New perspectives on the viable but nonculturable response

It has been demonstrated that numerous species of bacteria enter a viable b ut nonculturable (VBNC) state in response to environmental stress. There ha ve been numerous reports on the physiology of these cells as well as the co nditions which induce nonculturability. There have been fewer convincing re ports of resuscitation. Thus, our knowledge of the processes involved in in duction of the VBNC state has increased significantly while the processes i nvolved in resuscitation of these cells has been less forthcoming. Nonethel ess, it is apparent that VBNC formation and resuscitation are important ada ptive responses to environmental stress, much like starvation and outgrowth responses. Research in the field of nonculturability has recently seen a s hift from the purely physiological characterization of VBNC cells to the ex amination of the genetic regulation involved in the induction of noncultura bility and to the factors required for resuscitation. It has become apparen t that factors such as oxidative stress may play a large role in both the e ntry into and exit from the VBNC state. In addition, recent evidence indica tes that signaling molecules play an important role in adaptive responses. This review will summarize the current research in the field of nonculturab ility and discuss current directions being taken to further our knowledge o f such adaptive responses.