An Endophytic Fungal Isolate <i>Paecilomyces lilacinus</i> Produces Bioactive Secondary Metabolites and Promotes Growth of <i>Solanum lycopersicum</i> under Heavy Metal Stress

Heavy metal (HM) contamination in the soil and accumulation in plants poses a serious threat to crops and human health. HMs such as cadmium, mercury, lead and arsenic are widely acknowledged for their adverse effects on plants such as chlorosis, necrosis, low food quality and crop yields. Endophytic fungi secrete secondary metabolites and enhance the plant’s ability to tolerate stressful conditions. However, the role of most fungal endophytes in their host plant growth or production of metabolites under HM stress conditions needs further understanding. In the present study, we studied the HM stress alleviation capability of the endophytic fungus, <i>Paecilomyces lilacinus</i> (MRF), isolated from the roots of <i>Justicia adathoda</i>. We studied two heavy metals, namely lead and cobalt. The culture filtrate (CF) of <i>P. lilacinus</i> revealed IAA (68.17 µg/mL), phenols (43.31 µg/mL), flavonoids (40.59 µg/mL), sugar content (97.83 µg/mL) and proline (17 µg/mL). Additionally, DPPH-free radical scavenging activity and the antibacterial potential against <i>Salmonella typhi</i> and <i>Shigella sonnei</i> of the CF demonstrated positive results. The gas chromatography mass spectrometry analysis of the CF manifested different constituents, including (1) Trichloromethane, (2) 3,7,11,15-Tetramethyl-2-hexadecen-1-ol, (3) phytol, (4) 1,2-Benzenedicarboxylic acid, (5) bis(2-ethylhexyl) ester, (6) squalene and (7) Cyclotrisiloxane Hexamethyl. Moreover, the plant growth-promoting activity of the <i>P. lilacinus</i> (MRF) strain revealed a robust increase in root and shoot growth, and the fresh and dry weight of <i>S. lycoprsicum</i>. Further, the IAA, phenols, flavonoids, sugar, proline, relative water content and protein contents also increased in the <i>S. lycoprsicum</i> inoculated with <i>P. lilacinus</i> as compared to the control plants. The present study revealed that the inoculation of <i>P. lilacinus</i> alleviates the damages of HM stress and improves the physicochemical characteristics of <i>S. lycoprsicum</i>.