Cuticle-associated bacteria can inhibit crayfish pathogen Aphanomyces astaci: Opening the perspective of biocontrol in astaciculture

Abstract

Pathogenic oomycete Aphanomyces astaci, the causative agent of crayfish plague, is listed among the world's 100 worst invasive alien species due to its fast spread and detrimental impact on native European crayfish populations, as well as losses in crayfish aquaculture. During the infection process, A. astaci mycelium invades the host through its cuticle where it interacts with the resident epibiotic bacteria. Since host microbial communities may have an important role in the defense against pathogens, in this study we aimed to i) identify the epibiotic bacterial isolates from the cuticle of two commercially relevant crayfish – the signal crayfish Pacifastacus leniusculus and the narrow-clawed crayfish Pontastacus leptodactylus, and ii) distinguish those that can inhibit the growth of A. astaci mycelium. Results of 16S rRNA gene sequencing and MALDI–TOF mass spectrometry revealed that the majority of collected isolates belonged to the phylum Proteobacteria (69%), followed by Bacteroidetes (17%) and Firmicutes (8%). Using the in vitro plate assays, we tested the potential of the isolates to inhibit A. astaci mycelial growth and classified them as inhibitors (33%) or non-inhibitors (67%). More than half of the identified inhibitors (56%) belonged to the genus Pseudomonas. Our results represent the first step in the understanding of interactions between A. astaci and epibiotic bacteria on the crayfish cuticle and open the perspective for testing in vivo the application of selected bacterial inoculums for crayfish plague prevention and/or treatment. The development of such A. astaci biocontrol measures is urgently needed in astaciculture.