Article révisé par les pairs
Résumé : Abstract Aims Culture-independent studies in the literature suggest that marine habitats hold diversified chitin-degrading microbial communities. This study was conducted to isolate novel chitinolytic bacteria from two bacteria-rich marine biotopes, namely sponges and sediments, and compare the efficiency with which those strains degrade different forms of chitin. Methods and Results Bacterial colonies were isolated from chitinolytic consortia derived from the microbiota of the marine sponge Hymeniacidon perlevis of and its surrounding sediment collected at Audresselles beach, France. Many isolates (49%) produced a halo of chitin degradation on colloidal chitin agar plates, including isolates belonging to two genera (Motilimonas, Pseudophaeobacter) yet unknown as chitin degraders. However, 83% of the positive isolates degraded poorly insoluble chitin powder in liquid cultures. Nine isolates were further tested for colloidal chitin degradation in liquid cultures and exhibited contrasting results. One isolate, Motilimonas Spo1_1, exhibited the strongest chitinolytic activity in liquid culture containing insoluble chitin powder (i.e. 37% of degradation). The analysis of its genome and that of other Motilimonas spp. revealed an arsenal of genes for chitin degradation. Genomic analyses suggest that Spo1_1 is a new species within the genus Motilimonas, we propose the name Motilimonas chitinivorans. Conclusions Motilimonas Spo1_1 largely outperformed all 70 other strains in terms of its insoluble chitin degradation capabilities, including strains belonging to the well-known chitinolytic genera Vibrio and Pseudoalteromonas. Those results encourage further studies on the potential of Motilimonas spp. to eliminate chitinous waste. More generally, they confirm that marine habitats are a reservoir of chitinolytic microbes yet to be discovered.

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