Effects of Magnaporthe oryzae cell-free filtrate on the secondary metabolism of Streptomyces bikiniensis HD-087: a non-targeted metabolomics analysis

Rice blast, a disease caused by Magnaporthe oryzae, significantly threatens global rice production. To improve the anti-M. oryzae activity of Streptomyces bikiniensis HD-087 metabolites, the effects of inducer, Magnaporthe oryzae acellular filtrate, on secondary metabolism of S. bikiniensis HD-087 were studied. The results showed that M. oryzae cell-free filtrate cultured for 96 h served as the most effective inducer, significantly enhancing the anti-M. oryzae activity of metabolites of S. bikiniensis HD-087 and increasing the diameter of the inhibitory zone by 2.96 mm. The inhibition rates of M. oryzae colony diameter and spore germination in the induced group were 12.39% and 39.6% higher than those in the non-induced group, respectively. Metabolomic profiling of strain HD-087 highlighted substantial differences between the induced and non-induced groups. At 48 h of fermentation, a total of 705 distinct metabolites were identified, while at 96 h this number decreased to 321. Moreover, induction markedly altered primary pathways such as the tricarboxylic acid cycle, amino acid biosynthesis, and fatty acid metabolism in S. bikiniensis HD-087. qPCR analysis showed that nrps genes and pks genes in the induced group were significantly up-regulated by 9.92 ± 0.51 and 2.71 ± 0.17 times, respectively, and biotin carboxylase activity was also increased 26.63%. These results provide a theoretical basis for using inducers to enhance the antimicrobial ability of Streptomyces.