The hypothesis that sweet potato genotypes containing different starch yields in their tuberous roots can affect the bacterial communities present in the rhizosphere (soil adhering to tubers) was tested in this study. Tuberous roots of field-grown sweet potato of genotypes IPB-149 (commercial genotype), IPB-052, and IPB-137 were sampled three and six months after planting and analyzed by denaturing gradient gel electrophoresis (DGGE) and pyrosequencing analysis of 16S rRNA genes PCR-amplified from total community DNA. The statistical analysis of the DGGE fingerprints showed that both plant age and genotypes influenced the bacterial community structure in the tuber rhizosphere. Pyrosequencing analysis showed that the IPB-149 and IPB-052 (both with high starch content) displayed similar bacterial composition in the tuber rhizosphere, while IPB-137 with the lowest starch content was distinct. In comparison with bulk soil, higher 16S rRNA gene copy numbers (qPCR) and numerous genera with significantly increased abundance in the tuber rhizosphere of IPB-137 (Sphingobium, Pseudomonas, Acinetobacter, Stenotrophomonas, Chryseobacterium) indicated a stronger rhizosphere effect. The genus Bacillus was strongly enriched in the tuber rhizosphere samples of all sweet potato genotypes studied, while other genera showed a plant genotype-dependent abundance. This is the first report on the molecular identification of bacteria being associated with the tuber rhizosphere of different sweet potato genotypes.

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BackgroundHere we report the monitoring of the digestive tract colonization of Rhodnius prolixus by Trypanosoma cruzi using an accurate determination of the parasite load by qPCR coupled with fluorescence and bioluminescence imaging (BLI). These complementary methods revealed critical steps necessary for the parasite population to colonize the insect gut and establish vector infection.Methodology/Principal FindingsqPCR analysis of the parasite load in the insect gut showed several limitations due mainly to the presence of digestive-derived products that are thought to degrade DNA and inhibit further the PCR reaction. We developed a real-time PCR strategy targeting the T. cruzi repetitive satellite DNA sequence using as internal standard for normalization, an exogenous heterologous DNA spiked into insect samples extract, to precisely quantify the parasite load in each segment of the insect gut (anterior midgut, AM, posterior midgut, PM, and hindgut, H). Using combined fluorescence microscopy and BLI imaging as well as qPCR analysis, we showed that during their journey through the insect digestive tract, most of the parasites are lysed in the AM during the first 24 hours independently of the gut microbiota. During this short period, live parasites move through the PM to establish the onset of infection. At days 3–4 post-infection (p.i.), the parasite population begins to colonize the H to reach a climax at day 7 p.i., which is maintained during the next two weeks. Remarkably, the fluctuation of the parasite number in H remains relatively stable over the two weeks after refeeding, while the populations residing in the AM and PM increases slightly and probably constitutes the reservoirs of dividing epimastigotes.Conclusions/SignificanceThese data show that a tuned dynamic control of the population operates in the insect gut to maintain an equilibrium between non-dividing infective trypomastigote forms and dividing epimastigote forms of the parasite, which is crucial for vector competence.

Sweet sorghum (Sorghum bicolor) is a multipurpose crop used as a feedstock to produce bioethanol, sugar, energy, and animal feed. However, it requires high levels of N fertilizer application to achieve the optimal growth, which causes environmental degradation. Bacterial endophytes, which live inside plant tissues, play a key role in the health and productivity of their host. This particular community may be influenced by different agronomical practices. The aim of the work was to evaluate the effects of N fertilization on the structure, diversity, abundance, and composition of endophytic and diazotrophic bacterial community associated with field-grown sweet sorghum. PCR-DGGE, quantitative PCR, and high-throughput sequencing were performed based on the amplification of rrs and nifH genes. The level of N fertilization affected the structure and abundance but not the diversity of the endophytic bacterial communities associated with sweet sorghum plants. This effect was pronounced in the roots of both bacterial communities analyzed and may depend on the physiological state of the plants. Specific bacterial classes and genera increased or decreased when the fertilizer was applied. The data obtained here contribute to a better understanding on the effects of agronomical practices on the microbiota associated with this important crop, with the aim to improve its sustainability.

Prevention or cure of different illnesses through the use of plant latex is a worldwide known concept. The antifungal activity of Hancornia speciosa latex has been observed against Candida albicans. However, H. speciosa latex is not a sterile plant exudate and secondary metabolites produced by bacteria could be involved in fungal inhibition. In the present study, the bacterial communities of the latex from three H. speciosa trees were characterized using traditional plating and molecular methods. Twelve strains isolated from the latex samples were clustered into four groups by amplified ribosomal DNA restriction analysis (ARDRA). One representative of each group was sequenced and they were identified as belonging to the genera Bacillus, Klebsiella, Enterobacter and Escherichia. None of the 12 isolates showed antifungal activity against C. albicans. A lack of a microbial origin for the antifungal properties of latex was noted. DGGE profiles generated from each of the three latex samples showed unique patterns. Sequencing of the DGGE bands demonstrated the affiliation with the genera Klebsiella, Pantoea, Enterobacter and Burkholderia. In addition, clone libraries were generated and the phylogenetic distribution of the 50 analyzed clones was similar to that obtained using DGGE. The presence of some potential pathogens should be considered before using H. speciosa latex in folk medicine.