Untargeted metabolomics for evaluating the effects of inoculation on Lessertia frutescens under stress

Lessertia frutescens is a multipurpose medicinal plant indigenous to South Africa [ 1 ] [ 2 ]. The demand for L. frutescens raw materials has increased due to its anti-HIV [ 3 ], anti-inflammatory [ 4 ], anticancer [ 2 ] and antioxidant [ 1 ] properties, putting undue pressure on wild populations. Commercial propagation of the plant presents a feasible alternative to supplement the dwindling supply of wild populations, but the persistent drought climate poses a threat to growth and productivity of the plant. Rhizobia can improve yield, biological activities and the production of secondary metabolites plants under drought. The aim of this work was to evaluate the efficacy of three rhizobia isolates, TUTLFNC33, TUTLFNC37 and TUTLFWC74 trapped using a homologous host L. frutescens from rhizosphere soils sampled in the Western Cape and Northern Cape, South Africa to mitigate climate induced stress. The rhizobial isolates were used to inoculate L. frutescens seedlings under low, moderate and extreme drought. Metabolomic profiles were obtained using a Shimadzu UHPLC-qTOF-MS, followed by annotation and obtaining molecular networks of L. metabolites. Isolate TUTLFNC37 improved the drought tolerance through root proliferation and proline accumulation. Increased biomass, phenolic compounds, triterpenes and antioxidant activity, were evident in the extracts of Lessertia frutescens inoculated with TUTLFNC37. Metabolomics molecular network demonstrated the ability of the rhizobial isolate to withstand drastic changes in the composition of unique metabolites, sutherlandiosides A-D and sutherlandins A-D. Peptides and glycerolipids molecular families, which were never reported to be present in Lessertia frutescens before, were detected and annotated in the molecular networks ([ Fig. 1 ]). Therefore, isolate TUTLFNC37 is regarded the most promising, environmentally friendly intervention to enhance drought tolerance of L. frutescens . Fig. 1 Molecular network showing metabolites families in L. frutescens extracts inoculated with TUTLFNC37 after exposure to different drought stress levels. Each node colour represents a drought stress level to which the plants were subjected. Publication History Article published online: 05 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany