Environmental refuges from disease in host-parasite interactions under global change

The physiological performance of organisms depends on their environmental context, resulting in performance-response curves along environmental gradients. Parasite performance-response curves are generally expected to be broader than those of their hosts due to shorter generation times and hence faster adaptation. However, certain environmental conditions may limit parasite performance more than that of the host, thereby providing an environmental refuge from disease. Thermal disease refuges have been extensively studied in response to climate warming, but other environmental factors may also provide environmental disease refuges which, in turn, respond to global change. Here, we (1) showcase laboratory and natural examples of refuges from parasites along various environmental gradients, and (2) provide hypotheses on how global environmental change may affect these refuges. We strive to synthesize knowledge on potential environmental disease refuges along different environmental gradients including salinity and nutrients, in both natural and food-production systems. Although scaling up from single host-parasite relationships along one environmental gradient to their interaction outcome in the full complexity of natural environments remains difficult, integrating host and parasite performance-response can serve to formulate testable hypotheses about the variability in parasitism outcomes and the occurrence of environmental disease refuges under current and future environmental conditions.

β-Glucan-Induced Immuno-Modulation: A Role for the Intestinal Microbiota and Short-Chain Fatty Acids in Common Carp

Dietary supplementation of fish with β-glucans has been commonly associated with immunomodulation and generally accepted as beneficial for fish health. However, to date the exact mechanisms of immunomodulation by β-glucan supplementation in fish have remained elusive. In mammals, a clear relation between high-fibre diets, such as those including β-glucans, and diet-induced immunomodulation via intestinal microbiota and associated metabolites has been observed. In this study, first we describe by 16S rRNA sequencing the active naive microbiota of common carp intestine. Based on the abundance of the genus Bacteroides, well known for their capacity to degrade and ferment carbohydrates, we hypothesize that common carp intestinal microbiota could ferment dietary β-glucans. Indeed, two different β-glucan preparations (curdlan and MacroGard^®) were both fermented in vitro, albeit with distinct fermentation dynamics and distinct production of short-chain fatty acids (SCFA). Second, we describe the potential immunomodulatory effects of the three dominant SCFAs (acetate, butyrate, and propionate) on head kidney leukocytes, showing effects on both nitric oxide production and expression of several cytokines (il-1b, il-6, tnfα, and il-10) in vitro. Interestingly, we also observed a regulation of expression of several gpr40L genes, which were recently described as putative SCFA receptors. Third, we describe how a single in vivo oral gavage of carp with MacroGard^® modulated simultaneously, the expression of several pro-inflammatory genes (il-1b, il-6, tnfα), type I IFN-associated genes (tlr3.1, mx3), and three specific gpr40L genes. The in vivo observations provide indirect support to our in vitro data and the possible role of SCFAs in β-glucan-induced immunomodulation. We discuss how β-glucan-induced immunomodulatory effects can be explained, at least in part, by fermentation of MacroGard^® by specific bacteria, part of the naive microbiota of common carp intestine, and how a subsequent production of SFCAs could possibly explain immunomodulation by β-glucan via SCFA receptors present on leukocytes.

Plant- and Bacteria-Derived Compounds with Anti-Philasterides dicentrarchi Activity

Philasterides dicentrarchi is a scuticociliate that causes high mortalities in farmed fish. Although vaccination is an effective method to prevent scuticociliatosis caused by the homologous serotype, a universal vaccine has not been developed yet. Many compounds have been shown to be toxic to this ciliate species; moreover, most of them are toxic to aquatic life and cannot be used to prevent the disease. We have evaluated the toxicity to P. dicentrarchi of several compounds of natural origin to be used to reduce parasite levels in the seawater. Ciliates were exposed to several compound concentrations, and the mortality was determined at several incubation times. Tomatine, plumbagin and 2′,4′-dihydroxychalcone displayed the highest anticiliate activity, with a dose-dependent response. The effects of these compounds on the EPC cell line were also evaluated, finding that 2′,4′-dihydroxychalcone displayed the lowest toxicity to fish cells. At 7.54 μM, 2′,4′-dihydroxychalcone inhibited 50% parasite growth but only killed about 10% of EPC cells after 24 h incubation. Finally, we evaluated the toxicity of Pseudomonas H6 surfactant (PS) to P. dicentrarchi, finding that PS was toxic to the ciliate but showed lower toxicity to EPC cells. At a concentration of 7.8 μg/mL (LC₅₀ for the ciliate after 3 h incubation), PS killed 14.9% of EPC cells. We conclude that 2′,4′-dihydroxychalcone, and PS could be used to reduce parasite levels in seawater, thus decreasing the risk of scuticociliatosis infection in cultured fish.

Cell entry of a host-targeting protein of oomycetes requires gp96

The animal-pathogenic oomycete Saprolegnia parasitica causes serious losses in aquaculture by infecting and killing freshwater fish. Like plant-pathogenic oomycetes, S. parasitica employs similar infection structures and secretes effector proteins that translocate into host cells to manipulate the host. Here, we show that the host-targeting protein SpHtp3 enters fish cells in a pathogen-independent manner. This uptake process is guided by a gp96-like receptor and can be inhibited by supramolecular tweezers. The C-terminus of SpHtp3 (containing the amino acid sequence YKARK), and not the N-terminal RxLR motif, is responsible for the uptake into host cells. Following translocation, SpHtp3 is released from vesicles into the cytoplasm by another host-targeting protein where it degrades nucleic acids. The effector translocation mechanism described here, is potentially also relevant for other pathogen-host interactions as gp96 is found in both animals and plants.

Current Insights into the Role of Rhizosphere Bacteria in Disease Suppressive Soils

Disease suppressive soils offer effective protection to plants against infection by soil-borne pathogens, including fungi, oomycetes, bacteria, and nematodes. The specific disease suppression that operates in these soils is, in most cases, microbial in origin. Therefore, suppressive soils are considered as a rich resource for the discovery of beneficial microorganisms with novel antimicrobial and other plant protective traits. To date, several microbial genera have been proposed as key players in disease suppressiveness of soils, but the complexity of the microbial interactions as well as the underlying mechanisms and microbial traits remain elusive for most disease suppressive soils. Recent developments in next generation sequencing and other 'omics' technologies have provided new insights into the microbial ecology of disease suppressive soils and the identification of microbial consortia and traits involved in disease suppressiveness. Here, we review the results of recent 'omics'-based studies on the microbial basis of disease suppressive soils, with specific emphasis on the role of rhizosphere bacteria in this intriguing microbiological phenomenon.

Comparative genomics and metabolic profiling of the genus Lysobacter

Background

Lysobacter species are Gram-negative bacteria widely distributed in soil, plant and freshwater habitats. Lysobacter owes its name to the lytic effects on other microorganisms. To better understand their ecology and interactions with other (micro)organisms, five Lysobacter strains representing the four species L. enzymogenes, L. capsici, L. gummosus and L. antibioticus were subjected to genomics and metabolomics analyses.

Results

Comparative genomics revealed a diverse genome content among the Lysobacter species with a core genome of 2,891 and a pangenome of 10,028 coding sequences. Genes encoding type I, II, III, IV, V secretion systems and type IV pili were highly conserved in all five genomes, whereas type VI secretion systems were only found in L. enzymogenes and L. gummosus. Genes encoding components of the flagellar apparatus were absent in the two sequenced L. antibioticus strains. The genomes contained a large number of genes encoding extracellular enzymes including chitinases, glucanases and peptidases. Various nonribosomal peptide synthase (NRPS) and polyketide synthase (PKS) gene clusters encoding putative bioactive metabolites were identified but only few of these clusters were shared between the different species. Metabolic profiling by imaging mass spectrometry complemented, in part, the in silico genome analyses and allowed visualisation of the spatial distribution patterns of several secondary metabolites produced by or induced in Lysobacter species during interactions with the soil-borne fungus Rhizoctonia solani.

Conclusions

Our work shows that mining the genomes of Lysobacter species in combination with metabolic profiling provides novel insights into the genomic and metabolic potential of this widely distributed but understudied and versatile bacterial genus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2191-z) contains supplementary material, which is available to authorized users.

Lipopeptide biosurfactant viscosin enhances dispersal of Pseudomonas fluorescens SBW25 biofilms

Pseudomonads produce several lipopeptide biosurfactants that have antimicrobial properties but that also facilitate surface motility and influence biofilm formation. Detailed studies addressing the significance of lipopeptides for biofilm formation and architecture are rare. Hence, the present study sets out to determine the specific role of the lipopeptide viscosin in Pseudomonas fluorescens SBW25 biofilm formation, architecture and dispersal, and to relate viscA gene expression to viscosin production and effect. Initially, we compared biofilm formation of SBW25 and the viscosin-deficient mutant strain SBW25ΔviscA in static microtitre assays. These experiments demonstrated that viscosin had little influence on the amount of biofilm formed by SBW25 during the early stages of biofilm development. Later, however, SBW25 formed significantly less biofilm than SBW25ΔviscA. The indication that viscosin is involved in biofilm dispersal was confirmed by chemical complementation of the mutant biofilm. Furthermore, a fluorescent bioreporter showed that viscA expression was induced in biofilms 4 h prior to dispersal. Subsequent detailed studies of biofilms formed in flow cells for up to 5 days revealed that SBW25 and SBW25ΔviscA developed comparable biofilms dominated by well-defined, mushroom-shaped structures. Carbon starvation was required to obtain biofilm dispersal in this system. Dispersal of SBW25 biofilms was significantly greater than of SBW25ΔviscA biofilms after 3 h and, importantly, carbon starvation strongly induced viscA expression, in particular for cells that were apparently leaving the biofilm. Thus, the present study points to a role for viscosin-facilitated motility in dispersal of SBW25 biofilms.

Diversity of Aquatic Pseudomonas Species and Their Activity against the Fish Pathogenic Oomycete Saprolegnia

Emerging fungal and oomycete pathogens are increasingly threatening animals and plants globally. Amongst oomycetes, Saprolegnia species adversely affect wild and cultivated populations of amphibians and fish, leading to substantial reductions in biodiversity and food productivity. With the ban of several chemical control measures, new sustainable methods are needed to mitigate Saprolegnia infections in aquaculture. Here, PhyloChip-based community analyses showed that the Pseudomonadales, particularly Pseudomonas species, represent one of the largest bacterial orders associated with salmon eggs from a commercial hatchery. Among the Pseudomonas species isolated from salmon eggs, significantly more biosurfactant producers were retrieved from healthy salmon eggs than from Saprolegnia-infected eggs. Subsequent in vivo activity bioassays showed that Pseudomonas isolate H6 significantly reduced salmon egg mortality caused by Saprolegnia diclina. Live colony mass spectrometry showed that strain H6 produces a viscosin-like lipopeptide surfactant. This biosurfactant inhibited growth of Saprolegnia in vitro, but no significant protection of salmon eggs against Saprolegniosis was observed. These results indicate that live inocula of aquatic Pseudomonas strains, instead of their bioactive compound, can provide new (micro)biological and sustainable means to mitigate oomycete diseases in aquaculture.

The Novel Lipopeptide Poaeamide of the Endophyte Pseudomonas poae RE*1-1-14 Is Involved in Pathogen Suppression and Root Colonization

Endophytic Pseudomonas poae strain RE*1-1-14 was originally isolated from internal root tissue of sugar beet plants and shown to suppress growth of the fungal pathogen Rhizoctonia solani both in vitro and in the field. To identify genes involved in its biocontrol activity, RE*1-1-14 random mutagenesis and sequencing led to the identification of a nonribosomal peptide synthetase (NRPS) gene cluster predicted to encode a lipopeptide (LP) with a 10-amino-acid peptide moiety. The two unlinked gene clusters consisted of three NRPS genes, designated poaA (cluster 1) and poaB and poaC (cluster 2), spanning approximately 33.7 kb. In silico analysis followed by chemical analyses revealed that the encoded LP, designated poaeamide, is a structurally new member of the orfamide family. Poaeamide inhibited mycelial growth of R. solani and different oomycetes, including Phytophthora capsici, P. infestans, and Pythium ultimum. The novel LP was shown to be essential for swarming motility of strain RE*1-1-14 and had an impact on root colonization of sugar beet seedlings The poaeamide-deficient mutant colonized the rhizosphere and upper plant cortex at higher densities and with more scattered colonization patterns than the wild type. Collectively, these results indicate that Pseudomonas poae RE*1-1-14 produces a structurally new LP that is relevant for its antagonistic activity against soilborne plant pathogens and for colonization of sugar beet roots.

Lipopeptide biosynthesis in Pseudomonas fluorescens is regulated by the protease complex ClpAP

Background

Lipopeptides (LP) are structurally diverse compounds with potent surfactant and broad-spectrum antibiotic activities. In Pseudomonas and other bacterial genera, LP biosynthesis is governed by large multimodular nonribosomal peptide synthetases (NRPS). To date, relatively little is known about the regulatory genetic network of LP biosynthesis.

Results

This study provides evidence that the chaperone ClpA, together with the serine protease ClpP, regulates the biosynthesis of the LP massetolide in Pseudomonas fluorescens SS101. Whole-genome transcriptome analyses of clpA and clpP mutants showed their involvement in the transcription of the NRPS genes massABC and the transcriptional regulator massAR. In addition, transcription of genes associated with cell wall and membrane biogenesis, energy production and conversion, amino acid transport and metabolism, and pilus assembly were altered by mutations in clpA and clpP. Proteome analysis allowed the identification of additional cellular changes associated to clpA and clpP mutations. The expression of proteins of the citrate cycle and the heat shock proteins DnaK and DnaJ were particularly affected. Combined with previous findings, these results suggest that the ClpAP complex regulates massetolide biosynthesis via the pathway-specific, LuxR-type regulator MassAR, the heat shock proteins DnaK and DnaJ, and proteins of the TCA cycle.

Conclusions

Combining transcriptome and proteome analyses provided new insights into the regulation of LP biosynthesis in P. fluorescens and led to the identification of specific missing links in the regulatory pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0367-y) contains supplementary material, which is available to authorized users.

Deciphering microbial landscapes of fish eggs to mitigate emerging diseases

Animals and plants are increasingly suffering from diseases caused by fungi and oomycetes. These emerging pathogens are now recognized as a global threat to biodiversity and food security. Among oomycetes, Saprolegnia species cause significant declines in fish and amphibian populations. Fish eggs have an immature adaptive immune system and depend on nonspecific innate defences to ward off pathogens. Here, meta-taxonomic analyses revealed that Atlantic salmon eggs are home to diverse fungal, oomycete and bacterial communities. Although virulent Saprolegnia isolates were found in all salmon egg samples, a low incidence of Saprolegniosis was strongly correlated with a high richness and abundance of specific commensal Actinobacteria, with the genus Frondihabitans (Microbacteriaceae) effectively inhibiting attachment of Saprolegniato salmon eggs. These results highlight that fundamental insights into microbial landscapes of fish eggs may provide new sustainable means to mitigate emerging diseases.

Functional characterization of a tyrosinase gene from the oomycete Saprolegnia parasitica by RNAi silencing

Here we describe the first application of transient gene silencing in Saprolegnia parasitica, a pathogenic oomycete that infects a wide range of fish, amphibians, and crustaceans. A gene encoding a putative tyrosinase from S. parasitica, SpTyr, was selected to investigate the suitability of RNA-interference (RNAi) to functionally characterize genes of this economically important pathogen. Tyrosinase is a mono-oxygenase enzyme that catalyses the O-hydroxylation of monophenols and subsequent oxidation of O-diphenols to quinines. These enzymes are widely distributed in nature, and are involved in the melanin biosynthesis. Gene silencing was obtained by delivering in vitro synthesized SpTyr dsRNA into protoplasts. Expression analysis, tyrosinase activity measurements, and melanin content analysis confirmed silencing in individual lines. Silencing of SpTyr resulted in a decrease of tyrosinase activity between 38 % and 60 %, dependent on the level of SpTyr-expression achieved. The SpTyr-silenced lines displayed less pigmentation in developing sporangia and occasionally an altered morphology. Moreover, developing sporangia from individual silenced lines possessed a less electron dense cell wall when compared to control lines, treated with GFP-dsRNA. In conclusion, the tyrosinase gene of S. parasitica is required for melanin formation and transient gene silencing can be used to functionally characterize genes in S. parasitica.

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Successful transient gene silencing in Saprolegnia parasitica through RNAi.

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Silencing a tyrosinase in S. parasitica results in reduced melanin formation.

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Silencing a tyrosinase in S. parasitica results in aberrant sporangia formation.

The Gac regulon of Pseudomonas fluorescens SBW25

Transcriptome analysis of Pseudomonas fluorescens SBW25 showed that 702 genes were differentially regulated in a gacS::Tn5 mutant, with 300 and 402 genes up- and downregulated respectively. Similar to the Gac regulon of other Pseudomonas species, genes involved in motility, biofilm formation, siderophore biosynthesis and oxidative stress were differentially regulated in the gacS mutant of SBW25. Our analysis also revealed, for the first time, that transcription of 19 rhizosphere-induced genes and of genes involved in type II secretion, (exo)polysaccharide and pectate lyase biosynthesis, twitching motility and an orphan non-ribosomal peptide synthetase (NRPS) were significantly affected in the gacS mutant. Furthermore, the gacS mutant inhibited growth of oomycete, fungal and bacterial pathogens significantly more than wild type SBW25. Since RP-HPLC analysis did not reveal any potential candidate metabolites, we focused on the Gac-regulated orphan NRPS gene cluster that was predicted to encode an eight-amino-acid ornicorrugatin-like peptide. Site-directed mutagenesis indicated that the encoded peptide is not involved in the enhanced antimicrobial activity of the gacS mutant but may function as a siderophore. Collectively, this genome-wide analysis revealed that a mutation in the GacS/A two-component regulatory system causes major transcriptional changes in SBW25 and significantly enhances its antimicrobial activities by yet unknown mechanisms.

Distinctive expansion of potential virulence genes in the genome of the oomycete fish pathogen Saprolegnia parasitica

Oomycetes in the class Saprolegniomycetidae of the Eukaryotic kingdom Stramenopila have evolved as severe pathogens of amphibians, crustaceans, fish and insects, resulting in major losses in aquaculture and damage to aquatic ecosystems. We have sequenced the 63 Mb genome of the fresh water fish pathogen, Saprolegnia parasitica. Approximately 1/3 of the assembled genome exhibits loss of heterozygosity, indicating an efficient mechanism for revealing new variation. Comparison of S. parasitica with plant pathogenic oomycetes suggests that during evolution the host cellular environment has driven distinct patterns of gene expansion and loss in the genomes of plant and animal pathogens. S. parasitica possesses one of the largest repertoires of proteases (270) among eukaryotes that are deployed in waves at different points during infection as determined from RNA-Seq data. In contrast, despite being capable of living saprotrophically, parasitism has led to loss of inorganic nitrogen and sulfur assimilation pathways, strikingly similar to losses in obligate plant pathogenic oomycetes and fungi. The large gene families that are hallmarks of plant pathogenic oomycetes such as Phytophthora appear to be lacking in S. parasitica, including those encoding RXLR effectors, Crinkler's, and Necrosis Inducing-Like Proteins (NLP). S. parasitica also has a very large kinome of 543 kinases, 10% of which is induced upon infection. Moreover, S. parasitica encodes several genes typical of animals or animal-pathogens and lacking from other oomycetes, including disintegrins and galactose-binding lectins, whose expression and evolutionary origins implicate horizontal gene transfer in the evolution of animal pathogenesis in S. parasitica.

Fish are an increasingly important source of animal protein globally, with aquaculture production rising dramatically over the past decade. Saprolegnia is a fungal-like oomycete and one of the most destructive fish pathogens, causing millions of dollars in losses to the aquaculture industry annually. Saprolegnia has also been linked to a worldwide decline in wild fish and amphibian populations. Here we describe the genome sequence of the first animal pathogenic oomycete and compare the genome content with the available plant pathogenic oomycetes. We found that Saprolegnia lacks the large effector families that are hallmarks of plant pathogenic oomycetes, showing evolutionary adaptation to the host. Moreover, Saprolegnia harbors pathogenesis-related genes that were derived by lateral gene transfer from the host and other animal pathogens. The retrotransposon LINE family also appears to be acquired from animal lineages. By transcriptome analysis we show a high rate of allelic variation, which reveals rapidly evolving genes and potentially adaptive evolutionary mechanisms coupled to selective pressures exerted by the animal host. The genome and transcriptome data, as well as subsequent biochemical analyses, provided us with insight in the disease process of Saprolegnia at a molecular and cellular level, providing us with targets for sustainable control of Saprolegnia.

Immune gene expression in trout cell lines infected with the fish pathogenic oomycete Saprolegnia parasitica

The oomycete Saprolegnia parasitica causes significant losses in the aquaculture industry, mainly affecting salmon, trout and catfish. Since the ban of malachite green, effective control measures are currently not available prompting a re-evaluation of the potential for immunological intervention. In this study, the immune response of salmonid cells is investigated at the transcript level, by analysis of a large set of immune response genes in four different rainbow trout cell lines (RTG-2, RTGill, RTL and RTS11) upon infection with S. parasitica. Proinflammatory cytokine transcripts were induced in all four cell lines, including IL-1β1, IL-8, IL-11, TNF-α2, as well as other components of the innate defences, including COX-2, the acute phase protein serum amyloid A and C-type lectin CD209a and CD209b. However, differences between the four cell lines were found. For example, the fold change of induction was much higher in the epithelial RTL and macrophage-like RTS11 cell lines compared to the fibroblast cell lines RTG-2 and RTGill. Several antimicrobial peptides (AMPs) were also up-regulated in response to Saprolegnia infection, including hepcidin and cathelicidin 1 (rtCATH1) and 2 (rtCATH2). An rtCATH2 peptide was synthesised and tested for activity and whilst it showed no killing activity for zoospores, it was able to delay sporulation of S. parasitica. These results demonstrate that particular immune genes are up-regulated in response to S. parasitica infection and that AMPs may play a crucial role in the first line of defence against oomycetes in fish.

The putative RxLR effector protein SpHtp1 from the fish pathogenic oomycete Saprolegnia parasitica is translocated into fish cells

The fish pathogenic oomycete Saprolegnia parasitica causes the disease Saprolegniosis in salmonids and other freshwater fish, resulting in considerable economic losses in aquaculture. Very little is known about the molecular and cellular mechanisms underlying the infection process of fish pathogenic oomycetes. In order to investigate the interaction in detail, an in vitro infection assay using an Oncorhynchus mykiss (rainbow trout) cell line (RTG-2) was developed. In a zoospore/cyst cDNA library, we identified the ORF SpHtp1, which encodes a secreted protein containing an RxLR motif. Detailed expression analysis indicated that SpHtp1 is highly expressed in zoospores/cysts from S. parasitica and in the very early stages of infection on RTG-2 cells, when compared with in vitro-grown mycelium. Moreover, the protein, SpHtp1, was found to translocate into the RTG-2 trout cells, during the interaction with S. parasitica, and also when the RTG-2 cells were treated with recombinant SpHtp1 fused to a C-terminal His-tag. These findings suggest that protein translocation could play an important role in Saprolegniosis.

Protozoan-induced regulation of cyclic lipopeptide biosynthesis is an effective predation defense mechanism for Pseudomonas fluorescens

Environmental bacteria are exposed to a myriad of biotic interactions that influence their function and survival. The grazing activity of protozoan predators significantly impacts the dynamics, diversification, and evolution of bacterial communities in soil ecosystems. To evade protozoan predation, bacteria employ various defense strategies. Soil-dwelling Pseudomonas fluorescens strains SS101 and SBW25 produce the cyclic lipopeptide surfactants (CLPs) massetolide and viscosin, respectively, in a quorum-sensing-independent manner. In this study, CLP production was shown to protect these bacteria from protozoan predation as, compared to CLP-deficient mutants, strains SS101 and SBW25 exhibited resistance to grazing by Naegleria americana in vitro and superior persistence in soil in the presence of this bacterial predator. In the wheat rhizosphere, CLP-producing strains had a direct deleterious impact on the survival of N. americana. In vitro assays further showed that N. americana was three times more sensitive to viscosin than to massetolide and that exposure of strain SS101 or SBW25 to this protozoan resulted in upregulation of CLP biosynthesis genes. Enhanced expression of the massABC and viscABC genes did not require physical contact between the two organisms as gene expression levels were up to threefold higher in bacterial cells harvested 1 cm from feeding protozoans than in cells collected 4 cm from feeding protozoans. These findings document a new natural function of CLPs and highlight that bacterium-protozoan interactions can result in activation of an antipredator response in prey populations.

The PKC, HOG and Ca2+ signalling pathways co-ordinately regulate chitin synthesis in Candida albicans

Chitin is an essential component of the fungal cell wall and its synthesis is under tight spatial and temporal regulation. The fungal human pathogen Candida albicans has a four member chitin synthase gene family comprising of CHS1 (class II), CHS2 (class I), CHS3 (class IV) and CHS8 (class I). LacZ reporters were fused to each CHS promoter to examine the transcriptional regulation of chitin synthesis. Each CHS promoter had a unique regulatory profile and responded to the addition of cell wall damaging agents, to mutations in specific CHS genes and exogenous Ca2+. The regulation of both CHS gene expression and chitin synthesis was co-ordinated by the PKC, HOG MAP kinase and Ca2+/calcineurin signalling pathways. Activation of these pathways also resulted in increased chitin synthase activity in vitro and elevated cell wall chitin content. Combinations of treatments that activated multiple pathways resulted in synergistic increases in CHS expression and in cell wall chitin content. Therefore, at least three pathways co-ordinately regulate chitin synthesis and activation of chitin synthesis operates at both transcriptional and post-transcriptional levels.

Genome-based discovery, structure prediction and functional analysis of cyclic lipopeptide antibiotics in Pseudomonas species

Analysis of microbial genome sequences have revealed numerous genes involved in antibiotic biosynthesis. In Pseudomonads, several gene clusters encoding non-ribosomal peptide synthetases (NRPSs) were predicted to be involved in the synthesis of cyclic lipopeptide (CLP) antibiotics. Most of these predictions, however, are untested and the association between genome sequence and biological function of the predicted metabolite is lacking. Here we report the genome-based identification of previously unknown CLP gene clusters in plant pathogenic Pseudomonas syringae strains B728a and DC3000 and in plant beneficial Pseudomonas fluorescens Pf0-1 and SBW25. For P. fluorescens SBW25, a model strain in studying bacterial evolution and adaptation, the structure of the CLP with a predicted 9-amino acid peptide moiety was confirmed by chemical analyses. Mutagenesis confirmed that the three identified NRPS genes are essential for CLP synthesis in strain SBW25. CLP production was shown to play a key role in motility, biofilm formation and in activity of SBW25 against zoospores of Phytophthora infestans. This is the first time that an antimicrobial metabolite is identified from strain SBW25. The results indicate that genome mining may enable the discovery of unknown gene clusters and traits that are highly relevant in the lifestyle of plant beneficial and plant pathogenic bacteria.

Cyclic lipopeptide production by plant-associated Pseudomonas spp.: diversity, activity, biosynthesis, and regulation

Cyclic lipopeptides (CLPs) are versatile molecules produced by a variety of bacterial genera, including plant-associated Pseudomonas spp. CLPs are composed of a fatty acid tail linked to a short oligopeptide, which is cyclized to form a lactone ring between two amino acids in the peptide chain. CLPs are very diverse both structurally and in terms of their biological activity. The structural diversity is due to differences in the length and composition of the fatty acid tail and to variations in the number, type, and configuration of the amino acids in the peptide moiety. CLPs have received considerable attention for their antimicrobial, cytotoxic, and surfactant properties. For plant-pathogenic Pseudomonas spp., CLPs constitute important virulence factors, and pore formation, followed by cell lysis, is their main mode of action. For the antagonistic Pseudomonas sp., CLPs play a key role in antimicrobial activity, motility, and biofilm formation. CLPs are produced via nonribosomal synthesis on large, multifunctional peptide synthetases. Both the structural organization of the CLP synthetic templates and the presence of specific domains and signature sequences within peptide synthetase genes will be described for both pathogenic and antagonistic Pseudomonas spp. Finally, the role of various genes and regulatory mechanisms in CLP production by Pseudomonas spp., including two-component regulation and quorum sensing, will be discussed in detail.

The health care organization of the Dutch East India Company at home

The Dutch East India Company ('VOC') organized a health care service on board its vessels as well as its home bases and in its factories in Asia. This health care service was based initially on the Dutch navy model. This study addresses the problems manifesting in the VOC health care in the 200 years of its activities, framed within the general concept of the transition during that period from individual to mass health care. It is argued that the service proved inadequate because of a number of factors, chiefly including the inability of the organization to cope with large numbers of people already ill before boarding or falling ill during the Asia-bound voyages; the ignorance of the causes of malnutritional and (tropical) infectious diseases; the training of surgeons (focused on injury-caused disease rather than on systemic disorders); the inordinate frugality of the directors as well as the fear of junior officials to displease the managerial board; and the preoccupation of the VOC board with detail rather than with a policy addressing fundamental health problems.