Method for evaluation of Streptomyces growth and metabolism in the presence of glyphosate-based herbicide.

ABSTRACT

The use of pesticides, such as glyphosate, has increased due to population growth and the rising demand for food. Plant growth-promoting rhizobacteria (PGPR), such as Streptomyces, offer a more ecologically friendly alternative to the excessive use of pesticides. However, these bacteria undergo a complex life cycle involving the formation of hyphae, mycelia, and spores, which makes standardizing laboratory cultures challenging. In this context, we tested three methods for cultivating a Streptomyces isolate (CLV322) in the presence of the stressor agent glyphosate, denoted as M1, M2, and M3. These methods involved the simultaneous addition of the herbicide 24-48 h after the start of cultivation. We evaluated the growth and cell viability of CLV322 using the 2,3,5-triphenyl tetrazolium chloride (TTC) assay under glyphosate-based herbicide stress (Roundup® Original DI) at concentrations ranging from 0.002 to 7.2 mg mL- 1. We also assessed the ability of CLV322 to maintain PGPR characteristics in the presence of the herbicide by quantifying indolic compounds, siderophores, and phenazines. The cultivation method significantly influenced the production of metabolites by CLV322, with M3 yielding more consistent results across the evaluated parameters. Our findings suggest that germinating Streptomyces spores for 48 h before introducing glyphosate (M3) enables the analysis of bacterial tolerance to herbicide stress. This methodology may also apply to evaluate other abiotic stresses on Streptomyces strains.