P-039 - Evaluation of soil bacterial isolates as a source for biological controlling agents

Our previous 16s metagenomics study using citrus root DNA fractions indicated a potential positive effect of a certain soil bacterial group on maintaining a tree health. To evaluate this possibility, we explored the soil bacterial community that has antibacterial activity to evaluate them as a tool to improve the tree health under various abiotic stress conditions. To isolate bacteria with antibacterial activity, soil and citrus root samples were collected in the fields located in Lower Rio Grande Valley in South Texas, from which bacteria exerting antibacterial activity on the culture plate was isolated. In this study, we isolated 84 bacterial isolates with antibacterial activity, from which we confirmed that 8 bacterial isolates had antagonistic activity against Liberibacter crescens, a surrogate bacterium of Candidatus Liberibacter asiaticus (CLas) causing Huanglongbing in citrus. Partial 16S rDNA nucleotide sequence analysis of these 8 isolates showed that one belonged to Streptomyces, five to Bacillus, one to Pseudomonas and one to Stenotrophomonas. In order to examine their potential role as a biological controlling agent, these isolates were tested against CLas-positive explants. The preliminary data showed that four of the eight isolates were able to reduce the CLas titer in the CLas-positive explants. Further experiment is still in progress to confirm this preliminary data, which also includes testing these 8 isolates and a predatory bacterial isolate, known as Bdellovibrio and like organisms (BALOs), against other plant pathogens.