Location: Subtropical Plant Pathology Research
2013 Annual Report
We have investigated the mechanism that may be controlling how the tree and the bacteria respond to the heat and chemicals. At this time, two prophages have been identified in the Candidatus Liberibacter asiaticus (Las) genome. We have investigated if stress conditions such as heat and antibiotics can cause the conversion of the FP1 and FP2 prophages to phage (activation of the lytic cyle) by comparing the 16S rDNA copy number in HLB-affected periwinkle and citrus with the copy numbers of the two prophages. When HLB-affected periwinkle was exposed to heat stress for 4.0 hours, more FP1 and FP2 phage particles were released at 42°C and 45°C than at 37°C. A temperature increase from 23°C to 37°C caused the relative copy numbers of FP1 and FP2 to increase six-fold, while a shift from 23°C to 42°C or 45°C caused the relative copy numbers of FP1 and FP2 to increase between 7.5 and 15-fold compared to the initial samples. Meanwhile, similar results were found when HLB-affected citrus scions were treated with tetracycline at concentrations of 500 ppm to 2000 ppm by soaking for three days. These results indicate a shift from the lysogenic to the lytic cycle. Understanding this mechanism may have applications in terms of modulating HLB populations in naturally occurring infections and may also lead to potential control methods that exploit this conversion. A manuscript is in preparation.