erwinia psidii erwinia psidii erwinia psidii is a gram-negative bacterium and a phytopathogen of the common guava (psidium guajava), causing rot in branches, flowers and fruits. recently, it was demonstrated that this species produces two acyl homoserine lactones (s-(-)-n-hexanoyl- and n-heptanoyl-homoserine lactone), widely recognized bacterial quorum sensing signaling substances, and employed in bacterial cell-to-cell communication systems. erwinia psidii scientific classification domain: bacteria phylum: pseudomonadota class: gammaproteobacteria order: enterobacterales family: erwiniaceae genus: erwinia species: e. psidii binomial name erwinia psidiirodrigues neto et al. 1988