Lysobacter are new
biocontrol agents known for
their prolific production of lytic enzymes and bioactive metabolites. L. enzymogenes is a predator of fungi and produces several
structurally distinct antimicrobial compounds, such as the antifungal
HSAF (heat stable antifungal factor) and analogs. The mechanism by
which L. enzymogenes interacts with fungal prey is
not well understood. Here, we found that the production of HSAF and
analogs in L. enzymogenes OH11 was significantly
induced in media supplemented with ground fungal mycelia or chitin.
In the OH11 genome, we identified a gene (LeLPMO10A) that was annotated to encode a chitin-binding protein. The stimulation
of HSAF and analogs by chitin was diminished when LeLPMO10A was deleted. We expressed the gene in E. coli and
demonstrated that purified LeLPMO10A oxidatively cleaved chitin into
oligomeric products, including 1,5 δ-lactones and aldonic acids.
The results revealed that LeLPMO10A encodes a lytic
polysaccharide monooxygenase, which has not been reported in Lysobacter. The metabolite analysis, antifungal assay, and
proteomic analysis showed that the antifungal compounds and the chitin-cleaving
LeLPMO10A are colocalized in outer membrane vesicles. The enzymatic
products that resulted from in vitro LeLPMO10A-cleaved
chitin also significantly induced HSAF and analogs in OH11. Scanning
electron microscopic analysis indicated that spherical vesicles were
formed outside of OH11 cells, and fewer OH11 cells were observed to
attach to fungal hyphae when LeLPMO10A was deleted.
Together, the study revealed a previously uncharacterized synergistic
strategy utilized by the predatory Lysobacter during
interaction with fungal prey.
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