Xylella fastidiosa is an insect-borne bacterium that colonizes xylem vessels of a large number of host plants,
including several crops of economic importance. Chitin is a polysaccharide present in the cuticle of leafhopper
vectors of X. fastidiosa and may serve as a carbon source for this bacterium. Biological assays showed that X.
fastidiosa reached larger populations in the presence of chitin. Additionally, chitin induced phenotypic changes
in this bacterium, notably increasing adhesiveness. Quantitative PCR assays indicated transcriptional changes
in the presence of chitin, and an enzymatic assay demonstrated chitinolytic activity by X. fastidiosa. An ortholog
of the chitinase A gene (chiA) was identified in the X. fastidiosa genome. The in silico analysis revealed that the
open reading frame of chiA encodes a protein of 351 amino acids with an estimated molecular mass of 40 kDa.
chiA is in a locus that consists of genes implicated in polysaccharide degradation. Moreover, this locus was also
found in the genomes of closely related bacteria in the genus Xanthomonas, which are plant but not insect
associated. X. fastidiosa degraded chitin when grown on a solid chitin-yeast extract-agar medium and grew in
liquid medium with chitin as the sole carbon source; ChiA was also determined to be secreted. The gene
encoding ChiA was cloned into Escherichia coli, and endochitinase activity was detected in the transformant,
showing that the gene is functional and involved in chitin degradation. The results suggest that X. fastidiosa
may use its vectors’ foregut surface as a carbon source. In addition, chitin may trigger X. fastidiosa’s gene
regulation and biofilm formation within vectors. Further work is necessary to characterize the role of chitin
and its utilization in X. fastidiosa.
Xylella fastidiosa is an insect-borne bacterium that colonizes xylem vessels of a large number of host plants,
including several crops of economic importance. Chitin is a polysaccharide present in the cuticle of leafhopper
vectors of X. fastidiosa and may serve as a carbon source for this bacterium. Biological assays showed that X.
fastidiosa reached larger populations in the presence of chitin. Additionally, chitin induced phenotypic changes
in this bacterium, notably increasing adhesiveness. Quantitative PCR assays indicated transcriptional changes
in the presence of chitin, and an enzymatic assay demonstrated chitinolytic activity by X. fastidiosa. An ortholog
of the chitinase A gene (chiA) was identified in the X. fastidiosa genome. The in silico analysis revealed that the
open reading frame of chiA encodes a protein of 351 amino acids with an estimated molecular mass of 40 kDa.
chiA is in a locus that consists of genes implicated in polysaccharide degradation. Moreover, this locus was also
found in the genomes of closely related bacteria in the genus Xanthomonas, which are plant but not insect
associated. X. fastidiosa degraded chitin when grown on a solid chitin-yeast extract-agar medium and grew in
liquid medium with chitin as the sole carbon source; ChiA was also determined to be secreted. The gene
encoding ChiA was cloned into Escherichia coli, and endochitinase activity was detected in the transformant,
showing that the gene is functional and involved in chitin degradation. The results suggest that X. fastidiosa
may use its vectors’ foregut surface as a carbon source. In addition, chitin may trigger X. fastidiosa’s gene
regulation and biofilm formation within vectors. Further work is necessary to characterize the role of chitin
and its utilization in X. fastidiosa.
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