STS LE 1

• Bacteria


  Primitive and brainless, yet they communicate
• Bacterial communication


  Reacting to rapidly changing conditions in their environment like availability of nutrients, evasion of toxic molecules, defense against other bacteria
• Quorum sensing


  The language of bacteria in the form of chemical signals which they release
• Quorum sensing can never be achieved by a single bacterium
• Quorum


  A group with members competent of accomplishing an objective
• Chemical signals


  Must be in sufficient concentration, there should be enough cells releasing them to trigger the expression of specific genes as a response to a specific environmental condition
• Quorum sensing


  • The essence is strength and safety in numbers, a microbial version of the cooperative behavior seen in schools of fish moving in unison
• Quorum sensing first observed

  1965
• Alexander Tomasz observed quorum sensing in bacteria that caused pneumonia</b>
• Nealson, Platt and Hastings (1970) observed the glow from the nocturnal Hawaiian bobtail squid emitted by millions of marine bacterial cells called Vibrio Fischeri
• Vibrio fischeri


  Bacteria living underneath the skin of the squid
• Bioluminescence


  The ability of living organisms to emit light
• Cell density


  The number of cells determines the factor that triggers bioluminescence, a chemical signal which accumulates to a sufficient concentration excreted by enough number of cells, capable of triggering a group response like bioluminescence
• Acyl-homoserine lactone or AHL


  The identified excreted chemical signal, also called as autoinducer
• Lux


  Protein that triggers the expression of the set of genes for bioluminescence
• Luciferase


  Expressed enzyme or protein that catalyzes the chemical reaction to produce light
• Pathogenic or infectious disease-causing bacteria are very dependent on quorum sensing to launch virulence successfully
• Pathogenic bacteria can form a compact thin strip of their dense population called biofilm on any surface outside or inside the body like the lungs

  
• Vibrio fischeri


  Excretes AHLs as chemical signals to communicate
• Pseudomonas aeruginosa


  Uses both AHLs and the siderophore pyoveridine
• Other bacteria use peptides or short proteins as chemical signals
• Microbes use different kinds of chemical signals


  • AHLs
  • Peptides
  • ComX
  • SapB
  • Nod factor
  • A-factor
• Microbes have a universal language called autoinducer-2 or AI-2 that facilitates interspecies communication
• Plants that harbor bacteria in their roots excrete a chemical signal that triggers the expression via quorum sensing by the bacteria of molecules beneficial to the plant and vice versa

  
• A group of bacteria may use their chemical signals to destroy the quorum sensing system of other groups of bacteria in the vicinity, in cases of competition for available nutrients
• Pathogenic Pseudomonas aeruginosa uses deadly messages via quorum sensing
• Reason scientists are excited about quorum sensing


  Emergence of numerous virulent bacteria which are resistant to many antibiotics, as they can counter attack antibiotics by producing antibiotic-degrading enzymes
• Vaccines


  Specifically target autoinducers which trigger quorum sensing, hence blocking the expression of toxins and the formation of biofilms, resulting in resistant bacteria losing their virulence
• Quorum sensing is used by plant pathogens to colonize grapevines, potatoes, onions and other crops

  
• Quorum sensing is used to enhance the formation of biofilms of bacteria capable of degrading environmental toxins and pollutants, which are seeded in sewage treatment plants and industrial wastewaters

  
• Quorum sensing offers vast potentials for the improvement of the environment and the advancement of biotechnological and biomedical industries
• Scientists in natural sciences are closely working with sociologists to study human behavior and society making use of quorum sensing and other traits of microbial communities as models
• Democracy is like the bioluminescence or the light a nation must collectively express, with public servants and competent leaders being the autoinducers of this important expression
• A 4.5-billion-year-old Martian meteorite called ALH84001 may have shuttled life forms from Mars 11,000 years ago
• Magnetic crystals in Martian meteorite


  Aligned in chains embedded in the meteorite, with striking resemblance to the composition and arrangement of magnetic crystals found within a group of bacteria thriving on Earth called magnetotactic bacteria
• Magnetotactic bacteria


  Cells swim in the same direction with high speed when a magnet is brought near, due to the presence of nano-sized membrane-bound magnetic crystals of magnetite (Fe3O4) or greigite (F3S4) aligned in chains perpendicular to the cell axis

  
• Magnetosomes


  Highly organized structures in magnetotactic bacteria, referred to as magneto fossils by geochemists and paleontologists

  
• Magnetic particles


  Function as navigating compass needles for the bacterium to migrate through the Earth's geomagnetic field lines

  
• Microbes deal with the problem of iron unavailability by producing and releasing molecules called siderophores designed to bind with high specificity and affinity to insoluble iron
• Siderophores


  Special kinds of invisible boomerangs released by microbes to capture iron, which then return to the bacterial cells via specific receptors on the surface