Quorum-Sensing Mechanism in Rhizobium sp.: Revealing Complexity in a Molecular Dialogue

Nitrogen fixation by a biological process is an important phenomenon for improving agricultural soil fertility by fixing atmospheric nitrogen in the form of ammonia, which is mediated by the symbiotic association between Rhizobium species and leguminous plants. During symbiosis bacteria aggregate to form biofilms and coordinate their behavior in response to environmental conditions by a process called Quorum sensing (QS). The mechanism of quorum sensing depends on the interaction between signal molecule and a sensor that helps bacteria to communicate and regulate gene expression related to nodulation, biofilm formation and symbiosis and nitrogen fixation. Rhizobium utilizes N- acyl homoserine lactones (AHLs) as signalling molecules to coordinate and regulates gene expression. In addition to this, host response to bacteria is important to combat pathogenic bacteria and attract beneficial ones. For this leguminous plants sense the presence of bacteria precisely and release chemical compounds like flavonoids to make appropriate responses to symbiosis. The review clearly emphasizes interkingdom chemical signaling governing molecular interactions between leguminous plants and Rhizobium species in the establishment of symbiosis and nitrogen fixation.