In 1965, Dr. Alexander Tomasz identified a critical component of the DNA uptake mechanism used by competent Streptococcus pneumoniae: the pneumococci secrete a polypeptide that induces the expression of proteins to allow foreign DNA to pass through the bacterium's cell wall. This hormone-like substance was the first of numerous "quorum-sensing" factors that have since been identified in many microbial processes.  Detailed insights into the molecular mechanisms of quorum-sensing are now emerging, owing largely to studies focusing on the ability of marine organisms like Vibrio fischeri and Vibrio harveyi to produce light at high cell densities.  The complexities of bioluminescence induction, and indeed that of an ever increasing group of other quorum-sensing phenotypes, show that such signaling pathways are not just an interesting phenomenon but rather represent a widespread mechanism by which bacterial populations can communicate, coordinate behavior and act in a cooperative manner in the environment.