Characterization of the Vibrio cholerae El Tor lipase operon lipAB and a protease gene downstream of the hly region

Draft-genome analysis provides insights into the virulence properties and genome plasticity of Vibrio fluvialis organisms isolated from shrimp farms and Turag river in Bangladesh

Vibrio fluvialis is an opportunistic waterborne and seafood-borne enteric pathogen capable of causing severe diarrhea leading to death. This pathogen is endemic to Bangladesh, a country which is a major producer of cultured shrimp and wild-caught prawns. In this study, we carried out whole-genome sequencing of three V. fluvialis organisms isolated from shrimp farm and river sediment showing strong pathogenic characteristics in vivo and in vitro and compared their genomes against other V. fluvialis and related pathogenic species to glean insights into their potential as pathogens. Numerous virulence-associated genes including hemolysins, cytolysins, three separate Type IV pili, Types II and VI secretion systems, biofilm, and the V. cholerae pathogenesis regulating gene, toxR, were identified. Moreover, we found strain S-10 to have the propensity to acquire antibiotic resistance genes through horizontal gene transfer. These findings indicate that shrimp farms and rivers could be potential sources of V. fluvialis organisms which are an infection threat of public health concern.

Black pepper and tarragon essential oils suppress the lipolytic potential and the type II secretion system of P. psychrophila KM02

Given the increasing consumer demand for raw, nonprocessed, safe, and long shelf-life fish and seafood products, research concerning the application of natural antimicrobials as alternatives to preservatives is of great interest. The aim of the following paper was to evaluate the effect of essential oils (EOs) from black pepper (BPEO) and tarragon (TEO), and their bioactive compounds: limonene (LIM), β-caryophyllene (CAR), methyl eugenol (ME), and β-phellandrene (PHE) on the lipolytic activity and type II secretion system (T2SS) of Pseudomonas psychrophila KM02 (KM02) fish isolates grown in vitro and in fish model conditions. Spectrophotometric analysis with the p-NPP reagent showed inhibition of lipolysis from 11 to 46%. These results were confirmed by RT-qPCR, as the expression levels of lipA, lipB, and genes encoding T2SS were also considerably decreased. The supplementation of marinade with BPEO and TEO contributed to KM02 growth inhibition during vacuum packaging of salmon fillets relative to control samples. Whole-genome sequencing (WGS) provided insight into the spoilage potential of KM02, proving its importance as a spoilage microorganism whose metabolic activity should be inhibited to maintain the quality and safety of fresh fish in the food market.

Occurrence of Virulence and Antimicrobial Resistance Determinants in Vibrio harveyi Isolated from Marine Food Fish Cultured in Korea

Vibrio harveyi is a significant cause of infection in both marine animals and humans. It has been reported frequently in seafood-borne infections worldwide. This study was conducted to determine the potential health impact of the V. harveyi isolated from marine food fish cultured in Korea concerning their virulence and antimicrobial resistance. A total of 49 V. harveyi samples were isolated by biochemical tests and multiplex PCR. Phenotypic detection of virulence factors resulted DNase activity (81.63%), hemolysis (α = 75.51% and β = 12.25), gelatinase activity (71.43%), protease production (71.43%), phospholipase activity (65.31%), and lipase production (34.69%). Virulence genes, including VPI, tlh, tdh, toxR, VAC, and ctxAB, were detected in 57.14%, 44.90%, 36.73%, 22.45%, 12.24%, and 8.16% of the isolates, respectively. Resistance to ampicillin (77.55%), oxacillin (69.39%), nalidixic acid (53.06%), amoxicillin (46.94%), oxytetracycline (46.94%), colistin sulfate (34.69%), fosfomycin (34.69%), chloramphenicol (32.65%), streptomycin (32.65%), cephalothin (28.57%), oxytetracycline (26.53%), ceftriaxone (20.41%), erythromycin (14.29%), and cefoxitin (12.24%) was detected in disc diffusion assay. Most of the isolates were classified as multidrug resistant as they scored multiple antimicrobial resistance index ≥0.2. Furthermore, antimicrobial resistance genes tetB, qnrA, intI1 (Class 1 integron integrase), aac(6')-Ib, bla_SHV, bla_CTX-M, strA-strB, tetA, aphAI-IAB, qnrC, qnrS, and bla_TEM were found in 81.63%, 67.35%, 61.22%, 46.94%, 44.90%, 44.90%, 36.73%, 18.37%, 10.20%, 10.20%, 8.16% and 6.12% of the isolates, respectively. In conclusion, the development of antimicrobial resistance among V. harveyi will ultimately reduce the efficacy of antimicrobials used for treating and can favor the development of more virulent V. harveyi strains.

Immune Inhibitor A Metalloproteases Contribute to Virulence in Bacillus Endophthalmitis

Endophthalmitis is a devastating infection that can cause blindness. Over half of Bacillus endophthalmitis cases result in significant loss of useful vision. Bacillus produces many virulence factors that may contribute to retinal damage and robust inflammation. We analyzed Bacillus immune inhibitor A (InhA) metalloproteases in the context of this disease, hypothesizing that InhAs contribute to Bacillus intraocular virulence and inflammation. We analyzed phenotypes and infectivity of wild type (WT), InhA1-deficient (ΔinhA1), InhA2-deficient (ΔinhA2), or InhA1, A2, and A3-deficient (ΔinhA1-3) Bacillus thuringiensis. In vitro analysis of growth, proteolysis, and cytotoxicity were compared. WT and InhA mutants were similarly cytotoxic to retinal cells. Mutants ΔinhA1 and ΔinhA2 entered log phase growth earlier than WT. Proteolysis by the ΔinhA1-3 mutant was decreased, but this strain grew similar to WT in vitro. Experimental endophthalmitis was initiated by intravitreally infecting C57BL/6J mice with 200 CFU of B. thuringiensis WT or InhA mutants. Eyes were analyzed for intraocular Bacillus and myeloperoxidase concentrations, retinal function loss, and gross histological changes. Eyes infected with ΔinhA1 or ΔinhA2 strains contained greater numbers of bacteria than eyes infected with WT throughout the infection course. Eyes infected with single mutants had inflammation and retinal function loss similar to eyes infected with WT strain. Eyes infected with ΔinhA1-3 cleared the infection. RT-PCR results suggested that there may be compensatory expression of the other InhAs in the single InhA mutant. These results indicate that together, the InhA metalloproteases contribute to the severity of infection and inflammation in Bacillus endophthalmitis.

Microbial lipases and their industrial applications: a comprehensive review

Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.

New facet of non-O1/non-O139 Vibrio cholerae hemolysin A: a competitive factor in the ecological niche

Different serogroups of Vibrio cholerae may inhabit the same ecological niche. However, serogroup O1/O139 strains are rarely isolated from their ecological sources. Quite plausibly, the non-O1/non-O139 vibrios and other bacterial species suppress growth of O1/O139 strains that share the same niche. Our bacterial inhibition assay data indicated that certain non-O1/non-O139 strains used a contact-dependent type VI secretion system (T6SS) to suppress growth of the O1 El Tor, N16961 pandemic strain. Comparative proteomics of the O1 and the suppressive non-O1/non-O139 strains co-cultured in a simulated natural aquatic microcosm showed that SecB and HlyD were upregulated in the latter. The HlyD-related effective factor was subsequently found to be hemolysin A (HlyA). However, not all hlyA-positive non-O1/non-O139 strains mediated growth suppression of the N16961 V. cholerae; only strains harboring intact cluster I HlyA could exert this activity. The key feature of the HlyA is located in the ricin-like lectin domain (β-trefoil) that plays an important role in target cell binding. In conclusion, the results of this study indicated that non-O1/non-O139 V. cholerae suppressed the growth of the O1 pandemic strain by using contact-dependent T6SS as well as by secreting the O1-detrimental hemolysin A during their co-persistence in the aquatic habitat.

Molecular insights into Vibrio cholerae's intra-amoebal host-pathogen interactions

Vibrio cholerae, which causes the diarrheal disease cholera, is a species of bacteria commonly found in aquatic habitats. Within such environments, the bacterium must defend itself against predatory protozoan grazers. Amoebae are prominent grazers, with Acanthamoeba castellanii being one of the best-studied aquatic amoebae. We previously showed that V. cholerae resists digestion by A. castellanii and establishes a replication niche within the host's osmoregulatory organelle. In this study, we decipher the molecular mechanisms involved in the maintenance of V. cholerae's intra-amoebal replication niche and its ultimate escape from the succumbed host. We demonstrate that minor virulence features important for disease in mammals, such as extracellular enzymes and flagellum-based motility, have a key role in the replication and transmission of V. cholerae in its aqueous environment. This work, therefore, describes new mechanisms that provide the pathogen with a fitness advantage in its primary habitat, which may have contributed to the emergence of these minor virulence factors in the species V. cholerae.

Acinetobacter: an emerging pathogen with a versatile secretome

Acinetobacter baumannii is a notorious pathogen that has emerged as a healthcare nightmare in recent years because it causes serious infections that are associated with high morbidity and mortality rates. Due to its exceptional ability to acquire resistance to almost all available antibiotics, A. baumannii is currently ranked as the first pathogen on the World Health Organization’s priority list for the development of new antibiotics. The versatile range of effectors secreted by A. baumannii represents a large proportion of the virulence arsenal identified in this bacterium to date. Thus, these factors, together with the secretory machinery responsible for their extrusion into the extracellular milieu, are key targets for novel therapeutics that are greatly needed to combat this deadly pathogen. In this review, we provide a comprehensive, up-to-date overview of the organization and regulatory aspects of the Acinetobacter secretion systems, with a special emphasis on their versatile substrates that could be targeted to fight the deadly infections caused by this elusive pathogen.

Flagellar motility, extracellular proteases and Vibrio cholerae detachment from abiotic and biotic surfaces

Vibrio cholerae of serogroups O1 and O139, the causative agent of Asiatic cholera, continues to be a major global health threat. This pathogen utilizes substratum-specific pili to attach to distinct surfaces in the aquatic environment and the human small intestine and detaches when conditions become unfavorable. Both attachment and detachment are critical to bacterial environmental survival, pathogenesis and disease transmission. However, the factors that promote detachment are less understood. In this study, we examine the role of flagellar motility and hemagglutinin/protease (HapA) in vibrio detachment from a non-degradable abiotic surface and from the suckling mouse intestine. Flagellar motility facilitated V. cholerae detachment from abiotic surfaces. HapA had no effect on the stability of biofilms formed on abiotic surfaces despite representing >50% of the proteolytic activity present in the extracellular matrix. We developed a balanced lethal plasmid system to increase the bacterial cyclic diguanylate (c-di-GMP) pool late in infection, a condition that represses motility and HapA expression. Increasing the c-di-GMP pool enhanced V. cholerae colonization of the suckling mouse intestine. The c-di-GMP effect was fully abolished in hapA isogenic mutants. These results suggest that motility facilitates detachment in a substratum-independent manner. Instead, HapA appears to function as a substratum-specific detachment factor.

Classification of lipolytic enzymes and their biotechnological applications in the pulping industry

In the pulp and paper industry, during the manufacturing process, the agglomeration of pitch particles (composed of triglycerides, fatty acids, and esters) leads to the formation of black pitch deposits in the pulp and on machinery, which impacts on the process and pulp quality. Traditional methods of pitch prevention and treatment are no longer feasible due to environmental impact and cost. Consequently, there is a need for more efficient and environmentally friendly approaches. The application of lipolytic enzymes, such as lipases and esterases, could be the sustainable solution to this problem. Therefore, an understanding of their structure, mechanism, and sources are essential. In this report, we review the microbial sources for the different groups of lipolytic enzymes, the differences between lipases and esterases, and their potential applications in the pulping industry.

Medically Relevant Acinetobacter Species Require a Type II Secretion System and Specific Membrane-Associated Chaperones for the Export of Multiple Substrates and Full Virulence

Acinetobacter baumannii, A. nosocomialis, and A. pittii have recently emerged as opportunistic human pathogens capable of causing severe human disease; however, the molecular mechanisms employed by Acinetobacter to cause disease remain poorly understood. Many pathogenic members of the genus Acinetobacter contain genes predicted to encode proteins required for the biogenesis of a type II secretion system (T2SS), which have been shown to mediate virulence in many Gram-negative organisms. Here we demonstrate that Acinetobacter nosocomialis strain M2 produces a functional T2SS, which is required for full virulence in both the Galleria mellonella and murine pulmonary infection models. Importantly, this is the first bona fide secretion system shown to be required for virulence in Acinetobacter. Using bioinformatics, proteomics, and mutational analyses, we show that Acinetobacter employs its T2SS to export multiple substrates, including the lipases LipA and LipH as well as the protease CpaA. Furthermore, the Acinetobacter T2SS, which is found scattered amongst five distinct loci, does not contain a dedicated pseudopilin peptidase, but instead relies on the type IV prepilin peptidase, reinforcing the common ancestry of these two systems. Lastly, two of the three secreted proteins characterized in this study require specific chaperones for secretion. These chaperones contain an N-terminal transmembrane domain, are encoded adjacently to their cognate effector, and their disruption abolishes type II secretion of their cognate effector. Bioinformatic analysis identified putative chaperones located adjacent to multiple previously known type II effectors from several Gram-negative bacteria, which suggests that T2SS chaperones constitute a separate class of membrane-associated chaperones mediating type II secretion.

Acinetobacter baumannii Is Dependent on the Type II Secretion System and Its Substrate LipA for Lipid Utilization and In Vivo Fitness

Gram-negative bacteria express a number of sophisticated secretion systems to transport virulence factors across the cell envelope, including the type II secretion (T2S) system. Genes for the T2S components GspC through GspN and PilD are conserved among isolates of Acinetobacter baumannii, an increasingly common nosocomial pathogen that is developing multidrug resistance at an alarming rate. In contrast to most species, however, the T2S genes are dispersed throughout the genome rather than linked into one or two operons. Despite this unique genetic organization, we show here that the A. baumannii T2S system is functional. Deletion of gspD or gspE in A. baumannii ATCC 17978 results in loss of secretion of LipA, a lipase that breaks down long-chain fatty acids. Due to a lack of extracellular lipase, the gspD mutant, the gspE mutant, and a lipA deletion strain are incapable of growth on long-chain fatty acids as a sole source of carbon, while their growth characteristics are indistinguishable from those of the wild-type strain in nutrient-rich broth. Genetic inactivation of the T2S system and its substrate, LipA, also has a negative impact on in vivo fitness in a neutropenic murine model for bacteremia. Both the gspD and lipA mutants are outcompeted by the wild-type strain as judged by their reduced numbers in spleen and liver following intravenous coinoculation. Collectively, our findings suggest that the T2S system plays a hitherto-unrecognized role in in vivo survival of A. baumannii by transporting a lipase that may contribute to fatty acid metabolism.

IMPORTANCE

Infections by multidrug-resistant Acinetobacter baumannii are a growing health concern worldwide, underscoring the need for a better understanding of the molecular mechanisms by which this pathogen causes disease. In this study, we demonstrated that A. baumannii expresses a functional type II secretion (T2S) system that is responsible for secretion of LipA, an extracellular lipase required for utilization of exogenously added lipids. The T2S system and the secreted lipase support in vivo colonization and thus contribute to the pathogenic potential of A. baumannii.

Histopathological and combinatorial effects of the metalloprotease InhA1 and Cry proteins of Bacillus thuringiensis against Spodoptera littoralis

The zinc metalloprotease (InhA) of Bacillus thuringiensis specifically hydrolyzes cecropins and attacins, two antibacterial peptides in the immune hemolymph of insects, leading to a high resistance of the bacteria to the humoral defense system of its host. In the present study, the inhA gene of B. thuringiensis strain BUPM28 was cloned and the nucleotide sequence analysis revealed that it was identical to that of B. thuringiensis 8010. The expressed InhA1 protein in Escherichia coli showed toxicity to neonate Spodoptera littoralis larvae with a LC50 of 2.07±0.72μg/cm(2). Study of the effect of combining Cry proteins with InhA1 showed that one improves the toxicity of the other one against S. littoralis. Investigation of the histopathological effect of this metalloprotease showed an extensive damage of S. littoralis epithelium tissue. These results provide an insight to the use of InhA as supplement to Cry toxins to improve the efficacy of B. thuringiensis formulations and to overcome possible resistance problems.

Unique and conserved genome regions in Vibrio harveyi and related species in comparison with the shrimp pathogen Vibrio harveyi CAIM 1792

Vibrio harveyi CAIM 1792 is a marine bacterial strain that causes mortality in farmed shrimp in north-west Mexico, and the identification of virulence genes in this strain is important for understanding its pathogenicity. The aim of this work was to compare the V. harveyi CAIM 1792 genome with related genome sequences to determine their phylogenic relationship and explore unique regions in silico that differentiate this strain from other V. harveyi strains. Twenty-one newly sequenced genomes were compared in silico against the CAIM 1792 genome at nucleotidic and predicted proteome levels. The proteome of CAIM 1792 had higher similarity to those of other V. harveyi strains (78%) than to those of the other closely related species Vibrio owensii (67%), Vibrio rotiferianus (63%) and Vibrio campbellii (59%). Pan-genome ORFans trees showed the best fit with the accepted phylogeny based on DNA-DNA hybridization and multi-locus sequence analysis of 11 concatenated housekeeping genes. SNP analysis clustered 34/38 genomes within their accepted species. The pangenomic and SNP trees showed that V. harveyi is the most conserved of the four species studied and V. campbellii may be divided into at least three subspecies, supported by intergenomic distance analysis. blastp atlases were created to identify unique regions among the genomes most related to V. harveyi CAIM 1792; these regions included genes encoding glycosyltransferases, specific type restriction modification systems and a transcriptional regulator, LysR, reported to be involved in virulence, metabolism, quorum sensing and motility.

Hyper-activation of foldase-dependent lipase with lipase-specific foldase

The LST-03 lipase from Pseudomonas aeruginosa LST-03 requires lipase-specific foldase for activation. Abundant expression of the active lipase was successfully accomplished with individual expression of the lipase and foldase in a heterologous host and subsequent in vitro activation. Although the activity of the native lipase from culture supernatant of P. aeruginosa LST-03 was 110 kI.U./g, that after in vitro activation using individually expressed lipase and foldase was 228 kI.U./g. Furthermore, the activity after in vitro activation with afterwards adding calcium ions was 359 kI.U./g. However, the incubation of the lipase with the foldase in the presence of calcium ions resulted in a small conformational transition and low activation levels of the lipase by the foldase. The lipase showed high affinity for the foldase in the presence of calcium ions. The results indicate that in a cellular environment that contains calcium ions, the lipase would not become a hyperactive form by the foldase.

Two ABC transporter systems participate in siderophore transport in the marine pathogen Vibrio anguillarum 775 (pJM1)

ORF40 (named fatE) in the Vibrio anguillarum pJM1 plasmid-encoding anguibactin iron transport systems is a homolog of ATPase genes involved in ferric-siderophore transport. Mutation of fatE did not affect ferric-anguibactin transport, indicating that there must be other ATPase gene(s) in addition to fatE. By searching the genomic sequence of V. anguillarum 775(pJM1), we identified a homolog of fatE named fvtE on chromosome 2. It is of interest that in this locus, we also identified homologs of fatB, fatC, and fatD that we named fvtB, fvtC and fvtD, respectively. The fvtE mutant still showed ferric-anguibactin transport, while the double fatE and fvtE mutation completely abolished the ferric-anguibactin transport indicating that fatE and fvtE are functional ATPase homologs for ferric-anguibactin transport. Furthermore, we demonstrate that fvtB, fvtC, fvtD, and fvtE are essential for ferric-vanchrobactin and ferric-enterobactin transport.

Identification of a new lipase family in the Brazilian Atlantic Forest soil metagenome

Lipases are the most investigated class of enzymes in metagenomics. Phylogenetic classification of bacterial lipases comprises eight families. Here we describe the construction and screening of three metagenomic libraries from Brazilian Atlantic Forest soil and identification of a new lipase family. The metagenomic libraries, MAF1, MAF2 and MAF3, contained 34 560, 29 280 and 36 288 clones respectively. Lipase screening on triolein-rhodamine B plates resulted in one positive clone, Lip018. The DNA insert of Lip018 was fully sequenced and 20 ORFs were identified by comparison against the GenBank. Transposon mutagenesis revealed that ORF15, similar to serine peptidases, and ORF16, a hypothetical protein, were both required for lipase activity. ORF16 has a typical lipase conserved pentapeptide G-X-S-X-G and the comparison against the Pfam database showed that ORF16 belongs to family 5 of αβ-hydrolase. Phylogenetic analyses indicated that ORF16, together with other related proteins, may be a member of a new lipase family, named LipAP, activated by a putative serine protease. Partial characterization of ORF16 lipase showed that the enzyme has activity against a broad range of p-nitrophenyl esters, but only after activation by the predicted peptidase ORF15.

Proteases produced by vibrios

Bacteria of the genus Vibrio are normal habitants of the aquatic environment but the some species are believed to be human pathogens. Pathogenic vibrios produce various pathogenic factors, and the proteases are also recognized to play pathogenic roles in the infection: the direct roles by digesting many kinds of host proteins or indirect roles by processing other pathogenic protein factors. Especially VVP from Vibrio vulnificus is thought to be a major pathogenic factor of the vibrio. Although HA/P, the V. cholerae hemagglutinin/protease, is not a direct toxic factor of cholera vibrio, its significance is an undeniable fact. Production of HA/P is regulated together with major pathogenic factors such as CT (cholera toxin) or TCP (toxin co-regulated pilus) by a quorum-sensing system. HA/P is necessary for full expression of pathogenicity of the vibrio by supporting growth and translocation in the digestive tract. Processing of protein toxins such as CT or El Tor hemolysin is also an important pathogenic role.

Putative virulence genes in Moritella viscosa: activity during in vitro inoculation and in vivo infection

Moritella viscosa is considered to be the main aetiological agent of winter ulcer disease, primarily affecting farmed salmonid fish in cold marine waters. Transcription profiles of twelve M. viscosa genes, potentially involved in the pathogenesis, were studied during the course of an in vitro cell culture infection assay. Transcription of the same genes was compared in vivo, in head kidney and ulcer tissues of Atlantic salmon challenged with M. viscosa. During the in vitro infection, three putative toxins: a putative repeats in toxin gene (rtxA), a putative cytotoxic necrotizing factor (cnf) and a putative hemolysin increased their transcription significantly with time and coincident with cell rounding. Furthermore, the majority of the genes were stimulated by presence of fish cells and showed higher activity when adhered to fish cells compared to their planktonic counterpart. In vivo gene transcription studies revealed an up-regulation of a putative lateral flagellin in ulcer compared to head kidney tissues in the same individual. A similar trend was seen for cnf and a gene encoding a putative protease, indicating a role for these factors in colonization and tissue damage.

Studies on a novel serine protease of a ΔhapAΔprtV Vibrio cholerae O1 strain and its role in hemorrhagic response in the rabbit ileal loop model

Background

Two well-characterized proteases secreted by Vibrio cholerae O1 strains are hemagglutinin protease (HAP) and V. cholerae protease (PrtV). The hapA and prtV knock out mutant, V. cholerae O1 strain CHA6.8ΔprtV, still retains residual protease activity. We initiated this study to characterize the protease present in CHA6.8ΔprtV strain and study its role in pathogenesis in rabbit ileal loop model (RIL).

Methodology/Principal Findings

We partially purified the residual protease secreted by strain CHA6.8ΔprtV from culture supernatant by anion-exchange chromatography. The major protein band in native PAGE was identified by MS peptide mapping and sequence analysis showed homology with a 59-kDa trypsin-like serine protease encoded by VC1649. The protease activity was partially inhibited by 25 mM PMSF and 10 mM EDTA and completely inhibited by EDTA and PMSF together. RIL assay with culture supernatants of strains C6709 (FA ratio 1.1+/−0.3 n = 3), CHA6.8 (FA ratio 1.08+/−0.2 n = 3), CHA6.8ΔprtV (FA ratio 1.02+/−0.2 n = 3) and partially purified serine protease from CHA6.8ΔprtV (FA ratio 1.2+/−0.3 n = 3) induced fluid accumulation and histopathological studies on rabbit ileum showed destruction of the villus structure with hemorrhage in all layers of the mucosa. RIL assay with culture supernatant of CHA6.8ΔprtVΔVC1649 strain (FA ratio 0.11+/−0.005 n = 3) and with protease incubated with PMSF and EDTA (FA ratio 0.3+/−0.05 n = 3) induced a significantly reduced FA ratio with almost complete normal villus structure.

Conclusion

Our results show the presence of a novel 59-kDa serine protease in a ΔhapAΔprtV V. cholerae O1 strain and its role in hemorrhagic response in RIL model.

Vibrio cholerae hemolysin is required for lethality, developmental delay, and intestinal vacuolation in Caenorhabditis elegans

BACKGROUND

Cholera toxin (CT) and toxin-co-regulated pili (TCP) are the major virulence factors of Vibrio cholerae O1 and O139 strains that contribute to the pathogenesis of disease during devastating cholera pandemics. However, CT and TCP negative V. cholerae strains are still able to cause severe diarrheal disease in humans through mechanisms that are not well understood.

METHODOLOGY/PRINCIPAL FINDINGS

To determine the role of other virulence factors in V. cholerae pathogenesis, we used a CT and TCP independent infection model in the nematode Caenorhabditis elegans and identified the hemolysin A (hlyA) gene as a factor responsible for animal death and developmental delay. We demonstrated a correlation between the severity of infection in the nematode and the level of hemolytic activity in the V. cholerae biotypes. At the cellular level, V. cholerae infection induces formation of vacuoles in the intestinal cells in a hlyA dependent manner, consistent with the previous in vitro observations.

CONCLUSIONS/SIGNIFICANCE

Our data strongly suggest that HlyA is a virulence factor in C. elegans infection leading to lethality and developmental delay presumably through intestinal cytopathic changes.

The InhA metalloproteases of Bacillus cereus contribute concomitantly to virulence

The virulence of Bacillus cereus requires that bacteria have the capacity to colonize their host, degrade specific tissues, and circumvent the host immune system. To study this aspect of pathogenesis, we focused on three metalloproteases, InhA1, InhA2, and InhA3, which share more than 66% identity. The expression of these metalloprotease genes was assessed by transcriptional fusions with a lacZ reporter gene. The expression profiles suggest a complementary time course of InhA production. Indeed, the genes are simultaneously expressed but are oppositely controlled during stationary phase. We constructed single and multiple inhA mutants and assessed the bacterial locations of the proteins as well as their individual or additive roles in macrophage escape and toxicity, antibacterial-peptide cleavage, and virulence. InhA1, a major component of the spore exosporium, is the only InhA metalloprotease involved in bacterial escape from macrophages. A mutant lacking inhA1, inhA2, and inhA3 shows a strong decrease in the level of virulence for insects. Taken together, these results show that the InhA metalloproteases of B. cereus are important virulence factors that may allow the bacteria to counteract the host immune system.

Components of the E. coli envelope are affected by and can react to protein over-production in the cytoplasm

Background

Protein over-expression in bacteria is still the easiest, cheapest and therefore preferred way to obtain large amounts of proteins for industrial and laboratory scale preparations. Several studies emphasized the importance of understanding cellular and molecular mechanisms triggered by protein over-production in order to obtain higher yield and better quality of the recombinant product. Almost every step leading to a fully functional polypeptide has been investigated, from mRNA stability to the role of molecular chaperones, from aggregation to bottlenecks in the secretory pathway. In this context, we focused on the still poorly addressed relationship between protein production in the cytoplasm and the bacterial envelope, an active and reactive cell compartment that controls interactions with the environment and several major cellular processes. Results available to date show that the accumulation of foreign proteins in the cytoplasm induces changes in the membrane lipids and in the levels of mRNAs for some membrane proteins. However, a direct connection between membrane protein expression levels and soluble/aggregated protein accumulation in the cytoplasm has never been reported.

Results

By the use of a combined physiological and proteomic approach, we investigated the effects on the cell membrane of E. coli of the overexpression of two recombinant proteins, the B. cepacia lipase (BCL) and the green fluorescent protein (GFP). Both polypeptides are expressed in the cytoplasm at similar levels but GFP is fully soluble whereas inactive BCL accumulates in inclusion bodies.

Growth and viability of the transformed cells were tested in the presence of different drugs. We found that chloramphenycol preferentially inhibited the strain over-producing GFP while SDS was more effective when BCL inclusion bodies accumulated in the cytoplasm. In contrast, both proteins induced a similar response in the membrane proteome, i.e. increased levels of LamB, OmpF, OmpA and TolC. Under all tested conditions, the lipopolysaccharide was not affected, suggesting that a specific rather than a generalized rearrangement of the envelope was induced.

Conclusion

Taking together physiological and biochemical evidence, our work indicates that the E. coli envelope can sense protein over-expression in the cytoplasm and react by modulating the abundance of some membrane proteins, with possible consequences on the membrane traffic of small solutes, i.e. nutrients, drugs and metabolites. Such a response seems to be independent on the nature of the protein being over-expressed. On the other hand both our data reported herein and previous results indicate that membrane lipids may act as a second stress sensor responsive to the aggregation state of the recombinant protein and further contribute to changes in cellular exchanges with the environment.

Development of recombinant Escherichia coli whole-cell biocatalyst expressing a novel alkaline lipase-coding gene from Proteus sp. for biodiesel production

A lipase-producing bacterium K107 was isolated from soil samples of China and identified to be a strain of Proteus sp. With genome-walking method, the open reading frame of lipase gene lipK107, encoding 287 amino acids, was cloned and expressed in a heterologous host, Escherichia coli BL21 (DE3). The recombinant lipase was purified and characterized, and the optimum pH of the purified LipK107 was 9, at 35 degrees C. The recombinant E. coli expressing lipK107 was applied in biodiesel production in the form of whole-cell biocatalyst. Activity of the biocatalyst increased significantly when cells were permeabilized with 0.3% (w/v) cetyl-trimethylammoniumbromide (CTAB). This transesterification was carried out efficiently in a mixture containing 5M equivalents of methanol to the oil and 100% water by weight of the substrate. It was the first time to use E. coli whole-cell biocatalyst expressing lipase in biodiesel production, and the biodiesel reached a yield of nearly 100% after 12h reaction at the optimal temperature of 15 degrees C, which was the lowest temperature among all the known catalyst in biodiesel production.

Identification and characterization of Epp, the secreted processing protease for the Vibrio anguillarum EmpA metalloprotease

The zinc metalloprotease EmpA is a virulence factor for the fish pathogen Vibrio anguillarum. Previous studies demonstrated that EmpA is secreted as a 46-kDa proenzyme that is activated extracellularly by the removal of an approximately 10-kDa propeptide. We hypothesized that a specific protease is responsible for processing secreted pro-EmpA into mature EmpA. To identify the protease responsible for processing pro-EmpA, a minitransposon mutagenesis (using mini-Tn10Km) clone bank of V. anguillarum was screened for reduced protease activity due to insertions in undescribed genes. One mutant with reduced protease activity was identified. The region containing the mini-Tn10Km was cloned, sequenced, and found to contain epp, an open reading frame encoding a putative protease. Further characterization of epp was done using strain M101, created by single-crossover insertional mutagenesis. Protease activity was absent in M101 cultures even when empA protease activity was induced by salmon gastrointestinal mucus. When the epp mutation was complemented with a wild-type copy of epp (M102), protease activity was restored. Western blot analysis of sterile filtered culture supernatants from wild-type (M93Sm) cells, M101 cells, and M102 cells revealed that only pro-EmpA was present in M101supernatants; both pro-EmpA and mature EmpA were detected in M93Sm and M102 supernatants. When sterile filtered culture supernatants from the empA mutant strain (M99) and M101 were mixed, protease activity was restored. Western blot analysis revealed that pro-EmpA in M101 culture supernatant was processed to mature EmpA only after mixing with M99 culture supernatant. These data show that Epp is the EmpA-processing protease.

Identification of iron regulated genes in the fish pathogen Aeromonas salmonicida subsp. salmonicida: genetic diversity and evidence of conserved iron uptake systems

In this study we applied the Fur titration assay (FURTA) to isolate iron regulated genes in Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis in fish. We have identified genes for siderophore biosynthesis and for ferri-siderophore transport, some of which have been previously described in this species. A gene for a hitherto uncharacterized functional hemin receptor HutE was identified, but its inactivation did not affect significantly the use of hemin as sole iron source, suggesting that redundant genes encoding hemin receptors exist in the A. salmonicida genome. Additional FURTA positive clones contained genes encoding a Flavoprotein, a transcriptional regulator protein, a DNA binding protein Fis, as well as genes encoding putative DapD and Flp/Fap-pilin proteins. A screening of gene distribution demonstrated that all the analyzed strains shared genes for siderophore biosynthesis and transport and for heme utilization, indicating that these two systems of iron acquisition are a conserved trait in this subspecies, whereas other genes are not common to all the isolates. Thus, the Fur regulon of A. salmonicida subsp. salmonicida includes both conserved and differentially occurring genes, suggesting that the genetic diversity within this fish pathogen might be higher than expected.

Putative virulence traits and pathogenicity of Vibrio cholerae Non-O1, Non-O139 isolates from surface waters in Kolkata, India

Vibrio cholerae non-O1, non-O139 was isolated from natural surface waters from different sites sampled in diarrhea endemic zones in Kolkata, India. Twenty-one of these isolates were randomly selected and included in the characterization. The multiserogroup isolates were compared by their virulence traits with a group of clinical non-O1, non-O139 isolates from the same geographic area. Of the 21 environmental isolates, 6 and 14 strains belonged to Heiberg groups I and II, respectively. Three of the environmental isolates showed resistance to 2,2-diamine-6,7-diisopropylpteridine phosphate. All of the non-O1, non-O139 strains were positive for toxR, and except for one environmental isolate, none of them were positive for tcpA in the PCR assay. None of the isolates were positive for genes encoding cholera toxin (ctxA), heat-stable toxin (est), heat-labile toxin (elt), and Shiga toxin variants (stx) of Escherichia coli. Additionally, except for one environmental isolate (PC32), all were positive for the gene encoding El Tor hemolysin (hly). The culture supernatants of 86% (18 of 21) of the environmental isolates showed a distinct cytotoxic effect on HeLa cells, and some of these strains also produced cell-rounding factor. The lipase, protease, and cell-associated hemagglutination activities and serum resistance properties of the environmental and clinical isolates did not differ much. However, seven environmental isolates exhibited very high hemolytic activities (80 to 100%), while none of the clinical strains belonged to this group. The environmental isolates manifested three adherence patterns, namely, carpet-like, diffuse, and aggregative adherence, and the clinical isolates showed diffuse adherence on HeLa cells. Of the 11 environmental isolates tested for enteropathogenic potential, 8 (73%) induced positive fluid accumulation (>/=100) in a mouse model, and the reactivities of these isolates were comparable to those of clinical strains of non-O1, non-O139 and toxigenic O139 V. cholerae. Comparison of the counts of the colonized environmental and clinical strains in the mouse intestine showed that the organisms of both groups had similar colonizing efficiencies. These findings indicate the presence of potentially pathogenic V. cholerae non-O1, non-O139 strains in surface waters of the studied sites in Kolkata.

The metalloprotease PrtV from Vibrio cholerae

The Vibrio metalloprotease PrtV was purified from the culture supernatant of a Vibrio cholerae derivative that is deficient in several other secreted peptidases, including the otherwise abundant hemagglutinin/protease HapA. The PrtV is synthesized as a 102 kDa protein, but undergoes several N- and C-terminal processing steps during V. cholerae envelope translocation and prolonged incubation. Purified V. cholerae PrtV protease forms of 81 or 73 kDa were stabilized by calcium ions. Removal of calcium resulted in further rapid autoproteolysis. The two major products of autoproteolysis of the PrtV protease were approximately 37 and 18 kDa and could not be separated under non-denaturing conditions, indicating they are interacting domains. In an assay using cultured cells of the human intestinal cell line HCT8, the PrtV protein showed a cytotoxic effect leading to cell death. Using human blood plasma as a source of potential substrates of mammalian origin for the PrtV protease, we found that the extracellular matrix components fibronectin and fibrinogen were degraded by the enzyme. Additional tests with individual protein substrates revealed that plasminogen was also a possible target for the PrtV protease.

A Vibrio cholerae protease needed for killing of Caenorhabditis elegans has a role in protection from natural predator grazing

Vibrio cholerae is the causal bacterium of the diarrheal disease cholera, and its growth and survival are thought to be curtailed by bacteriovorous predators, e.g., ciliates and flagellates. We explored Caenorhabditis elegans as a test organism after finding that V. cholerae can cause lethal infection of this nematode. By reverse genetics we identified an extracellular protease, the previously uncharacterized PrtV protein, as being necessary for killing. The killing effect is associated with the colonization of bacteria within the Caenorhabditis elegans intestine. We also show that PrtV is essential for V. cholerae in the bacterial survival from grazing by the flagellate Cafeteria roenbergensis and the ciliate Tetrahymena pyriformis. The PrtV protein appears to have an indirect role in the interaction of V. cholerae with mammalian host cells as judged from tests with tight monolayers of human intestinal epithelial cells. Our results demonstrate a key role for PrtV in V. cholerae interaction with grazing predators, and we establish Caenorhabditis elegans as a convenient organism for identification of V. cholerae factors involved in host interactions and environmental persistence.

Identification and characterization of a hemolysin gene cluster in Vibrio anguillarum

Vibrio anguillarum is a causative agent of vibriosis in fish. Hemolytic activity has been suggested as a virulence factor by contributing to hemorrhagic septicemia and diarrhea. In order to identify and characterize the hemolysin genes and examine the role of hemolytic activity in virulence, a mini-Tn10Kan mutagenesis clone bank of V. anguillarum was screened. While no hemolysin-negative strains were observed, several mutants with two- to threefold-increased hemolytic activity were found. The region containing the insertion mutation was cloned, sequenced, and found to contain the V. anguillarum hemolysin (vah1) and two other open reading frames, coding for a putative lactonizing lipase (llpA) and a putative phospholipase (plp). The mini-Tn10Kan was inserted into plp. Site-directed mutagenesis of each gene revealed that mutations in vah1 and llpA did not affect hemolytic activity, but insertions into plp caused a two- to threefold increase in hemolysis. Double mutations in plp and either vah1 or llpA resulted in wild-type hemolytic activity. Complementation of plp restored hemolytic activity to wild-type levels. Spectrophotometric determination of hemolysin specific activity revealed that activity on a per cell basis peaked during the first 2 h of growth in LB20. Real-time quantitative reverse transcriptase PCR used to quantitate transcription of the hemolysin genes plp and vah1 in V. anguillarum wild-type strains M93Sm and NB10 revealed that transcription of plp and vah1 peaked at 2 h of growth in LB20. Additionally, expression of vah1 measured in the plp mutant strain, JL01, during the first 2 h of growth was >8 times higher than that in M93Sm. Mutations in plp and llpA did not affect virulence of V. anguillarum. The mutation in vah1 attenuated V. anguillarum virulence in fish. These data show that several genes are responsible for hemolytic activity in V. anguillarum. At least three genes (plp, llpA, and vah1) are responsible for one hemolytic activity. The data also suggest that plp acts as a negative regulator of vah1 and llpA.

Iron and fur regulation in Vibrio cholerae and the role of fur in virulence

Regulation of iron uptake and utilization is critical for bacterial growth and for prevention of iron toxicity. In many bacterial species, this regulation depends on the iron-responsive master regulator Fur. In this study we report the effects of iron and Fur on gene expression in Vibrio cholerae. We show that Fur has both positive and negative regulatory functions, and we demonstrate Fur-independent regulation of gene expression by iron. Nearly all of the known iron acquisition genes were repressed by Fur under iron-replete conditions. In addition, genes for two newly identified iron transport systems, Feo and Fbp, were found to be negatively regulated by iron and Fur. Other genes identified in this study as being induced in low iron and in the fur mutant include those encoding superoxide dismutase (sodA), fumarate dehydratase (fumC), bacterioferritin (bfr), bacterioferritin-associated ferredoxin (bfd), and multiple genes of unknown function. Several genes encoding iron-containing proteins were repressed in low iron and in the fur mutant, possibly reflecting the need to reserve available iron for the most critical functions. Also repressed in the fur mutant, but independently of iron, were genes located in the V. cholerae pathogenicity island, encoding the toxin-coregulated pilus (TCP), and genes within the V. cholerae mega-integron. The fur mutant exhibited very weak autoagglutination, indicating a possible defect in expression or assembly of the TCP, a major virulence factor of V. cholerae. Consistent with this observation, the fur mutant competed poorly with its wild-type parental strain for colonization of the infant mouse gut.

Active lactonizing lipase (LipL) efficiently overproduced by Pseudomonas strains as heterologous expression hosts

Pseudomonas sp. strain 109 secretes lactonizing lipase (LipL), which catalyzes efficient intramolecular transesterification of omega-hydroxyfatty acid esters to form macrocyclic lactones. Because Escherichia coli was found to be unsuitable as an expression host due to the predominant formation of inactive LipL-inclusion bodies and a lack of proper secretion machinery which is also required for the formation of active LipL, Pseudomonas strains were surveyed as expression hosts. Pseudomonas sp. strain 109, an original LipL producer, showed a 7.1-fold higher level of active LipL when the lipL gene under the control of tac-lacUV5 tandem promoter was introduced together with a limL gene encoding a LipL-specific chaperon. Pseudomonas aeruginosa ADD 1976 containing a T7 RNA polymerase gene in the chromosome and plasmid-borne lipL-limL genes under the control of T7 promoter showed a 13-fold higher level of active LipL. Several combinations in the number of lipL and/or limL genes on the plasmid were investigated, and (lipL)3-limL was found to be most efficient, yielding a 67-fold greater production of active LipL than that obtained by the wild-type Pseudomonas sp. strain 109.

Cloning and characterization of the lipase and lipase activator protein from Vibrio vulnificus CKM-1

The gene (lipA) encoding the extracellular lipase and its downstream gene (lipB) from Vibrio vulnificus CKM-1 were cloned and sequenced. Nucleotide sequence analysis and alignments of amino acid sequences suggest that Lip Ais a member of bacterial lipase family I.1 and that LipB is a lipase activator of LipA. The active LipA was produced in recombinant Escherichia coli cells only in the presence of the lipB. In the hydrolysis of p-nitrophenyl esters and triacylglycerols, using the reactivated LipA, the optimum chain lengths for the acyl moiety on the substrate were C14 for ester hydrolysis and C10 to C12 for triacylglycerol hydrolysis.

Quorum sensing-dependent biofilms enhance colonization in Vibrio cholerae

Vibrio cholerae is the causative agent of the diarrheal disease cholera. By an incompletely understood developmental process, V. cholerae forms complex surface-associated communities called biofilms. Here we show that quorum sensing-deficient mutants of V. cholerae produce thicker biofilms than those formed by wild-type bacteria. Microarray analysis of biofilm-associated bacteria shows that expression of the Vibrio polysaccharide synthesis (vps) operons is enhanced in hapR mutants. CqsA, one of two known autoinducer synthases in V. cholerae, acts through HapR to repress vps gene expression. Vibrio biofilms are more acid resistant than planktonic cells. However, quorum sensing-deficient biofilms have lower colonization capacities than those of wild-type biofilms, suggesting that quorum sensing may promote cellular exit from the biofilm once the organisms have traversed the gastric acid barrier of the stomach. These results shed light on the relationships among biofilm development, quorum sensing, infectivity, and pathogenesis in V. cholerae.

Identification of the Vibrio cholerae enterobactin receptors VctA and IrgA: IrgA is not required for virulence

The gram-negative enteric pathogen Vibrio cholerae requires iron for growth. V. cholerae has multiple iron acquisition systems, including utilization of heme and hemoglobin, synthesis and transport of the catechol siderophore vibriobactin, and transport of several siderophores that it does not itself make. One siderophore that V. cholerae transports, but does not make, is enterobactin. Enterobactin transport requires TonB and is independent of the vibriobactin receptor ViuA. In this study, two candidate enterobactin receptor genes, irgA (VC0475) and vctA (VCA0232), were identified by analysis of the V. cholerae genomic sequence. A single mutation in either of these genes did not significantly impair enterobactin utilization, but a strain defective in both genes did not use enterobactin. When either irgA or vctA was supplied on a plasmid, the ability of the irgA vctA double mutant to use enterobactin was restored. This indicates that both VctA and IrgA transport enterobactin. We also identify the genes vctPDGC, which are linked to vctA and encode a periplasmic binding protein-dependent ABC transport system that functions in the utilization of both enterobactin and vibriobactin (VCA0227-0230). An irgA::TnphoA mutant strain, MBG40, was shown in a previous study to be highly attenuated and to have a strong colonization defect in an infant mouse model of V. cholerae infection (M. B. Goldberg, V. J. DiRita, and S. B. Calderwood, Infect. Immun. 58:55-60, 1990). In this work, a new irgA mutation was constructed, and this mutant strain was not significantly impaired in its ability to compete with the parental strain in infant mice and was not attenuated for virulence in an assay of 50% lethal dose. These data indicate that the virulence defect in MBG40 is not due to the loss of irgA function and that irgA is unlikely to be an important virulence factor.

The InhA2 metalloprotease of Bacillus thuringiensis strain 407 is required for pathogenicity in insects infected via the oral route

The entomopathogenic bacterium Bacillus thuringiensis is known to secrete a zinc metalloprotease (InhA) that specifically cleaves antibacterial peptides produced by insect hosts. We identified a second copy of the inhA gene, named inhA2, in B. thuringiensis strain 407 Cry(-). The inhA2 gene encodes a putative polypeptide showing 66.2% overall identity with the InhA protein and harboring the zinc-binding domain (HEXXH), which is characteristic of the zinc-requiring metalloproteases. We used a transcriptional inhA2'-lacZ fusion to show that inhA2 expression is induced at the onset of the stationary phase and is overexpressed in a Spo0A minus background. The presence of a reverse Spo0A box in the promoter region of inhA2 suggests that Spo0A directly regulates the transcription of inhA2. To determine the role of the InhA and InhA2 metalloproteases in pathogenesis, we used allelic exchange to isolate single and double mutant strains for the two genes. Spores and vegetative cells of the mutant strains were as virulent as those of the parental strain in immunized Bombyx mori larvae infected by the intrahemocoelic route. Exponential phase cells of all the strains displayed the same in vitro potential for colonizing the vaccinated hemocoel. We investigated the synergistic effect of the mutant strain spores on the toxicity of Cry1C proteins against Galleria mellonella larvae infected via the oral pathway. The spores of DeltainhA2 mutant strain were ineffective in providing synergism whereas those of the DeltainhA mutant strain were not. These results indicate that the B. thuringiensis InhA2 zinc metalloprotease has a vital role in virulence when the host is infected via the oral route.

Identification of genes involved in the activation of the Bacillus thuringiensis inhA metalloprotease gene at the onset of sporulation

The immune inhibitor A (InhA) metalloprotease from Bacillus thuringiensis specifically cleaves antibacterial proteins produced by the insect host, suggesting that it may contribute to the overall virulence of B. thuringiensis. The transcriptional regulation of the inhA gene in both B. thuringiensis and Bacillus subtilis was investigated. Using a transcriptional inhA'-lacZ fusion, it was shown that inhA expression is activated at the onset of sporulation. However, the transcriptional start site of inhA is similar to sigma(A)-dependent promoters, and deletion of the sporulation-specific sigma factors sigma(F) or sigma(E) had no effect on inhA expression in B. subtilis. The DNA region upstream from inhA contains two genes encoding polypeptides similar to the SinI and SinR regulators of B. subtilis. SinR is a DNA-binding protein regulating gene expression and SinI inhibits SinR activity. Overexpression of the sin genes affects the expression of the inhA'-lacZ transcriptional fusion in B. thuringiensis: early induction of inhA expression was observed when sinI was overexpressed, whereas inhA expression was reduced in a strain overexpressing sinR, suggesting that inhA transcription is repressed, directly or indirectly, by SinR. inhA transcription was greatly reduced in B. thuringiensis and B. subtilis spo0A mutants. Analysis of the inhA'-lacZ expression in abrB and abrB-spo0A mutants of B. subtilis indicates that the Spo0A-dependent regulation of inhA expression depends on AbrB, which is known to regulate expression of transition state and sporulation genes in B. subtilis.

Expression of the Staphylococcus hyicus lipase in Lactococcus lactis

The extracellular Staphylococcus hyicus lipase was expressed under the control of different promoters in Lactococcus lactis and Bacillus subtilis. Its expression at high and moderate levels is toxic for the former and the latter hosts, respectively. In L. lactis, the lipase was expressed at a high level, up to 30% of the total cellular proteins, under the control of the inducible promoter PnisA. About 80% of the lipase remained associated with the cells. Close to half of this amount remained associated with the inner side of the cytoplasmic membrane as unprocessed pre-pro-lipase. The other half was trapped by the cell wall and partially degraded at the N-terminal end. This result suggests that extracellular proteases degrade the lipase. Surprisingly, the kinetics and the pattern of lipase degradation were different in the two L. lactis subspecies, L. lactis subsp. cremoris and L. lactis subsp. lactis. The extracellular proteolytic systems that degrade lipase are thus different in these closely related subspecies. The incorrect export of the lipase is not due to an inappropriate leader peptide but may be due to an inefficiency of several steps of lipase secretion. We propose that (i) the S. hyicus lipase may require a special accessory system to be correctly exported or (ii) the kinetics of lipase synthesis may be a critical factor for proper folding.

A low-Mr lipase activation factor cooperating with lipase modulator protein LimL in Pseudomonas sp. strain 109

Pseudomonas sp. strain 109 produces a unique lipase (LipL) which efficiently catalyses intramolecular transesterification of omega-hydroxyesters to form macrocyclic lactones. In vivo production of enzymically active LipL requires lipase modulator protein (LimL), which functions as a molecular chaperone for the correct folding of LipL. However, previous work has shown that LipL forms a tight complex with LimL in vitro and the resulting LipL-LimL complex is only partially active, suggesting an additional mechanism that facilitates the dissociation of the complex to form enzymically active LipL. In the present work, a low-Mr compound (lipase activation factor, LAF) was found in Pseudomonas sp. strain 109 that when added to the LipL-LimL complex resulted in the activation of LipL. Ca2+ ions also enhanced lipase activity, but the instantaneous activation by Ca2+ was different from the gradual and time-dependent activation by LAF, indicating the novel nature of this compound. LAF passed through an ultrafiltration membrane with an Mr cut-off of 3000 and showed an apparent Mr of 330+/-30 on Superdex Peptide gel-filtration chromatography. Treatment of the LipL-LimL complex with LAF liberated free active LipL, indicating that LAF was necessary to dissociate the LipL-LimL complex.

Cloning and sequence analysis of the lipase and lipase chaperone-encoding genes from Acinetobacter calcoaceticus RAG-1, and redefinition of a proteobacterial lipase family and an analogous lipase chaperone family

The genes encoding the lipase (LipA) and lipase chaperone (LipB) from Acinetobacter calcoaceticus RAG-1 were cloned and sequenced. The genes were isolated from a genomic DNA library by complementation of a lipase-deficient transposon mutant of the same strain. Transposon insertion in this mutant and three others was mapped to a single site in the chaperone gene. The deduced amino acid (aa) sequences for the lipase and its chaperone were found to encode mature proteins of 313 aa (32.5kDa) and 347 aa (38.6kDa), respectively. The lipase contained a putative leader sequence, as well as the conserved Ser, His, and Asp residues which are known to function as the catalytic triad in other lipases. A possible trans-membrane hydrophobic helix was identified in the N-terminal region of the chaperone. Phylogenetic comparisons showed that LipA, together with the lipases of A. calcoaceticus BD413, Vibrio cholerae El Tor, and Proteus vulgaris K80, were members of a previously described family of Pseudomonas and Burkholderia lipases. This new family, which we redefine as the Group I Proteobacterial lipases, was subdivided into four subfamilies on the basis of overall sequence homology and conservation of residues which are unique to the subfamilies. LipB, moreover, was found to be a member of an analogous family of lipase chaperones. We propose that the lipases produced by P. fluorescens and Serratia marcescens, which comprise a second sequence family, be referred to as the Group II Proteobacterial lipases. Evidence is provided to support the hypothesis that both the Group I and Group II families have evolved from a combination of common descent and lateral gene transfer.