Sarah Avery

Poster Presentation

A Study of the Antagonistic Activity of Bacillus subtilis Strain T1 Against Shrimp Pathogen Vibrio parahaemolyticus Strain D4

Acute hepatopancreatic necrosis disease (AHPND), also known as early mortality syndrome (EMS), is caused by strains of Vibrio parahaemolyticus containing the PirAB toxin and has been devastating the shrimp aquaculture globally. Current methods for prevention rely on the use of antibiotics, which leads to the development of antibiotic-resistant bacteria. Bacillus subtilis strain T1 has antagonistic activity against EMS causing V. parahaemolyticus strain D4 and is a candidate for use as a probiotic for shrimp culture. A mutagenesis study using the mariner transposon was conducted to identify T1 genes involved in the inhibition of growth of D4. An overlay assay was used to screen ~3,000 T1 mutants for loss of activity against D4 and 18 were identified as having complete or partial loss of activity. Eleven mutants had transposon insertions within a 30-kb DNA cluster encoding lipopeptide and polyketide biosynthetic processes. Two mutants had insertions within stationary phase regulators, spo0A (sporulation gene regulator) and oppA(first gene of the oligopeptide transporter system operon). Competitive growth experiments were done in liquid media to examine the effect of T1 on growth of D4 followed by quantification of target genes by qPCR. Preliminary results showed that T1 inhibits growth of D4 when the starting cell density of T1 was 100 times that of D4. Additionally, T1 supernatant fractions were found to inhibit D4 growth. Our results suggest that T1 secretes a secondary metabolite that has inhibitory activity against D4. The nature of the molecule(s) and its mechanism of action are currently under investigation.