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

Zhang M, Powell CA, Guo Y, Benyon L, Duan Y - BMC Microbiol. (2013)

Bottom Line: Both antibiotic treatments resulted in significantly lower Las bacterial titers (Pr<0.05) and hybridization scores.In the antibiotic treated samples, the number of OTUs decreased to a total of 5,599.In addition, the level of bacterial diversity found in the leaf midribs of field citrus was greater than previously described.

View Article: PubMed Central - HTML - PubMed

Affiliation: Indian River Research and Education Center, IFAS-UF, Fort Pierce, FL 34945, USA.

ABSTRACT

Background: Huanglongbing (HLB) is a worldwide devastating disease of citrus. There are no effective control measures for this newly emerging but century-old disease. Previously, we reported a combination of Penicillin G and Streptomycin was effective in eliminating or suppressing the associated bacterium, 'Candidatus Liberibacter asiaticus' (Las).

Results: Here we report the bacterial composition and community structure in HLB-affected citrus plants during a growing season and while being treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the Phylochip™ G3 array. Both antibiotic treatments resulted in significantly lower Las bacterial titers (Pr<0.05) and hybridization scores. Of the 50,000+ available operational taxonomic units (OTUs) on PhyloChip™ G3, 7,028 known OTUs were present in citrus leaf midribs. These OTUs were from 58 phyla, of which five contained 100 or more OTUs, Proteobacteria (44.1%), Firmicutes (23.5%), Actinobacteria (12.4%), Bacteroidetes (6.6%) and Cyanobacteria (3.2%). In the antibiotic treated samples, the number of OTUs decreased to a total of 5,599. The over-all bacterial diversity decreased with the antibiotic treatments, as did the abundance of 11 OTUs within Proteobacteria, Firmicutes, Bacteroidetes and Planctomycetes. Within the Proteobacteria, ten OTUs representing the class γ-proteobacteria increased in abundance after four months of treatment, when the Las bacterium was at its lowest level in the HLB-affected citrus field plants.

Conclusions: Our data revealed that Proteobacteria was constantly the dominant bacterial phylum recovered from citrus leaf midribs, with the α-proteobacterial and the γ-proteobacterial classes vying for prevalence. In addition, the level of bacterial diversity found in the leaf midribs of field citrus was greater than previously described. Bacterial cells in close proximity may be able to modify their microenvironment, making the composition of the microbial community an important factor in the ability of Las to cause HLB progression. A low Las level was seen as an annual fluctuation, part of the bacterial population dynamics, and as a response to the antibiotic treatments.

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Bacterial richness and diversity in phyla detected by PhyloChip™ G3 hybridization of Huanglongbing (HLB)-affected citrus. The citrus plants were treated with different antibiotic combinations, and leaf samples were collected at different times (October 2010, April 2011 and October 2011) over a year. A, Total operational taxonomic units (OTUs) in each treatment; B, Simpson’s diversity index (SDI) and Shannon-Weiner index (DIT). Each bar represents the coded relative abundance of bacteria in a single phylum. For each treatment, the Simpson’s and Shannon’s diversity statistics, which reflect both species numbers and evenness of species distribution, were plotted below the histogram. PS: 5 g/tree penicillin G potassium and 0.5 g/tree streptomycin; KO: 2 g/tree oxytetracycline and 1.0 g/tree kasugamycin; and CK: water as control.
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Figure 3: Bacterial richness and diversity in phyla detected by PhyloChip™ G3 hybridization of Huanglongbing (HLB)-affected citrus. The citrus plants were treated with different antibiotic combinations, and leaf samples were collected at different times (October 2010, April 2011 and October 2011) over a year. A, Total operational taxonomic units (OTUs) in each treatment; B, Simpson’s diversity index (SDI) and Shannon-Weiner index (DIT). Each bar represents the coded relative abundance of bacteria in a single phylum. For each treatment, the Simpson’s and Shannon’s diversity statistics, which reflect both species numbers and evenness of species distribution, were plotted below the histogram. PS: 5 g/tree penicillin G potassium and 0.5 g/tree streptomycin; KO: 2 g/tree oxytetracycline and 1.0 g/tree kasugamycin; and CK: water as control.

Mentions: The PhyloChip data indicated a change in the community profile over the sampling time points and showed fewer unique OTUs in populations subjected to antibiotic treatments (Additional file 1: Table S1; Figure 3A). The lowest number of OTUs was detected in April 2011 after the antibiotics had been applied four times (Additional file 1: Table S1). The phylum Bacteriodetes, and specifically the class Flavobacteria, significantly decreased (Pr<0.05). While the phylum Proteobacteria did not decrease, both the classes α- and β-proteobacteria did decrease significantly (Pr<0.05). OTUs within the order of Rhizobiales and the family of Rhizobiaceae were significantly decreased by the antibiotic treatments. Shannon’s and Simpson’s indices both revealed greater diversity in the water control (Figure 3B), indicating that antibiotic treatments lead to lower phylum diversity.


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

Zhang M, Powell CA, Guo Y, Benyon L, Duan Y - BMC Microbiol. (2013)

Bacterial richness and diversity in phyla detected by PhyloChip™ G3 hybridization of Huanglongbing (HLB)-affected citrus. The citrus plants were treated with different antibiotic combinations, and leaf samples were collected at different times (October 2010, April 2011 and October 2011) over a year. A, Total operational taxonomic units (OTUs) in each treatment; B, Simpson’s diversity index (SDI) and Shannon-Weiner index (DIT). Each bar represents the coded relative abundance of bacteria in a single phylum. For each treatment, the Simpson’s and Shannon’s diversity statistics, which reflect both species numbers and evenness of species distribution, were plotted below the histogram. PS: 5 g/tree penicillin G potassium and 0.5 g/tree streptomycin; KO: 2 g/tree oxytetracycline and 1.0 g/tree kasugamycin; and CK: water as control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3672075&req=5

Figure 3: Bacterial richness and diversity in phyla detected by PhyloChip™ G3 hybridization of Huanglongbing (HLB)-affected citrus. The citrus plants were treated with different antibiotic combinations, and leaf samples were collected at different times (October 2010, April 2011 and October 2011) over a year. A, Total operational taxonomic units (OTUs) in each treatment; B, Simpson’s diversity index (SDI) and Shannon-Weiner index (DIT). Each bar represents the coded relative abundance of bacteria in a single phylum. For each treatment, the Simpson’s and Shannon’s diversity statistics, which reflect both species numbers and evenness of species distribution, were plotted below the histogram. PS: 5 g/tree penicillin G potassium and 0.5 g/tree streptomycin; KO: 2 g/tree oxytetracycline and 1.0 g/tree kasugamycin; and CK: water as control.
Mentions: The PhyloChip data indicated a change in the community profile over the sampling time points and showed fewer unique OTUs in populations subjected to antibiotic treatments (Additional file 1: Table S1; Figure 3A). The lowest number of OTUs was detected in April 2011 after the antibiotics had been applied four times (Additional file 1: Table S1). The phylum Bacteriodetes, and specifically the class Flavobacteria, significantly decreased (Pr<0.05). While the phylum Proteobacteria did not decrease, both the classes α- and β-proteobacteria did decrease significantly (Pr<0.05). OTUs within the order of Rhizobiales and the family of Rhizobiaceae were significantly decreased by the antibiotic treatments. Shannon’s and Simpson’s indices both revealed greater diversity in the water control (Figure 3B), indicating that antibiotic treatments lead to lower phylum diversity.

Bottom Line: Both antibiotic treatments resulted in significantly lower Las bacterial titers (Pr<0.05) and hybridization scores.In the antibiotic treated samples, the number of OTUs decreased to a total of 5,599.In addition, the level of bacterial diversity found in the leaf midribs of field citrus was greater than previously described.

View Article: PubMed Central - HTML - PubMed

Affiliation: Indian River Research and Education Center, IFAS-UF, Fort Pierce, FL 34945, USA.

ABSTRACT

Background: Huanglongbing (HLB) is a worldwide devastating disease of citrus. There are no effective control measures for this newly emerging but century-old disease. Previously, we reported a combination of Penicillin G and Streptomycin was effective in eliminating or suppressing the associated bacterium, 'Candidatus Liberibacter asiaticus' (Las).

Results: Here we report the bacterial composition and community structure in HLB-affected citrus plants during a growing season and while being treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the Phylochip™ G3 array. Both antibiotic treatments resulted in significantly lower Las bacterial titers (Pr<0.05) and hybridization scores. Of the 50,000+ available operational taxonomic units (OTUs) on PhyloChip™ G3, 7,028 known OTUs were present in citrus leaf midribs. These OTUs were from 58 phyla, of which five contained 100 or more OTUs, Proteobacteria (44.1%), Firmicutes (23.5%), Actinobacteria (12.4%), Bacteroidetes (6.6%) and Cyanobacteria (3.2%). In the antibiotic treated samples, the number of OTUs decreased to a total of 5,599. The over-all bacterial diversity decreased with the antibiotic treatments, as did the abundance of 11 OTUs within Proteobacteria, Firmicutes, Bacteroidetes and Planctomycetes. Within the Proteobacteria, ten OTUs representing the class γ-proteobacteria increased in abundance after four months of treatment, when the Las bacterium was at its lowest level in the HLB-affected citrus field plants.

Conclusions: Our data revealed that Proteobacteria was constantly the dominant bacterial phylum recovered from citrus leaf midribs, with the α-proteobacterial and the γ-proteobacterial classes vying for prevalence. In addition, the level of bacterial diversity found in the leaf midribs of field citrus was greater than previously described. Bacterial cells in close proximity may be able to modify their microenvironment, making the composition of the microbial community an important factor in the ability of Las to cause HLB progression. A low Las level was seen as an annual fluctuation, part of the bacterial population dynamics, and as a response to the antibiotic treatments.

Show MeSH
Related in: MedlinePlus