Number–volume trade-off and restriction strategy for legume nodule against fluoroquinolone resistance development in rhizobia: Nanospectroscopy and molecular dynamics simulations

Outbreaks of infections by antibiotic-resistant endophytes caused by the consumption of edible plants are continually increased worldwide. Despite the high transmission potential of endophytic rhizobia to humans via the ingestion of edible legumes, the acquisition and evolution of antibiotic resistance by these endophytes in closed-root nodule microhabitats are poorly understood. Herein, we established a novel Pisum sativum–Rhizobium symbiotic system to reveal the responses of nodule development and antibiotic resistance acquisition of rhizobia in nodules under external stress by two typical fluoroquinolones (FQs), ciprofloxacin and norfloxacin, using infrared nanospectroscopy and molecular dynamics simulation (MDS). Legume nodules adopted a number – volume trade-off strategy against FQ stress despite impeded nodule primordium development. FQs induced heritable FQ resistance in Rhizobium in liquid medium but not in root nodules. Moreover, nanoscale infrared mappings of FQs in nodules showed that nodule peripheral tissues significantly impeded FQ diffusion towards a rhizobia-inhabited central zone owing to strong FQ immobilization. The MDS results revealed that electrostatics and van der Waals forces dominated the binding of FQs to cell-wall cellulose and pectin, respectively. Collectively, these findings offer novel insights into the physiological response of legume nodules to FQs and elucidate the pivotal role of nodule tissues in shaping endophytic antibiotic resistance. • Root nodules take a number–volume trade-off development strategy against FQ stress. • Nodule periphery impeded FQ diffusion towards the rhizobia-inhabited central zone. • Legume root nodules blocked the emergence of FQ resistance in rhizobia. • Electrostatics and van der Waals forces dominated FQ immobilization on the cell wall.