# Plant Growth‐Promoting Rhizobacteria Colonize Δ9 ‐Tetrahydrocannabinolic Acid Drug‐Type Cannabis sativa L. Roots and Modulate Cannabinoid Metabolism

## TL;DR

This study shows that certain bacteria can colonize cannabis roots and alter the production of cannabinoids, which are important for medicinal use.

## Contribution

The study demonstrates that PGPR can modulate cannabinoid metabolism in high-THCA Cannabis sativa.

## Key findings

- PGPR increased CBGA concentration by 27.37% and reduced Δ9-THC by 15.76%.
- Bacterial treatments shifted CBGA/THCA and THCA/CBDA ratios, favoring CBGA and CBDA.
- PGPR reduced in vivo and post-harvest decarboxylation of THCA into Δ9-THC.

## Abstract

Plant growth‐promoting rhizobacteria (PGPR) establish beneficial associations with plants, enhancing nutrient uptake, growth, and stress tolerance.
Cannabis sativa
L., a medicinal plant producing over 300 specialized metabolites with relevant medicinal properties, remains underexplored for PGPR influence on its metabolism. This study assessed the ability of four PGPR taxa: Bacillus, Pseudomonas, Flavobacterium, and Burkholderia to colonize roots and modulate cannabinoid metabolism. Two Δ9‐tetrahydrocannabinolic acid (THCA) drug‐type
C. sativa
cultivars, Amnesia Haze and Gorilla Glue, were tested. Plants grown hydroponically were inoculated under controlled conditions. Root colonization was confirmed via endophyte‐specific assays. Phenotypic analyses revealed no effects on plant phenotype, while chemical analyses revealed a response shared across taxa and cultivars. Bacterial inoculation increased the precursor cannabinoid Cannabigerolic acid (CBGA) concentration significantly by +27.37% while reducing Δ9‐tetrahydrocannabinol (Δ9‐THC) by −15.76%. The CBGA/THCA and THCA/CBDA ratios shifted significantly, indicating a favored CBGA accumulation and CBDA production, respectively. PGPR treatments reduced in vivo and post‐harvest decarboxylation of THCA into Δ9‐THC, preserving the acidic cannabinoid profile. Under a standardized, soilless hydroponic regimen with a single shared reservoir and identical fertigation across groups, PGPR colonization was associated with shifts in cannabinoid metabolism and reduced decarboxylation. This study demonstrates that PGPR can influence the specialized metabolism of high‐THCA
C. sativa
, offering insights into sustainable cultivation and pharmaceutical exploitation of this relevant medicinal plant species.