Microbial degradation of two major phytotoxic alkaloids from barley

Barley (Hordeum vulgare L.) produces phytotoxic alkaloids hordenine and gramine as defense compounds against pests and pathogens. These alkaloids also influence rhizosphere microbial communities, and their persistence in soil poses potential ecological risks due to their phytotoxicity. However, the microorganisms and pathways involved in their degradation have not yet been characterized. Here, a Gram-negative bacterium (Pseudomonas sp. strain NyZ201) and a Gram-positive bacterium (Paenarthrobacter sp. strain NyZ202) were successfully isolated from barley rhizosphere for their respective evident growth with hordenine (doubling time = 2.5 h) and gramine (doubling time = 3.8 h) as sole sources of carbon, nitrogen and energy. High-resolution mass spectrometry and ¹⁸O-labeling experiments identified key catabolic intermediates formed by hydrolysis or dehydrogenation. Through whole-genome sequencing analysis, we proposed degradation pathways for these two barley alkaloids and predicted the associated gene clusters harbored by these strains. These findings offer novel insights into the microbial degradation of phytotoxic alkaloids from barley, and provide a basis for the detoxification of phytotoxic alkaloids in agricultural ecosystems.