β-Ketoacyl-acyl carrier protein
synthase III (KAS III, FabH)
is essential for bacterial fatty acid biosynthesis. Recent studies
indicate that FabH can be a potential target for bactericide development.
In the present study, an immobilized FabH column was developed and
used to screen FabH inhibitors from complex natural product extracts.
Combined with HPLC, four secondary metabolites, alternariol (1), altenuisol (2), alterlactone (3), and dehydroaltenusin (4), were site-directed, isolated,
and identified from the crude extract of Alternaria
alternata ZHJG5. These compounds showed inhibitory
activities on FabH of Xanthomonas oryzae pv. oryzae (Xoo) with IC50 values from 29.5 to 74.1 μM and also displayed a varying degree
of antibacterial activities against Xoo with minimal
inhibitory concentration values from 4 to 64 μg/mL. Molecular
modeling was then used to picture how the compounds interact with XooFabH. Two inhibitors, compounds 1 and 3, exhibited significant bactericidal activity against rice
bacterial leaf blight with a protective efficiency of 66.2 and 82.5%
at the concentration of 200 μg/mL, respectively, suggesting
that they could be lead candidates to develop novel bactericides.
The fermentation of endophytic Nigrospora chinensis GGY-3 resulted in the isolation
of tropolone stipitaldehyde (1), which exhibited broad-spectrum
inhibition activity against
fungi and bacteria, especially against Phytophthora
capsici, with an EC50 value of 0.83 μg/mL
and Xanthomonas oryzae pv. oryzicola, with a minimum inhibitory concentration
value of 4.0 μg/mL. The in vitro and in vivo assays demonstrated
that 1 had a significant protective effect on P. capsici. Furthermore, 1 inhibited
the spore germination of P. capsici and damaged the plasma membrane structure. As observed by SEM and
TEM, after exposure to 1, mycelia exhibited swelling,
shrunken, branch-increasing phenomena, cell wall and membrane damage,
and disordered content. Transcriptome analysis revealed that 1 might affect starch and sucrose metabolism and fatty acid
biosynthesis by suppressing the expression of genes relevant to cell
wall synthetases and cell membrane-associated genes. These findings
indicate that 1 may be a potential agrochemical fungicide
for controlling phytophthora blight.
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