Jae-Hyung Ahn

Draft Genome Sequence of the Biocontrol Bacterium Bacillus amyloliquefaciens Strain M27

Bacillus amyloliquefaciens strain M27 is a biocontrol agent with antagonistic activities against a wide range of fungal pathogens. Here we present the 3.86-Mb draft genome sequence of the bacterium with the aims of providing insights into the genomic basis of its antifungal mechanism and facilitating its application in the biocontrol of plant diseases.

Quantitative improvement of 16S rDNA DGGE analysis for soil bacterial community using real-time PCR

Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments has been frequently used to profile a structure of the bacterial community in a given soil. However, this procedure has various types of intrinsic error and bias, thus often misleads the relative abundance of bacterial populations. In order to establish a reliability for the current 16S rDNA DGGE method, we investigated various parameters and potential sources of errors in the DGGE procedures, such as primer mismatch, dNTP concentration, DNA polymerase, PCR cycles, uneven amplification of templates, secondary structure of PCR product, melting domain profiles, and acrylamide/bis concentration. Our result showed that the relative band intensities of the corresponding 16S rDNA templates were closely correlated with the differences of the melting temperature between the higher and lower melting domains of the PCR products. In addition, application of i) real-time PCR, ii) combination of PCR primers and iii) optimization of both dNTP and acrylamide/bis concentrations significantly improved the quantitative representation of bacterial 16S rDNA levels in the mixed samples. Especially, identification of the inflection points of DNA samples through the real-time PCR was crucial for the accurate representation of soil bacterial populations. Beyond these points DNA templates can be over-amplified to a saturated level independently of their initial amounts. Therefore for the accurate analysis of soil bacterial community, a quantitative 16S rDNA DGGE analysis needs to be performed in combination with a real-time PCR.

Analysis of Community Structure of Metabolically Active Bacteria in a Rice Field Subjected to Long-Term Fertilization Practices

To estimate the effect of long-term fertilization on metabolically active bacterial communities in a rice field, RNA was extracted from endosphere (rice root), rhizosphere, and bulk soil that had been subjected to different fertilization regimes for 59 years, and the 16S rRNAs were analyzed using the pyrosequencing method. The richness and diversity of metabolically active bacteria were higher in bulk soil than in the endosphere and rhizosphere, and showed no significant difference between non-fertilized and fertilized plots. Weighted UniFrac analysis showed that each compartment had characteristic bacterial communities and that the effect of long-term fertilization on the structure of bacterial community was more pronounced in bulk soil than in the endosphere and rhizosphere. The 16S rRNAs affiliated with Alphaproteobacteria and Firmicutes were more abundant in the endosphere than in bulk soil while those affiliated with Chloroflexi and Acidobacteria were more abundant in bulk soil than in the endosphere. Several dominant operational taxonomic units (clustered at a 97% similarity cut-off) showed different frequencies between non-fertilized and fertilized plots, suggesting that the fertilization affected their activities in the rice field.

Application of Amplicon Pyrosequencing in Soil Microbial Ecology

Soil microbial communities are immensely diverse and complex with respect to species richness and community size. These communities play essential roles in agricultural soil because they are responsible for most of the nutrient cycles in the soil and influence the plant diversity and productivity. However, the majority of these microbes remain uncharacterized because of poor culturability. Next-generation sequencing techniques have revolutionized many areas of biology by providing cheaper and faster alternatives to Sanger sequencing. Among them, amplicon pyrosequencing is a powerful tool developed by 454 Life Sciences for assessing the diversity of complex microbial communities by sequencing PCR products or amplicons. This review summarizes the current opinions in amplicon sequencing of soil microbial communities, and provides practical guidance and advice on sequence quality control, aligning, clustering, OTU- and taxon-based analysis. The last section of this article includes a few representative studies conducted using amplicon pyrosequencing.

Comparative Analysis of Endophytic Bacterial Communities in the Roots of Rice Grown under Long-term Fertilization Practice using Pyrosequencing Method

Bacterial endophytes may be important factors in plant growth and ecologically relevant functions in rice. Using pyrosequencing technology, we analyzed the composition of endophytic bacterial communities that colonized the roots of rice cultivated in long-term fertilized (APK) and non-fertilized (NF) paddy soils. A total of 1,900 reads were obtained from 2 samples. All sequences were classified into 177 OTUs (APK sample) or 72 OTUs (NF sample) at a 97% similarity cut-off. Twenty-two OTUs were shared between the 2 samples, and these were also the most dominant OTUs in both samples. Proteobacteria was the most dominant phylum with 90.2%, followed by Actinobacteria (7.1%) and Bacteroidetes (1.1%). Furthermore, Pseudomonas was the most abundant genus in both samples. We observed clear differences in the structure of the endophytic bacterial community structure between the 2 samples. Notably, the distributions of Alphaproteobacteria and Gammaproteobacteria were markedly different. The diversity index of the APK sample was higher than that of the NF sample. These findings showed that the endophytic bacterial community of rice roots was affected by the presence of fertilizers in the rice field soil.