Figure 9.18 Cell-cell communication enables these (a) Staphylococcus aureus bacteria to work together to
form a biofilm inside a hospital patient’s catheter, seen here via scanning electron microscopy. S. aureus is the
main cause of hospital-acquired infections. (b) Hawaiian bobtail squid have a symbiotic relationship with the
bioluminescent bacteria Vibrio fischeri. The luminescence makes it difficult to see the squid from below because it
effectively eliminates its shadow. In return for camouflage, the squid provides food for the bacteria. Free-living V.
fischeri do not produce luciferase, the enzyme responsible for luminescence, but V. fischeri living in a symbiotic
relationship with the squid do. Quorum sensing determines whether the bacteria should produce the luciferase
enzyme. (credit a: modifications of work by CDC/Janice Carr; credit b: modifications of work by Cliff1066/Flickr)