Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress in Plants

Microorganisms have a variety of evolutionary adaptations and physiological acclimation mechanisms that allow them to survive and remain active to face environmental stress. Among the mechanisms identified in microbes, tolerance to low temperatures is of paramount significance, considering the area of the earth’s surface that is exposed to varying degrees of low temperatures. Based on low temperature preference, microbes have been classified as psychrophiles or cold loving, and psychrotrophs or cold tolerant. Psychrophiles are exposed to extremes of cold for major part of the year, while psychrotrophs are exposed to transient cold conditions in nature. The ability of psychrotolerant bacteria to survive and proliferate at low temperatures implies that they have devised a number of mechanisms that help them to tide over the transient cold. These adaptations include lipid modification to maintain membrane fluidity, induction of specific proteins (Csp and Cap), synthesis and utilization of cryoprotectants, cold adapted enzymes, synthesis of ROS detoxifying enzymes, ice binding proteins, and RNA degradosomes. This review highlights the current knowledge on cold tolerance/adaptation mechanisms operating in psychrotolerant bacteria and their utility in alleviation of cold stress and modern biotechnology.