Hwei-Ling Peng (彭慧玲), Department of Biological Science and Technology, National Chiao Tung University
I. Diversity in Microbial Chemotaxis
- The first section covers the properties of Rhodobacter, E. coli, and P. aeruginosa. “ Rewiring the chemosensory pathways of Rhodobacter sphaeroides” given by Dr J. Armitage from Oxford University UK focused on why 4 CheA and 6 MCP are encoded by 3 operons in the genome and how do they play roles for the motility. He has shown that the different chemosory machineries play similar role but at different parts of the cell. Control mechanism for the location determination has also been studied.
- Dr R. Parales from UC Davis USA reported “Bacterial chemotaxis to environmental pollutants”
mainly on the Pseudomonas chemotactic receptor proteins. In E. coli, 4 sets of MCP were identified.
On the other hand, a total of 26 chemotactic receptor proteins were identified in Pseudomonas. The equipped with large numbers of chemosensory machineries may ensure the bacteria survive the diverse environmental challenges.
II. Intracellular Signaling in Bacteria
- Using microarray approach, Dr Ann Stock from UMDNJ-Robert Wood Johnson Medical Schooll described their investigation of “ Regulating response regulators”. In general, response regulator (RR) contains in the regulatory domain the conserved residues including Ser, Thr, and Tyr next to the Asp residue for the reception of the phosphate signaling molecule. Approximately 14% of RR contain only the regulatory domain, 12% have enzymatic domain at the C-terminus, while most RR act as transcription factor carrying with a DNA domain.
- M Laub (MIT) introduced in “Specificity and evolution of two-component signaling pathways” his theory about new pathways arise in order to ensure the specificity to prevent from unwanted cross-talk between 2CSs. By comparative analysis of the phosphor-relaying rate at different time-intervals of approximately 4500 2CS pairs, he showed that the 2CS with strong kinetics preference ensure the specificity of the phosphor-relay.
- M Goulian (U Penn) in the talk “Feedback regulation in the PhoQ/PhoP two-component
system” mentioned how they measured the feedback regulation using YFP to report the target gene expression and CFP to report the activity of the reference promoter. He concluded that a small molecule of 47 aa is involved in the feed-back regulation for the PhoQ/PhoP signaling pathway.
They also demonstrated using 2-hybrid analysis that the small protein MgrB exerted its regulatory role by direct binding to PhoQ. The mgrB deletion conferred the bacteria an abnormal filamentous cell morphology implying an essential role of the MgrB-mediated control.
- L McCarter (U Iowa) reported in “Surface specific gene expression” of Vibrio
parahaemolyticus. They used microarray comparison to differentiate the swarmmer cells, 200~ 400 μm filaments with peri-flagella, and the swimmer cells with polar flagella. The analysis revealed, in addition to the LafK regulon, several groups of the LafK-independent genes including virulence genes, the genes involved in modulation of the c-di-GMP level were also identified in the swarmmer cells. Most interestingly, the secreted collagenase increased production of ~550 fold higher than the swimmer cells.
- U Jenal from U Basel, Switzerland in the talk “Coordination of Caulobacter cresentus cell cycle and pole morphogenesis” described the involvement of second messenger c-di-GMP in the control of the single cell to community stage. The interacting regulation YhjH, YcgR, YedQ, YfiN, YddV, and YegE were demonstrated.
III. Motility Apparatus and Regulation
- Dr. J Liu (U Texas Medical School) in the talk “Molecular architecture of spiral flagellar motor in situ” presented the use of Cryo-EM tomography to build up the model for the assembly of the spiral flagella motor; - D Blair (U Utah) in “Organization and mechanism of the flagellar switch” described the use of EM analysis revealed that the switching machinery is composed of 3 protein complex including 25 copies of FliG, 35 copies of FliM, and 140 copies of FliN.
- R Harshey (U Texas Austin) described in “The cyclic-di-GMP receptor protein YcgR localizes to the flagellar basal body and inhibits chemotaxis in Salmonella“ the use of co-IP analysis
demonstrated an interaction between YcgR and the rotor protein. The in vivo analysis for the
expression of YcgR-GFP in either fliM, fliG, or fliN deletion mutant further supported the presence of an interaction between YcgR and FliM and FliG. In contrast to the interaction between B. subtilis EpsE and FliG, of which EpsE acts as clutch to interact with FliG at late stage to inhibit the flagellar switch leading to the biofilm formation, the Salmonella YcgR interacts with FliM in the early stage to inhibit dhemotaxis.
IV. Intracellular Signaling in Eukaryotic Microorganisms
The 2CS of eukaryotic microorganism are mainly hybrid type and the phosphate group transferred from histidine kinase to Hpt module and then to response regulator (RR). Two types of RR are
transcription factors and MAPK pathway effectors involved in stress response.
- In the talk “ Osmosensory signal transduction in the budding yeast”, Dr H. Saito (U Tokyo) introduced the signal transduction pathway in order for the budding yeast growing in ripen fruit in
which the sugar concentration could reach to 5 M. The osmostress in the hyperosmotic environment was received by the sensor kinase and the signal relay eventually led to glycerol accumulation.
- In the talk “HKs, cell wall biosynthesis, and relationships to Candida albicans and
candidiasis”, R. Calderone (Georgetown UMC) introduced the fungal HK could be classified into 11 families on the basis of phylogenic analysis. Among them, ChKI, SinI, and NiKI are conserved and required for virulence. In the study, they have shown that ChkI is required for invasive candidiasis, QS, biofilm formation, adherence of Candida to host cells via regulating the enzymes for reconstitution of the cell wall system (rich in mannoprotein~ 30-40%).
- K. Shiozaki (UC Davis) reported in “ Stress sensing and response in fission yeast S. pombe”
the use of 2-hybrid analysis to identify the SinI (stress MapK-interacting protein I)- dependent stress response pathway; - K. Borkovich (UCR) in “Two-component systems in Neurospora” introduced that11 hybrid HK, 1 Hpt, and 2 RR have been identified in Neurospora. She also described in details the signal relayed following the path from HK to Hpt then to RR and finally to the MAPK cascade.
V. Intercellular Communication
In ”What’s new with QS”, E. P. Greenberg (UW) introduced the term “Sociomicrobiology” of which QS allows coordination of group activities which induced by the signals of LuxI family. He described the discovery of a new class Aryl-HSL from Rhodopseudomonas palustris for the synthesis of QS products including light, exoenzymes, toxins, and aggregation factors. The bioassay excluded the signals of LuxN- 3-OH-C4, LuxR-C5-C8, RhlR-C4-C6, LasR C8-14, GtaR C14-16, or TraR C4-14. Finally, p-coumarate p-coumaroyl-HSL was shown to be the QS inducer for the RpaI-RpaR mediated regulon.
- K.L. Visick described in “The regulatory network controlling biofilm formation and
colonization by Vibrio fisheri” the identification of a RscS hybrid HK. He has shown the sensor kinase regulates the signal transduction control for the synthesis of polysaccharide (Syp), which is an
essential step for the bacterial colonization and biofilm formation. He also showed the experiments used including knock out the sypG gene, overexpression of rscS or sypE, interaction of SypE and SypA (the anti-sigma antagonist) to establish the phosphorelay from RscS to SypG-P then to SypA-P, and finally affects the biosynthesis of the polysaccharide, biofilm formation and the development of a symbiosis lifestyle.
- F Yildiz (UC Santa Cruz) in the talk “Regulation of biofilm formation in Vibrio cholerae” the role of c-di-GMP signaling potential effectors including PilZ (PlzA, PlzB, PlzC, PlzD, and PlzE) and RXXD, CdgG riboswitch in the control of the expression of the 62 GGDEF, EAL, HD-GYP domain proteins. He showed that the deletion of PilZ protein, CdgG had no effect on the colony rugosity or the biofilm formation. He has also shown that VpsT dimmer functions as a c-di-GMP effector to
determine the colony conversion from smooth to rugose.
- D. Kearns (Indiana U) described in “Bistable expression of motility genes in Bacillus subtilis”
the heterogenous population phenotype: some are motile, while some are in chains and non-motile. To investigate how the gene expression differs in the different cell types, the reporters including
P-flagellin-GFP and P-autolysin-CFP were used. The monitoring in short cells and long chain cells revealed that Sigma D dependent gene expression is bi-stable.
- D. Zusman (UC Berkeley) also reported the use of reporter systems in “Coupling the FrzCD receptor to the A motility”. He has shown that using the A motility complex GST-FrzCD has pulled down from the Myxococcus lysate AlgZ and AgmU. The interaction with FrzCD was further
demonstrated using AglZ-YFP or AgmU-mcherry. He has shown that both proteins co-localized and the clusters appeared stationary as cells move forward. In addition, AgmU decorates a double helix showing a same periodicity of MreB which supports the previous finding that the A motility is MreB dependent. Finally, he showed the use of AgmU-GST in the pull down assay that in addition to FrzCD, AglZ, AglT, AglW and the MotAB homologues are required for the A motility.
VI. Pathogenesis and Virulence mechanisms
- Dr E. Groisman from Washington University gave an overview of “Controlling the activity of two-component regulatory systems”. He introduced genetic basis differences for the different control between related species, which include the presence or absence of the gene, differential regulation, allelic difference, and different genetic context. In Salmonella, PmrD-dependent pathway is involved in the regulation of the polymyxin resistance. While in E. coli, the drug resistance is mediated by a PmrD-independent control. However, although sharing less than 50% sequence identity, Ec-PmrD in Salmonella works as Salmonella PmrD. On the other hand, Ec-PmrBc which shares much higher sequence identity with Salmonella PmrBc exerts different dephosphorylation activity.
- “Inter-kingdom chemical signaling in bacterial pathogenesis” by Dr V. Sperandio from UTS Medical Center introduced the identified signaling molecules such as AI3, Epinepharine,
Norepinepharine, and Tyrosine in GI tract.
- “When is a predator not a predator? Prey dependent versus axenic growth in Bdellovibrio”
given by Dr. L. Sockett from U Nottingham UK introduced the life styles of the 3.8 Mbp genome G(-) bacteria. They are host independent (HI) growth, which takes 2 wk on peptone-rich medium and host dependent (HD) growth. The microarray analysis has identified predation specific genes namely predatosome, which include genes for the expression of type IV pilus and flagella, 15 PilZ domain proteins, 1 EAL and 5 GGDEF domain proteins, and MreB, MreC, and MreD proteins.
Overall, I was impressed and overwhelmed with the stimulations of most of the reports. Most
importantly, I find the meeting extremely informative and inspiring for the future study of the sensory transduction in bacteria.
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