The complex world of gastrointestinal bacteria

The world of gastrointestinal (GI) bacteria is one of the most complex and intricate of the microbial domain. These bacteria are confronted with a constantly changing (and often hostile) environment, including fluctuations in both physical and chemical conditions. Neighboring microorganisms not only contend for substrate but even launch complex chemical attacks with the apparent purpose of disrupting the activity of their competitors. Yet, some species not only survive, they even flourish, in the GI tract because they possess the ability to adapt to these environmental fluctuations and assaults from other microbes. Such adaptation involves sophisticated programs in the bacterial cell that enable it to monitor its environment and make necessary adjustments of physiological activity and gene expression. Among these adjustments is the ability of cell-to-cell communication, biofilm formation, regulation of cytoplasmic pH, and maintenance of genetic diversity through mutation and horizontal gene transfer. As a consequence, bacteria in the GI tract often manifest very different physiological features than are observed for the same bacteria during routine laboratory cultivation.