Mechanism of adverse conditions causing lack of flagella in Escherichia coli

Role of the histidine kinase, EnvZ, in the production of outer membrane proteins in the symbiotic-pathogenic bacterium Xenorhabdus nematophilus

We show that inactivation of envZ, the gene encoding the histidine kinase sensor protein, EnvZ, of Xenorhabdus nematophilus, affected the production of several outer membrane proteins (Opns). X. nematophilus produced five major Opns during exponential growth. Insertional inactivation of envZ led to a decrease in the production of OpnP, the OmpF-like pore-forming protein which constitutes approximately 50% of the total outer membrane protein in X. nematophilus. OpnA production was also reduced, while the remaining Opns were produced normally. During the transition to stationary phase, three new outer membrane proteins, OpnB, OpnS, and OpnX, were induced in the wild-type strain. The envZ-minus strain, ANT1, did not produce OpnB and OpnX, while OpnS was induced at markedly reduced levels. These results suggest that EnvZ was required for the high-level production of OpnP during exponential growth and may be involved in the production of OpnB, OpnS, and OpnX during stationary-phase growth. We also show that ANT1 was more pathogenic than the wild-type strain when as few as five cells were injected into the hemolymph of the larval stage of the tobacco hornworm (Manduca sexta). The larvae died before significant numbers of bacteria were detectable in the hemolymph. These results are discussed in relation to the role of EnvZ in the life cycle of X. nematophilus.

Effect of glucose concentration on swimming motility in enterobacteria

Since the observation that glucose prevents the synthesis of flagella in Escherichia coli was first reported in 1967, many studies have addressed the underlying mechanism. Currently, it is thought that an increase in glucose concentration decreases the intracellular CRP/cAMP concentration. This leads to an inhibitory effect on the expression of the flhD operon, the master operon for flagella synthesis. In our study on defining factors influencing the cell differentiation of Serratia marcescens, glucose catabolite repression of hag expression and swimming/swarming motility was not observed. Further experiments using a simple swimming motility assay extended this observation to other members of Enterobacteriaceae. Although the underlying mechanism is still uncharacterised, our results suggest that glucose catabolite repression of swimming motility may not be a common phenomenon in Enterobacteriaceae.

Regulation of RNA polymerase sigma subunit synthesis in Escherichia coli: intracellular levels of four species of sigma subunit under various growth conditions

By a quantitative Western immunoblot analysis, the intracellular levels of two principal sigma subunits, sigma 70 (sigma D, the rpoD gene product) and sigma 38 (sigma S, the rpoS gene product), and of two minor sigma subunits, sigma 54 (sigma N, the rpoN gene product) and sigma 28 (sigma F, the rpoF gene product), were determined in two Escherichia coli strains, W3110 and MC4100. The results indicated that the levels of sigma 54 and sigma 28 are maintained at 10 and 50%, respectively, of the level of sigma 70 in both strains growing at both exponential and stationary phases, but in agreement with the previous measurement for strain MC4100 (M. Jishage and A. Ishihama, J. Bacteriol. 177:6832-6835, 1995), the level of sigma 38 was undetectable at the exponential growth phase but increased at 30% of the level of sigma 70 at the stationary phase. Stress-coupled change in the intracellular level was observed for two sigma subunits: (i) the increase in sigma 38 level and the decrease in sigma 28 level upon exposure to heat shock at the exponential phase and (ii) the increase in sigma 38 level under high-osmolality conditions at both the exponential and stationary phases.

Btcd, a mouse protein that binds to curved DNA, can substitute in Escherichia coli for H-NS, a bacterial nucleoid protein

In an Escherichia coli mutant devoid of H-NS, a bacterial nucleoid protein, mouse protein Btcd was able to substitute for H-NS in two tested functions. It restored cell motility and repression of the expression of the bgl operon. Btcd1, a mutant Btcd protein deleted of its zinc finger and thus having reduced DNA binding, failed to substitute for H-NS. Mouse protein Btcd was shown to repress the bgl operon at the level of transcription initiation and to bind preferentially to a curved DNA fragment encompassing the bgl promoter. These effects of Btcd on bacterial gene transcription can be accounted for by the binding of Btcd or H-NS to a curved DNA sequence near a promoter. A few mammalian proteins have been shown to substitute for their Escherichia prototypes involved in DNA and RNA transactions. The efficiency of Btcd protein in substituting for H-NS in Escherichia suggests its possible involvement in regulating gene expression in mouse cells.

Control by phosphatidylglycerol of expression of the flhD gene in Escherichia coli

We reported elsewhere that mutation in the pgsA gene, responsible for the synthesis of phosphatidylglycerol, repressed the synthesis of flagellin and caused the loss of motility of Escherichia coli (Tomura et al., FEBS Letters 329, 287-290, 1993). We now describe evidence for a decrease in promoter activity of the flhD gene, a master gene for flagellum synthesis, in the pgsA3 mutant. We constructed a plasmid with a promoter region of the flhD gene connected with the structure region of the lacZ gene. The activity of beta-galactosidase in the extract prepared from the pgsA3 mutant harboring the fusion plasmid was 30% of that in the wild type cells. This result means that phosphatidylglycerol is likely to be required for the initiation of transcription of the flhD gene. We also found that the motility-less phenotype of the mutant was partially suppressed by elevating incubation temperature. This suppression is caused by restoration of transcription of the flhD gene by high temperature. As the content of phosphatidylglycerol did not increase by elevating incubation temperature, we proposed that this suppression is caused by alternation of a physical structure of phospholipid bilayers in cytoplasmic membranes.

Modulation of flagellar expression in Escherichia coli by acetyl phosphate and the osmoregulator OmpR

During the search for unknown factors involved in motility, we have found that expression of the flagellar master operon flhDC is affected by mutations of the pta and ackA genes, encoding phosphotransacetylase and acetate kinase, respectively (S. Shin, J. Sheen, and C. Park, Korean J. Microbiol. 31:504-511, 1993). Here we describe results showing that this effect is modulated by externally added acetate, except when both pta and ackA are mutated, suggesting the role of acetyl phosphate, an intermediate of acetate metabolism, as a regulatory effector. Furthermore, the following evidence indicates that the phosphorylation of OmpR, a trans factor for osmoregulation, regulates flagellar expression. First, in a strain lacking ompR, the expression of flhDC is no longer responsive to a change in the level of acetyl phosphate. Second, an increase in medium osmolarity does not decrease flhDC expression in an ompR mutant. It is known that such an increase normally enhances OmpR phosphorylation. Third, OmpR protein binds to the DNA fragment containing the flhDC promoter, and its affinity is increased with phosphorylation by acetyl phosphate. DNase I footprinting revealed the regions of the flhDC promoter protected by OmpR in the presence or absence of phosphorylation. Therefore, we propose that the phosphorylated OmpR, generated by either osmolarity change or the internal level of acetyl phosphate, negatively regulates the expression of flagella.

Effect of salicylate on expression of flagella by Escherichia coli and Proteus, Providencia, and Pseudomonas spp

Osmotic stress, salicylate, and Mar (multiple antibiotic resistance) mutation are known to block the expression of the OmpF porin. Since these conditions have also been shown to inhibit the expression of P and CFA fimbriae in Escherichia coli, we speculated that they might affect the expression of flagella as well. Hyperosmotic conditions have been shown to block the synthesis of flagellin and expression of flagella in E. coli (C. Li, C. J. Louise, W. Shi, and J. Adler, J. Bacteriol. 175:2229-2235, 1993). In the current study, sodium salicylate was found to inhibit the motility of E. coli, Proteus mirabilis, Proteus vulgaris, Providencia rettgeri, and Providencia stuartii in a reversible, concentration-dependent manner. Swarming did not occur at 20 mM sodium salicylate. Salicylate also blocked the synthesis of flagellin in E. coli. Phenotypic Mar mutants of E. coli derived from motile strains were amotile. Flagella were markedly reduced as determined by scanning electron microscopy when P. mirabilis was grown in broth containing 20 mM salicylate. Salicylate had no apparent effect, however, on expression of a 40-kDa porin protein in P. mirabilis. This finding suggests that the noted effect of salicylate on Proteus spp. may be mediated through a mechanism other than porin production or that the Proteus porin may not be analogous to OmpF in E. coli. Salicylate decreased the motility of Pseudomonas cepacia but had no effect on Pseudomonas aeruginosa. The exact mechanism by which salicylate exerts its effect is not known, but it appears to be related to osmoregulation.

The H-NS protein is involved in the biogenesis of flagella in Escherichia coli

The function of the flagellum-chemotaxis regulon requires the expression of many genes and is positively regulated by the cyclic AMP-catabolite activator protein (cAMP-CAP) complex. In this paper, we show that motile behavior was affected in Escherichia coli hns mutants. The loss of motility resulted from a complete lack of flagella. A decrease in the level of transcription of the flhD and fliA genes, which are both required for the synthesis of flagella, was observed in the presence of an hns mutation. Furthermore, the Fla- phenotype was not reversed to the wild type in the presence of a cfs mutation which renders the flagellum synthesis independent of the cAMP-CAP complex. These results suggest that the H-NS protein acts as a positive regulator of genes involved in the biogenesis of flagella by a mechanism independent of the cAMP-CAP pathway.

Thermoregulation in Yersinia enterocolitica is coincident with changes in DNA supercoiling

Yersinia enterocolitica is a facultative intracellular parasite, displaying the ability to grow saprophytically or invade and persist intracellularly in the mammalian reticuloendothelial system. The transition between such diverse environments requires the co-ordinated regulation of specific sets of genes on both the chromosome and virulence plasmid. Temperature has a profound pleiotropic effect on gene expression and phenotypically promotes alterations in cell morphology, outer-membrane protein synthesis, urease production, lipopolysaccharide synthesis, motility, and synthesis of genes involved in invasion of eukaryotic host cells. By examining thermoregulated flagella biosynthesis, we have determined that motility is repressed at 25 degrees C (permissive temperature) with subinhibitory concentrations of novobiocin. These conditions also induce virulence gene expression suggesting novobiocin addition simulates, at least partially, a high-temperature environment. Furthermore, temperature-shift experiments, using Y. enterocolitica containing pACYC184 as a reporter plasmid, indicate that thermo-induced alterations of DNA supercoiling coincide with temperature-induced phenotypic changes. A class of putative DNA gyrase mutant (novobiocin resistant) likewise demonstrates the 37 degrees C phenotype when cultured at 25 degrees C; it is non-motile, urease negative, calcium growth dependent, and positive for Yop expression. These results support a model implicating DNA topology as a contributing factor of Y. enterocolitica thermoregulation.

Nonmotility and phagocytic resistance of Pseudomonas aeruginosa isolates from chronically colonized patients with cystic fibrosis

Although Pseudomonas aeruginosa chronically colonizes most older patients with cystic fibrosis (CF), bacterial features responsible for its persistence are understood poorly. We observed that many P. aeruginosa isolates from chronically colonized patients were nonmotile and resistant to phagocytosis by macrophages. P. aeruginosa isolates were collected from 20 CF patients for up to 10 years. Isolates from early colonization were highly motile and expressed both flagellin and pilin. However, many isolates from chronically colonized patients lacked flagellin expression and were nonmotile; a total of 1,030 P. aeruginosa CF isolates were examined, of which 39% were nonmotile. Moreover, sequential isolates recovered from several of the CF patients were consistently nonmotile for up to 10 years. Lack of motility was rare among environmental isolates (1.4%) and other clinical isolates (3.7%) of P. aeruginosa examined. Partial complementation of motility in nonmotile P. aeruginosa isolates was achieved by introduction of extra copies of the rpoN locus carried on plasmid pPT212, indicating that the alternate sigma factor, RpoN, may be involved in the coordinate regulation of virulence factors during CF infection. We hypothesize that the nonmotile phenotype may provide P. aeruginosa a survival advantage in chronic CF infection by enabling it to resist phagocytosis and conserve energy.

The pss and psd genes are required for motility and chemotaxis in Escherichia coli

Mutants of Escherichia coli defective in phosphatidylserine synthase (encoded by pss) and phosphatidylserine decarboxylase (encoded by psd) make cell membranes deficient in phosphatidylethanolamine. In this report we show that wild-type pss and psd genes are required for motility and chemotaxis. Null mutants or strains with temperature-sensitive pss or psd mutations grown at high temperature (35 degrees C) were nonmotile. They lacked flagella and showed reduced rates of transcription of the flhD master operon (encoding FlhD and FlhC), the fliA operon (encoding sigma F), and the fliC operon (encoding flagellin). At low temperature (25 degrees C), the temperature-sensitive mutant cells showed motility and chemotaxis but at reduced levels. The extent of the motility and chemotaxis defects in the mutants was correlated with the amount of phosphatidylethanolamine in the membranes, suggesting a link between membrane phospholipid composition and expression of the flagellum chemotaxis regulon.

Adverse conditions which cause lack of flagella in Escherichia coli

Wild-type Escherichia coli was not motile when grown in tryptone broth under the following adverse conditions: the presence of high temperature [J. Adler and B. Templeton, J. Gen. Microbiol. 46:175-184, 1967; R. B. Morrison and J. McCapra, Nature (London) 192:774-776, 1961; K. Ogiuti, Jpn. J. Exp. Med. 14:19-28, 1936], high concentrations of salts, high concentrations of carbohydrates, high concentrations of low-molecular-weight alcohols, or the pressure of gyrase inhibitors. Under all these conditions, growth was necessary for the loss of motility. This loss of motility was correlated with a reduction in the amount of cellular flagellin. We isolated and studied mutants that are resistant to suppression of motility by some of these conditions, because of the ability to synthesize flagella under these conditions. The mutations were mapped to 42 min, a region of the chromosome where many of the flagellar genes map. We also studied the effect of a preexisting gyrA mutation which allowed flagellar formation in the presence of nalidixate.