How Rhizobia Survive in the Absence of a Legume Host, a Stressful World Indeed

Abstract

In the preceding decade, numerous advances have been made in understanding the genes and proteins involved in rhizobial responses to stress, particularly those caused by desiccation, pH, and nutrient deprivation. Often, the genes and proteins that are expressed under one stress condition overlap with those induced under other stress conditions. Although most studies on rhizobial stress responses employ planktonic cells, one way that rhizobia, as nonspore formers, could maximize their survival under stress conditions is to establish biofilms, surface-attached communities. However, few studies of this life style for rhizobia have been undertaken especially with regard to stress. The knowledge gained from learning about how planktonic cells respond to stress must now be applied to rhizobial biofilms because they serve as reservoirs of bacteria in the rhizosphere when a legume host is absent. By so doing, we will gain a much better understanding of how this fascinating and important group of soil bacteria lives in the “real world.”