Xanthobaccin A

Appl Environ Microbiol. 1999 Oct;65(10):4334-9.

Possible role of xanthobaccins produced by Stenotrophomonas sp. strain SB-K88 in suppression of sugar beet damping-off disease.[Pubmed: 10508056]

Three antifungal compounds, designated xanthobaccins A, B, and C, were isolated from the culture fluid of Stenotrophomonas sp. strain SB-K88, a rhizobacterium of sugar beet that suppresses damping-off disease.
METHODS AND RESULTS:
Production of Xanthobaccin A in culture media was compared with the disease suppression activities of strain SB-K88 and less suppressive strains that were obtained by subculturing. Strain SB-K88 was applied to sugar beet seeds, and production of Xanthobaccin A in the rhizosphere of seedlings was confirmed by using a test tube culture system under hydroponic culture conditions; 3 microg of Xanthobaccin A was detected in the rhizosphere on a per-plant basis. Direct application of purified Xanthobaccin A to seeds suppressed damping-off disease in soil naturally infested by Pythium spp.
CONCLUSIONS:
We suggest that Xanthobaccin A produced by strain SB-K88 plays a key role in suppression of sugar beet damping-off disease.

Appl Environ Microbiol. 2005 Jul;71(7):3786-96.

Suppression of damping-off disease in host plants by the rhizoplane bacterium Lysobacter sp. strain SB-K88 is linked to plant colonization and antibiosis against soilborne Peronosporomycetes.[Pubmed: 16000790]

METHODS AND RESULTS:
We previously demonstrated that Xanthobaccin A from the rhizoplane bacterium Lysobacter sp. strain SB-K88 suppresses damping-off disease caused by Pythium sp. in sugar beet. Interestingly, zoospores of A. cochlioides became immotile within 1 min after exposure to a SB-K88 cell suspension, a cell-free supernatant of SB-K88, or pure Xanthobaccin A (MIC, 0.01 microg/ml). In all cases, lysis followed within 30 min in the presence of the inhibiting factor(s).
CONCLUSIONS:
Our data indicate that Lysobacter sp. strain SB-K88 has a direct inhibitory effect on A. cochlioides, suppressing damping-off disease. Furthermore, this inhibitory effect of Lysobacter sp. strain SB-K88 is likely due to a combination of antibiosis and characteristic biofilm formation at the rhizoplane of the host plant.