The role of EII complex in the bacterial responses to the glucose-survey in clinical Klebsiella pneumoniae isolates.

Type 3 fimbriae in Klebsiella pneumoniae are important for bacterial colonization on abiotic and biotic surfaces. The major subunit of type 3 fimbriae (MrkA) is increased by overexpression of EtcABC, an EII complex of phosphoenolpyruvate:carbohydrate phosphotransferase systems (PTSs), through cAMP-cAMP receptor protein (cAMP-CRP) in K. pneumoniae STU1. Here, we further characterized the relations between the amount of etcABC mRNA and MrkA in 78 clinical K. pneumoniae isolates incubated in high levels of glucose. By Western blotting, we observed that MrkA of 29 isolates were not decreased much by high levels of glucose (Group A) but MrkA of other 49 isolates were significantly reduced (Group B) in the same condition. The bacterial biofilms on abiotic surfaces and colonization in the Caenorhabditis elegans of representative isolates in the Group A were not affected by high levels of glucose. However, the biofilm and colonization in the worm of clinical isolates in the Group B were much reduced by high levels of glucose. After quantification by real time RT-PCR, 76% of Group A but just 10% of Group B showed high amount of etcA mRNA. In summary, our results suggested that for most of K. pneumoniae clinical isolates, the amount of etcABC mRNA was positively related to their type 3 fimbriae production in a high level of glucose, thereby to their biofilm formation and colonization in the worm.

Rapid Quantification of Polyhydroxybutyrate Polymer from Single Bacterial Cells with Mass Spectrometry.

Polyhydroxyalkanoate (PHA) is one of the biocompatible and biodegradable plastics that can be produced and accumulated as granules inside microorganisms. In this study, a new approach to rapidly quantify a short-chain-length PHA, polyhydroxybutyrate (PHB), produced from genetically engineered Escherichia coli containing phaCAB is presented. The mass of each bacterial cell was measured using a laser-induced radio frequency (rf) plasma charge detection quadrupole ion trap mass spectrometer (LIRFP CD QIT-MS), and then, the PHB contents were determined by calculating the change in cellular mass. The quantitative results showed that the PHB contents measured by LIRFP CD QIT-MS were consistent with those by reference analysis, gas chromatography (GC). The PHB content of each bacterial sample can be obtained within 20 min from sampling using LIRFP CD QIT-MS while GC analysis takes 2 days. In addition, LIRFP CD QIT-MS does not use any hazardous chemicals in cellular mass quantification as compared to GC. This indicates that LIRFP CD QIT-MS has potential in routine monitoring of PHB production.

A protein containing the DUF1471 domain regulates biofilm formation and capsule production in Klebsiella pneumoniae.

BACKGROUND/PURPOSE: Biofilms formed by Klebsiella pneumoniae on medical devices increase infection risk. Fimbriae and capsule polysaccharides (CPSs) are important factors involved in biofilm formation. KP1_4563 in K. pneumoniae NTUH-K2044, a small protein containing the DUF1471 domain, was reported to inhibit type 3 fimbriae function. In this study, we aimed to determine whether the KP1_4563 homolog is conserved in each K. pneumoniae isolate and what role it has in Klebsiella biofilms. METHODS: The genomes of K. pneumoniae NTUH-K2044, CG43, MGH78578, KPPR1 and STU1 were compared. The KP1_4563 homolog in K. pneumoniae STU1 was named orfX. Biofilms of wild-type and orfX mutant strains from K. pneumoniae STU1 and one clinical isolate, 83535, were quantified. Transcription levels of the type 3 fimbrial genes, mrkA and mrkH, were investigated by RT-qPCR. MrkA of the wild-type and orfX mutant were observed by Western blotting. The morphology of bacterial cells was observed by transmission electron microscopy (TEM). Bacterial CPSs were quantified. RESULTS: The gene and upstream region of orfX were conserved among the five K. pneumoniae isolates. Deletion of orfX enhanced Klebsiella biofilm formation. However, the amount of mRNA from mrkA and mrkH and the level of MrkA protein were not different between the wild type and orfX mutant. In contrast, the amount of CPS in orfX mutants was increased, compared to their parental strains, STU1 and 83535. CONCLUSION: The role of orfX is speculated to be conserved in most K. pneumoniae isolates. OrfX negatively controlled biofilm formation by reducing CPS, not type 3 fimbriae, production.

The PTS Components in Klebsiella pneumoniae Affect Bacterial Capsular Polysaccharide Production and Macrophage Phagocytosis Resistance.

Capsular polysaccharide (CPS) is a crucial virulence factor for Klebsiella pneumoniae infection. We demonstrated an association of CPS production with two phosphoenolpyruvate:carbohydrate phosphotransferase systems (PTSs). Deficiency of crr, encoding enzyme IIA of PTS, in K. pneumoniae enhanced the transcriptional activities of galF, wzi and gnd, which are in the cps gene cluster, leading to high CPS production. A crr mutant exhibited a higher survival rate in 1% hydrogen peroxide than the wild-type. The crr mutant showed less sensitivity to engulfment by macrophage (RAW 264.7) than the wild-type by observing the intracellular bacteria using confocal laser scanning microscopy (CLSM) and by calculating the colony-forming units (CFU) of intracellular bacteria. After long-term incubation, the survival rate of the intracellular crr mutant was higher than that of the wild-type. Deficiency of crr enhanced the transcriptional activities of etcABC which encodes another putative enzyme II complex of a PTS. Deletion of etcABC in the crr mutant reduced CPS production and the transcriptional activities of galF compared to those of the crr mutant. These results indicated that one PTS component, Crr, represses CPS production by repressing another PTS component, EtcABC, in K. pneumoniae. In addition, PTS plays a role in bacterial resistance to macrophage phagocytosis.

EtcABC, a Putative EII Complex, Regulates Type 3 Fimbriae via CRP-cAMP Signaling in Klebsiella pneumoniae.

Biofilm formation by Klebsiella pneumoniae on indwelling medical devices increases the risk of infection. Both type 1 and type 3 fimbriae are important factors in biofilm formation by K. pneumoniae. We found that a putative enzyme II (EII) complex of the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), etcA (EIIA)-etcB (EIIB)-etcC (EIIC), regulated biofilm and type 3 fimbriae formation by K. pneumoniae STU1. In this study, the regulatory mechanism of etcABC in K. pneumoniae type 3 fimbriae formation was investigated. We found via quantitative RT-PCR that overexpression of etcABC enhanced the transcription level of the mrk operon, which is involved in type 3 fimbriae synthesis, and reduced the transcription level of the fim operon, which is involved in type 1 fimbriae synthesis. To gain further insight into the role of etcABC in type 3 fimbriae synthesis, we analyzed the region upstream of the mrk operon and found the potential cyclic 3'5'-adenosine monophosphate (cAMP) receptor protein (CRP) binding site. After crp was deleted in K. pneumoniae STU1 and two clinical isolates, these three crp mutant strains could not express MrkA, the major subunit of the fimbrial shaft, indicating that CRP positively regulated type 3 fimbriae synthesis. Moreover, a crp mutant overexpressing etcABC could not express MrkA, indicating that the regulation of type 3 fimbriae by etcABC was dependent on CRP. In addition, deletion of cyaA, which encodes the adenylyl cyclase that synthesizes cAMP, and deletion of crr, which encodes the glucose-specific EIIA, led to a reduction in lac operon regulation and therefore bacterial lactose uptake in K. pneumoniae. Exogenous cAMP but not etcABC overexpression compensated for the role of cyaA in bacterial lactose uptake. However, either etcABC overexpression or exogenous cAMP compensated for the role of crr in bacterial lac operon regulation that would eventually restore lactose uptake. We also found via ELISA and the luxCDABE reporter system that overexpression of etcABC increased intracellular cAMP levels and the transcription level of crp, respectively, in K. pneumoniae. In conclusion, overexpression of etcABC positively regulated cAMP production and cAMP-CRP activity to activate the mrk operon, resulting in increased type 3 fimbriae synthesis in K. pneumoniae.

Phosphoenolpyruvate phosphotransferase system components positively regulate Klebsiella biofilm formation.

BACKGROUND/PURPOSE: Klebsiella pneumoniae is one of the leading causes of device-related infections (DRIs), which are associated with attachment of bacteria to these devices to form a biofilm. The latter is composed of not only bacteria but also extracellular polymeric substances (EPSes) consisting of extracellular DNAs, polysaccharides, and other macromolecules. The phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS) regulates diverse processes of bacterial physiology. In the genome of K. pneumoniae MGH 78578, we found an uncharacterized enzyme II complex homolog of PTS: KPN00353 (EIIA homolog), KPN00352 (EIIB homolog), and KPN00351 (EIIC homolog). The aim of this study was to characterize the potential physiological role of KPN00353, KPN00352, and KPN00351 in biofilm formation by K. pneumoniae. METHODS/RESULTS: We constructed the PTS mutants and recombinant strains carrying the gene(s) of PTS. The recombinant K. pneumoniae strain overexpressing KPN00353-KPN00352-KPN00351 produced more extracellular matrix than did the vector control according to transmission and scanning electron microscopy. Judging by quantification of biofilm formation, of extracellular DNA (eDNA), and of capsular polysaccharide, the recombinant strain overexpressing KPN00353-KPN00352-KPN00351 produced more biofilm and capsular polysaccharide after overnight culture and more eDNA in the log phase as compared to the vector control. CONCLUSION: The genes, KPN00353-KPN00352-KPN00351, encode a putative enzyme II complex in PTS and positively regulate biofilm formation by enhancing production of eDNA and capsular polysaccharide in K. pneumoniae. Five proteins related to chaperones, to the citric acid cycle, and to quorum sensing are upregulated by the KPN00353-KPN00352-KPN00351 system.

The Negative Effects of KPN00353 on Glycerol Kinase and Microaerobic 1,3-Propanediol Production in Klebsiella pneumoniae.

1,3-Propanediol (1,3-PD) is a valuable chemical intermediate in the synthesis of polyesters, polyethers, and polyurethanes, which have applications in various products such as cloth, bottles, films, tarpaulins, canoes, foam seals, high-resilience foam seating, and surface coatings. Klebsiella pneumoniae can produce 1,3-PD from glycerol. In this study, KPN00353, an EIIA homologue in the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS), was found to play a negative regulatory role in 1,3-PD production under microaerobic conditions via binding to glycerol kinase (GlpK). The primary sequence of KPN00353 is similar to those of the fructose-mannitol EIIA (EIIFru and EIIAMtl) family. The interaction between KPN00353 and GlpK resulted in inhibition of the synthesis of glycerol-3-phosphate (G3P) and correlated with reductions in glycerol uptake and the production of 1,3-PD. Based on structure modeling, we conclude that residue H65 of KPN00353 plays an important role in the interaction with GlpK. We mutated this histidine residue to aspartate, glutamate, arginine and glutamine to assess the effects of each KPN00353 variant on the interaction with GlpK, on the synthesis of G3P and on the production of 1,3-PD. Our results illuminate the role of KPN00353 in 1,3-PD production by K. pneumoniae under microaerobic conditions.

The assessment of host and bacterial proteins in sputum from active pulmonary tuberculosis.

Pulmonary tuberculosis (TB) is caused by Mycobacterium tuberculosis. The protein composition of sputum may reflect the immune status of the lung. This study aimed to evaluate the protein profiles in spontaneous sputum samples from patients with active pulmonary TB. Sputum samples were collected from patients with pulmonary TB and healthy controls. Western blotting was used to analyze the amount of interleukin 10 (IL-10), interferon-gamma (IFN-γ), IL-25, IL-17, perforin-1, urease, albumin, transferrin, lactoferrin, adenosine deaminase (also known as adenosine aminohydrolase, or ADA), ADA-2, granzyme B, granulysin, and caspase-1 in sputum. Results of detection of IL-10, IFN-γ, perforin-1, urease, ADA2, and caspase-1, showed relatively high specificity in distinguishing patients with TB from healthy controls, although sensitivities varied from 13.3% to 66.1%. By defining a positive result as the detection of any two proteins in sputum samples, combined use of transferrin and urease as markers increased sensitivity to 73.2% and specificity to 71.1%. Furthermore, we observed that the concentration of transferrin was proportional to the number of acid-fast bacilli detected in sputum specimens. Detection of sputum transferrin and urease was highly associated with pulmonary TB infection. In addition, a high concentration of transferrin detected in sputum might correlate with active TB infection. This data on sputum proteins in patients with TB may aid in the development of biomarkers to assess the severity of pulmonary TB.

Validation of nanodiamond-extracted CFP-10 antigen as a biomarker in clinical isolates of Mycobacterium tuberculosis complex in broth culture media.

With detonation nanodiamonds (DNDs) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS), we previously identified early secreted cell filtrate protein 10 (CFP-10) as a candidate Mycobacterium tuberculosis complex (MTC) biomarker. The performance of the CFP-10 biomarker was initially evaluated in relatively small mycobacterial samples (n = 42 samples) in our previous study. In this study, we conducted DND MALDI-TOF MS experiments to investigate the specificity and sensitivity of the MTC biomarker with 312 MTC and 52 nontuberculous mycobacteria (NTM) clinical samples. The frequency and intensity of the acquired CFP-10 mass-to-charge (m/z) peaks were checked with a program to validate that the singly and doubly charged CFP-10 antigen can be treated as a MTC biomarker. We confirmed that by detecting the singly charged species of CFP-10 antigen, the sensitivity and the specificity of MTC samples could reach 97.4% and 100% and no CFP-10 biomarker could be found in NTM samples. This indicates with CFP-10 biomarker it is easy to distinguish MTC from NTM. Besides, the observed intensity ratio of singly and doubly charged species of CFP-10 antigen was 3.3 ± 2.6 and the CFP-10 antigen could maintain good signal intensity for a week. Our results suggest that, with the DND MALDI-TOF mass spectrometry approach, CFP-10 antigen can be used as an early diagnosis biomarker in clinical practice.

Molecular analysis of codon 548 in the rpoB gene involved in Mycobacterium tuberculosis resistance to rifampin.

Most Mycobacterium tuberculosis rifampin-resistant strains have been associated with mutations in an 81-bp rifampin resistance-determining region (RRDR) in the gene rpoB. However, if this region alone were targeted, rifampin-resistant strains with mutations outside the RRDR would not be detected. In this study, among 51 rifampin-resistant clinical isolates analyzed by sequencing 1,681-bp-long DNA fragments containing the RRDR, 47 isolates contained mutations within the RRDR, three isolates contained mutations both within and outside the RRDR, and only one isolate had a single missense mutation (Arg548His) located outside the RRDR. A drug susceptibility test of recombinant Mycobacterium smegmatis and M. tuberculosis isolates carrying mutated rpoB (Arg548His) showed an increased MIC for rifampin compared to that of the control strains. Modeling of the Arg548His mutant RpoB-DNA complex revealed that the His548 side chain formed a more stable hydrogen bond structure than did Arg548, reducing the flexibility of the rifampin-resistant cluster II region of RpoB, suggesting that the RpoB Arg548His mutant does not effectively interact with rifampin and results in bacterial resistance to the drug. This is the first report on the relationship between the mutation in codon 548 of RpoB and rifampin resistance in tuberculosis. The novel mutational profile of the rpoB gene described here will contribute to the comprehensive understanding of rifampin resistance patterns and to the development of a useful tool for simple and rapid drug susceptibility tests.

ManA is regulated by RssAB signaling and promotes motility in Serratia marcescens.

Serratia marcescens swarms on 0.8% LB agar at 30 °C but not at 37 °C. To understand the molecular mechanism regulating Serratia swarming, transposon mutagenesis was performed to screen for mutants that swarmed at 37 °C. In one mutant, S. marcescens WW100, the transposon was inserted in the upstream region of manA, which encodes mannose-6-phosphate isomerase, a type I phosphomannose isomerase. The transcriptional and translational levels of manA were higher in S. marcescens WW100 than in the wild-type strain. S. marcescens WW100 produced more serrawettin W1 (biosurfactant) than the wild-type, as detected by thin-layer chromatography, to promote surface motility by reducing surface tension. Serratia swarming was previously shown to be negatively regulated by the RssA-RssB two-component system. An electrophoretic mobility shift assay (EMSA) indicated that phosphorylated RssB (the response regulator) binds upstream of the transposon insertion site and manA in S. marcescens WW100. Analysis by real-time RT-PCR (qRT-PCR) revealed that, compared to the wild-type level, manA mRNA was increased in the rssA deletion mutant. The results indicated that RssA-RssB signaling directly represses the expression of manA and that overexpression of manA increases the production of serrawettin for Serratia swarming at 37 °C.

Detonation nanodiamonds for rapid detection of clinical isolates of Mycobacterium tuberculosis complex in broth culture media.

Routinely used molecular diagnostic methods for mycobacterium identification are expensive and time-consuming. To tackle this problem, we develop a method to streamline identification of Mycobacterium tuberculosis complex (MTBC) in broth culture media by using detonation nanodiamonds (DNDs) as a platform to effectively capture the antigen secreted by MTBC which is cultured in BACTEC MGIT 960, followed by the analysis of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). The 5 nm DNDs can capture the MTBC secretory antigen without albumin interference. With on diamond digestion, we confirm the DND captured antigen is cell filtrate protein 10 (CFP-10) because its Mascot analysis shows a score of 68. The dot blotting method further verifies a positive reaction with anti-CFP-10, indicating that CFP-10 is secreted in the medium of mycobacterium growth indicator tube (MGIT) and captured by DNDs. The minimal CFP-10 protein detection limit was 0.09 µg/mL. Furthermore, our approach can avoid the false-positive identification of MTBC by immunological methods due to cross-reactivity. Five hundred consecutive clinical specimens subjected to routine mycobacteria identification in hospital were used in this study, and the sensitivity of our method is 100% and the specificity is 98%. The analysis of each MTBC sample from culture solution can be finished within 1 h and thus shortens the turnaround time of MTBC identification of gold standard culture methods. In sum, DND MALDI-TOF MS for the detection of MTBC is rapid, specific, safe, reliable, and inexpensive.

Inactivation of dhaD and dhaK abolishes by-product accumulation during 1,3-propanediol production in Klebsiella pneumoniae.

1,3-Propanediol (1,3-PD) can be used for the industrial synthesis of a variety of compounds, including polyesters, polyethers, and polyurethanes. 1,3-PD is generated from petrochemical and microbial sources. 1,3-Propanediol is a typical product of glycerol fermentation, while acetate, lactate, 2,3-butanediol, and ethanol also accumulate during the process. Substrate and product inhibition limit the final concentration of 1,3-propanediol in the fermentation broth. It is impossible to increase the yield of 1,3-propanediol by using the traditional whole-cell fermentation process. In this study, dhaD and dhaK, the genes for glycerol dehydrogenase and dihydroxyacetone kinase, respectively, were inactivated by homologous recombination in Klebsiella pneumoniae. The dhaD/dhaK double mutant (designated TC100), selected from 5,000 single or double cross homologous recombination mutants, was confirmed as a double cross by using polymerase chain reaction. Analysis of the cell-free supernatant with high-performance liquid chromatography revealed elimination of lactate and 2,3-butanediol, as well as ethanol accumulation in TC100, compared with the wild-type strain. Furthermore, 1,3-propanediol productivity was increased in the TC100 strain expressing glycerol dehydratase and 1,3-PDO dehydrogenase regulated by the arabinose P(BAD) promoter. The genetic engineering and medium formulation approaches used here should aid in the separation of 1,3-propanediol from lactate, 2,3-butanediol, and ethanol and lead to increased production of 1,3-propanediol in Klebsiella pneumoniae.

The RssB/RssA two-component system regulates biosynthesis of the tripyrrole antibiotic, prodigiosin, in Serratia marcescens.

Serratia marcescens CH-1 produces a red, cell-associated pigment, prodigiosin, synthesized by enzymes encoded in the pig operon. The underlying regulatory mechanism, especially its relationship with the RssAB two-component system signaling, remained uncharacterized. Here, we show that phosphorylated RssB (RssB-P) directly binds to the promoter region of the pig operon (pigA promoter), as observed using an electrophoretic mobility shift assay. Furthermore, we identify the RssB-P binding site located downstream of the -10 and -35 regions in pigA using a DNase I footprinting assay. A compilation of the RssB-P binding sites in flhDC, rssB and pigA promoter regions reveals the presence of a conserved core sequence, GAGATTTTAGCTAAATTAATBTTT (B=C, G, or T), which we believe is the RssB binding sequence. Site-specific mutation of conserved nucleotides within the conserved RssB binding sequence in the pigA promoter region leads to absence of retardation in the presence of RssB-P in vitro and elevated transcription of pigA in vivo. These data suggest that RssAB signaling negatively regulates prodigiosin production, and such inhibition is mediated through direct and specific repression of transcriptional activity of the pig operon.

A simple gold nanoparticle probes assay for identification of Mycobacterium tuberculosis and Mycobacterium tuberculosis complex from clinical specimens.

We had previously developed a nested polymerase chain reaction (PCR)-immunochromatography test (ICT) for identification of Mycobacterium tuberculosis (MTB) and differentiation of MTB from other members of M. tuberculosis complex (MTBC) from clinical sputum samples (Soo P.C. et al., Journal of Microbiological Methods. 2006, 66(3):440-8.). To further improve the detection flexibility, simplicity and efficiency, and reduce the cost, in this study, an alternative molecular diagnosis assay that utilizes gold nanoparticles derivatized with thiol modified oligonucleotides was developed. The gold nanoparticles probes, GP-1/GP-2 for IS6110 and GP-3/GP-4 for Rv3618, were designed to specifically hybridize with target DNAs of MTBC and MTB strains, respectively. Efficacy of the gold nanoparticle probes assay was evaluated by directly and simultaneously detecting not only MTBC but also MTB from 600 clinical sputum specimens. Results were compared with traditional culture and biochemical identification methods together with patients' clinical assessments. This assay showed a 96.6% sensitivity and 98.9% specificity towards detection of MTBC, and a 94.7% sensitivity and 99.6% specificity for detection of MTB. In conclusion, the gold nanoparticle probes assay is a simple, rapid, cost-effective and accurate detection system and shows great potential in clinical application of MTBC and MTB detection, especially in developing countries.

A potential acyltransferase regulates swarming in Serratia marcescens.

Swarming in Serratia marcescens is a specialized form of bacterial populational surface migration behavior. A precocious swarming mutant S. marcescens O6 whose rssC is interrupted by mini-Tn5 transposon was obtained. The 364 amino-acid RssC showed a high identity to members of acyltransferase family. Characterization of the rssC knock-out mutant S. marcescens PC105 showed aberrant and hypervirulent phenotypes including precocious swarming behavior, reduced cell attachment ability and increase in swimming motility, flagellin synthesis, capsular polysaccharide (CPS) production, hemolysin activity, and cytotoxicity activity. Besides a more intense pattern of O-antigen sugar unit ladder, S. marcescens PC105 also showed an altered cell surface topology. A potential FlhDC binding site was identified at the rssC promoter region. In accordance, rssC transcriptional activity was up-regulated by FlhDC(Sm). Briefly, rssC is hierarchically classified as class II members in FlhDC(Sm) regulon, and reciprocally defect in rssC results in aberrant swarming and hypervirulence in S. marcescens.

Regulation of swarming motility and flhDC(Sm) expression by RssAB signaling in Serratia marcescens.

Serratia marcescens cells swarm at 30 degrees C but not at 37 degrees C, and the underlying mechanism is not characterized. Our previous studies had shown that a temperature upshift from 30 to 37 degrees C reduced the expression levels of flhDC(Sm) and hag(Sm) in S. marcescens CH-1. Mutation in rssA or rssB, cognate genes that comprise a two-component system, also resulted in precocious swarming phenotypes at 37 degrees C. To further characterize the underlying mechanism, in the present study, we report that expression of flhDC(Sm) and synthesis of flagella are significantly increased in the rssA mutant strain at 37 degrees C. Primer extension analysis for determination of the transcriptional start site(s) of flhDC(Sm) revealed two transcriptional start sites, P1 and P2, in S. marcescens CH-1. Characterization of the phosphorylated RssB (RssB approximately P) binding site by an electrophoretic mobility shift assay showed direct interaction of RssB approximately P, but not unphosphorylated RssB [RssB(D51E)], with the P2 promoter region. A DNase I footprinting assay using a capillary electrophoresis approach further determined that the RssB approximately P binding site is located between base pair positions -341 and -364 from the translation start codon ATG in the flhDC(Sm) promoter region. The binding site overlaps with the P2 "-35" promoter region. A modified chromatin immunoprecipitation assay was subsequently performed to confirm that RssB-P binds to the flhDC(Sm) promoter region in vivo. In conclusion, our results indicated that activated RssA-RssB signaling directly inhibits flhDC(Sm) promoter activity at 37 degrees C. This inhibitory effect was comparatively alleviated at 30 degrees C. This finding might explain, at least in part, the phenomenon of inhibition of S. marcescens swarming at 37 degrees C.

The bacterial metabolite 2,3-butanediol ameliorates endotoxin-induced acute lung injury in rats.

Widely identified in bacteria, yeasts and human beings, 2,3-butanediol has been studied for decades. This chemical reportedly functions as a neutralization agent to counteract lethal acidification by bacterial growth and as a signaling molecule involved in interactions among insects, and between bacteria and the plant host. While 2,3-butanediol is produced by many pathogenic bacterial species, its significance and effect on mammals remains basically uncharacterized. Herein, we show that gastric intubation of 2,3-butanediol in rats significantly ameliorates acute lung injury (ALI) and the inflammatory responses induced by the bacterial endotoxin lipopolysaccharide (LPS), with an efficacy comparable to that of the polyphenol compound resveratrol. Such effect was further demonstrated to occur via modulation of the NF-kappaB signaling pathway. These results indicate that bacterial metabolite, 2,3-butanediol has a negative regulatory effect on host innate immunity response, suggesting bacteria may use some metabolites for host immune evasion.

Pirin regulates pyruvate catabolism by interacting with the pyruvate dehydrogenase E1 subunit and modulating pyruvate dehydrogenase activity.

The protein pirin, which is involved in a variety of biological processes, is conserved from prokaryotic microorganisms, fungi, and plants to mammals. It acts as a transcriptional cofactor or an apoptosis-related protein in mammals and is involved in seed germination and seedling development in plants. In prokaryotes, while pirin is stress induced in cyanobacteria and may act as a quercetinase in Escherichia coli, the functions of pirin orthologs remain mostly uncharacterized. We show that the Serratia marcescens pirin (pirin(Sm)) gene encodes an ortholog of pirin protein. Protein pull-down and bacterial two-hybrid assays followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrospray ionization-tandem mass spectrometry analyses showed the pyruvate dehydrogenase (PDH) E1 subunit as a component interacting with the pirin(Sm) gene. Functional analyses showed that both PDH E1 subunit activity and PDH enzyme complex activity are inhibited by the pirin(Sm) gene in S. marcescens CH-1. The S. marcescens CH-1 pirin(Sm) gene was subsequently mutated by insertion-deletion homologous recombination. Accordingly, the PDH E1 and PDH enzyme complex activities and cellular ATP concentration increased up to 250%, 140%, and 220%, respectively, in the S. marcescens CH-1 pirin(Sm) mutant. Concomitantly, the cellular NADH/NAD(+) ratio increased in the pirin(Sm) mutant, indicating increased tricarboxylic acid (TCA) cycle activity. Our results show that the pirin(Sm) gene plays a regulatory role in the process of pyruvate catabolism to acetyl coenzyme A through interaction with the PDH E1 subunit and inhibiting PDH enzyme complex activity in S. marcescens CH-1, and they suggest that pirin(Sm) is an important protein involved in determining the direction of pyruvate metabolism towards either the TCA cycle or the fermentation pathways.

Regulatory roles of spnT, a novel gene located within transposon TnTIR.

The transposon TnTIR contains spnIR quorum-sensing system regulating sliding motility and the production of nuclease, biosurfactant, and prodigiosin in Serratia marcescens. Within TnTIR, a gene named spnT is upstream of and co-transcribed with spnI. SpnT is a cytoplasmic protein and its level peaks during early stationary phase. spnT over-expression resulted in inhibition of sliding motility and synthesis of prodigiosin, and biosurfactant similar to spnR. spnT but not spnR over-expression induced cell elongation and aberrant DNA replication in S. marcescens and Escherichia coli strains. In comparison with wild-type E. coli strain, over-expression of spnT in an E. coli priA and dnaC double-mutant strain did not lead to the aberrant cell morphology phenotypes, suggesting SpnT may act through the recombination-dependent DNA replication system. As spnT over-expression inhibited swarming but not swimming motility, SpnT may indirectly function as a negative regulator of surface-dependent migration and secondary metabolite production.