Breno Leite

Colony aggregation and biofilm formation in xylem chemistry-based media for Xylella fastidiosa

Two chemically defined media based on xylem fluid chemistry were developed for Xylella fastidiosa. These media were tested and compared to chemically defined media XDM2, XDM4 and XF-26. New media were evaluated for the Pierces disease (PD) strain UCLA-PD. Our media either was similar to the concentration of some amino acids found in the xylem fluid of the PD-susceptible Vitis vinifera cv. Chardonnay (medium CHARD2) or incorporated the tripeptide glutathione found in xylem fluid composition (medium 3G10-R). CHARD2 and 3G10-R are among the simplest chemically defined media available. Xylem fluid chemistry-based media supported X. fastidiosa growth and especially stimulated aggregation and biofilm formation.

Citrus sinensis leaf petiole and blade colonization by Xylella fastidiosa: details of xylem vessel occlusion

Citrus variegated chlorosis (CVC), caused by Xylella fastidiosa, is an important disease of citrus in Brazil. X. fastidiosa is restricted to xylem vessels of plants and knowledge regarding xylem colonization is still limited. Our goal was to verify how this bacterium colonizes and spreads within xylem vessels of sweet orange Citrus sinensis cv. Pera. Petioles and pieces of leaf blades from naturally infected plant exhibiting characteristic symptoms were prepared for light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and immunogold labeling (IGL). Petioles from healthy plants were used as control. IGL results, using an antibody against wall hemicelluloses, revealed that the pit membrane of vessels was altered. Bacterial cells were observed in the pit between adjacent vessels. Results support the contention that X. fastidiosa produces cellulases to reach adjacent vessels. SEM revealed that colonization of sweet orange started with X. fastidiosa cells attaching to the xylem wall, followed by an increase in the number of bacterial cells, the production of fibrous material, and finally vessel occlusion by biofilm composed of copious amounts of amorphous material, strands and cells. Phenolic materials, hyperplasia and hypertrophy were noticed in leaves with gummy material. Xylem vessels frequently contained an unknown needle-like, crystallized matter blocking the vessel.

Microstructural Characterization of Solid State Reaction Phase Formed During Sintering of Hexagonal Boron Nitride with Iron

In the development of dry self-lubricating composites, not only solid lubricant particle size and distribution are important, but also the correct selection of the solid lubricant characteristics, which should be stable, i.e. not reactive, during the whole processing. In this work, Fe+9 vol% h-BN composites were produced by uniaxial cold compaction and sintering, for which a reaction between h-BN and iron was detected after sintering at 1,150°C. The reaction phase was characterized by optical and scanning electron microscopy and identified by X-ray diffraction and energy-dispersive X-ray spectroscopy. The newly formed phase had high hardness when compared with the iron matrix. The resulting composites presented a high friction coefficient and high wear.

Solid State Reaction Detected Between Hexagonal Boron Nitride and Iron During Sintering

Nowadays the development of new materials is mainly dependent on performance requirements, which are related to the functional conditions, environmental aspects and application design. Dry selflubricating materials (containing solid lubricants) are examples of material specifically designed to operate in conditions where the presence of liquid lubricants (namely oils and greases) is not allowed or does not provide enough lubrication for better performance [1]. Solid lubricants can replace liquid lubricants when used as films or incorporated in the bulk of the component (volumetric dispersion). In the latter case, powder metallurgy is the common process path. Through powder metallurgy it is possible to include a large number of distinct solid lubricant particles, such as MoS2, WS2, MoSe2 and h-BN, to the metallic matrix. The selection of the solid lubricant phase depends on the matrix chemical makeup to avoid undesirable reactions among materials. In this work iron powder (Höganäs, AHC 100.29, d50=100 μm) and h-BN powder (9% volume, Momentive AC6004, d50=13 μm) were mixed in a Yshape mixer for 60 minutes, compacted in a semi-automatic press (700 MPa) and sintered at 1150 °C for 60 minutes inside a tubular resistive furnace under a 95% Ar 5% H2 atmosphere.

The use of Microcontact Printing of Thiols to Evaluate Attachment of Xylella fastidiosa Under Distinct Conditions of Calcium Availability

Plant Pathogenic bacteria attach to surfaces to form biofilms and effectively colonize the host plant. Xylem vessels internal surface attachment is the first step towards colonization during the infection of grapevines by Xylella fastidiosa [1], causative agent of Pierce’s disease, an economically important factor for the California wine industry. Auburn University [2,3] is devoted to identify and test factors that are favorable to attachment and those that are not. The study of this xylem-limited pathogen is critical to establish how pathogenic cells reach massive growth inside vessels and eventually alter plant growth and/or cause death. Massive growth also means enormous production of virulence factors, such as toxins, and extended vessels blockage of normal flow of nutrients and water. The goal of this investigation is to test a methodology that can reduce the time of initial screening of chemical influencing factors and speed up experimental protocols. We accomplished these goals by: 1) monitoring biofilm formation under controlled conditions on glass surfaces coated with gold vs. gold surfaces coated with thiol (SH rich moieties), and 2) comparing obtained results with published results.

Testate Amoebae Diversity, from the Atlantic Forest Aquatic and Edaphic Environments, Collected Within the Rio de Janeiro State, Brazil

Atlantic Forest is considered one of world’s most species-diverse ecosystems, with high endemism rate and often referred as a diversity hot-spot. [1, 2]. Due to anthropic activity since the 1500’s, it has been constantly reduced until only ca. 7.9% of its original area remains intact [2]. In the state of Rio de Janeiro, the Atlantic Forest originally covered 98% of its territory, while currently its extension is less than 17%. Considering such scenario and the eventual possible implications of huge diversity losses, it is important to study species diversity within an alpha-taxonomy (i.e. descriptive taxonomy) context. The present study is part of a Brazilian program called BIOTA-FAPERJ (E26/110.022/2011), which aims to investigate the diversity of microeukaryotic organisms present in various environments of the Atlantic Forest in Rio de Janeiro, using morphological and molecular approaches. The program also has the objective to investigate the biotechnological potential of these organisms in improving environment quality.

2013 Vicência Meteorite Found in Brazil: Preliminary Classification Efforts Based on Traditional Approaches and Cathodoluminescence (CL) Maps.

A meteorite fall took place on September 21, 2013 in a tiny village called Vicência (also known as Vila da Borracha), located at Brazil’s northeast region, more specifically on the northwest of Pernambuco State. The meteorite almost struck a man (Mr. Adeildo) who noticed that one of the rock sides was still warm. The meteorite is now at the Rio de Janeiro National Museum for petrological classification. In this paper we describe the study of cathodoluminescence (CL) emission after exposing thin specimen of the meteorite slices to an electron beam, as an aid to traditional classification methods.