Results Dynamic variations of the bacterial community in HLB-affected field citrus The most prevalent bacterial phylum in citrus leaves in October 2010 was Proteobacteria with an average of 1,301 OTUs out of 2,948 OTUs (44.1%). The next most prevalent phylums were the Firmicutes (566 Daporinad of 2,948; 19.2%) and the Actinobacteria (458 of 2,948; 15.5%) (Additional file 1: Table S1). The number of OTUs in the Bacteriodetes

decreased at a statistically significant level (Pr<0.05) between October 2010 and April 2011, and that difference appeared to be concentrated in the class of Flavobacteria. While the phylum Proteobacteria itself remained at 44% of the bacterial community, the number of OTUs in the α-proteobacterial and β-proteobacterial classes decreased significantly (Pr<0.05). Among ALK targets the α-proteobacteria, the orders Rhizobiales (Pr<0.05) and Sphingomonadales (Pr<0.01) had decreased OTUs, and among the β-proteobacteria the order Burkholderiales had decreased OTUs (Pr<0.05). While the number of OTUs in the γ-proteobacteria as a class increased, they decreased

in the order Pseudomonadales (Pr<0.05). The increase in the γ-proteobacterial class was statistically significant, and the difference appears concentrated in the Enterobacteriales (Pr<0.05). This was the only member of the bacterial community to show an increase in the number of OTUs in April 2011 over October 2010. The total OTUs for all phyla had dropped to 67% of the October 2010 level. In the period from April 2011 to October 2011, many of the bacterial phyla that had a decrease in OTUs during the proceeding period began to recover. Actinobacteria, Firmicutes, and SPTLC1 Spirochaetes all had

increased numbers of OTUs, and as a percentage of total OTUs they had all surpassed their October 2010 levels. Proteobacteria was still the most abundant phylum but it represented only 39% of the total OTUs in October 2011. The β-proteobacterial class had significantly more OTUs (Pr<0.05) as did the order Burkholderiales (Pr<0.05). The number of OTUs in the γ-proteobacterial class decreased significantly (Pr<0.05), and this difference appears concentrated in the order Enterobacteriales (Pr<0.05). While the bacterial OTU levels appeared to be trending upward, by October of 2011 the overall abundance of bacteria was still only 72% of the October 2010 level. Las bacterium in HLB-affected citrus treated with antibiotic combinations The dynamic variations of Las bacterial titers from August 2010 to October 2011 at the USHRL farm, Fort Pierce, FL are presented in Figure 1. The results showed that the Las bacterial population fluctuated throughout the year in HLB-affected citrus plants with or without antibiotic treatments. The highest Las bacterial titers (lowest Ct values) were observed in December 2010, and the lowest Las bacterial titers (highest Ct values) were recorded in April 2011. This variation generally coincided with HLB-symptoms in the field.