Spontaneous nanoemulsification of cinnamon essential oil: Formulation, characterization, and antibacterial and antibiofilm activity against fish spoilage caused by Serratia rubidaea BFMO8.

The contemporary food industry's uses of nanoemulsions (NEs) include food processing, effective nutraceutical delivery, the development of functional chemicals, and the synthesis of natural preservatives, such as phytocompounds. Although cinnamon essential oil (CEO) is widely used in the cosmetic, pharmaceutical, and food industries, it is difficult to add to aqueous-based food formulations due to its weak stability and poor water solubility. This study describes the formulation of a CEO nanoemulsion (CEONE) by spontaneous emulsification and evaluates its antibacterial and antibiofilm properties against biofilm-forming Serratia rubidaea BFMO8 isolated from spoiled emperor fish (Lethrinus miniatus). Bacteria causing spoilage in emperor fish were isolated and identified as S. rubidaea using common morphological, cultural, and 16S RNA sequencing methods, and their ability to form biofilms and their susceptibility to CEONE were assessed using biofilm-specific methods. The spontaneous emulsification formulation of CEONE was accomplished using water and Tween 20 surfactant by manipulating organic and aqueous phase interface properties and controlling particle growth by capping surfactant increases. The best emulsification, with highly stable nano-size droplets, was accomplished at 750 rpm and a 1:3 ratio concentration. The stable CEONE droplet size, polydispersity index, and zeta potential values were 204.8 nm, 0.115, and -6.05 mV, respectively. FTIR and high-resolution liquid chromatography-mass spectrometry (HR-LCMS) analyses have revealed carboxyl, carbonyl, and phenol-like primary phytochemical functional groups in CEO and CEONE, which contribute to their antibacterial and antibiofilm properties.

Potential use of two Serratia strains for cadmium remediation based on microbiologically induced carbonate precipitation and their cadmium resistance.

Cadmium (Cd) presence and bioavailability in soils is a serious concern for cocoa producers. Cocoa plants can bioaccumulate Cd that can reach humans through the food chain, thus posing a threat to human health, as Cd is a highly toxic metal. Currently, microbiologically induced carbonate precipitation (MICP) by the ureolytic path has been proposed as an effective technique for Cd remediation. In this work, the Cd remediation potential and Cd resistance of two ureolytic bacteria, Serratia sp. strains 4.1a and 5b, were evaluated. The growth of both Serratia strains was inhibited at 4 mM Cd(II) in the culture medium, which is far higher than the Cd content that can be found in the soils targeted for remediation. Regarding removal efficiency, for an initial concentration of 0.15 mM Cd(II) in liquid medium, the maximum removal percentages for Serratia sp. 4.1.a and 5b were 99.3% and 99.57%, respectively. Their precipitates produced during Cd removal were identified as calcite by X-ray diffraction. Energy dispersive X-ray spectroscopy analysis showed that a portion of Cd was immobilized in this matrix. Finally, the presence of a partial gene from the czc operon, involved in Cd resistance, was observed in Serratia sp. 5b. The expression of this gene was found to be unaffected by the presence of Cd(II), and upregulated in the presence of urea. This work is one of the few to report the use of bacterial strains of the Serratia genus for Cd remediation by MICP, and apparently the first one to report differential expression of a Cd resistance gene due to the presence of urea.

Host-Cell-Dependent Roles of E-Cadherin in Serratia Invasion.

Bacteria use cell surface proteins to mediate host-pathogen interactions. Proteins responsible for cell adhesion, including E-cadherin, serve as receptors for entry into the host cell. We have previously shown that an increase in eukaryotic cell sensitivity to Serratia grimesii correlates with an increase in E-cadherin expression. On the other hand, Serratia proteamaculans invasion involves the EGFR, which can interact with E-cadherin on the surface of host cells. Therefore, we investigated the role of E-cadherin in Serratia invasion into M-HeLa and Caco-2 cells. Bacterial infection increased E-cadherin expression in both cell lines. Moreover, E-cadherin was detected in the Caco-2 cells in a full-length form and in the M-HeLa cells in only a truncated form in response to incubation with bacteria. Transfection with siRNA targeting E-cadherin inhibited S. proteamaculans invasion only into the Caco-2 cells. Thus, only full-length E-cadherin is involved in S. proteamaculans invasion. On the other hand, transfection with siRNA targeting E-cadherin inhibited S. grimesii invasion into both cell lines. Thus, not only may full-length E-cadherin but also truncated E-cadherin be involved in S. grimesii invasion. Truncated E-cadherin can be formed as a result of cleavage by bacterial proteases or the Ca2+-activated cellular protease ADAM10. The rate of Ca2+ accumulation in the host cells depends on the number of bacteria per cell upon infection. During incubation, Ca2+ accumulates only when more than 500 S. grimesii bacteria are infected per eukaryotic cell, and only under these conditions does the ADAM10 inhibitor reduce the sensitivity of the cells to bacteria. An EGFR inhibitor has the same quantitative effect on S. grimesii invasion. Apparently, as a result of infection with S. grimesii, Ca2+ accumulates in the host cells and may activate the ADAM10 sheddase, which can promote invasion by cleaving E-cadherin and, as a result, triggering EGFR signaling. Thus, the invasion of S. proteamaculans can only be promoted by full-length E-cadherin, and S. grimesii invasion can be promoted by both full-length and truncated E-cadherin.

Involvement of Lipid Rafts in the Invasion of Opportunistic Bacteria Serratia into Eukaryotic Cells.

Cell membrane rafts form signaling platforms on the cell surface, controlling numerous protein-protein and lipid-protein interactions. Bacteria invading eukaryotic cells trigger cell signaling to induce their own uptake by non-phagocytic cells. The aim of this work was to reveal the involvement of membrane rafts in the penetration of the bacteria Serratia grimesii and Serratia proteamaculans into eukaryotic cells. Our results show that the disruption of membrane rafts by MßCD in the three cell lines tested, M-HeLa, MCF-7 and Caco-2, resulted in a time-dependent decrease in the intensity of Serratia invasion. MßCD treatment produced a more rapid effect on the bacterial susceptibility of M-HeLa cells compared to other cell lines. This effect correlated with a faster assembly of the actin cytoskeleton upon treatment with MßCD in M-HeLa cells in contrast to that in Caco-2 cells. Moreover, the 30 min treatment of Caco-2 cells with MßCD produced an increase in the intensity of S. proteamaculans invasion. This effect correlated with an increase in EGFR expression. Together with the evidence that EGFR is involved in S. proteamaculans invasion but not in S. grimesii invasion, these results led to the conclusion that an increase in EGFR amount on the plasma membrane with the undisassembled rafts of Caco-2 cells after 30 min of treatment with MßCD may increase the intensity of S. proteamaculans but not of S. grimesii invasion. Thus, the MßCD-dependent degradation of lipid rafts, which enhances actin polymerization and disrupts signaling pathways from receptors on the host cell's surface, reduces Serratia invasion.

Structures, biosynthesis, and bioactivities of prodiginine natural products.

Prodiginines are a large family of microbial secondary metabolites with a core structure of tripyrrole rings. They exhibit not only diverse chemical structures but also rich biological activities, such as anti-cancer, anti-microbial, anti-algae, anti-parasitic, pesticides, and UV radiation resistance. The preferred cytotoxicity to cancer cells rather than normal cells indicates a good biological selectivity and safety, which makes the prodiginines promising candidates for drug development and novel additives for food processing. Until now, 33 prodiginine natural products have been identified in various bacteria, including Serratia, Hahella, Pseudoalteromonas, Vibrio, Zooshikella, Streptomyces, and Actinomadura. However, most efforts are still focused on the star molecule prodigiosin, while little yet is known about other prodiginine members, which retards the research and application of prodiginine compounds. To gain insight into the prodiginine family, we reviewed the recent discoveries on their chemical structures, biosynthesis, biological activities, and mechanisms of action. We believe this article will provide a guideline for new research on prodiginines, such as the discovery of new congeners and drug development. KEY POINTS: • The prodiginines are a large family of natural products with a core structure of tripyrrole rings and exhibit various bioactivities. • The prodiginines have a widespread distribution among many environmental microbes and diverse biosynthetic pathways, indicating important ecological roles and a great potential for new congeners. • The potent biological activities and good selectivity of action make prodiginines good lead compounds for drug development.

Bacterial Outer Membrane Protein OmpX Regulates ß1 Integrin and Epidermal Growth Factor Receptor (EGFR) Involved in Invasion of M-HeLa Cells by Serratia proteamaculans.

Opportunistic pathogen Serratia proteamaculans are able to penetrate the eukaryotic cells. The penetration rate can be regulated by bacterial surface protein OmpX. OmpX family proteins are able to bind to host cell surface to the epidermal growth factor receptor (EGFR) and the extracellular matrix protein fibronectin, whose receptors are in return the α5 ß1 integrins. Here we elucidated the involvement of these host cell proteins in S. proteamaculans invasion. We have shown that, despite the absence of fibronectin contribution to S. proteamaculans invasion, ß1 integrin was directly involved in invasion of M-HeLa cells. Herewith ß1 integrin was not the only receptor that determines sensitivity of host cells to bacterial invasion. Signal transfer from EGFR was also involved in the penetration of these bacteria into M-HeLa cells. However, M-HeLa cells have not been characterized by large number of these receptors. It turned out that S. proteamaculans attachment to the host cell surface resulted in an increment of EGFR and ß1 integrin genes expression. Such gene expression increment also caused Escherichia coli attachment, transformed with a plasmid encoding OmpX from S. proteamaculans. Thus, an OmpX binding to the host cell surface caused an increase in the EGFR and ß1 integrin expression involved in S. proteamaculans invasion.

Potential of Serratia plymuthica IV-11-34 strain for biodegradation of polylactide and poly(ethylene terephthalate).

Serratia plymuthica strain IV-11-34 belongs to the plant growth promoting bacteria (PGPR). In the sequenced genome of S. plymuthica IV-11-34, we have identified the genes involved in biodegradation and metabolisms of xenobiotics. The potential of S. plymuthica IV-11-34 for the degradation of biodegradable aliphatic polyester polylactide (PLA) and resistant to biodegradation - poly(ethylene terephthalate) (PET) was assessed by biochemical oxygen consumption (BOD) and carbon dioxide methods. After seven days of growth, the bacteria strain showed more than 80% and 60% increase in respiratory activity in the presence of PLA and PET, respectively. We assume that during biodegradation, S. plymuthica IV-11-34 colonise the surface of PLA and PET, since the formation of a biofilm on the surface of polymers was shown by the LIVE/DEAD method. We have demonstrated for the relA gene, which is an alarmone synthetase, a 1.2-fold increase in expression in the presence of PLA, and a 4-fold decrease in expression in the presence of PET for the spoT gene, which is a hydrolase of alarmones. Research has shown that the bacterium has the ability to biodegrade PLA and PET, and the first stage of this process involves bacterial stringent response genes responsible for survival under extreme conditions.

Solution Structure and Conformational Dynamics of a Doublet Acyl Carrier Protein from Prodigiosin Biosynthesis.

The acyl carrier protein (ACP) is an indispensable component of both fatty acid and polyketide synthases and is primarily responsible for delivering acyl intermediates to enzymatic partners. At present, increasing numbers of multidomain ACPs have been discovered with roles in molecular recognition of trans-acting enzymatic partners as well as increasing metabolic flux. Further structural information is required to provide insight into their function, yet to date, the only high-resolution structure of this class to be determined is that of the doublet ACP (two continuous ACP domains) from mupirocin synthase. Here we report the solution nuclear magnetic resonance (NMR) structure of the doublet ACP domains from PigH (PigH ACP1-ACP2), which is an enzyme that catalyzes the formation of the bipyrrolic intermediate of prodigiosin, a potent anticancer compound with a variety of biological activities. The PigH ACP1-ACP2 structure shows each ACP domain consists of three conserved helices connected by a linker that is partially restricted by interactions with the ACP1 domain. Analysis of the holo (4'-phosphopantetheine, 4'-PP) form of PigH ACP1-ACP2 by NMR revealed conformational exchange found predominantly in the ACP2 domain reflecting the inherent plasticity of this ACP. Furthermore, ensemble models obtained from SAXS data reveal two distinct conformers, bent and extended, of both apo (unmodified) and holo PigH ACP1-ACP2 mediated by the central linker. The bent conformer appears to be a result of linker-ACP1 interactions detected by NMR and might be important for intradomain communication during the biosynthesis. These results provide new insights into the behavior of the interdomain linker of multiple ACP domains that may modulate protein-protein interactions. This is likely to become an increasingly important consideration for metabolic engineering in prodigiosin and other related biosynthetic pathways.

Bacterial Actin-Specific Endoproteases Grimelysin and Protealysin as Virulence Factors Contributing to the Invasive Activities of Serratia.

The article reviews the discovery, properties and functional activities of new bacterial enzymes, proteases grimelysin (ECP 32) of Serratia grimesii and protealysin of Serratia proteamaculans, characterized by both a highly specific "actinase" activity and their ability to stimulate bacterial invasion. Grimelysin cleaves the only polypeptide bond Gly42-Val43 in actin. This bond is not cleaved by any other proteases and leads to a reversible loss of actin polymerization. Similar properties were characteristic for another bacterial protease, protealysin. These properties made grimelysin and protealysin a unique tool to study the functional properties of actin. Furthermore, bacteria Serratia grimesii and Serratia proteamaculans, producing grimelysin and protealysin, invade eukaryotic cells, and the recombinant Escherichia coli expressing the grimelysin or protealysins gene become invasive. Participation of the cellular c-Src and RhoA/ROCK signaling pathways in the invasion of eukaryotic cells by S. grimesii was shown, and involvement of E-cadherin in the invasion has been suggested. Moreover, membrane vesicles produced by S. grimesii were found to contain grimelysin, penetrate into eukaryotic cells and increase the invasion of bacteria into eukaryotic cells. These data indicate that the protease is a virulence factor, and actin can be a target for the protease upon its translocation into the host cell.

Effects of oil substrate supplementation on production of prodigiosin by Serratia nematodiphila for dye-sensitized solar cell.

Bacterial pigments are potential substitute of chemical photosensitizer for dye-sensitized solar cell (DSSC) due to its non-toxic property and cost-effective production from microbial fermentation. Serratia nematodiphila YO1 was isolated from waterfall in Malaysia and identified using 16S ribosomal RNA. Characterization of the red pigment produced by the bacteria has confirmed the pigment as prodigiosin. Prodigiosin was produced from the fermentation of the bacteria in the presence of different oil substrates. Palm oil exhibited the best performance of cell growth and equivalent prodigiosin yield compared to olive oil and peanut oil. Prodigiosin produced with palm oil supplementation was 93 mg/l compared to 7.8 mg/l produced without supplementation, which recorded 11.9 times improvement. Specific growth rate of the cells improved 1.4 times when palm oil was supplemented in the medium. The prodigiosin pigment produced showed comparable performance as a DSSC sensitizer by displaying an open circuit voltage of 336.1 mV and a maximum short circuit current of 0.098 mV/cm2. This study stands a novelty in proving that the production of prodigiosin is favorable in the presence of palm oil substrate with high saturated fat content, which has not been studied before. This is also among the first bacterial prodigiosin tested as photosensitizer for DSSC application.

Antimicrobial secondary metabolites from agriculturally important bacteria as next-generation pesticides.

The whole organisms can be packaged as biopesticides, but secondary metabolites secreted by microorganisms can also have a wide range of biological activities that either protect the plant against pests and pathogens or act as plant growth promotors which can be beneficial for the agricultural crops. In this review, we have compiled information about the most important secondary metabolites of three important bacterial genera currently used in agriculture pest and disease management.

Effect of Serratia sp. K3 combined with organic materials on cadmium migration in soil-vetiveria zizanioides L. system and bacterial community in contaminated soil.

Phytoremediation is an economical strategy to harvest cadmium (Cd) from contaminated soil, but the efficiency of phytoremediation was affected by many factors. This study investigated the potential of Serratia sp. K3 (K3) assisted with straw biogas residue (SBR) or leavening fertilizer (LF) on improving the Cd migration efficiency and micro-environment in soil-vetiveria zizanioides L. system. The results showed that the acid soluble Cd in soil was increased by 2.83-29.79% in treatments compared with control (CK). In addition, Cd accumulation in the roots and shoots of vetiveria zizanioides were significantly enhanced by the combination of K3 and SBR/LF. Especially, the translocation factor of Cd increased by 21.53-62.37% in groups with K3 compared with the groups without K3, correspondingly. Furthermore, SBR/LF effectively changed bacterial community structure, and improved bacterial abundance. Relative abundance of functional genes related with carbohydrate/energy/amino acid metabolism were increased in groups of SBRB/LFB rhizosphere compared with CK. These results provide insight into the change of phytoremediation efficiency and soil bacterial communities in the vetiveria zizanioides rhizosphere after inoculation. This study may provide a promising method for improving phytoremediation in Cd contaminated soil.

Metabolic response of bacteria to elevated concentrations of glyphosate-based herbicide.

Glyphosate-based herbicides (GBHs) are the most widespread commonly used broad-spectrum herbicides that contaminate soils and waters, are toxic to bacteria, plants and animals, and have been classified as 'probably carcinogenic to humans' by the International Agency for Research on Cancer in 2015. Particular soil bacteria and fungi can degrade GBHs, hence, search for new GBH-degrading strains or microbial consortia, effective under specific growth conditions and local environment, seems to be a promising solution for bio-remediation of glyphosate-contaminated environment. Consequently, there is a need for rapid and informative methods to evaluate the GBH-induced changes of the metabolic pathways in cells, that may serve as indicators of GBH-degrading potential. Three new GBH-degrading bacterial strains, Pseudomonas sp., Actinobacteria and Serratia sp. were isolated from sludge of municipal waste water treatment plant (Daugavgriva, Riga, Latvia), agricultural soil and plant tissue, respectively. This study examined the response of these isolates to elevated concentrations of glyphosate (GLP) (100 and 500 mg/L) in GBH Klinik® 360 SL. The GBH-induced shift of metabolic activity in cells of Pseudomonas sp. was shown by tests on EcoPlates™. Fourier transform infrared (FTIR) spectroscopy analyses were used to evaluate the metabolomic response of bacteria to elevated concentrations of GBH in the growth environment. The spectra of Pseudomonas sp. and Serratia sp., incubated with and without GBH, were similar, thus indicating their GBH-resistance. The absorption at 1736 cm-1, assigned to ester carbonyl stretch vibrations, was detected in spectra of all three bacteria. The highest ester content was detected in Actinobacteria grown in medium with 1.0% molasses and 100 or 500 mg/L GLP in GBH Klinik®. An increase of cellular amounts of esters, either those of phospholipids or poly-ß-hydroxybutyrates, indicates degradation of GLP. Therefore, monitoring the ester carbonyl stretch vibration band in FTIR spectra of bacterial biomass may speed up the search GBH-degrading strains. Microbiological tests and cell metabolic response studies by FTIR spectroscopy showed that the three new isolates of Pseudomonas sp., Actinobacteria and Serratia sp. were resistant to elevated concentrations of GBH Klinik® in growth environment and exhibited the potential for GBH degradation.

Biosurfactants produced by Serratia species: Classification, biosynthesis, production and application.

Biosurfactants are surface-active molecules that are synthesised non-ribosomally by a wide range of microorganisms including bacteria, yeast and filamentous fungi. The bacterial genus Serratia is gaining international interest, as biosurfactants produced by this genus have emerged as a promising source of antimicrobial, antifouling and antitumour compounds that possess emulsification and surface activity. Various species of Serratia have been identified as biosurfactant producers, including Serratia marcescens, Serratia rubidaea and Serratia surfactantfaciens. Members of the Serratia genus have been reported to principally produce two classes of biosurfactants, namely lipopeptides and glycolipids. Lipopeptides produced by Serratia species include serrawettins and stephensiolides, while identified glycolipids include rubiwettins and rhamnolipids. This review will primarily focus on the classification of biosurfactants produced by Serratia species and the genes and mechanisms involved in the biosynthesis of these biosurfactant compounds. Thereafter, an indication of the primary growth conditions and nutrient composition required for the optimum production of biosurfactants by this genus will be outlined. An overview of the latest advances and potential applications of the biosurfactants produced by Serratia in the medical, pharmaceutical, agricultural and petroleum industries is also provided.

Bifunctional Immunity Proteins Protect Bacteria against FtsZ-Targeting ADP-Ribosylating Toxins.

ADP-ribosylation of proteins can profoundly impact their function and serves as an effective mechanism by which bacterial toxins impair eukaryotic cell processes. Here, we report the discovery that bacteria also employ ADP-ribosylating toxins against each other during interspecies competition. We demonstrate that one such toxin from Serratia proteamaculans interrupts the division of competing cells by modifying the essential bacterial tubulin-like protein, FtsZ, adjacent to its protomer interface, blocking its capacity to polymerize. The structure of the toxin in complex with its immunity determinant revealed two distinct modes of inhibition: active site occlusion and enzymatic removal of ADP-ribose modifications. We show that each is sufficient to support toxin immunity; however, the latter additionally provides unprecedented broad protection against non-cognate ADP-ribosylating effectors. Our findings reveal how an interbacterial arms race has produced a unique solution for safeguarding the integrity of bacterial cell division machinery against inactivating post-translational modifications.

Sodorifen Biosynthesis in the Rhizobacterium Serratia plymuthica Involves Methylation and Cyclization of MEP-Derived Farnesyl Pyrophosphate by a SAM-Dependent C-Methyltransferase.

The rhizobacterium Serratia plymuthica 4Rx13 releases a unique polymethylated hydrocarbon (C16H26) with a bicyclo[3.2.1]octadiene skeleton called sodorifen. Sodorifen production depends on a gene cluster carrying a C-methyltransferase and a terpene cyclase along with two enzymes of the 2- C-methyl-d-erythritol 4-phosphate (MEP) pathway of isoprenoid biosynthesis. Comparative analysis of wild-type and mutant volatile organic compound profiles revealed a C-methyltransferase-dependent C16 alcohol called pre-sodorifen, the production of which is upregulated in the terpene cyclase mutant. The monocyclic structure of this putative intermediate in sodorifen biosynthesis was identified by NMR spectroscopy. In vitro assays with the heterologously expressed S. plymuthica C-methyltransferase and terpene cyclase demonstrated that these enzymes act sequentially to convert farnesyl pyrophosphate (FPP) into sodorifen via a pre-sodorifen pyrophosphate intermediate, indicating that the S-adenosyl methionine (SAM)-dependent C-methyltransferase from S. plymuthica exhibits unprecedented cyclase activity. In vivo incorporation experiments with 13C-labeled succinate, l-alanine, and l-methionine confirmed a MEP pathway to FPP via the canonical glyceraldehyde-3-phosphate and pyruvate, as well as its SAM-dependent methylation in pre-sodorifen and sodorifen biosynthesis. 13C{1H} NMR spectroscopy facilitated the localization of 13C labels and provided detailed insights into the biosynthetic pathway from FPP via pre-sodorifen pyrophosphate to sodorifen.

Diesel oil removal by Serratia sp. W4-01 immobilized in chitosan-activated carbon beads.

Serratia sp. W4-01 was immobilized in chitosan-activated carbon beads and used for diesel oil removal. The type and concentration of chitosan, activated carbon content, and bead diameter were investigated as factors affecting diesel oil removal. The results showed that 2% (w/v) squid pen chitosan beads modified with 1% activated carbon (w/v) and with a 3-mm diameter had a good spherical shape and strength as well as diesel oil removal capability. The immobilized W4-01 cells removed more than 40% of diesel oil after 7 days when the initial diesel oil concentration was 100 to 400 mg L-1, whereas 29-36% of diesel oil was removed after 14 days when the initial concentration was 800 to 1000 mg L-1. Additionally, the immobilized cells maintained the ability to remove diesel oil over a pH range of 5-11. The addition of a biosurfactant increased the diesel oil removal from 62 to 75%. The reusability tests revealed that the ability of immobilized cells to remove diesel oil was enhanced after reuse, and 50-90% of diesel oil was removed during 2 to 12 reuse cycles. The stability and survival of W4-01 cells was confirmed by scanning electron microscopy and confocal laser scanning microscopy. The results of this study showed the potential use of W4-01 cells immobilized in chitosan-activated carbon beads for future applications in remediating diesel contamination.

Discovery of Antimicrobial Lipodepsipeptides Produced by a Serratia sp. within Mosquito Microbiomes.

The Anopheles mosquito that harbors the Plasmodium parasite contains a microbiota that can influence both the vector and the parasite. In recent years, insect-associated microbes have highlighted the untapped potential of exploiting interspecies interactions to discover bioactive compounds. In this study, we report the discovery of nonribosomal lipodepsipeptides that are produced by a Serratia sp. within the midgut and salivary glands of Anopheles stephensi mosquitoes. The lipodepsipeptides, stephensiolides A-K, have antibiotic activity and facilitate bacterial surface motility. Bioinformatic analyses indicate that the stephensiolides are ubiquitous in nature and are likely important for Serratia spp. colonization within mosquitoes, humans, and other ecological niches. Our results demonstrate the usefulness of probing insect-microbiome interactions, enhance our understanding of the chemical ecology within Anopheles mosquitoes, and provide a secondary-metabolite scaffold for further investigate of this complex relationship.

Complete genome sequence of Serratia sp. YD25 (KCTC 42987) presenting strong antagonistic activities to various pathogenic fungi and bacteria.

Serratia sp. YD25 (KCTC 42987) was originally isolated from rhizosphere soil in a continuous cropping tobacco-planting farm. Here, we show that its metabolites efficiently suppress the growth of various important pathogenic fungi and bacteria, causing infection in both plants and humans. In addition, Serratia sp. YD25 has a special trait of simultaneous production of both serrawettin W2 and prodigiosin, two important bioactive secondary metabolites produced by Serratia strains. Such co-production has not been reported in other Serratia strains. The complete genome sequence of Serratia sp. YD25 is presented, which is valuable for further exploration of its biotechnological applications in agriculture and medicine. The genome sequence reported here is also useful for understanding the unique regulatory mechanisms underlying biosynthesis of active compounds.

Analysis of the genomic sequences and metabolites of Serratia surfactantfaciens sp. nov. YD25T that simultaneously produces prodigiosin and serrawettin W2.

BACKGROUND: Gram-negative bacteria of the genus Serratia are potential producers of many useful secondary metabolites, such as prodigiosin and serrawettins, which have potential applications in environmental bioremediation or in the pharmaceutical industry. Several Serratia strains produce prodigiosin and serrawettin W1 as the main bioactive compounds, and the biosynthetic pathways are co-regulated by quorum sensing (QS). In contrast, the Serratia strain, which can simultaneously produce prodigiosin and serrawettin W2, has not been reported. This study focused on analyzing the genomic sequence of Serratia sp. strain YD25T isolated from rhizosphere soil under continuously planted burley tobacco collected from Yongding, Fujian province, China, which is unique in producing both prodigiosin and serrawettin W2. RESULTS: A hybrid polyketide synthases (PKS)-non-ribosomal peptide synthetases (NRPS) gene cluster putatively involved in biosynthesis of antimicrobial serrawettin W2 was identified in the genome of YD25T, and its biosynthesis pathway was proposed. We found potent antimicrobial activity of serrawettin W2 purified from YD25T against various pathogenic bacteria and fungi as well as antitumor activity against Hela cells. Subsequently, comparative genomic analyses were performed among a total of 133 Serratia species. The prodigiosin biosynthesis gene cluster in YD25T belongs to the type I pig cluster, which is the main form of pig-encoding genes existing in most of the pigmented Serratia species. In addition, a complete autoinducer-2 (AI-2) system (including luxS, lsrBACDEF, lsrGK, and lsrR) as a conserved bacterial operator is found in the genome of Serratia sp. strain YD25T. Phylogenetic analysis based on concatenated Lsr and LuxS proteins revealed that YD25T formed an independent branch and was clearly distant from the strains that solely produce either prodigiosin or serrawettin W2. The Fe (III) ion reduction assay confirmed that strain YD25T could produce an AI-2 signal molecule. Phylogenetic analysis using the genomic sequence of YD25T combined with phylogenetic and phenotypic analyses support this strain as a member of a novel and previously uncharacterized Serratia species. CONCLUSION: Genomic sequence and metabolite analysis of Serratia surfactantfaciens YD25T indicate that this strain can be further explored for the production of useful metabolites. Unveiling the genomic sequence of S. surfactantfaciens YD25T benefits the usage of this unique strain as a model system for studying the biosynthesis regulation of both prodigiosin and serrawettin W2 by the QS system.