Linnemannia elongata: A Key Species in Chitin-Based Plant Growth Promotion

Abstract

Chitin has proven to be a valuable alternative to mineral fertilizers in growing media. We recently hypothesized that chitin might work as a biostimulant, attracting plant growth-promoting microbes to the rhizosphere. In particular, Mortierellales species increase in abundance massively with 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 postulated that this growth promotion was induced through auxin production, translocation of calcium to the plant, or both. The synergy between chitin and L. elongata was demonstrated by (i) the chitinase activity and chitin degradation potential of all isolates and (ii) the positive effect of chitin and L. elongata seed coating on germination of A. thaliana seeds compared with L. elongata seed coating without chitin. We conclude that chitin-related growth promotion is dependent on activation of the microbial community, with L. elongata as a key species.