Engineering Bacillus subtilis ATCC 6633 for improved production of the lantibiotic subtilin

Heterologous expression of recombinant nattokinase in Escherichia coli BL21(DE3) and media optimization for overproduction of nattokinase using RSM

Nattokinase, a serine protease, was discovered in Bacillus subtilis during the fermentation of a soybean byproduct. Nattokinase is essential for the lysis of blood clots and the treatment of cardiac diseases including atherosclerosis, thrombosis, high blood pressure, and stroke. The demand for thrombolytic drugs rises as the prevalence of cardiovascular disease rises, and nattokinase is particularly effective for the treatment of cardiovascular diseases due to its long duration of action. In this study, we cloned the nattokinase gene from the Bacillus subtilis strain into the pET32a vector and expressed the protein in the E. coli BL21(DE3) strain. The active recombinant nattokinase was purified using Ni-NTA affinity chromatography and then evaluated for fibrinolytic and blood clot lysis activity. Physiological parameters for optimizing protein production at optimal pH, temperature, IPTG concentration, and incubation time were investigated. A statistical technique was used to optimize media components for nattokinase overproduction, and Central Composite Design-Response Surface Methodology-based optimization was used to select significant components for protein production. The optimized media produced 1805.50 mg/L of expressed nattokinase and 42.80 gm/L of bacterial mass. The fibrinolytic activity obtained from refolded native protein was 58FU/mg, which was five times higher than the available orokinase drug (11FU/mg). The efficiency with which a statistical technique for media optimization was implemented improved recombinant nattokinase production and provides new information for scale - up nattokinase toward industrial applications.

Classification and Multifaceted Potential of Secondary Metabolites Produced by Bacillus subtilis Group: A Comprehensive Review

Despite their remarkable biosynthetic potential, Bacillus subtilis have been widely overlooked. However, their capability to withstand harsh conditions (extreme temperature, Ultraviolet (UV) and γ-radiation, and dehydration) and the promiscuous metabolites they synthesize have created increased commercial interest in them as a therapeutic agent, a food preservative, and a plant-pathogen control agent. Nevertheless, the commercial-scale availability of these metabolites is constrained due to challenges in their accessibility via synthesis and low fermentation yields. In the context of this rising in interest, we comprehensively visualized the antimicrobial peptides produced by B. subtilis and highlighted their prospective applications in various industries. Moreover, we proposed and classified these metabolites produced by the B. subtilis group based on their biosynthetic pathways and chemical structures. The biosynthetic pathway, bioactivity, and chemical structure are discussed in detail for each class. We believe that this review will spark a renewed interest in the often disregarded B. subtilis and its remarkable biosynthetic capabilities.

Engineering of global transcription factors in Bacillus, a genetic tool for increasing product yields: a bioprocess overview

Transcriptional factors are well studied in bacteria for their global interactions and the effects they produce at the phenotypic level. Particularly, Bacillus subtilis has been widely employed as a model Gram-positive microorganism used to characterize these network interactions. Bacillus species are currently used as efficient commercial microbial platforms to produce diverse metabolites such as extracellular enzymes, antibiotics, surfactants, industrial chemicals, heterologous proteins, among others. However, the pleiotropic effects caused by the genetic modification of specific genes that codify for global regulators (transcription factors) have not been implicated commonly from a bioprocess point of view. Recently, these strategies have attracted the attention in Bacillus species because they can have an application to increase production efficiency of certain commercial interest metabolites. In this review, we update the recent advances that involve this trend in the use of genetic engineering (mutations, deletion, or overexpression) performed to global regulators such as Spo0A, CcpA, CodY and AbrB, which can provide an advantage for the development or improvement of bioprocesses that involve Bacillus species as production platforms. Genetic networks, regulation pathways and their relationship to the development of growth stages are also discussed to correlate the interactions that occur between these regulators, which are important to consider for application in the improvement of commercial-interest metabolites. Reported yields from these products currently produced mostly under laboratory conditions and, in a lesser extent at bioreactor level, are also discussed to give valuable perspectives about their potential use and developmental level directed to process optimization at large-scale.

Antibiotic profiling of wild-type bacilli led to the discovery of new lanthipeptide subtilin-producing Bacillus spizizenii strains whose 16S rDNA sequences differ from the B. spizizenii typing strain

Two dozen field-collected Bacillus and a dozen Bacillus spizizenii wild-type strains from strain collections were selected on the basis of their antagonistic properties against the Gram-positive strain Micrococcus luteus. Based on their genetic and antibiotic profiles, they were characterized (subtilin encoding spaS gene sequences, mass spectrometric, and quantitative-reversed phase liquid chromatographic analyses, as well as the presence of the lanthionine cyclase protein SpaC by western blotting), seven novel producers of the lanthipeptide subtilin. Phylogenetic analyses of the subtilin-producing wild-type strains based on their 16S rRNA sequences showed that all seven strains could be classified as B. spizizenii: The field-collected strains HS and N5, as well as strains DSM 618, 1087, 6395, 6405, and 8439 from the German Collection of Microorganisms and Cell Cultures. To the best of our knowledge, all B. spizizenii strains described so far are characterized by the fact that they can produce a lanthipeptide of the subtilin family. Both the lanthipeptide structures and the organization and sequences of the 16S rRNA-encoding genes suggest a subdivision of B. spizizenii into subspecies: The subtilin-producing B. spizizenii strains are distinctly different from the entianin-producing B. spizizenii typing strain TU-B-10 ^T (DSM 15029 ^T).

MiniBacillus PG10 as a Convenient and Effective Production Host for Lantibiotics

Efficient bacterial cell factories are important for the screening and characterization of potent antimicrobial peptides such as lantibiotics. Although lantibiotic production systems have been established in Lactococcus lactis and Escherichia coli, the industrial workhorse Bacillus subtilis has been left relatively unexplored as a lantibiotic production host. Therefore, we tested different B. subtilis strains for their ability to produce lantibiotic peptides by using the subtilin modification and transport enzymes derived from the natural subtilin producer B. subtilis ATCC 6633. Our study shows that although B. subtilis ATCC 6633 and 168 are able to produce various processed lantibiotic peptides, an evident advantage of using either the 8-fold protease-deficient strain WB800 or the genome-minimized B. subtilis 168 strain PG10 is the lack of extracellular serine protease activity. Consequently, leader processing of lantibiotic precursor peptides is circumvented and thus potential toxicity toward the production host is prevented. Furthermore, PG10 provides a clean secondary metabolic background and therefore appears to be the most promising B. subtilis lantibiotic production host. We demonstrate the production of various lantibiotic precursor peptides by PG10 and show different options for their in vitro activation. Our study thus provides a convenient B. subtilis-based lantibiotic production system, which facilitates the search for novel antimicrobial peptides.

Control strategies for the timing of intracellular events

While the timing of intracellular events is essential for many cellular processes, gene expression inside a single cell can exhibit substantial cell-to-cell variability, raising the question of how cells ensure precision in event timing despite such stochasticity. We address this question by analyzing a biologically reasonable model of gene expression in the context of first passage time (FPT), focusing on two experimentally measurable statistics: mean FPT (MFPT) and timing variability (TV). We show that (1) transcriptional burst size (BS) and burst frequency (BF) can minimize the TV; (2) translational BS monotonically reduces the MFPT to a nonzero low bound; (3) the timescale of promoter kinetics can minimize both the MFPT and the TV, depending on the ratio of the on-switching rate over the off-switching rate; and (4) positive feedback regulation of any form can all minimize the TV, whereas negative feedback regulation of transcriptional BF or BS always enhances the TV. These control strategies can have broad implications for diverse cellular processes relying on precise temporal triggering of events.

Overview of the Antimicrobial Compounds Produced by Members of the Bacillus subtilis Group

Over the last seven decades, applications using members of the Bacillus subtilis group have emerged in both food processes and crop protection industries. Their ability to form survival endospores and the plethora of antimicrobial compounds they produce has generated an increased industrial interest as food preservatives, therapeutic agents and biopesticides. In the growing context of food biopreservation and biological crop protection, this review suggests a comprehensive way to visualize the antimicrobial spectrum described within the B. subtilis group, including volatile compounds. This classification distinguishes the bioactive metabolites based on their biosynthetic pathways and chemical nature: i.e., ribosomal peptides (RPs), volatile compounds, polyketides (PKs), non-ribosomal peptides (NRPs), and hybrids between PKs and NRPs. For each clade, the chemical structure, biosynthesis and antimicrobial activity are described and exemplified. This review aims at constituting a convenient and updated classification of antimicrobial metabolites from the B. subtilis group, whose complex phylogeny is prone to further development.

Genome-guided identification of novel head-to-tail cyclized antimicrobial peptides, exemplified by the discovery of pumilarin

The need for novel antibiotics in an era where antimicrobial resistance is on the rise, and the number of new approved antimicrobial drugs reaching the market is declining, is evident. The underused potential of post-translationally modified peptides for clinical use makes this class of peptides interesting candidates. In this study, we made use of the vast amounts of available genomic data and screened all publicly available prokaryotic genomes (~3000) to identify 394 novel head-to-tail cyclized antimicrobial peptides. To verify these in silico results, we isolated and characterized a novel antimicrobial peptide from Bacillus pumilus that we named pumilarin. Pumilarin was demonstrated to have a circular structure and showed antimicrobial activity against several indicator strains, including pathogens.

Thusin, a Novel Two-Component Lantibiotic with Potent Antimicrobial Activity against Several Gram-Positive Pathogens

Due to the rapidly increasing prevalence of multidrug-resistant bacterial strains, the need for new antimicrobial drugs to treat infections has become urgent. Bacteriocins, which are antimicrobial peptides of bacterial origin, are considered potential alternatives to conventional antibiotics and have attracted widespread attention in recent years. Among these bacteriocins, lantibiotics, especially two-component lantibiotics, exhibit potent antimicrobial activity against some clinically relevant Gram-positive pathogens and have potential applications in the pharmaceutical industry. In this study, we characterized a novel two-component lantibiotic termed thusin that consists of Thsα, Thsβ, and Thsβ' (mutation of Thsβ, A14G) and that was isolated from a B. thuringiensis strain BGSC 4BT1. Thsα and Thsβ (or Thsβ') exhibit optimal antimicrobial activity at a 1:1 ratio and act sequentially to affect target cells, and they are all highly thermostable (100°C for 30 min) and pH tolerant (pH 2.0 to 9.0). Thusin shows remarkable efficacy against all tested Gram-positive bacteria and greater activities than two known lantibiotics thuricin 4A-4 and ticin A4, and one antibiotic vancomycin against various bacterial pathogens (Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus (MRSA), Staphylococcus sciuri, Enterococcus faecalis, and Streptococcus pneumoniae). Moreover, thusin is also able to inhibit the outgrowth of B. cereus spores. The potent antimicrobial activity of thusin against some Gram-positive pathogens indicates that it has potential for the development of new drugs.

Class I and Class II Lanthipeptides Produced by Bacillus spp

The increasing number of multidrug-resistant pathogens, along with the small number of new antimicrobials under development, leads to an increased need for novel alternatives. Class I and class II lanthipeptides (also known as lantibiotics) have been considered promising alternatives to classical antibiotics. In addition to their relevant medical applications, they are used as probiotics, prophylactics, preservatives, and additives in cosmetics and personal-care products. The genus Bacillus is a prolific source of bioactive compounds including ribosomally and nonribosomally synthesized antibacterial peptides. Accordingly, there is significant interest in the biotechnological potential of members of the genus Bacillus as producers of antimicrobial lanthipeptides. The present review focuses on aspects of the biosynthesis, gene cluster organization, structure, antibacterial spectrum, and bioengineering approaches of lanthipeptides produced by Bacillus strains. Their efficacy and potency against some clinically relevant strains, including MRSA and VRE, are also discussed. Although no lanthipeptides are currently in clinical use, the information herein highlights the potential of these compounds.

Development of a homologous expression system for and systematic site-directed mutagenesis analysis of thurincin H, a bacteriocin produced by Bacillus thuringiensis SF361

Thurincin H is an antimicrobial peptide produced by Bacillus thuringiensis SF361. With a helical back bone, the 31 amino acids of thurincin H form a hairpin structure maintained by four pairs of very unique sulfur-to-α-carbon thioether bonds. The production of thurincin H depends on a putative gene cluster containing 10 open reading frames. The gene cluster includes three tandem structural genes (thnA1, thnA2, and thnA3) encoding three identical 40-amino-acid thurincin H prepeptides and seven other genes putatively responsible for prepeptide processing, regulation, modification, exportation, and self-immunity. A homologous thurincin H expression system was developed by transforming a thurincin H-deficient host with a novel expression vector, pGW133. The host, designated B. thuringiensis SF361 ΔthnA1 ΔthnA2 ΔthnA3, was constructed by deletion of the three tandem structural genes from the chromosome of the natural thurincin H producer. The thurincin H expression vector pGW133 was constructed by cloning the thurincin H native promoter, thnA1, and a Cry protein terminator into the Escherichia coli-B. thuringiensis shuttle vector pHT315. Thirty-three different pGW133 variants, each containing a different point mutation in the thnA1 gene, were generated and separately transformed into B. thuringiensis SF361 ΔthnA1 ΔthnA2 ΔthnA3. Those site-directed mutants contained either a single radical or conservative amino acid substitution on the thioether linkage-forming positions or a radical substitution on all other nonalanine amino acids. The bacteriocin activities of B. thuringiensis SF361 ΔthnA1 ΔthnA2 ΔthnA3 carrying different pGW133 variants against three different indicator strains were subsequently compared.

The Bacillus cereus group is an excellent reservoir of novel lanthipeptides

Lantibiotics are ribosomally synthesized peptides that contain multiple posttranslational modifications. Research on lantibiotics has increased recently, mainly due to their broad-spectrum antimicrobial activity, especially against some clinical Gram-positive pathogens. Many reports about various bacteriocins in the Bacillus cereus group have been published, but few were about lantibiotics. In this study, we identified 101 putative lanthipeptide gene clusters from 77 out of 223 strains of this group, and these gene clusters were further classified into 20 types according to their gene organization and the homologies of their functional genes. Among them, 18 types were novel and have not yet been experimentally verified. Two novel lantibiotics (thuricin 4A-4 and its derivative, thuricin 4A-4D) were identified in the type I-1 lanthipeptide gene cluster and showed activity against all tested Gram-positive bacteria. The mode of action of thuricin 4A-4 was studied, and we found that it acted as a bactericidal compound. The transcriptional analysis of four structural genes (thiA1, thiA2, thiA3, and thiA4) in the thuricin 4A gene cluster showed that only one structural gene, thiA4, showed efficient transcription in the exponential growth phase; the other three structural genes did not. In addition, the putative transmembrane protein ThiI was responsible for thuricin 4A-4 immunity. Genome analysis and functional verification illustrated that B. cereus group strains were a prolific source of novel lantibiotics.

Synthesis and succinylation of subtilin-like lantibiotics are strongly influenced by glucose and transition state regulator AbrB

Subtilin and the closely related entianin are class I lantibiotics produced by different subspecies of Bacillus subtilis. Both molecules are ribosomally synthesized peptide antibiotics with unusual ring structures. Subtilin-like lantibiotics develop strong antibiotic activities against various Gram-positive organisms with an efficiency similar to that of nisin from Lactococcus lactis. In contrast to nisin, subtilin-like lantibiotics partially undergo an additional posttranslational modification, where the N-terminal tryptophan residue becomes succinylated, resulting in drastically reduced antibiotic activities. A highly sensitive high-performance liquid chromatography (HPLC)-based quantification method enabled us to determine entianin and succinylated entianin (S-entianin) concentrations in the supernatant during growth. We show that entianin synthesis and the degree of succinylation drastically change with culture conditions. In particular, increasing glucose concentrations resulted in higher entianin amounts and lower proportions of S-entianin in Landy-based media. In contrast, no succinylation was observed in medium A with 10% glucose. Interestingly, glucose retarded the expression of entianin biosynthesis genes. Furthermore, deletion of the transition state regulator AbrB resulted in a 6-fold increased entianin production in medium A with 10% glucose. This shows that entianin biosynthesis in B. subtilis is strongly influenced by glucose, in addition to its regulation by the transition state regulator AbrB. Our results suggest that the mechanism underlying the succinylation of subtilin-like lantibiotics is enzymatically catalyzed and occurs in the extracellular space or at the cellular membrane.

The presence of sboA and spaS genes and antimicrobial peptides subtilosin A and subtilin among Bacillus strains of the Amazon basin

This report demonstrates the usefulness of PCR for the genes spaS and sboA as a means of identifying Bacillus strains with a potential to produce subtilin and subtilosin A. One collection strain and five Bacillus spp. isolated from aquatic environments in the Amazon basin were screened by PCR using primers for sboA and spaS designed specifically for this study. The sequences of the PCR products showed elevated homology with previously described spaS and sboA genes. Antimicrobial peptides were isolated from culture supernatants and analyzed by mass spectrometry. For all samples, the mass spectra revealed clusters with peaks at m/z 3300-3500 Da, corresponding to subtilosin A, subtilin and isoforms of these peptides. These results suggest that the antimicrobial activity of these strains may be associated with the production of subtilosin A and/or subtilin. The PCR used here was efficient in identifying novel Bacillus strains with the essential genes for producing subtilosin A and subtilin.

Characterization of an antimicrobial peptide produced by Bacillus subtilis subsp. spizezinii showing inhibitory activity towards Haemophilus parasuis

Haemophilus parasuis is the pathogen that causes Glässer's disease, a major illness affecting young pigs. The aim of this work was to investigate the antagonistic activity of antimicrobial substances produced by Bacillus species against H. parasuis. Among the tested strains, only Bacillus subtilis ATCC 6633 inhibited H. parasuis growth. The antibacterial substance was purified by ammonium sulfate precipitation, gel filtration chromatography on Sephadex G-50 and ion-exchange chromatography on DEAE-cellulose. The purification was about 100-fold with a yield of 0.33 %. The purified substance was resistant up to 80 °C and pH ranging 3-7, but the substance lost its activity when it was treated with proteases. The peptide had a molecular mass of 1083 Da and its sequence was determined by MS as NRWCFAGDD, which showed no homology with other known antimicrobial peptides. The complete inhibition of H. parasuis growth was observed at 20 µg peptide ml(-1) after 20 min of exposure. The peptide obtained by chemical synthesis also showed antimicrobial activity on H. parasuis. The identification of antimicrobial substances that can be effective against H. parasuis is very relevant to combat this pathogen that causes important losses in swine production.

Strategies to improve the bacteriocin protection provided by lactic acid bacteria

Lactic acid bacteria (LAB) produce a wide variety of antimicrobial peptides (bacteriocins) which contribute to the safety and preservation of fermented foods. This review discusses strategies that have been or could be employed to further enhance the commercial application of bacteriocins and/or bacteriocin-producing LAB for food use.

Synergistic effects of probiotic Leuconostoc mesenteroides and Bacillus subtilis in malted ragi (Eleucine corocana) food for antagonistic activity against V. cholerae and other beneficial properties

Finger millet (Elucine corocana), locally known as ragi, and probiotics have been recognized for their health benefits. In the present work we describe novel probiotic ragi malt (functional food) that has been prepared using ragi and probiotic Leuconostoc mesenteroides (Lm) and Bacillus subtilis natto (Bs), alone and in combination, for antagonistic activity against Vibrio cholerae (Vc). In vitro studies using pure cultures showed that each probiotic strain (Lm or Bs) was able to inhibit the planktonic growth of Vc as well as its ability to make biofilms and adhere to extracellular matrix proteins (fibronectin, Fn) that may function in vivo as initial ports of entrance of the pathogen. Interestingly, the combination of both probiotic strains (Lm plus Bs) produced the strongest activity against the Vc. When both cultures were used together in the ragi malt the antimicrobial activity against Vc was enhanced due to synergistic effect of both probiotic strains. The inclusion of both probiotic strains in the functional food produced higher amounts of beneficial fatty acids like linoleic and linolenic acid and increased the mineral content (iron and zinc). The viability and activity of Lm and Bs against Vc was further enhanced with the use of adjuvants like ascorbic acid, tryptone, cysteine hydrochloride and casein hydrolysate in the ragi malt. In sum, the intake of probiotic ragi malt supplemented with Lm and Bs may provide nutrition, energy, compounds of therapeutic importance and antagonistic activity against Vc to a large extent to the consumer.

Enhanced production of nukacin D13E in Lactococcus lactis NZ9000 by the additional expression of immunity genes

Nukacin D13E (D13E) is a variant of type-A(II) lantibiotic nukacin ISK-1 produced by Staphylococcus warneri ISK-1. D13E exhibited a twofold higher specific antimicrobial activity than nukacin ISK-1 against a number of Gram-positive bacteria. We previously reported the heterologous production of D13E in Lactococcus lactis NZ9000 under the control of nisin-controlled gene expression system. In this study, we demonstrated enhanced production of D13E by the additional expression of immunity genes, nukFEG. The nukacin ISK-1 immunity, conferred by the ABC transporter complex, NukFEG, and the lantibiotic-binding protein, NukH, was not overwhelmed by D13E. The additional NukFEG resulted in a fourfold increase in the immunity level of the strain and a 5.2-fold increase in D13E production. The additional NukFEGH-expressing strain with the highest D13E immunity showed reduced level of production. Further improvement in D13E production was achieved by using pH-controlled batch fermentation.

The Lcn972 bacteriocin-encoding plasmid pBL1 impairs cellobiose metabolism in Lactococcus lactis

pBL1 is a Lactococcus lactis theta-replicating 10.9-kbp plasmid that encodes the synthetic machinery of the bacteriocin Lcn972. In this work, the transcriptomes of exponentially growing L. lactis strains with and without pBL1 were compared. A discrete response was observed, with a total of 10 genes showing significantly changed expression. Upregulation of the lactococcal oligopeptide uptake (opp) system was observed, which was likely linked to a higher nitrogen demand required for Lcn972 biosynthesis. Strikingly, celB, coding for the membrane porter IIC of the cellobiose phosphoenolpyruvate-dependent phosphotransferase system (PTS), and the upstream gene llmg0186 were downregulated. Growth profiles for L. lactis strains MG1363, MG1363/pBL1, and MG1363 ΔcelB grown in chemically defined medium (CDM) containing cellobiose confirmed slower growth of MG1363/pBL1 and MG1363 ΔcelB, while no differences were observed with growth on glucose. The presence of pBL1 shifted the fermentation products toward a mixed acid profile and promoted substantial changes in intracellular pool sizes for glycolytic intermediates in cells growing on cellobiose as determined by high-pressure liquid chromatography (HPLC) and nuclear magnetic resonance (NMR). Overall, these data support the genetic evidence of a constriction in cellobiose uptake. Notably, several cell wall precursors accumulated, while other UDP-activated sugar pools were lower, which could reflect rerouting of precursors toward the production of structural or storage polysaccharides. Moreover, cells growing slowly on cellobiose and those lacking celB were more tolerant to Lcn972 than cellobiose-adapted cells. Thus, downregulation of celB could help to build up a response against the antimicrobial activity of Lcn972, enhancing self-immunity of the producer cells.

Validation of the intact zwittermicin A biosynthetic gene cluster and discovery of a complementary resistance mechanism in Bacillus thuringiensis

Zwittermicin A (ZmA) is a hybrid polyketide-nonribosomal peptide produced by certain Bacillus cereus group strains. It displays broad-spectrum antimicrobial activity. Its biosynthetic pathway in B. cereus has been proposed through analysis of the nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) modules involved in ZmA biosynthesis. In this study, we constructed a bacterial artificial chromosome (BAC) library from Bacillus thuringiensis subsp. kurstaki strain YBT-1520 genomic DNA. The presence of known genes involved in the biosynthesis of ZmA in this BAC library was investigated by PCR techniques. Nine positive clones were identified, two of which (covering an approximately 60-kb region) could confer ZmA biosynthesis ability upon B. thuringiensis BMB171 after simultaneous transfer into this host by two compatible shuttle BAC vectors. Another previously unidentified gene cluster, named zmaWXY, was found to improve the yield of ZmA and was experimentally defined to function as a ZmA resistance transporter which expels ZmA from the cells. Putative transposase genes were detected on the flanking regions of the two gene clusters (the ZmA synthetic cluster and zmaWXY), which suggests a mobile nature of these two gene clusters. The intact ZmA gene cluster was validated, and a resistance mechanism complementary to that for zmaR (the previously identified ZmA self-resistance gene) was revealed. This study also provided a straightforward strategy to isolate and identify a huge gene cluster from Bacillus.

Entianin, a novel subtilin-like lantibiotic from Bacillus subtilis subsp. spizizenii DSM 15029T with high antimicrobial activity

Lantibiotics, such as nisin and subtilin, are lanthionine-containing peptides that exhibit antimicrobial as well as pheromone-like autoinducing activity. Autoinduction is specific for each lantibiotic, and reporter systems for nisin and subtilin autoinduction are available. In this report, we used the previously reported subtilin autoinduction bioassay in combination with mass spectrometric analyses to identify the novel subtilin-like lantibiotic entianin from Bacillus subtilis subsp. spizizenii DSM 15029(T). Linearization of entianin using Raney nickel-catalyzed reductive cleavage enabled, for the first time, the use of tandem mass spectrometry for the fast and efficient determination of an entire lantibiotic primary structure, including posttranslational modifications. The amino acid sequence determined was verified by DNA sequencing of the etnS structural gene, which confirmed that entianin differs from subtilin at 3 amino acid positions. In contrast to B. subtilis ATCC 6633, which produces only small amounts of unsuccinylated subtilin, B. subtilis DSM 15029(T) secretes considerable amounts of unsuccinylated entianin. Entianin was very active against several Gram-positive pathogens, such as Staphylococcus aureus and Enterococcus faecalis. The growth-inhibiting activity of succinylated entianin (S-entianin) was much lower than that of unsuccinylated entianin: a 40-fold higher concentration was required for inhibition. For succinylated subtilin (S-subtilin), a concentration 100-fold higher than that of unsuccinylated entianin was required to inhibit the growth of a B. subtilis test strain. This finding was in accordance with a strongly reduced sensing of cellular envelope stress provided by S-entianin relative to that of entianin. Remarkably, S-entianin and S-subtilin showed considerable autoinduction activity, clearly demonstrating that autoinduction and antibiotic activity underlie different molecular mechanisms.

Maturation and processing of SpaI, the lipoprotein involved in subtilin immunity in Bacillus subtilis ATCC 6633

SpaI is a small lipoprotein that provides Bacillus subtilis with autoimmunity against the lantibiotic subtilin. We have investigated the maturation of SpaI through the lipoprotein biosynthesis pathway, and analyzed the consequences of maturations in the acylation of the target lipobox in subtilin immunity. Further specificity of lipid acylation of the cysteine within the conserved sequence of the candidate lipobox (LSAC) was studied by site-directed mutagenesis. The mutants LSAA and LSCA blocked lipid attachment to the SpaI protein. Cell-wall stress-sensing B. subtilis BSF 2470 was exploited to study the function of each mutant upon heterologous expression. This system allowed the monitoring of beta-galactosidase activity to the added subtilin at a sublethal dose. Mutants exhibited 2-fold reduction in beta-Gal activity, suggesting their contribution in subtilin autoimmunity.

Continuous nisin production with bioengineered Lactococcus lactis strains

Nisin production in continuous cultures of bioengineered Lactococcus lactis strains that incorporate additional immunity and regulation genes was studied. Highest nisin activities were observed at 0.2 h(-1) dilution rate and 12.5 g l(-1) fructose concentration for all strains. Recombinant strains were able to produce greater amounts of nisin at dilution rates below 0.3 h(-1) compared to the control strain. However, this significant difference disappeared at dilution rates of 0.4 and 0.5 h(-1). For the strains LL27, LAC338, LAC339, and LAC340, optimum conditions for nisin production were determined to be at 0.29, 0.26, 0.27, and 0.27 h(-1) dilution rates and 11.95, 12.01, 11.63, and 12.50 g l(-1) fructose concentrations, respectively. The highest nisin productivity, 496 IU ml(-1) h(-1), was achieved with LAC339. The results of this study suggest that low dilution rates stabilize the high specific nisin productivity of the bioengineered strains in continuous fermentation. Moreover, response surface methodology analysis showed that regulation genes yielded high nisin productivity at wide ranges of dilution rates and fructose concentrations.

Metabolic engineering of microorganisms: general strategies and drug production

Many drugs and drug precursors found in natural organisms are rather difficult to synthesize chemically and to extract in large amounts. Metabolic engineering is playing an increasingly important role in the production of these drugs and drug precursors. This is typically achieved by establishing new metabolic pathways leading to the product formation, and enforcing or removing the existing metabolic pathways toward enhanced product formation. Recent advances in system biology and synthetic biology are allowing us to perform metabolic engineering at the whole cell level, thus enabling optimal design of a microorganism for the efficient production of drugs and drug precursors. In this review, we describe the general strategies for the metabolic engineering of microorganisms for the production of drugs and drug precursors. As successful examples of metabolic engineering, the approaches taken toward strain development for the production of artemisinin, an antimalarial drug, and benzylisoquinoline alkaloids, a family of antibacterial and anticancer drugs, are described in detail. Also, systems metabolic engineering of Escherichia coli for the production of L-valine, an important drug precursor, is showcased as an important strategy of future metabolic engineering effort.

Microtiter plate bioassay to monitor the interference of antibiotics with the lipid II cycle essential for peptidoglycan biosynthesis

Specific drug-sensing systems that coordinate appropriate genetic responses assure the survival of microorganisms in the presence of antibiotics. We report on the development and application of a microtiter plate-based bioassay for the identification of antibiotics interfering with the lipid II cycle essential for peptidoglycan biosynthesis. A Bacillus subtilis reporter strain sensing specifically lipid II - interfering cell wall biosynthesis stress (T. Mascher, S.L. Zimmer, T.-A. Smith and J. Helmann, Antibiotic-inducible promoter regulated by the cell envelope stress-sensing two-component system LiaRS of Bacillus subtilis; Antimicrob. Agents Chemother., Vol 48 (2004) pp. 2888-2896) was analyzed in the presence of different lantibiotics. We could show dose-dependent cell wall biosynthesis stress of reporter cells in response to the action of the lantibiotics subtilin produced by B. subtilis, epidermin and gallidermin of Staphylococcus epidermidis or S. gallinarum, respectively, in both, agar-plate and liquid culture-based assays. Surprisingly, also cinnamycin of Streptomyces cinnamoneus cinnamoneus), previously known to bind specifically to phosphatidylethanolamin of biological membranes, provoked strong cell wall biosynthetic stress. Our results show that our system can be used for screening purposes, for example to discover novel inhibitors of cell wall biosynthesis.

Whole-cell matrix-assisted laser desorption/ionization mass spectrometry for rapid identification of bacteriocin/lantibiotic-producing bacteria

The potential of whole-cell matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) for the discovery of microorganisms that produce lantibiotics and/or bacteriocins in the mass range 3-5 kDa is demonstrated. Cells of the antibiotic-producing model strain Bacillus subtilis ATCC 6633 were grown on Landy agar plates, and prepared with a 9:1 mixture of 2,5-dihydroxybenzoic acid and 2-hydroxy-5-methoxybenzoic acid (DHBs) as matrix using the bottom-layer method. Time-course analyses showed that cells grown for 1-2 days on agar plates gave the best results in terms of intensity of the bacteriocin/lantibiotic signals. Even after storage of matrix-crystal-embedded cells for several days high-resolution spectra (>10,000) could be obtained. To verify the applicability of this technique, different Bacillus wild-type and gene deletion mutant cells were analyzed. In most of the cases the known antibiotic phenotype of the producer could be corroborated by whole-cell MALDI-TOFMS, particularly for the lantibiotics subtilin and ericin. The preparation recipe for whole-cell analysis by MALDI-TOF was also highly sensitive for hydrophobic lipopeptide antibiotics like surfactin, mycosubtilin, fengycin, and bacillomycin in the lower mass range (1-1.5 kDa).

Lantibiotics: peptides of diverse structure and function

The current need for antibiotics with novel target molecules has coincided with advances in technical approaches for the structural and functional analysis of the lantibiotics, which are ribosomally synthesized peptides produced by gram-positive bacteria. These peptides have antibiotic or morphogenetic activity and are structurally defined by the presence of unusual amino acids introduced by posttranslational modification. Lantibiotics are complex polycyclic molecules formed by the dehydration of select Ser and Thr residues and the intramolecular addition of Cys thiols to the resulting unsaturated amino acids to form lanthionine and methyllanthionine bridges, respectively. Importantly, the structural and functional diversity of the lantibiotics is much broader than previously imagined. Here we discuss this growing collection of molecules and introduce some recently discovered peptides, review advances in enzymology and protein engineering, and discuss the regulatory networks that govern the synthesis of the lantibiotics by the producing organisms.

Development and application of a microtiter plate-based autoinduction bioassay for detection of the lantibiotic subtilin

Production of the lantibiotic subtilin in Bacillus subtilis ATCC 6633 is regulated in a quorum sensing-like mechanism with subtilin acting as autoinducer and signal transduction via the subtilin-specific two-component regulation system SpaRK. Here, we report the construction and application of a subtilin reporter strain in which subtilin induced lacZ gene expression in a B. subtilis ATCC 6633 spaS gene deletion mutant is monitored and visualized by the beta-galactosidase in a chromogenic plate assay. A quantitative microtiter plate subtilin bioassay was developed and optimized. Maximal sensitivity of the system was achieved after 6 h of incubation of the reporter strain together with subtilin in a medium containing 300 mM NaCl. This sensitive and unsusceptible method was applied to identify subtilin producing B. subtilis wild type strains from both, culture collections and soil samples. The B. subtilis lantibiotic ericin S with four amino acid exchanges compared to subtilin induces the subtilin reporter strain, in contrast to the structurally closely related Lactococcus lactis lantibiotic nisin. These observations suggest a certain substrate specificity of the histidine kinase SpaK, which however, also would allow the identification of subtilin-isoform producing microorganisms.

Overproduction of wild-type and bioengineered derivatives of the lantibiotic lacticin 3147

Lacticin 3147 is a broad-spectrum two-peptide lantibiotic whose genetic determinants are located on two divergent operons on the lactococcal plasmid pMRC01. Here we introduce each of 14 subclones, containing different combinations of lacticin 3147 genes, into MG1363 (pMRC01) and determine that a number of them can facilitate overproduction of the lantibiotic. Based on these studies it is apparent that while the provision of additional copies of genes encoding the biosynthetic/production machinery and the regulator LtnR is a requirement for high-level overproduction, the presence of additional copies of the structural genes (i.e., ltnA1A2) is not.