PhD ceremony Ms. M.S. Cretoiu: Metagenomics-guided exploration of natural habitats for bacterial chitinases

PhD ceremony: Ms. M.S. Cretoiu

Dissertation: Metagenomics-guided exploration of natural habitats for bacterial chitinases

Promotor(s): prof. J.D. van Elsas

Faculty: Mathematics and Natural Sciences

Silvia Cretoiu studied the chitinolytic potential of bacteria inhabiting various terrestrial and aquatic habitats. This was investigated by using new tools that have become available through molecular microbiology and metagenomics. Chitin is a widely distributed biopolymer and is produced by organisms belonging to various taxonomic groups. Despite the considerable amount produced globally (up to 10¹¹ tons per year), chitin does not accumulate in natural habitats, thus indicating the efficient recycling of this polymer. Enzymatic degradation by chitinases is the main mechanism of converting chitin into its oligomers. During the last decade, the use of chitin in agriculture, industry and biomedicine called for an increasing biotechnological demand for novel chitinases. The investigation of the bacterial succession within the chitinolytic process was coupled to the mining for bacterial chitinases with putative enhanced properties. Ten terrestrial and aquatic environments were selected and assessed with respect to their chitin-degrading microbial communities. Genetic screening based on the sequencing of the chiA gene indicated that the Dutch chitin-amended soil from Vredepeel proved to be the most promising habitat in terms of the presence of putative novel chitinases. Linkage of chitinolytic bacteria to the capacity of soil to suppress plant pathogens was also revealed. This analysis showed the crucial role of two bacterial groups (Oxalobacteraceae and Actinobacteria) in the chitinolytic process. By degrading the chitin these bacteria decrease the success of the plant pathogens.