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In Archaea, the preflagellin peptidase (a type IV prepilin-like peptidase designated FlaK in Methanococcus voltae and Methanococcus maripaludis) is the enzyme that cleaves the N-terminal signal peptide from preflagellins. In methanogens and several other archaeal species, the typical flagellin signal peptide length is 11 to 12 amino acids, while in other archaea preflagellins possess extremely short signal peptides. A systematic approach to address the signal peptide length requirement for preflagellin processing is presented in this study. M. voltae preflagellin FlaB2 proteins with signal peptides 3 to 12 amino acids in length were generated and used as a substrate in an in vitro assay utilizing M. voltae membranes as an enzyme source. Processing by FlaK was observed in FlaB2 proteins containing signal peptides shortened to 5 amino acids; signal peptides 4 or 3 amino acids in length were unprocessed. In the case of Sulfolobus solfataricus, where the preflagellin peptidase PibD has broader substrate specificity, some predicted substrates have predicted signal peptides as short as 3 amino acids. Interestingly, the shorter signal peptides of the various mutant FlaB2 proteins not processed by FIaK were processed by PibD, suggesting that some archaeal preflagellin peptidases are likely adapted toward cleaving shorter signal peptides. The functional complementation of signal peptidase activity by FlaK and PibD in an M. maripaludis [DELTA]flaK mutant indicated that processing of preflageilins was detected by complementation with either FlaK or PibD, yet only FlaK-complemented cells were flagellated. This suggested that a block in an assembly step subsequent to signal peptide removal occurred in the PibD complementation. doi: 10.1128/JB.00673-09

Salmonella flgG point mutations produce filamentous rod structures whose lengths are determined by FliK. FliK length variants produce rods with lengths proportional to the corresponding FliK molecular size, suggesting that FliK controls the length of not only the hook but also the rod by the same molecular mechanism. doi: 10.1128/JB.00509-09

The flagellar cytoplasmic ring (C ring), which consists of three proteins, FliG, FliM, and FliN, is located on the cytoplasmic side of the flagellum. The C ring is a multifunctional structure necessary for flagellar protein secretion, torque generation, and switching of the rotational direction of the motor. The deletion of any one of the fliG, fliM, and fliN genes results in a [Fla.sup.-] phenotype. Here, we show that the overproduction of the flagellum-specific ATPase FliI overcomes the inability of basal bodies with partial C-ring structures to produce complete flagella. Flagella made upon FliI overproduction were paralyzed, indicating that an intact C ring is essential for motor function. In FliN-or FliM-deficient mutants, flagellum production was about 10% of the wild-type level, while it was only a few percent in FliG-deficient mutants, suggesting that the size of partial C rings affects the extent of flagellation. For flagella made in C-ring mutants, the hook length varied considerably, with many being markedly shorter or longer than that of the wild type. The broad distribution of hook lengths suggests that defective C rings cannot control the hook length as tightly as the wild type even though FliK and FlhB are both intact. doi: 10.1128/JB.00601-09

Silicibacter sp. TM1040 is a member of the marine Roseobacter clade of Alphaproteobacteria that forms symbioses with unicellular eukaryotic phytoplankton, such as dinoflagellates. The symbiosis is complex and involves a series of steps that physiologically change highly motile bacteria into cells that readily form biofilms on the surface of the host. The initial phases of symbiosis require bacterial motility and chemotaxis that drive the swimming bacteria toward their planktonic host. Cells lacking wild-type motility fail to establish biofilms on host cells and do not produce effetive symbioses, emphasizing the importance of understanding the molecular mechanisms controlling flagellar biosynthesis and the biphasic 'swim-or-stick' switch. In the present study, we used a combination of bioinformatic and genetic approaches to identify the genes critical for swimming of Silicibacter sp. TM1040. More than 40 open reading frames with homology to known flagellar structural and regulatory genes were identified, most of which are organized into approximately eight operons comprising a 35.4-kb locus, with surprising similarity to the fla2 locus of Rhodobacter sphaeroides. The genome has homologs of CckA, CtrA, FlbT, and FlaF, proteins that in Caulobacter crescentus regulate flagellum biosynthesis. In addition, we uncovered three novel genes, flaB, flaC, and flaD, which encode flagellar regulatory proteins whose functions are likely to involve regulation of motor function (FlaD) and modulation of the swim-or-stick switch (FlaC). The data support the conclusion that Silicibacter sp. TM1040 uses components found in other Alphaproteobacteria, as well as novel molecular mechanisms, to regulate the expression of the genes required for motility and biofilm formation. These unique molecular mechanisms may enhance the symbiosis and survival of Roseobacter clade bacteria in the marine environment.

Upon completion of the flagellar hook-basal body (HBB) structure, the flagellar type III secretion system switches from secreting rod/hook-type to filament-type substrates. The secretion specificity switch has been reported to occur prematurely (prior to HBB completion) in flk-null mutants (P. Aldridge, J. E. Karlinsey, E. Becker, F. F. Chevance, and K. T. Hughes, Mol. Microbiol. 60:630-643, 2006) and in distal rod gene gain-of-function mutants (flgG* mutants) that produce filamentous rod structures (F. F. Chevance, N. Takahashi, J. E. Karlinsey, J. Gnerer, T. Hirano, R. Samudrala, S. Aizawa, and K. T. Hughes, Genes Dev. 21:2326-2335, 2007). A fusion of [beta]-lactamase (Bla) to the C terminus of the filament-type secretion substrate FlgM was used to select for mutants that would secrete FlgM-Bla into the periplasmic space and show ampicillin resistance ([Ap.sup.r]). [Ap.sup.r] resulted from null mutations in the flhE gene, C-terminal truncation mutations in the flhA gene, null and dominant mutations in the flk gene, and flgG* mutations. All mutant classes required the hook length control protein (FliK) and the rod cap protein (Fig J) for the secretion specificity switch to occur. However, neither the hook (FlgE) nor the hook cap (FlgD) protein was required for premature FlgM-Bla secretion in the flgG* and flk mutant strains, but it was in the flhE mutants. Unexpectedly, when deletions of either flgE or flgD were introduced into flgG* mutant strains, filaments were able to grow directly on the filamentous rod structures.

Glycosylation is a posttranslational modification utilized in all three domains of life. Compared to eukary. otic and bacterial systems, knowledge of the archaeal processes involved in glycosylation is limited. Recently, Methanococcus voltae flagellin proteins were found to have an N-linked trisaccharide necessary for proper flagellum assembly. Current analysis by mass spectrometry of Methanococcus maripaludis flagellin proteins also indicated the attachment of an N-glycan containing acetylated sugars. To identify genes involved in sugar biosynthesis in M. maripaludis, a putative acetyltransferase was targeted for in-frame deletion. Deletion of this gene (MMP0350) resulted in a flagellin molecular mass shift to a size comparable to that expected for underglycosylated or completely nonglycoslyated flagellins, as determined by immunoblotting. Assembled flagellar filaments were not observed by electron microscopy. Interestingly, the deletion also resulted in defective pilus anchoring. Mutant cells with a deletion of MMP0350 had very few, if any, pili attached to the cell surface compared to a nonflagellated but piliated strain. However, pili were obtained from culture supernatants of this strain, indicating that the defect was not in pilus assembly but in stable attachment to the cell surface. Complementation of MMP0350 on a plasmid restored pilus attachment, but it was unable to restore flagellation, likely because the mutant ceased to make detectable flagellin. These findings represent the first report of a biosynthetic gene involved in flagellin glycosylation in archaea. Also, it is the first gene to be associated with pili, linking flagellum and pilus structure and assembly through posttranslationai modifications.

Salmonella enterica serovar Typhimurium secretes virulence factors for invasion called Sip proteins or Sips into its hosts through a type III secretion system (T3SS). In the absence of a host, S. enterica induces Sip secretion in response to sucrose or simple salts, such as NaCl. We analyzed induction of host-independent Sip secretion by monitoring protein secretion by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), assembly of needle complexes by electron microscopy, and transcription of virulence regulatory genes by quantitative reverse transcriptase PCR (real-time PCR). SDS-PAGE showed that addition of sucrose or simple salts, such as NaCl, to the growth medium induced Sip secretion without altering flagellar protein secretion, which requires a distinct T3SS. Electron microscopy confirmed that the amount of secreted Sips increased as the number of assembled needle complexes increased. Real-time PCR revealed that added sucrose or NaCl enhanced transcription of hilA, hilC, and hilD, which encode known regulators of Salmonella virulence. However, epistasis analysis implicated HilD and HilA, but not HilC, in the direct pathway from the salt stimulus to the Sip secretion response. Further analyses showed that the BarA/SirA two-component signal transduction pathway, but not the two-component sensor kinase EnvZ, directly activated hilD and hiLA transcription and thus Sip secretion in response to either sucrose or NaCl. Finally, real-time PCR showed that salt does not influence transcription of the BarA/SirA-dependent csrB and csrC genes. A model is proposed for the major pathway in which sucrose or salt signals to enhance virulence gene expression.

Helicobacter pylori requires flagellar motility and chemotaxis to establish and maintain chronic infection of the human stomach. The pH gradient in the stomach mucus is essential for bacterial orientation and guides the bacterium toward a narrow layer of the mucus, suggesting that H. pylori is capable of energy sensing or taxis. In the present study, H. pylori wild-type behavior in a temporal swimming assay could be altered by electron transport inhibitors, indicating that a connection between metabolism and behavior exists. In order to elucidate mechanisms of behavioral responses of H. pylori related to energy sensing, we investigated the phenotypes of single and multiple mutants of the four proposed chemotaxis sensor proteins. All sensor mutants were motile, but they diverged in their behavior in media supporting different energy yields. One proposed intracellular sensor, TlpD, was crucial for behavioral responses of H. pylori in defined media which did not permit growth and led to reduced bacterial energy levels. Suboptimal energetic conditions and inhibition of electron transport induced an increased frequency of stops and direction changes in the wild type but not in tlpD mutants. Loss of metabolism-dependent behavior in tlpD mutants could be reversed by complementation but not by electron donors bypassing the activity of the electron transport chain, in contrast to the case for the wild type. TlpD, which apparently lacks transmembrane domains, was detected both in the bacterial cytoplasm and at the bacterial periphery. The proposed energy sensor TlpD was found to mediate a repellent tactic response away from conditions of reduced electron transport.

Borrelia burgdorferi is a flat-wave, motile spirochete that causes Lyme disease. Motility is provided by periplasmic flagella (PFs) located between the cell cylinder and an outer membrane sheath. The structure of these PFs, which are composed of a basal body, a hook, and a filament, is similar to the structure of flagella of other bacteria. To determine if hook formation influences flagellin gene transcription in B. burgdorferi, we inactivated the hook structural gene flgE by targeted mutagenesis. In many bacteria, completion of the hook structure serves as a checkpoint for transcriptional control of flagellum synthesis and other chemotaxis and motility genes. Specifically, the hook allows secretion of the anti-sigma factor FlgM and concomitant late gene transcription promoted by [[sigma].sup.28] However, the control of B. burgdorferi PF synthesis differs from the control of flagellum synthesis in other bacteria; the gene encoding [[sigma].sup.28] is not present in the genome of B. burgdorferi, nor are any [[sigma].sup.28] promoter recognition sequences associated with the motility genes. We found that B. burgdorferi flgE mutants lacked PFs, were rod shaped, and were nonmotile, which substantiates previous evidence that PFs are involved in both cell morphology and motility. Although most motility and chemotaxis gene products accumulated at wild-type levels in the absence of FlgE, mutant cells had markedly decreased levels of the flagellar filament proteins FlaA and FlaB. Further analyses showed that the reduction in the levels of flagellin proteins in the spirochetes lacking FlgE was mediated at the posttranscriptional level. Taken together, our results indicate that in B. burgdorferi, the completion of the hook does not serve as a checkpoint for transcriptional regulation of flagellum synthesis. In addition, we also present evidence that the hook protein in B. burgdorferi forms a high-molecular-weight complex and that formation of this complex occurs in the periplasmic space.

The role of flagellin glycosylation on motility was investigated in Pseudomonas syringae pv. tabaci. The swimming activity of glycosylation-defective mutants was prominently decreased in a highly viscous medium. The mutants showed differences in polymorphic transitions and in the bundle formation of flagella, indicating that glycosylation stabilizes the filament structure and lubricates the rotation of the bundle.

The ability of Escherichia coli cells to produce type 1 pili depends upon the orientation of the fimA promoter. The orientation depends upon the ratios of the FimB and FimE recombinases. Here, we report that the two-component response regulator RcsB influences the piliation state by controlling fimB and timE transcription.

Three flagellar proteins, FliG, FliM, and FliN (FliGMN), are the components of the C ring of the flagellar motor. The genes encoding these proteins are multifunctional; they show three different phenotypes ([Fla.sup.-], [Mot.sup.-], and [Che.sup.-]), depending on the sites and types of mutations. Some of the [Mot.sup.-] mutants previously characterized are found to be motile. Reexamination of all [Mot.sup.-] mutants in fliGMN genes so far studied revealed that many of them are actually temperature sensitive (TS); that is, they are motile at 20oC but nonmotile at 37[degrees]C. There were two types of TS mutants: one caused a loss of function that was not reversed by a return to the permissive temperature (rigid TS), and the other caused a loss that was reversed (hyper-TS). The rigid TS mutants showed an all-or-none phenotype; that is, once a structure was formed, the structure and function were stable against temperature shifts. All of fliM and fliN and most of the fliG TS mutants belong to this group. On the other hand, the hyper-TS mutants (three of the fliG mutants) showed a temporal swimming/ stop phenotype, responding to temporal temperature shifts when the structure was formed at a permissive temperature. Those hyper-TS mutation sites are localized in the C-terminal domain of the FliG molecules at sites that are different from the previously proposed functional sites. We discuss a role for this new region of FliG in the torque generation of the flagellar motor.

Bradyrhizobium japonicum is one of the soil bacteria that form nodules on soybean roots. The cell has two sets of flagellar systems, one thick flagellum and a few thin flagella, uniquely growing at subpolar positions. The thick flagellum appears to be semicoiled in morphology, and the thin flagella were in a tight-curly form as observed by dark-field microscopy. Flagellin genes were identified from the amino acid sequence of each flageflin. Flagellar genes for the thick flagellum are scattered into several clusters on the genome, while those genes for the thin flagellum are compactly organized in one cluster. Both types of flagella are powered by proton-driven motors. The swimming propulsion is supplied mainly by the thick flagellum. B. japonicum flagellar systems resemble the polar-lateral flagellar systems of Vibrio species but differ in several aspects.

Buchnera aphidicola is the endosymbiotic bacterium of the pea aphid. Due to its small genome size, Buchnera lacks many essential genes for autogenous life but obtains nutrients from the host. Although the Buchnera cell is nonmotile, it retains clusters of flagellar genes that lack the late genes necessary for motility, including the flagellin gene. In this study, we show that the flagellar genes are actually transcribed and translated and that the Buchnera cell surface is covered with hundreds of hook--basal-body (HBB) complexes. The abundance of HBB complexes suggests a role other than motility. We discuss the possibility that the HBB complex may serve as a protein transporter not only for the flagellar proteins but also for other proteins to maintain the symbiotic system.

The bacterium Vibrio fischeri requires bacterial motility to initiate colonization of the Hawaiian squid Euprymna scolopes. Once colonized, however, the bacterial population becomes largely unflagellated. To understand environmental influences on V. fischeri motility, we investigated migration of this organism in tryptone-based soft agar media supplemented with different salts. We round that optimal migration required divalent cations and, in particular, [Mg.sup.2+]. At concentrations naturally present in seawater, [Mg.sup.2+] improved migration without altering the growth rate of the cells. Transmission electron microscopy and Western blot experiments suggested that [Mg.sup.2+] addition enhanced flagellation, at least in part through an effect on the steady-state levels of flagellin protein.

Results reveal the presence of two new of the four flagellins in Methanococcus voltae. The flagellin FlaA is distributed throughout the filament whereas FlaB3 appears to be seen in the proximal end of the cell surface, perhaps similar to the bacterial hook. Both FlaA and FlaB3 are structural components of the flagella.

This review article discusses transmembrane signaling pathway of chemotaxis in Escherichia coli. Research data to near atomic resolution on the two-component regulatory systems controlling chemotactic behavior and gene expression in relation to environmental interaction are presented.

Research conducted on the overexpressed and underexpressed flgE wild-type cell and flagellar mutant gene in Salmonella is presented. The effects of the hook subunit concentration on the hook length control process are examined.

The SJW2811 strain of Salmonella typhimurium is a switch-gene parenteral mutant strain that exhibits region II suppressor mutations involving motA and motB. The SJW2811 mutant strain exhibited strong clockwise motor bias with normal torque-generating mechanisms and lower swimming speed in liquid medium compared to wild type Salmonella typhimurium. The mechanism of suppression in the flagellar region II involved a small in-frame deletion in the middle of the fliG sequence which reduced motor function.

The early stages of flagellar assembly and the cytoplasmic components of the flagella were analyzed in Salmonella typhimurium by utilizing anti-FliG, -FliM and -FliN antibodies. Analysis of flagellar assembly by immunoblotting indicated the role of the FliF MS ring protein in mediating the association between the cell membrane and the switch complex formed by FliG, FliM and FliN. Furthermore, the switch complex assembled on the MS ring complex during the early stages of flagellar assembly.

Mutations in the C-terminal of the Salmonella typhimurium fliK gene produce the polyhook phenotype in which there is no hook assembly termination and filament assembly initiation. The defect in filament assembly is removed by extragenic suppressors in the flaB gene. Small deletions in the FliK N-terminal and central regions produce normal hook length control and wild-type swarming. Larger deletions result in loss of hook length control and poor swarming. FliK probably measures the hook length and at a specific length signals FlhB to export flagellin instead of hook proteins.

Experimental studies enable the isolation of spontaneous mutants of Salmonella typhimurium exhibiting ability to swim in the presence of antifilament antibodies. Analysis of the domains structures of flagellins associated with two mutants by trypsin digestion reveals that the two flagellins exhibit deletions at Ala-204 to Lys-292 and Thr-183 to Lys-279, respectively. Outer domains of flagellin have these deleted portions, and side by side aggregation of these mutant filaments leads to motility disorder.

Electron micrograph measurements of flagellar hook lengths in mutant and wild-type cells of Salmonella typhimurium reveal that the flik polyhook mutants have broader hook length distributions between 40 and 900 nm, compared to the narrow 55.0 plus or minus 5.9 nm range of wild-type cells. The broad distribution range of the mutants confirms their involvement in defining the hook length. Flik intragenic suppressors isolated from the flik mutants produce polyhook filaments that are longer than the hooks, with abnormal length produced by flhB intragenic suppressors. A double mutation in flgK and flhB results in polyhooks.

Ultracentrifugation and gel electrophoresis studies reveal that during the interaction of flagellar switch proteins FliG, FliM and FliN of S. typhimurium with MS ring complexes constituting HiF proteins, FliG binds to MS ring complex at 1:1 molar ratio whereas FliM binds att 1:5 molar ratio. This shows that the binding sites for FliM on MS ring are limited. FliN does not bind to MS ring complexes. The interaction of switch proteins with MS ring complex leads to flagellar rotation.

The flagellar hook assembly process requires a scaffolding protein called FlgD in Salmonella typhimurium. FlgD functions as a hook-capping protein and is transferred to the distal hook end from distal rod end. Exogeneous addition of FlgD protein causes cell mobility in FlgD mutants. FlgD protein is discarded with competition of a hook-assembly process and is not required for hook protein export.

Escherichia coli and Salmonella typhimurium flagellar systems are encoded by at least 40 genes presently grouped into regions I, II, IIIa, and IIIb. One of the genes, fliE, which lies at the start of region IIIb, is a monocistronic operon oriented divergently from the large fliF operon. DNA sequencing showed that its product, FliE, is part of the flagellar hook-basal body. Nine subunits of the FliE proteins was estimated to be part of one basal body. Its functional role remains to be elucidated.

Research has been conducted on Escherichia coli cultures. Results suggest that the increase in glycogen contributes to the increase in weight-to-volume ratio of E. coli cell stationary-phase.

Unlabelled: The flagellar hook is a short tubular structure located between the external filament and the membrane-bound basal body. The average hook length is 55 nm and is determined by the soluble protein FliK and the integral membrane protein FlhB. Hook elongation is terminated by FliK-mediated cessation of hook protein secretion, followed by the secretion of filamentous proteins. This process is referred to as the substrate specificity switch. Switching of the secretion modes results from a direct interaction between the FliK C-terminal domain (FliKC) and the secretion gate in FlhB. FliKC consists of two α-helices and four β-strands. Loop 2 connects the first two β-sheets and contains a conserved sequence of 9 residues. Genetic and physiological analyses of various fliK partial deletion mutants pointed to loop 2 as essential for induction of a conformational change in the FlhB gate. We constructed single-amino-acid substitutions in the conserved region of loop 2 of FliK and discovered that the loop sequence LRL is essential for the timely switching of secretion modes., Importance: Flagellar protein secretion is controlled by the soluble protein FliK. We discovered that the loop 2 sequence LRL in the FliK C terminus was essential for timely switching of secretion modes. This mechanism is applicable to type three secretions systems that secrete virulence factors in bacterial pathogens., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

N-glycosylation is a protein posttranslational modification found in all three domains of life. Many surface proteins in Archaea, including S-layer proteins, pilins, and archaellins (archaeal flagellins) are known to contain N-linked glycans. In Methanococcus maripaludis, the archaellins are modified at multiple sites with an N-linked tetrasaccharide with the structure Sug-1,4-β-ManNAc3NAmA6Thr-1,4-β-GlcNAc3NAcA-1,3-β-GalNAc, where Sug is the unique sugar (5S)-2-acetamido-2,4-dideoxy-5-O-methyl-α-l-erythro-hexos-5-ulo-1,5-pyranose. In this study, four genes--mmp1084, mmp1085, mmp1086, and mmp1087--were targeted to determine their potential involvement of the biosynthesis of the sugar components in the N-glycan, based on bioinformatics analysis and proximity to a number of genes which have been previously demonstrated to be involved in the N-glycosylation pathway. The genes mmp1084 to mmp1087 were shown to be cotranscribed, and in-frame deletions of each gene as well as a Δmmp1086Δmmp1087 double mutant were successfully generated. All mutants were archaellated and motile. Mass spectrometry examination of purified archaella revealed that in Δmmp1084 mutant cells, the threonine linked to the third sugar of the glycan was missing, indicating a putative threonine transferase function of MMP1084. Similar analysis of the archaella of the Δmmp1085 mutant cells demonstrated that the glycan lacked the methyl group at the C-5 position of the terminal sugar, indicating that MMP1085 is a methyltransferase involved in the biosynthesis of this unique sugar. Deletion of the remaining two genes, mmp1086 and mmp1087, either singularly or together, had no effect on the structure of the archaellin N-glycan. Because of their demonstrated involvement in the N-glycosylation pathway, we designated mmp1084 as aglU and mmp1085 as aglV.

N-linked glycosylation of protein is a posttranslational modification found in all three domains of life. The flagellin proteins of the archaeon Methanococcus maripaludis are known to be modified with an N-linked tetrasaccharide consisting of N-acetylgalactosamine (GalNAc), a diacetylated glucuronic acid (GlcNAc3NAc), an acetylated and acetamidino-modified mannuronic acid with a substituted threonine group (ManNAc3NAmA6Thr), and a novel terminal sugar residue [(5S)-2-acetamido-2,4-dideoxy-5-O-methyl-α-L-erythro-hexos-5-ulo-1,5-pyranose]. To identify genes involved in biosynthesis of the component sugars of this glycan, three genes, mmp1081, mmp1082, and mmp1083, were targeted for in-frame deletion, based on their annotation and proximity to glycosyltransferase genes known to be involved in assembly of the glycan. Mutants carrying a deletion in any of these three genes remained flagellated and motile. A strain with a deletion of mmp1081 had lower-molecular-mass flagellins in Western blots. Mass spectrometry of purified flagella revealed a truncated glycan with the terminal sugar absent and the threonine residue and the acetamidino group missing from the third sugar. No glycan modification was seen in either the Δmmp1082 or Δmmp1083 mutant grown in complex Balch III medium. However, a glycan identical to the Δmmp1081 glycan was observed when the Δmmp1082 or Δmmp1083 mutant was grown under ammonia-limited conditions. We hypothesize that MMP1082 generates ammonia and tunnels it through MMP1083 to MMP1081, which acts as the amidotransferase, modifying the third sugar residue of the M. maripaludis glycan with the acetamidino group.