Aug 2026· Frontiers in Microbiology· Vol 17· 0 citations· 31 references
TL;DR
Findings suggest that strain J36 has potential as a biocontrol candidate, although further in vivo evaluation is needed to confirm its efficacy against Phytophthora blight of Panax notoginseng.
Abstract
The Phytophthora blight of
Panax notoginseng
, caused by
Phytophthora cactorum
, is a devastating oomycete disease. Biocontrol strategies hold immense potential for inhibiting the spread of
P. cactorum
. We isolated 72 actinobacteria from soil and screened their antagonistic activity against
P. cactorum
. Both strain J36 and its cell-free filtrate exhibited strong antagonistic activity against
P. cactorum
and were therefore selected. Based on the 16S rRNA gene phylogenetic tree, strain J36 formed a well supported subclade with
Streptomyces zaomyceticus
NRRL B-2038 (bootstrap value 100%). However, because 16S rRNA sequences often lack sufficient resolution for species-level discrimination, we performed multilocus sequence analysis (MLSA) using three housekeeping genes (rpoB, recA, and atpD). The MLSA results consistently placed strain J36 within the same cluster as
S. zaomyceticus
NRRL B-2038, with a bootstrap support of 99%, indicating a close phylogenetic relationship. To further clarify the taxonomic status, we calculated the average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between strain J36 and the type strain of
S. zaomyceticus
NBC-00415
T
. The ANI value was 90.91% and the dDDH value was 39.30%, both well below the accepted thresholds for species demarcation (ANI < 95%, dDDH < 70%). These genomic indices therefore strongly support that strain J36 represents a novel species within the genus
Streptomyces
. Through whole-genome sequencing and CAZymes analysis, a total of 98 carbohydrate-active enzymes (CAZymes) were detected, including 2 cellulase and 2 β-1,3-glucanases. The cell-free filtrate, which exhibited strong antagonistic activity against
P. cactorum
, also showed high activities of cellulase and β-1,3-glucanase, suggesting that these enzymes may be involved in its anti-oomycete activity. These findings suggest that J36 has potential as a biocontrol candidate, although further
in vivo
evaluation is needed to confirm its efficacy against
Phytophthora
blight of
P. notoginseng
.
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