Environmental Stress Response and Adaptation Mechanisms in Rhizobia

Rhizobia are bacteria that can fi xate atmospheric nitrogen in association within the root or the stem nodules of legume plants and transform atmospheric nitrogen to ammonia. Soil environmental conditions are critical factors for the persistence and survival of rhizobia in the soil. Th e changes in the rhizosphere environment can aff ect both growth and saprophytic competence, which will infl uence competitiveness and persistence. Environmental stress imposes a major threat to symbiotic nitrogen fi xation and agriculture that can be limited by soil and climatic factors such as salinity, drought, temperature, acidity/alkalinity and heavy metals. In this review we present several diff erent mechanisms in rhizobia adaptation under stress factors.