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United States Department of Agriculture

Agricultural Research Service

Research Project: EMERGING DISEASES OF CITRUS, VEGETABLES, AND ORNAMENTALS

Location: Subtropical Plant Pathology Research

Title: Characterization of the microbial community structure in Candidatus Liberibacter asiaticus-infected citrus plants treated with antibiotics in the field

Authors
item Zhang, Muqing -
item Powell, Charles -
item Guo, Ying -
item Benyon, Lesley
item Duan, Ping

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2012
Publication Date: January 4, 2013
Repository URL: http://doi:10.1186/1471-2180-13-112
Citation: Zhang, M., Powell, C., Guo, Y., Benyon, L.S., Duan, Y. 2013. Characterization of the microbial community structure in Candidatus Liberibacter asiaticus-infected citrus plants treated with antibiotics in the field. Journal of Applied Microbiology. 13:112.

Interpretive Summary: Huanglongbing (HLB) is one of the most serious diseases of citrus worldwide and is devastating the citrus industry in Florida. Currently there are no effective control measures and it will likely take over 10 years to produce and evaluate resistant varieties. Thus it is essential to develop a treatment to combat the disease in the interim. In the search for a therapeutic compound we tested a combination of Penicillin G and Streptomycin and found it was effective in eliminating or suppressing the HLB bacterium, ‘Candidatus Liberibacter asiaticus’ (Las). Here we report the bacterial composition and community structure in HLB-affected citrus plants treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the Phylochip™ G3 array. This microarray assesses microbial community structure based on amplified 16S rRNA gene sequences. Understanding the bacterial populations present in citrus may play a key role in controlling HLB since it has been postulated that Las interacts with other endophytic bacteria in order to cause the disease. The Phylochip™ G3 analysis indicated 7,028 operational taxonomic units (OTUs) in the citrus leaf midribs. The OTUs are entities whose affinities are studied by numerical taxonomy. Depending on the level and the type of investigation an OTU may be of any taxonomic rank or an individual organism. The identified OTUs were from 58 different phyla and five phyla contained over 100 OTUs. One of these was Cyanobacteria which showed more OTUs present after antibiotic treatments; however, on the whole the bacterial diversity decreased with the antibiotic treatments. Three oxytetracycline-resistant bacteria were detected in all KO treatments but no antibiotic-resistant bacteria were detected in any PS treatment. These data reveal the bacterial population dynamics were affected by both the antibiotic treatments and seasonal changes in HLB-affected citrus plants.

Technical Abstract: Huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide. There are no effective control measures for this newly emerging and century-old disease. Previously, we reported a combination of Penicillin G and Streptomycin were effective in eliminating or suppressing the HLB bacterium, ‘Candidatus Liberibacter asiaticus’. Here we report the bacterial composition and community structure in HLB-affected citrus plants treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the Phylochip™ G3 array. The results indicate that both antibiotic treatments eliminated or suppressed the HLB bacteria resulting in significant lower titers (P<0.05) and hybridization scores. PhyloChip™ G3 analysis indicated that a total of 7,028 operational taxonomic units (OTUs) out of 10,912 known OTUs were present in the citrus leaf midribs. The OTUs were from 58 phyla, and five, Proteobacteria (44.1%), Firmicutes (23.5%), Actinobacteria (12.4%), Bacteroidetes (6.6%) and Cyanobacteria (3.2%), contained 100 or more OTUs. Surprisingly, the antibiotic treatments increased the OTUs in Cyanobacteria while the over-all diversity of bacteria decreased, including the dominant phyla of Firmicutes, Actinobacteria, Tenericutes and Bacteriodetes. Three oxytetracycline-resistant bacteria were detected in all KO treatments but no antibiotic-resistant bacteria were detected in any PS treatment. These data reveal the bacterial population dynamics were affected by both the antibiotic treatments and seasonal changes in HLB-affected citrus plants.

Last Modified: 4/16/2014
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