its action on multiple aspects as compared to monotherapies. In this study, we used prodigiosin, a bacterial pigment endowed with magnificent biological properties, in combination with six antibiotics to study its effect on Pseudomonas aeruginosa, Staphylococcus aureus and Chromobacterium violaceum. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of prodigiosin against the test organisms was determined and a checkerboard assay of prodigiosin with various antibiotic combinations was performed with an aim to abate antimicrobial resistance. MIC and MBC of prodigiosin was obtained in the range of 4–16 μg/mL, which was lower than that of most test antibiotics. Coupling prodigiosin with other test antibiotics exhibited an excellent synergy profile against all test organisms and the effects were reported to be either synergistic or additive. In the case of S. aureus and C. violaceum, all combinations were found to be synergic, and remarkably for S. aureus, FBC index was reported to be as low as ≤0.25 with all of the test antibiotics. Therefore, it is deduced that prodigiosin augments and intensifies the action of antibiotics, and results in a double-whammy against the MDR strains.

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Prodigiosin showed excellent bactericidal activity against P. aeruginosa, S. aureus and C. violaceum.

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Prodigiosin in combination with antibiotics exhibited synergic effect in majority of the cases against all test pathogens.

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For S. aureus, prodigiosin-antibiotic combinations showed excellent synergic effect with an FBC index as low as ≤0.25.

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Prodigiosin augments the action of antibiotics against pathogenic bacteria.

A Straightforward Assay for Screening and Quantification of Biosurfactants in Microbial Culture Supernatants

A large variety of microorganisms produces biosurfactants with the potential for a number of diverse industrial applications. To identify suitable wild-type or engineered production strains, efficient screening methods are needed, allowing for rapid and reliable quantification of biosurfactants in multiple cultures, preferably at high throughput. To this end, we have established a novel and sensitive assay for the quantification of biosurfactants based on the dye Victoria Pure Blue BO (VPBO). The assay allows the colorimetric assessment of biosurfactants directly in culture supernatants and does not require extraction or concentration procedures. Working ranges were determined for precise quantification of different rhamnolipid biosurfactants; titers in culture supernatants of recombinant Pseudomonas putida KT2440 calculated by this assay were confirmed to be the same ranges detected by independent high-performance liquid chromatography (HPLC)-charged aerosol detector (CAD) analyses. The assay was successfully applied for detection of chemically different anionic or non-ionic biosurfactants including mono- and di-rhamnolipids (glycolipids), mannosylerythritol lipids (MELs, glycolipids), 3-(3-hydroxyalkanoyloxy) alkanoic acids (fatty acid conjugates), serrawettin W1 (lipopeptide), and N-acyltyrosine (lipoamino acid). In summary, the VPBO assay offers a broad range of applications including the comparative evaluation of different cultivation conditions and high-throughput screening of biosurfactant-producing microbial strains.

Molecular dynamics of the membrane interaction and localisation of prodigiosin

The tripyrrolic antibiotic prodigiosin causes diverse reactions on its targets like energy spilling, membrane leakage, loss of motility and phototoxicity. It has bacteriostatic, bactericidal, anti-fungal, anti-cancer and immunosuppressive properties. Most of the functions suggest the role of prodigiosin in membrane disruption but the exact mechanism remains unknown. A molecular dynamics study was performed to understand the interactions of prodigiosin with the membrane. It was seen that prodigiosin from the solvent enters the membrane immediately either individually or as small clusters. Prodigiosin clusters with more than eight molecules do not appear to enter the membrane. Upon entry, the molecules orient themselves along the membrane-water interface with the pyrrole rings interacting with lipid head groups and with water. This orientation is stabilised by hydrogen bonding and hydrophobic interactions. The presence of prodigiosin molecules in the membrane changes the local lipid architecture and reduces the solvent accessibility of the membrane. The membrane fluidity, thickness or area per lipid head are largely unaffected. This suggests that prodigiosin could cause most damage in the vicinity of a membrane protein and thus could also explain the reason for varied effects on the targets.

The production and bioactivity of prodigiosin: quo vadis?

Prodigiosin (PG), a red tripyrrole pigment, belongs to a member of the prodiginine family and is normally secreted by various sources including Serratia marcescens and other Gram-negative bacteria. The studies of PG have received innovative devotion as a result of reported antimicrobial, larvicidal and anti-nematoid immunomodulation and antitumor properties, owing to its antibiotic and cytotoxic activities. This review provides a comprehensive summary of research undertaken toward the isolation and structural elucidation of the prodiginine family of natural products. Additionally, the current evidence-based understanding of the biological activities and medicinal potential of PG is employed to determine the efficacy, with some reports of information related to pharmacokinetics, pharmacodynamics and toxicology.

Dynamic Environmental Control in Microfluidic Single-Cell Cultivations: From Concepts to Applications

Microfluidic single-cell cultivation (MSCC) is an emerging field within fundamental as well as applied biology. During the last years, most MSCCs were performed at constant environmental conditions. Recently, MSCC at oscillating and dynamic environmental conditions has started to gain significant interest in the research community for the investigation of cellular behavior. Herein, an overview of this topic is given and microfluidic concepts that enable oscillating and dynamic control of environmental conditions with a focus on medium conditions are discussed, and their application in single-cell research for the cultivation of both mammalian and microbial cell systems is demonstrated. Furthermore, perspectives for performing MSCC at complex dynamic environmental profiles of single parameters and multiparameters (e.g., pH and O₂ ) in amplitude and time are discussed. The technical progress in this field provides completely new experimental approaches and lays the foundation for systematic analysis of cellular metabolism at fluctuating environments.

Microfluidic systems for rapid antibiotic susceptibility tests (ASTs) at the single-cell level

Infectious diseases caused by multidrug resistant (MDR) bacterial pathogens are impending threats to global health. Since delays in identifying drug resistance would significantly increase mortality, fast and accurate antibiotic susceptibility tests (ASTs) are critical for addressing the antibiotic resistance issue. However, the conventional methods for ASTs are always labor-intensive, imprecise, complex and slow (taking 2-3 days). To address these issues, some advanced microfluidic systems have been designed for rapid phenotypic and genotypic analysis of antibiotic resistance. This review highlights the recent development of microfluidics-based ASTs at the single-cell or single-molecule level for guiding antibiotic treatment decisions and predicting therapeutic outcomes.

Biologically active pigment and ShlA cytolysin of Serratia marcescens induce autophagy in a human ocular surface cell line

BACKGROUND

The cellular process of autophagy is essential for maintaining the health of ocular tissue. Dysregulation of autophagy is associated with several ocular diseases including keratoconus and macular degeneration. It is known that autophagy can be used to respond to microbial infections and that certain microbes can exploit the autophagic process to their benefit. In this study, a genetic approach was used to identify surface-associated and secreted products generated by the opportunistic pathogen Serratia marcescens involved in activation of autophagy.

METHODS

A recombinant human corneal limbal epithelial cell line expressing a LC3-GFP fusion protein was challenged with normalized secretomes from wild-type and mutant S. marcescens derivatives. LC3-GFP fluorescence patterns were used to assess the ability of wild-type and mutant bacteria to influence autophagy. Purified prodigiosin was obtained from stationary phase bacteria and used to challenge ocular cells.

RESULTS

Mutations in the global regulators eepR and gumB genes highly reduced the ability of the bacteria to activate autophagy in corneal cells. This effect was further narrowed down to the secreted cytolysin ShlA and the biologically active pigment prodigiosin. Purified prodigiosin and ShlA from Escherichia coli further supported the role of these factors in activating autophagy in human corneal cells. Additional genetic data indicate a role for flagellin and type I pili, but not the nuclease, S-layer protein, or serratamolide biosurfactant in activation of autophagy.

CONCLUSIONS

This work identifies specific bacterial components that activate autophagy and give insight into potential host-pathogen interactions or compounds that can be used to therapeutically manipulate autophagy.

Medical-Grade Silicone Coated with Rhamnolipid R89 Is Effective against Staphylococcus spp. Biofilms

Staphylococcus aureus and Staphylococcus epidermidis are considered two of the most important pathogens, and their biofilms frequently cause device-associated infections. Microbial biosurfactants recently emerged as a new generation of anti-adhesive and anti-biofilm agents for coating implantable devices to preserve biocompatibility. In this study, R89 biosurfactant (R89BS) was evaluated as an anti-biofilm coating on medical-grade silicone. R89BS is composed of homologues of the mono- (75%) and di-rhamnolipid (25%) families, as evidenced by mass spectrometry analysis. The antimicrobial activity against Staphylococcus spp. planktonic and sessile cells was evaluated by microdilution and metabolic activity assays. R89BS inhibited S. aureus and S. epidermidis growth with minimal inhibitory concentrations (MIC₉₉) of 0.06 and 0.12 mg/mL, respectively and dispersed their pre-formed biofilms up to 93%. Silicone elastomeric discs (SEDs) coated by R89BS simple adsorption significantly counteracted Staphylococcus spp. biofilm formation, in terms of both built-up biomass (up to 60% inhibition at 72 h) and cell metabolic activity (up to 68% inhibition at 72 h). SEM analysis revealed significant inhibition of the amount of biofilm-covered surface. No cytotoxic effect on eukaryotic cells was detected at concentrations up to 0.2 mg/mL. R89BS-coated SEDs satisfy biocompatibility requirements for leaching products. Results indicate that rhamnolipid coatings are effective anti-biofilm treatments and represent a promising strategy for the prevention of infection associated with implantable devices.

Broad-spectrum antimicrobial activity of secondary metabolites produced by Serratia marcescens strains

The genus Serratia is a predominantly unexplored source of antimicrobial secondary metabolites. The aim of the current study was thus to isolate and evaluate the antimicrobial properties of biosurfactants produced by Serratia species. Forty-nine (n = 34 pigmented; n = 15 non-pigmented) biosurfactant producing Serratia strains were isolated from environmental sources and selected isolates (n = 11 pigmented; n = 11 non-pigmented) were identified as Serratia marcescens using molecular typing. The swrW gene (serrawettin W1 synthetase) was detected in all the screened pigmented strains and one non-pigmented strain and primers were designed for the detection of the swrA gene (non-ribosomal serrawettin W2 synthetase), which was detected in nine non-pigmented strains. Crude extracts obtained from S. marcescens P1, NP1 and NP2 were chemically characterised using ultra-performance liquid chromatography coupled to electrospray ionisation mass spectrometry (UPLC-ESI-MS), which revealed that P1 produced serrawettin W1 homologues and prodigiosin, while NP1 produced serrawettin W1 homologues and glucosamine derivative A. In contrast, serrawettin W2 analogues were predominantly identified in the crude extract obtained from S. marcescens NP2. Both P1 and NP1 crude extracts displayed broad-spectrum antimicrobial activity against clinical, food and environmental pathogens, such as multidrug-resistant Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus and Cryptococcus neoformans. In contrast, the NP2 crude extract displayed antibacterial activity against a limited range of pathogenic and opportunistic pathogens. The serrawettin W1 homologues, in combination with prodigiosin and glucosamine derivatives, produced by pigmented and non-pigmented S. marcescens strains, could thus potentially be employed as broad-spectrum therapeutic agents against multidrug-resistant bacterial and fungal pathogens.

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.

Thermoregulation of Prodigiosin Biosynthesis by Serratia marcescens is Controlled at the Transcriptional Level and Requires HexS

Several biotypes of the Gram-negative bacterium Serratia marcescens produce the tri-pyrole pigment and secondary metabolite prodigiosin. The biological activities of this pigment have therapeutic potential. For over half a century it has been known that biosynthesis of prodi giosin is inhibited when bacteria are grown at elevated temperatures, yet the fundamental mechanism underlying this thermoregulation has not been characterized. In this study, chromosomal and plasmid-borne luxCDABE transcriptional reporters revealed reduced transcription of the prodigiosin biosynthetic operon at 37°C compared to 30°C indicating transcriptional control of pigment production. Moreover, induced expression of the prodigiosin biosynthetic operon at 37°C was able to produce pigmented colonies and cultures demonstrating that physiological conditions at 37°C allow prodigiosin production and indicating that post-transcriptional control is not a major contributor to the thermoregulation of prodigiosin pigmentation. Genetic experiments support the model that the HexS transcription factor is a key contributor to thermoregulation of pigmentation, whereas CRP plays a minor role, and a clear role for EepR and PigP was not observed. Together, these data indicate that thermoregulation of prodigiosin production at elevated temperatures is controlled largely, if not exclusively, at the transcriptional level.

Insights into the anti-infective properties of prodiginines

Prodiginines are a large family of tripyrrole alkaloids that contain natural members produced by various bacteria and non-natural members obtained from chemical synthesis, enzymatic synthesis, and mutasynthesis. These compounds have attracted a great deal of attention due to their wide range of fascinating properties including anti-infective, anticancer, and immunosuppressive activities. In consideration of the great need for novel and effective anti-infective agents, this review is mainly focused on the current status of research on the anti-infective properties of prodiginines, highlighting their antibacterial, antifungal, antiprotozoal, anti-larval, and antiviral activities. Additionally, the multiple mechanisms by which prodiginines exert their anti-infective effects will also be discussed.