Linnemannia elongata: a key species in chitin-based plant growth promotion

Chitin has proven to be a valuable alternative for mineral fertilizers in growing media. We recently hypothesized that chitin might work as a biostimulant, attracting plant growth promoting microbes to the rhizosphere. Especially Mortierellales increase massively in abundance by chitin application and might have a profound role in chitin-mediated plant growth promotion. We isolated four strains of this order, classified as Linnemannia elongata, from chitin-enriched growing medium and the lettuce rhizosphere. The isolates induced a consistent increase in shoot and root fresh weight and increased chlorophyll content of Arabidopsis thaliana in vitro as measured by multispectral imaging. By studying the isolate’s genomes, we postulate that this growth promotion is induced through auxin production and/or translocation of Ca to the plant. The synergy between chitin and L. elongata was demonstrated by (1) the chitinase activity and chitin degradation potential of all isolates and (2) the positive effect of chitin and L. elongata seed coating on germination of A. thaliana seeds as compared to L. elongata seed coating without chitin. We conclude that chitin-related growth promotion is depending on the activation of the microbial community, with L. elongata as a key species.