Steven Forst - Academia.edu (original) (raw)
Papers by Steven Forst
Journal of Bacteriology, 2003
The response regulator OmpR is involved in numerous adaptive responses to environmental challenge... more The response regulator OmpR is involved in numerous adaptive responses to environmental challenges. The role that OmpR plays in swarming behavior and swarm-cell differentiation in the symbiotic-pathogenic bacterium Xenorhabdus nematophila was examined in this study. Swarming began 4 h sooner in an ompR mutant strain than in wild-type cells. Precocious swarming was correlated with elevated expression of fliC , early flagellation, and cell elongation. The level of flhDC mRNA was elevated during the early period of swarming in the ompR strain relative to the level in the wild type. These findings show that OmpR is involved in the temporal regulation of flhDC expression and flagellum production and demonstrate that this response regulator plays a role in the swarming behavior of X. nematophila .
Biochemistry and Molecular Biology Education, 2012
Microbiology, 2004
Xenorhabdus nematophila, a Gram-negative bacterium belonging to the Proteus clade of the family E... more Xenorhabdus nematophila, a Gram-negative bacterium belonging to the Proteus clade of the family Enterobacteriaceae, forms a mutualistic association with the soil nematode Steinernema carpocapsae. The nematode invades insects and releases Xenorhabdus into the haemolymph, where it participates in insect killing. To begin to understand the role of fimbriae in the unique life cycle of Xenorhabdus, the organization and expression of the mrx fimbrial operon was analysed. The mrx operon contained only five structural genes (mrxACDGH), making it one of the smallest chaperone-usher fimbrial operons studied to date. Unlike the mrp operon of Proteus mirabilis, a site-specific recombinase was not linked to the mrx operon. The intergenic region between the major fimbrial gene (mrxA) and the usher gene (mrxC) lacked a mrpB-like gene, but contained three tandem inverted repeat sequences located downstream of mrxA. A 940 nt mrxA-containing mRNA was the major transcript produced in cells growing on ...
spp. bacteria Xenorhabdus spp. and Photorhabdus Molecular biology of the symbiotic-pathogenic
Applied and Environmental Microbiology, 1995
We have examined the production of the outer membrane proteins of the primary and secondary forms... more We have examined the production of the outer membrane proteins of the primary and secondary forms of Xenorhabdus nematophilus during exponential- and stationary-phase growth at different temperatures. The most highly expressed outer membrane protein of X. nematophilus was OpnP. The amino acid composition of OpnP was very similar to those of the porin proteins OmpF and OmpC of Escherichia coli. N-terminal amino acid sequence analysis revealed that residues 1 to 27 of the mature OpnP shared 70 and 60% sequence identities with OmpC and OmpF, respectively. These results suggest that OpnP is a major porin protein in X. nematophilus. Three additional proteins, OpnA, OpnB, and OpnS, were induced during stationary-phase growth. OpnB was present at a high level in stationary-phase cells grown at 19 to 30 degrees C and was repressed in cells grown at 34 degrees C. OpnA was optimally produced at 30 degrees C and was not present in cells grown at lower and higher temperatures. The production of...
T he gram-negative bacterium Xenorhabdus nematophila engages in a mutualistic relationship with a... more T he gram-negative bacterium Xenorhabdus nematophila engages in a mutualistic relationship with a specific soil nematode and also can mount potent pathogenic attacks on a variety of insects. During its mutualisticpathogenic life cycle, Xenorhabdus produces a wide range of exoenzymes, antimicrobial and nematicidal compounds, and insect toxins. Moreover, the nematode-bacteria complex is useful for managing diverse agricultural pests. These properties, plus its genetic tractability, make Xenorhabdus an excellent model system for studying both bacterial-animal mutualism and pathogenicity, and for developing useful products for medicine, agriculture, and biotechnology. The tripartite X. nematophila-Steinernema carpocapsae-insect interaction is also useful for studying the molecular mechanisms governing both symbiotic and pathogenic interactions between bacteria and animal hosts.
The major outer membrane proteins of the primary and secondary phase variants of Xenorhabdus nema... more The major outer membrane proteins of the primary and secondary phase variants of Xenorhabdus nematophilus produced during exponential and stationary phase growth were characterized. OpnP, the most highly expressed QUter membrane J2rotein of X. 11.ematophilus, was purified as a monomer with a molecular weight of 30,000. The amino acid composition of OpnP was very similar to that of the porin proteins, OmpF and OmpC, of Escherichia coli. N-terminal amino acid sequence analysis revealed that residues 1-27 of the mature OpnP shared 60% sequence identity with OmpF. In vitro pore function analysis of purified OpnP indicated that the single channel conductance values were similar to that measured for OmpF. These results suggest that OpnP is the OmpF-like porin protein in X. nematophilus. Three additional proteins, OpnA, OpnB and OpnS were induced during stationary phase growth. We show that the stationary phase proteins, OpnA and OpnB, were not produced in secondary phase cells. OpnB was p...
Microbiology
Xenorhabdus species are bacterial symbionts of Steinernema nematodes and pathogens of susceptible... more Xenorhabdus species are bacterial symbionts of Steinernema nematodes and pathogens of susceptible insects. Different species of Steinernema nematodes carrying specific species of Xenorhabdus can invade the same insect, thereby setting up competition for nutrients within the insect environment. While Xenorhabdus species produce both diverse antibiotic compounds and prophage-derived R-type bacteriocins (xenorhabdicins), the functions of these molecules during competition in a host are not well understood. Xenorhabdus bovienii (Xb-Sj), the symbiont of Steinernema jollieti, possesses a remnant P2-like phage tail cluster, xbp1, that encodes genes for xenorhabdicin production. We show that inactivation of either tail sheath (xbpS1) or tail fibre (xbpH1) genes eliminated xenorhabdicin production. Preparations of Xb-Sj xenorhabdicin displayed a narrow spectrum of activity towards other Xenorhabdus and Photorhabdus species. One species, Xenorhabdus szentirmaii (Xsz-Sr), was highly sensitive ...
Microbiology
Xenorhabdus species are symbionts of entomopathogenic nematodes and pathogens of susceptible inse... more Xenorhabdus species are symbionts of entomopathogenic nematodes and pathogens of susceptible insects. Nematodes enter insect hosts and perforate the midgut to invade the haemocoel where Xenorhabdus bacteria are released transitioning to their pathogenic stage. During nematode invasion microbes from the insect gut translocate into the haemocoel. Different species of nematodes carrying specific strains of Xenorhabdus can also invade the same insect. Xenorhabdus species thereby compete for nutrients and space with both related strains and non-related gut microbes. While Xenorhabdus species produce diverse antimicrobial compounds in complex media, their functions in insect hosts are not well understood. We show that Xenorhabdus szentirmaii produced ngrA-dependent antibiotics that were active against both gut-derived microbes and Xenorhabdus nematophila whereas antibiotics of X. nematophila were not active against X. szentirmaii. X. nematophila growth was inhibited in co-cultures with wild-type X. szentirmaii in medium that mimics insect haemolymph. An antibiotic-deficient strain of X. szentirmaii was created by inactivating the ngrA gene that encodes the enzyme that attaches the 4' phosphopantetheinyl moiety to non-ribosomal peptide synthetases involved in antibiotic biosynthesis. X. nematophila growth was not inhibited in co-cultures with the ngrA strain. The growth of X. nematophila was suppressed in Manduca sexta co-injected with wild-type X. szentirmaii and X. nematophila. In contrast, growth of X. nematophila was not suppressed in M. sexta co-injected with the ngrA strain. Two unique compounds were detected by MALDI-TOF MS analysis in haemolymph infected with the wild-type but not with the ngrA strain. Finally, killing of M. sexta was delayed in insects infected with the ngrA strain. These findings indicate that in the insect host X. szentirmaii produces ngrA-dependent products involved in both interspecies competition and virulence.
Advances in Environmental Microbiology, 2016
The Gram-negative proteobacterium, Xenorhabdus nematophila, engages in a mutualistic association ... more The Gram-negative proteobacterium, Xenorhabdus nematophila, engages in a mutualistic association with a nematode partner, Steinernema carpocapsae, which infects susceptible insect hosts. After entering the insect, the nematode carrying X. nematophila penetrates the intestine and enters the insect body cavity (hemocoel) where X. nematophila is released transitioning to its pathogenic stage. Together, X. nematophila and the nematode kill the insect host. Microbiota from the insect gut is assumed to translocate into the hemocoel during nematode invasion. In the hemocoel, X. nematophila encounters the dual challenge of inhibiting potential microbial competitors that may proliferate in the insect blood (hemolymph) and suppressing the host innate immune response. X. nematophila produces a plethora of small molecule antimicrobial compounds and secondary metabolites that function in interspecies competition and immune suppression. Suppressing growth of potential competitors and neutralizing an activated immune response not only benefit X. nematophila directly but also enhance fitness of the nematode that reproduces in the hemocoel. Thus, the secondary metabolites support a defensive mutualism between the bacterium and nematode. While secondary metabolites produced at high levels in broth culture can have antimicrobial properties in in vitro assays, their role in a natural infection of an insect host where they may be produced at subinhibitory concentrations is yet to be elucidated. In the present chapter, we discuss the diverse antimicrobial and immunosuppressive compounds produced by X. nematophila and their potential roles in this intriguing defensive mutualism and describe the microbial population dynamics in the hemocoel during the early phase of infection.
Research in Microbiology, 1994
ABSTRACT Xenorhabdus spp. are motile Gram-negative insect-killing bacteria carried by its symbiot... more ABSTRACT Xenorhabdus spp. are motile Gram-negative insect-killing bacteria carried by its symbiotic partner, an entomopathogenic nematode. Here we review our current understanding of the role of the flagella regulon in symbiosis and pathogenesis of Xenorhabdus. The flhDC master flagellar operon is involved not only in flagellar production but also in virulence and hemolysin and lipase production in X. nematophila. Recent studies have shown that the EnvZ-OmpR two-component system is involved in the temporal expression of flhDC. Inactivation of either ompR or envZ causes precocious swarming and hemolysin production. Genomic analysis of the flagella regulons in Xenorhabdus bovienii and Photorhabdus luminescens reveals that while the basic flagellar gene clusters are highly conserved, the nonflagellar genes located within the flagella regulons are widely divergent. Thus, recent studies reveal that the FlhDC-OmpR regulatory circuit plays an integral role in both the virulence properties and protein export in Xenorhabdus.
Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 1987
Agricultural and Biological Chemistry, 1991
Applied and environmental microbiology, 1998
Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic... more Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic nematodes. The bacterium-nematode symbiotic pair is pathogenic for larval-stage insects. The phase I cell type is the form of the bacterium normally associated with the nematode. A variant cell type, referred to as phase II, can form spontaneously under stationary-phase conditions. Phase II cells do not elaborate products normally associated with the phase I cell type. To better define phase variation in X. nematophilus, several strains (19061, AN6, F1, N2-4) of this bacterium were analyzed for new phenotypic traits. An analysis of pathogenicity in Manduca sexta larvae revealed that the phase II form of AN6 (AN6/II) was significantly less virulent than the phase I form (AN6/I). The variant form of N2-4 was also avirulent. On the other hand, F1/II and 19061/II were as virulent as the respective phase I cells. Strain 19061/II was found to be motile, and AN6/II regained motility when the b...
Antonie van Leeuwenhoek, 2002
Xenorhabdus nematophila is an insect pathogen that forms a symbiotic association with the nematod... more Xenorhabdus nematophila is an insect pathogen that forms a symbiotic association with the nematode, Steinernema carpocapsae. Xenorhabdus is carried into the insect host by the nematode, is released into the hemolymph and participates in killing the insect. The bacteria grow to high concentrations supporting the development of the nematode in the hemolymph. OmpR is a global regulatory protein involved in the regulation of porin genes, motility, acid tolerance and virulence in several enteric bacteria. To study the role of ompR in the lifecyle of XenorhabdIs, an ompR -minus strain was constructed. The ompR strain produced markedly reduced levels of the porin protein, OpnP and was both hypermotile and exhibited a hyperhemolysis phenotype. Inactivation of flhDC, the master regulator for flagella synthesis, eliminated hemolysin production in the ompR strain, suggesting that ompR regulates hemolysin production via flhDC. The ompR mutant strain was virulent towards insect hosts. However, w...
Journal of bacteriology, 1999
To determine whether N-terminal sequences are involved in the transmembrane signaling mechanism o... more To determine whether N-terminal sequences are involved in the transmembrane signaling mechanism of EnvZ, the nucleotide sequences of envZ genes from several enteric bacteria were determined. Comparative analysis revealed that the amino acid sequence between Pro41 and Glu53 was highly conserved. To further analyze the role of the conserved sequence, envZ of Escherichia coli was subjected to random PCR mutagenesis and mutant alleles that produced a high-osmolarity phenotype, in which ompF was repressed, were isolated. The mutations identified clustered within, as well as adjacent to, the Pro41-to-Glu53 sequence. These findings suggest that the conserved Pro41-to-Glu53 sequence is involved in the signal transduction mechanism of EnvZ.
Journal of Bacteriology, 2003
The response regulator OmpR is involved in numerous adaptive responses to environmental challenge... more The response regulator OmpR is involved in numerous adaptive responses to environmental challenges. The role that OmpR plays in swarming behavior and swarm-cell differentiation in the symbiotic-pathogenic bacterium Xenorhabdus nematophila was examined in this study. Swarming began 4 h sooner in an ompR mutant strain than in wild-type cells. Precocious swarming was correlated with elevated expression of fliC , early flagellation, and cell elongation. The level of flhDC mRNA was elevated during the early period of swarming in the ompR strain relative to the level in the wild type. These findings show that OmpR is involved in the temporal regulation of flhDC expression and flagellum production and demonstrate that this response regulator plays a role in the swarming behavior of X. nematophila .
Biochemistry and Molecular Biology Education, 2012
Microbiology, 2004
Xenorhabdus nematophila, a Gram-negative bacterium belonging to the Proteus clade of the family E... more Xenorhabdus nematophila, a Gram-negative bacterium belonging to the Proteus clade of the family Enterobacteriaceae, forms a mutualistic association with the soil nematode Steinernema carpocapsae. The nematode invades insects and releases Xenorhabdus into the haemolymph, where it participates in insect killing. To begin to understand the role of fimbriae in the unique life cycle of Xenorhabdus, the organization and expression of the mrx fimbrial operon was analysed. The mrx operon contained only five structural genes (mrxACDGH), making it one of the smallest chaperone-usher fimbrial operons studied to date. Unlike the mrp operon of Proteus mirabilis, a site-specific recombinase was not linked to the mrx operon. The intergenic region between the major fimbrial gene (mrxA) and the usher gene (mrxC) lacked a mrpB-like gene, but contained three tandem inverted repeat sequences located downstream of mrxA. A 940 nt mrxA-containing mRNA was the major transcript produced in cells growing on ...
spp. bacteria Xenorhabdus spp. and Photorhabdus Molecular biology of the symbiotic-pathogenic
Applied and Environmental Microbiology, 1995
We have examined the production of the outer membrane proteins of the primary and secondary forms... more We have examined the production of the outer membrane proteins of the primary and secondary forms of Xenorhabdus nematophilus during exponential- and stationary-phase growth at different temperatures. The most highly expressed outer membrane protein of X. nematophilus was OpnP. The amino acid composition of OpnP was very similar to those of the porin proteins OmpF and OmpC of Escherichia coli. N-terminal amino acid sequence analysis revealed that residues 1 to 27 of the mature OpnP shared 70 and 60% sequence identities with OmpC and OmpF, respectively. These results suggest that OpnP is a major porin protein in X. nematophilus. Three additional proteins, OpnA, OpnB, and OpnS, were induced during stationary-phase growth. OpnB was present at a high level in stationary-phase cells grown at 19 to 30 degrees C and was repressed in cells grown at 34 degrees C. OpnA was optimally produced at 30 degrees C and was not present in cells grown at lower and higher temperatures. The production of...
T he gram-negative bacterium Xenorhabdus nematophila engages in a mutualistic relationship with a... more T he gram-negative bacterium Xenorhabdus nematophila engages in a mutualistic relationship with a specific soil nematode and also can mount potent pathogenic attacks on a variety of insects. During its mutualisticpathogenic life cycle, Xenorhabdus produces a wide range of exoenzymes, antimicrobial and nematicidal compounds, and insect toxins. Moreover, the nematode-bacteria complex is useful for managing diverse agricultural pests. These properties, plus its genetic tractability, make Xenorhabdus an excellent model system for studying both bacterial-animal mutualism and pathogenicity, and for developing useful products for medicine, agriculture, and biotechnology. The tripartite X. nematophila-Steinernema carpocapsae-insect interaction is also useful for studying the molecular mechanisms governing both symbiotic and pathogenic interactions between bacteria and animal hosts.
The major outer membrane proteins of the primary and secondary phase variants of Xenorhabdus nema... more The major outer membrane proteins of the primary and secondary phase variants of Xenorhabdus nematophilus produced during exponential and stationary phase growth were characterized. OpnP, the most highly expressed QUter membrane J2rotein of X. 11.ematophilus, was purified as a monomer with a molecular weight of 30,000. The amino acid composition of OpnP was very similar to that of the porin proteins, OmpF and OmpC, of Escherichia coli. N-terminal amino acid sequence analysis revealed that residues 1-27 of the mature OpnP shared 60% sequence identity with OmpF. In vitro pore function analysis of purified OpnP indicated that the single channel conductance values were similar to that measured for OmpF. These results suggest that OpnP is the OmpF-like porin protein in X. nematophilus. Three additional proteins, OpnA, OpnB and OpnS were induced during stationary phase growth. We show that the stationary phase proteins, OpnA and OpnB, were not produced in secondary phase cells. OpnB was p...
Microbiology
Xenorhabdus species are bacterial symbionts of Steinernema nematodes and pathogens of susceptible... more Xenorhabdus species are bacterial symbionts of Steinernema nematodes and pathogens of susceptible insects. Different species of Steinernema nematodes carrying specific species of Xenorhabdus can invade the same insect, thereby setting up competition for nutrients within the insect environment. While Xenorhabdus species produce both diverse antibiotic compounds and prophage-derived R-type bacteriocins (xenorhabdicins), the functions of these molecules during competition in a host are not well understood. Xenorhabdus bovienii (Xb-Sj), the symbiont of Steinernema jollieti, possesses a remnant P2-like phage tail cluster, xbp1, that encodes genes for xenorhabdicin production. We show that inactivation of either tail sheath (xbpS1) or tail fibre (xbpH1) genes eliminated xenorhabdicin production. Preparations of Xb-Sj xenorhabdicin displayed a narrow spectrum of activity towards other Xenorhabdus and Photorhabdus species. One species, Xenorhabdus szentirmaii (Xsz-Sr), was highly sensitive ...
Microbiology
Xenorhabdus species are symbionts of entomopathogenic nematodes and pathogens of susceptible inse... more Xenorhabdus species are symbionts of entomopathogenic nematodes and pathogens of susceptible insects. Nematodes enter insect hosts and perforate the midgut to invade the haemocoel where Xenorhabdus bacteria are released transitioning to their pathogenic stage. During nematode invasion microbes from the insect gut translocate into the haemocoel. Different species of nematodes carrying specific strains of Xenorhabdus can also invade the same insect. Xenorhabdus species thereby compete for nutrients and space with both related strains and non-related gut microbes. While Xenorhabdus species produce diverse antimicrobial compounds in complex media, their functions in insect hosts are not well understood. We show that Xenorhabdus szentirmaii produced ngrA-dependent antibiotics that were active against both gut-derived microbes and Xenorhabdus nematophila whereas antibiotics of X. nematophila were not active against X. szentirmaii. X. nematophila growth was inhibited in co-cultures with wild-type X. szentirmaii in medium that mimics insect haemolymph. An antibiotic-deficient strain of X. szentirmaii was created by inactivating the ngrA gene that encodes the enzyme that attaches the 4' phosphopantetheinyl moiety to non-ribosomal peptide synthetases involved in antibiotic biosynthesis. X. nematophila growth was not inhibited in co-cultures with the ngrA strain. The growth of X. nematophila was suppressed in Manduca sexta co-injected with wild-type X. szentirmaii and X. nematophila. In contrast, growth of X. nematophila was not suppressed in M. sexta co-injected with the ngrA strain. Two unique compounds were detected by MALDI-TOF MS analysis in haemolymph infected with the wild-type but not with the ngrA strain. Finally, killing of M. sexta was delayed in insects infected with the ngrA strain. These findings indicate that in the insect host X. szentirmaii produces ngrA-dependent products involved in both interspecies competition and virulence.
Advances in Environmental Microbiology, 2016
The Gram-negative proteobacterium, Xenorhabdus nematophila, engages in a mutualistic association ... more The Gram-negative proteobacterium, Xenorhabdus nematophila, engages in a mutualistic association with a nematode partner, Steinernema carpocapsae, which infects susceptible insect hosts. After entering the insect, the nematode carrying X. nematophila penetrates the intestine and enters the insect body cavity (hemocoel) where X. nematophila is released transitioning to its pathogenic stage. Together, X. nematophila and the nematode kill the insect host. Microbiota from the insect gut is assumed to translocate into the hemocoel during nematode invasion. In the hemocoel, X. nematophila encounters the dual challenge of inhibiting potential microbial competitors that may proliferate in the insect blood (hemolymph) and suppressing the host innate immune response. X. nematophila produces a plethora of small molecule antimicrobial compounds and secondary metabolites that function in interspecies competition and immune suppression. Suppressing growth of potential competitors and neutralizing an activated immune response not only benefit X. nematophila directly but also enhance fitness of the nematode that reproduces in the hemocoel. Thus, the secondary metabolites support a defensive mutualism between the bacterium and nematode. While secondary metabolites produced at high levels in broth culture can have antimicrobial properties in in vitro assays, their role in a natural infection of an insect host where they may be produced at subinhibitory concentrations is yet to be elucidated. In the present chapter, we discuss the diverse antimicrobial and immunosuppressive compounds produced by X. nematophila and their potential roles in this intriguing defensive mutualism and describe the microbial population dynamics in the hemocoel during the early phase of infection.
Research in Microbiology, 1994
ABSTRACT Xenorhabdus spp. are motile Gram-negative insect-killing bacteria carried by its symbiot... more ABSTRACT Xenorhabdus spp. are motile Gram-negative insect-killing bacteria carried by its symbiotic partner, an entomopathogenic nematode. Here we review our current understanding of the role of the flagella regulon in symbiosis and pathogenesis of Xenorhabdus. The flhDC master flagellar operon is involved not only in flagellar production but also in virulence and hemolysin and lipase production in X. nematophila. Recent studies have shown that the EnvZ-OmpR two-component system is involved in the temporal expression of flhDC. Inactivation of either ompR or envZ causes precocious swarming and hemolysin production. Genomic analysis of the flagella regulons in Xenorhabdus bovienii and Photorhabdus luminescens reveals that while the basic flagellar gene clusters are highly conserved, the nonflagellar genes located within the flagella regulons are widely divergent. Thus, recent studies reveal that the FlhDC-OmpR regulatory circuit plays an integral role in both the virulence properties and protein export in Xenorhabdus.
Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 1987
Agricultural and Biological Chemistry, 1991
Applied and environmental microbiology, 1998
Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic... more Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic nematodes. The bacterium-nematode symbiotic pair is pathogenic for larval-stage insects. The phase I cell type is the form of the bacterium normally associated with the nematode. A variant cell type, referred to as phase II, can form spontaneously under stationary-phase conditions. Phase II cells do not elaborate products normally associated with the phase I cell type. To better define phase variation in X. nematophilus, several strains (19061, AN6, F1, N2-4) of this bacterium were analyzed for new phenotypic traits. An analysis of pathogenicity in Manduca sexta larvae revealed that the phase II form of AN6 (AN6/II) was significantly less virulent than the phase I form (AN6/I). The variant form of N2-4 was also avirulent. On the other hand, F1/II and 19061/II were as virulent as the respective phase I cells. Strain 19061/II was found to be motile, and AN6/II regained motility when the b...
Antonie van Leeuwenhoek, 2002
Xenorhabdus nematophila is an insect pathogen that forms a symbiotic association with the nematod... more Xenorhabdus nematophila is an insect pathogen that forms a symbiotic association with the nematode, Steinernema carpocapsae. Xenorhabdus is carried into the insect host by the nematode, is released into the hemolymph and participates in killing the insect. The bacteria grow to high concentrations supporting the development of the nematode in the hemolymph. OmpR is a global regulatory protein involved in the regulation of porin genes, motility, acid tolerance and virulence in several enteric bacteria. To study the role of ompR in the lifecyle of XenorhabdIs, an ompR -minus strain was constructed. The ompR strain produced markedly reduced levels of the porin protein, OpnP and was both hypermotile and exhibited a hyperhemolysis phenotype. Inactivation of flhDC, the master regulator for flagella synthesis, eliminated hemolysin production in the ompR strain, suggesting that ompR regulates hemolysin production via flhDC. The ompR mutant strain was virulent towards insect hosts. However, w...
Journal of bacteriology, 1999
To determine whether N-terminal sequences are involved in the transmembrane signaling mechanism o... more To determine whether N-terminal sequences are involved in the transmembrane signaling mechanism of EnvZ, the nucleotide sequences of envZ genes from several enteric bacteria were determined. Comparative analysis revealed that the amino acid sequence between Pro41 and Glu53 was highly conserved. To further analyze the role of the conserved sequence, envZ of Escherichia coli was subjected to random PCR mutagenesis and mutant alleles that produced a high-osmolarity phenotype, in which ompF was repressed, were isolated. The mutations identified clustered within, as well as adjacent to, the Pro41-to-Glu53 sequence. These findings suggest that the conserved Pro41-to-Glu53 sequence is involved in the signal transduction mechanism of EnvZ.