MICR 221 - Sensing and Communication PDF

Midterm Exam 1 Midterm Exam 1 grades posted on onQ Class average: ~75% You can review your midterm: Today (Feb. 10), 12 – 1 PM, Botterell Room 449 In office hour on Feb. 11, 12 – 1 PM, Botterell Room 449 1 Lecture...

Midterm Exam 1 Midterm Exam 1 grades posted on onQ Class average: ~75% You can review your midterm: Today (Feb. 10), 12 – 1 PM, Botterell Room 449 In office hour on Feb. 11, 12 – 1 PM, Botterell Room 449 1 Lecture 15: Sensing and Communication Feb. 10, 2025 2 Lecture Learning Outcomes After this lecture, students will be able to describe… How two-component signal transduction systems (TCSs) and phosphorelays control transcription How TCSs are used by vancomycin-resistant enterococci and Agrobacterium tumefaciens How bacteria use quorum sensing (QS) to sense population density How QS regulates Vibrio fischeri bioluminescence, EHEC virulence, and the formation of dental plaque 3  Bacterial Sensing Sense environmental conditions Nutrient levels, antibiotics, pH, etc Sense other bacteria Work together Kill each other Sense host organisms Commensals Pathogens Often respond by changing gene expression 4 Image from: https://twitter.com/jorgepena9/status/1407782734492094469/photo/1  Direct Interactions with Regulators Stimuli can directly Without lactose: impact transcription E.g., lac operon If lactose is present, allolactose formed Allolactose binds to LacI With lactose: Prevents LacI from binding to operator 5 Image from: Prescott’s Microbiology, 11th Edn  Two-Component Signal Transduction Systems Sensing and response can be carried out by separate proteins Two-component signal transduction systems (TCSs) >200 in some species Sensor kinase: membrane protein, sensor detects stimulus kinase Response regulator: cytoplasmic DNA-binding protein Sense external stimuli response regulator Nutrients, antibiotics, etc Host environment (e.g., hormones, high osmolarity) 6 Image from: https://doi.org/10.1098/rsob.180023  Two-Component Signal Transduction Systems Stimulus activates sensor kinase Kinase domain is autophosphorylated Transfers phosphate group to response regulator Phosphorylation changes response regulator structure Can now bind to DNA Changes transcription Activator or repressor 7 Image from: https://doi.org/10.1128/MMBR.05004-11  Example: Enterococci and Vancomycin Enterococcus faecalis, E. faecium are common gut bacteria Major nosocomial pathogens Healthcare-associated infections Persist in hospital environments Cause infections in immunosuppressed patients E.g., bacteremia, endocarditis, urinary tract infections 8 Image from: https://cupe.ca/health-care-associated-infections-backgrounder-and-fact-sheet  Example: Enterococci and Vancomycin Enterococci have high genome plasticity Can easily acquire, incorporate new DNA E.g., genomic islands Accumulate antibiotic resistance genes Vancomycin used for resistant Gram-positive infections Vancomycin-resistant enterococci (VRE) increasing in prevalence 9 Image from: https://www.cdc.gov/drugresistance/pdf/vancomycin-resistant-enterococcus.pdf  Example: Enterococci and Vancomycin Changes to PG structure confer vancomycin resistance van genes: PG made with D-lactate, not D-alanine But, there is a major fitness cost (impairs growth) TCS used to regulate van genes Only make PG with D-lactate if vancomycin present Otherwise, PG is normal and growth not impaired vancomycin 10 Image from: https://doi.org/10.1038/s41598-020-62557-z  Agrobacterium tumefaciens Plant pathogen Forms tumorlike growths Crown gall disease Gall-causing strains carry tumour-inducing (Ti) plasmid Transfer part of Ti plasmid (T DNA) to plant cells Genes in T DNA are transcribed in plant cell Causes tumour formation Encode enzymes that make nutrients for bacteria 11 Image from: Prescott’s Microbiology, 12th Edn  A. tumefaciens Pathogenesis Enters plant through surface wound Senses plant using a TCS Sensor kinase VirA detects phenolics Plant metabolites Response regulator VirG phosphorylated vir (virulence) genes on Ti plasmid transcribed 12 Image from: Prescott’s Microbiology, 11th Edn  A. tumefaciens Pathogenesis vir genes encode type IV secretion system (T4SS) Similar to T4SS used in conjugation Forms bridge between bacterium, plant Vir proteins excise T DNA from Ti plasmid T DNA secreted into plant by T4SS 13 Image from: Prescott’s Microbiology, 11th Edn  A. tumefaciens Pathogenesis T DNA enters plant nucleus Integrates into genome Plant cell produces enzymes encoded by T DNA Makes phytohormones Causes cell proliferation Forms tumours Makes opines Nutrient (source of energy, carbon, nitrogen) Consumed by A. tumefaciens 14 Image from: Prescott’s Microbiology, 11th Edn  Plant Bioengineering A. tumefaciens is used to genetically engineer plants Recombinant Ti plasmid prepared in the lab Desired gene(s) added Tumor-inducing genes removed T DNA (and desired genes) transferred to plant Changes plant properties Resistance to insects, viruses Greater nutrition 15 Image from: Prescott’s Microbiology, 12th Edn  Phosphorelays More complex version of TCS Phosphate transferred from protein to protein One or more proteins between sensor kinase, response regulator Why? More opportunities for regulation 16 Image from: https://doi.org/10.1128/MMBR.05004-11  Sporulation Phosphorelay Endospore formation in sensor kinases Bacillus spp. is very highly regulated Each step of phosphorelay is controlled by different factors Positive and negative signals Ensures that endospores only formed when absolutely necessary Response regulator Spo0A controls >500 genes Irreversible once started response regulator 17 Image from: https://doi.org/10.1128/MMBR.00025-14  Chemotaxis and Sensing Sensing can impact processes other than transcription E.g., methyl- accepting chemotaxis proteins (MCPs) Senses: attractants, repellants Response: change in flagellum rotation 18 Image from: Prescott’s Microbiology, 11th Edn  Quorum Sensing Bacteria live with lots of other bacterial cells Often helpful to work together Use quorum sensing (QS) to sense population density Cell-cell communication Both intraspecies and interspecies If density is high enough, leads to changes in gene expression 19 Image from: DOI: 10.1126/science.ade251 Quorum Sensing Functions QS regulates functions that work best when carried out by multiple cells Virulence factor production E.g., toxins are ineffective if amount is too low Biofilm formation Requires coordinated production of EPS Competence Most useful if other bacteria (and their DNA) present 20  Quorum Sensing (QS) Vibrio fischeri lives in light organs of fish, squid High density: V. fischeri emits light Benefits host (confuses predators, lures prey) Benefits bacterium (safe, nutrients) Low density: no bioluminescence Light wouldn’t be bright enough; waste of energy bobtail squid light organ V. fischeri 21 Image from: Prescott’s Microbiology, 11th Edn; https://doi.org/10.1111/j.1574-6976.2010.00250.x  Quorum Sensing and Autoinducers Bacteria constantly make autoinducers (AIs) Signalling molecules E.g., N-acylhomoserine lactones (AHLs) AI level is related to number of cells At certain level, impacts gene expression AIs can be sensed by: Transcriptional regulators Sensor kinases (TCS) 22 Image from: https://researchblog.duke.edu/2022/02/16/quorum-sensing-the-social-network-of-bacteria/  QS and V. fischeri Luminescence Proteins encoded by lux operon produce light LuxAB: luciferase LuxCDEG: enzymes that make luciferase substrate lux operon regulated by: LuxI (makes AIs) LuxR (transcriptional activator) 23 Image from: Prescott’s Microbiology, 11th Edn  QS and V. fischeri Luminescence High cell density: High concentration of AIs AIs binds to LuxR LuxR binds near promoter, recruits RNAP Lux proteins produced, cells emit light 24 Image from: Prescott’s Microbiology, 11th Edn  QS and V. fischeri Luminescence Low cell density: Low concentration of AIs Not enough to bind to LuxR LuxR doesn’t bind near promoter No transcription, no Lux proteins, no luminescence 25 Image from: Prescott’s Microbiology, 11th Edn  QS and EHEC Virulence Enterohemorrhagic E. coli (EHEC) Hemorrhagic colitis, hemolytic uremic syndrome Produces virulence factors if cell density is high enough Genome contains pathogenicity island Encodes type 3 secretion system T3SS effectors help infection 26 Image from: Prescott’s Microbiology, 12th Edn  QS and EHEC Virulence Tir (effector) secreted into host epithelial cells Tir then binds to intimin protein on EHEC surface Attaches EHEC to host Tir remodels host cell cytoskeleton Forms pedestal-like structures (“attaching- effacing lesions”) Helps EHEC colonize gut EHEC releases Shiga toxin 27 Image from: https://doi.org/10.1128/mBio.00115-19 QS and EHEC Virulence EHEC virulence factors regulated by QS through a TCS QseC (sensor kinase) senses AIs Activates QseB (response regulator) Upregulates genes for motility, toxins, lesion formation QseC also activated by adrenaline (hormone) 28 Probiotics and EHEC QS is potential therapeutic target Antivirulence (cf. antimicrobials) E.g., Lactobacillus spp. commonly used as probiotics Live microbes which offer health benefit Some Lactobacillus acidophilus strains interfere with EHEC AIs Disrupt QS Prevent EHEC from transcribing virulence factor genes EHEC can’t attach, colonize GI tract 29  Dental Plaque Plaque: biofilm on surface of tooth Dental enamel is covered with pellicle Mucin glycoproteins from saliva Negative charge limits colonization Commensal bacteria can attach to pellicle Pathogens can attach to commensals 30 Image from: Prescott’s Microbiology, 12th Edn  Dental Plaque Oral microbiota must be able to attach Otherwise, swallowed Commensals (e.g., Streptococcus mitis) have surface proteins that bind to mucins in pellicle Initial colonizers release autoinducers (AIs) Commensals can detect very low levels of AIs Shift to biofilm mode 31 Image from: https://doi-org.proxy.queensu.ca/10.1038/nrmicro2381  Dental Plaque As biofilm grows, AI concentration increases Then, pathogens can detect, respond to AIs made by commensals Less sensitive to these AIs than commensals Interspecies communication Pathogens attach to commensals Become part of biofilm 32 Image from: https://doi-org.proxy.queensu.ca/10.1038/nrmicro2381  Dental Plaque Pathogens release insoluble extracellular polymeric substances (EPS) Tooth surface becomes anoxic Pathogens ferment sugars, make acids Plaque impermeable; saliva doesn’t dilute acid Acid demineralizes enamel Dental caries Biofilm causes inflammation, periodontal disease 33 Image from: Prescott’s Microbiology, 12th Edn Reminders Midterm 2 Review In class on Feb. 11 Midterm Exam 2 Feb. 13, 9:30 – 10:20 AM 15 multiple choice questions, 5 short answer questions Lectures 9 – 15 Bring a pencil Accommodated exams administered by Exam’s Office (check Ventus) Lab Assignment 2 due: Feb. 13 at 2:30 PM – section 004 Feb. 14 at 2:30 PM – sections 003, 005 34