Fabiana de Souza Cannavan

Comparative Analyses of the Complete Genome Sequences of Pierce's Disease and Citrus Variegated Chlorosis Strains of Xylella fastidiosa

Xylella fastidiosa is a xylem-dwelling, insect-transmitted, gamma-proteobacterium that causes diseases in many plants, including grapevine, citrus, periwinkle, almond, oleander, and coffee. X. fastidiosa has an unusually broad host range, has an extensive geographical distribution throughout the American continent, and induces diverse disease phenotypes. Previous molecular analyses indicated three distinct groups of X. fastidiosa isolates that were expected to be genetically divergent. Here we report the genome sequence of X. fastidiosa (Temecula strain), isolated from a naturally infected grapevine with Pierces disease (PD) in a wine-grape-growing region of California. Comparative analyses with a previously sequenced X. fastidiosa strain responsible for citrus variegated chlorosis (CVC) revealed that 98% of the PD X. fastidiosa Temecula genes are shared with the CVC X. fastidiosa strain 9a5c genes. Furthermore, the average amino acid identity of the open reading frames in the strains is 95.7%. Genomic differences are limited to phage-associated chromosomal rearrangements and deletions that also account for the strain-specific genes present in each genome. Genomic islands, one in each genome, were identified, and their presence in other X. fastidiosa strains was analyzed. We conclude that these two organisms have identical metabolic functions and are likely to use a common set of genes in plant colonization and pathogenesis, permitting convergence of functional genomic strategies.

Amazonian Dark Earth and Plant Species from the Amazon Region Contribute to Shape Rhizosphere Bacterial Communities

Amazonian Dark Earths (ADE) or Terra Preta de Índio formed in the past by pre-Columbian populations are highly sustained fertile soils supported by microbial communities that differ from those extant in adjacent soils. These soils are found in the Amazon region and are considered as a model soil when compared to the surrounding and background soils. The aim of this study was to assess the effects of ADE and its surrounding soil on the rhizosphere bacterial communities of two leguminous plant species that frequently occur in the Amazon region in forest sites (Mimosa debilis) and open areas (Senna alata). Bacterial community structure was evaluated using terminal restriction fragment length polymorphism (T-RFLP) and bacterial community composition by V4 16S rRNA gene region pyrosequencing. T-RFLP analysis showed effect of soil types and plant species on rhizosphere bacterial community structure. Differential abundance of bacterial phyla, such as Acidobacteria, Actinobacteria, Verrucomicrobia, and Firmicutes, revealed that soil type contributes to shape the bacterial communities. Furthermore, bacterial phyla such as Firmicutes and Nitrospira were mostly influenced by plant species. Plant roots influenced several soil chemical properties, especially when plants were grown in ADE. These results showed that differences observed in rhizosphere bacterial community structure and composition can be influenced by plant species and soil fertility due to variation in soil attributes.

Functional diversity of bacterial genes associated with aromatic hydrocarbon degradation in anthropogenic dark earth of Amazonia

The objective of this work was to evaluate the catabolic gene diversity for the bacterial degradation of aromatic hydrocarbons in anthropogenic dark earth of Amazonia (ADE) and their biochar (BC). Functional diversity analyses in ADE soils can provide information on how adaptive microorganisms may influence the fertility of soils and what is their involvement in biogeochemical cycles. For this, clone libraries containing the gene encoding for the alpha subunit of aromatic ring‑hydroxylating dioxygenases (α‑ARHD bacterial gene) were constructed, totaling 800 clones. These libraries were prepared from samples of an ADE soil under two different land uses, located at the Caldeirao Experimental Station - secondary forest (SF) and agriculture (AG) -, and the biochar (SF_BC and AG_BC, respectively). Heterogeneity estimates indicated greater diversity in BC libraries; and Venn diagrams showed more unique operational protein clusters (OPC) in the SF_BC library than the ADE soil, which indicates that specific metabolic processes may occur in biochar. Phylogenetic analysis showed unidentified dioxygenases in ADE soils. Libraries containing functional gene encoding for the alpha subunit of the aromatic ring‑hydroxylating dioxygenases (ARHD) gene from biochar show higher diversity indices than those of ADE under secondary forest and agriculture.

Fungal Community Assembly in the Amazonian Dark Earth.

Here, we compare the fungal community composition and diversity in Amazonian Dark Earth (ADE) and the respective non-anthropogenic origin adjacent (ADJ) soils from four different sites in Brazilian Central Amazon using pyrosequencing of 18S ribosomal RNA (rRNA) gene. Fungal community composition in ADE soils were more similar to each other than their ADJ soils, except for only one site. Phosphorus and aluminum saturation were the main soil chemical factors contributing to ADE and ADJ fungal community dissimilarities. Differences in fungal richness were not observed between ADE and ADJ soil pairs regarding to the most sites. In general, the most dominant subphyla present in the soils were Pezizomycotina, Agaricomycotina, and Mortierellomycotina. The most abundant operational taxonomic units (OTUs) in ADE showed similarities with the entomopathogenic fungus Cordyceps confragosa and the saprobes Fomitopsis pinicola, Acremonium vitellinum, and Mortierellaceae sp., whereas OTUs similar to Aspergillus niger, Lithothelium septemseptatum, Heliocephala gracillis, and Pestalosphaeria sp. were more abundant in ADJ soils. Differences in fungal community composition were associated to soil chemical factors in ADE (P, Ca, Zn, Mg, organic matter, sum of bases, and base saturation) and ADJ (Al, potential acidity, Al saturation, B, and Fe) soils. These results contribute to a deeper view of the fungi communities in ADE and open new perspectives for entomopathogenic fungi studies.

Biodiversity in Amazonian Dark Earth: A Contribution for the Sustainability of Tropical Soils from the Microbial Symbioses

The anthropogenic addition of organic amendments, including plant and animal material, pottery, and charcoal, into extant soil formed what are known as Terra Preta do Indio (TPI) or Amazonian Dark Earth (ADE). Whether or not these soil amendments were part of an agricultural management strategy by pre-Colombian cultures, today ADE soils are prized by farmers for their sustained fertility, in regions where chronic soil infertility has lead, in part, to on-going destruction of primary forest to create marginal cropland. However, although prehistoric practices have left a legacy of fertile soil for a few isolated farmers, expanding the benefits of ADE to other soils will require more than serendipity. The unusual chemistry resulting from organic amendments to ADE results in distinct microbial communities that are involved in nutrient cycling and ecological processes. The ongoing biogeochemical activity in ADE is the true legacy of prehistoric practices, and the microbial processes at work in these unique soils are crucial to these

Amazonian Dark Earth and Its Black Carbon Particles Harbor Different Fungal Abundance and Diversity

Amazonian Dark Earth (ADE) is a highly fertile soil of anthropogenic origin characterized by higher amount of charred black carbon (BC). ADE is considered a fertility model, however knowledge about the fungal community structure and diversity inhabiting ADE and BC is scarce. Fungal community structure and diversity of ADE and BC from four sites under different land use (three agricultural systems and a secondary pristine forest) in the Brazilian Central Amazon was evaluated by 18S rRNA gene pyrosequencing. Fungal communities in ADE and BC were dissimilar and showed differential abundances of fungal Operational Taxonomic Units (OTUs). Estimated fungal species richness (ACE and Chao-1) and diversity (Shannon and Simpsons reciprocal) indices were higher in ADE than BC in all agricultural areas. No differences were observed in the same estimators in ADE and BC samples under secondary forest. Pezizomycotina fungi, and OTUs assigned to Cordyceps confragosa, Acremonium vitellinum, Camarops microspora and Hirsutella rhossiliensis were more abundant in BC particles than in ADE. This study is a breakthrough in understanding the fungal communities in BC particles from ADE and can also be valuable in future studies considering biochar application in soil.

Metagenome sequencing of the microbial community of two Brazilian anthropogenic Amazon dark earth sites, Brazil

The Anthropogenic Amazon Dark Earth soil is considered one of the worlds most fertile soils. These soils differs from conventional Amazon soils because its higher organic content concentration. Here we describe the metagenome sequencing of microbial communities of two sites of Anthropogenic Amazon Dark Earth soils from Amazon Rainforest, Brazil. The raw sequence data are stored under Short Read Accession number: PRJNA344917.