Production and identification of iturin A lipopeptide from Bacillus methyltrophicus TEB1 for control of Phoma tracheiphila

A lipopeptide-producing endophytic Bacillus methyltrophicus TEB1 strain exhibited potent antifungal activity against Phoma tracheiphila. Lipopeptide production started at the early growth phase plateaued after 36 h of culture where it reduced the mycelium growth by 80%. The crude lipopeptide extract harvested at the stationary phase efficiently inhibited the growth of P. tracheiphila mycelium and MIC values displaying 50 and 90% inhibition of conidia germination were around 47.5 and 100 μg ml(-1) , respectively. Increasing lipopeptide extract till 3 mg ml(-1) induced 10% swelling and 3% crumbling of P. tracheiphila conidia whereas 5 mg ml(-1) induced 40% swelling and 20% crumbling. Mass spectrometry analysis of the lipopeptide extract indicated that surfactin production took place from 12 to 20 h, iturin A from 16 to 72 h, and fengycin from 12 to 72 h and that the main active compound against P. tracheiphila was identified as C15 iturin A lipopeptide. Iturin A appeared as a potential biological control agent able to substitute the currently used chemical pesticides in agriculture.

Protective effect of Bacillus amyloliquefaciens against infections of Citrus aurantium seedlings by Phoma tracheiphila

Isolate TEB1 an antagonistic endophytic bacterium, obtained from citrus leaves and identified as Bacillus amyloliquefaciens by 16S rDNA sequencing, was used for the biological control of mal secco disease of Citrus aurantium seedlings caused by the mitosporic fungus Phoma tracheiphila. The isolate TEB1 exhibited a good in vitro activity against P. tracheiphila in dual cultures as well as with the well diffusion method. C. aurantium seedlings watered with a suspension of TEB1 cells showed a reduction of 53.61 and 48.63% in disease severity and incidence, respectively. A PCR test with specific primers was performed 365 days after inoculation and P. tracheiphila was detected along the whole stem in inoculated control plant while no amplification product was obtained in TEB1 treated seedlings. Molecular analysis of TEB1 revealed a positive amplification of fenD and ituC genes responsible of the biosynthesis of fengycin and iturin lipopeptides, respectively. Moreover, observations by optical microscope showed that TEB1 reduced by 55% the germination of P. tracheiphila conidia and exhibited a marked effect on mycelia structure. Data suggest that lipopeptides produced by the bacterium interact with the cytoplasmic membrane of the fungus causing pore formation. TEB1 appears a potential candidate for the biological control of citrus mal secco disease.