Antagonistic Effect of Intestinal Bacteria from the Microflora of Holoxenic (Conventional) Piglets, Against Clostridium Perfringens in the Digestive Tract of Gnotoxenic Mice and Gnotoxenic Piglets

Antagonistic effect of piglet microflora against Clostridium perfringens was studied in germfree mice, to isolate bacterial strains responsible for this colonization resistance. The 1:100 dilution of the feces of a 2 day-old conventional piglet, given per os to germfree mice already harboring C. perfringens, led to the elimination of C. perfringens. From this piglet flora, 8 bacterial strains were selected, belonging to the genera Bacteroides, Clostridium, Eubacterium, Bifidobacterium, Lactobacillus and a strain belonging to the class of Mollicutes. When the 8 strains were given to germfree mice 3 days after C. perfringens inoculation, they led to rapid elimination of C. perfringens from feces. Sixteen other mixtures of 2 to 7 strains were similarly tested, but none was able to fully antagonize C. perfringens. When the 8 strains were given per os to germfree piglets after C. perfringens inoculation, they led to the rapid elimination of C. perfringens from pig feces, and to a quick recovery from diarrhea. This study led to the identification of a simplified fraction of gut microflora, able to exert a barrier effect against C. perfringens comparable to the entire flora of the piglet. This study suggests that gnotoxenic mice can be a suitable model for simplifying the flora responsible for a given effect in another host, animal or human

Preliminary Observations on Zelus Obscuridorsis (Stål) (Hemiptera: Reduviidae) as Predator of the Corn Leafhopper (Hemiptera: Cicadellidae) in Argentina

The corn leafhopper Dalbulus maidis (Hemiptera: Cicadellidae), is an important corn pest in most of tropical and subtropical America. This leafhopper has a rich natural enemy complex of which parasitoids and pathogens are the most studied; knowledge on its predators is limited. We noted the presence of the native assassin bug Zelus obscuridorsis (Hemiptera: Reduviidae) predating diverse motile insects, including the corn leafhopper, on corn plants cultivated in household vegetable gardens in San Miguel de Tucumán (Argentina); in order to verify its predatory actions, we exposed lab-bred individuals of D. maidis to adults of Z. obscuridorsis. The predators were starved for 24 h before trials in which the corn leafhopper in different developmental stages were exposed. Zelus obscuridorsis is highly skilled in catching specimens in motion, but it was not able to prey on eggs. The predator was capable to catch and prey on nymphs and adults.Fil: Virla, Eduardo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucuman. Planta Piloto de Procesos Industriales Microbiologicos; ArgentinaFil: Melo, María Cecilia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Speranza, Stefano. Universita Degli Studi Della Tuscia; Itali

Permanent residents or temporary lodgers: characterizing intracellular bacterial communities in the siphonous green alga Bryopsis

The ecological success of giant celled, siphonous green algae in coastal habitats has repeatedly been linked to endophytic bacteria living within the cytoplasm of the hosts. Yet, very little is known about the relative importance of evolutionary and ecological factors controlling the intracellular bacterial flora of these seaweeds. Using the marine alga Bryopsis (Bryopsidales, Chlorophyta) as a model, we explore the diversity of the intracellular bacterial communities and investigate whether their composition is controlled by ecological and biogeographic factors rather than the evolutionary history of the host. Using a combination of 16S rDNA clone libraries and denaturing gradient gel electrophoresis analyses, we show that Bryopsis harbours a mixture of relatively few but phylogenetically diverse bacterial species. Variation partitioning analyses show a strong impact of local environmental factors on the presence of Rickettsia and Mycoplasma in their association with Bryopsis. The presence of Flavobacteriaceae and Bacteroidetes, on the other hand, reflects a predominant imprint of host evolutionary history, suggesting that these bacteria are more specialized in their association. The results highlight the importance of interpreting the presence of individual bacterial phylotypes in the light of ecological and evolutionary principles such as phylogenetic niche conservatism to understand complex endobiotic communities and the parameters shaping them

Phase and antigenic variation in mycoplasmas

With their reduced genome bound by a single membrane, bacteria of the Mycoplasma species represent some of the simplest autonomous life forms. Yet, these minute prokaryotes are able to establish persistent infection in a wide range of hosts, even in the presence of a specific immune response. Clues to their success in host adaptation and survival reside, in part, in a number of gene families that are affected by frequent, stochastic genotypic hanges. These genetic events alter the expression, the size and the antigenic structure of abundant surface proteins, thereby creating highly versatile and dynamic surfaces within a clonal population. This phenomenon provides these wall-less pathogens with a means to escape the host immune response and to modulate surface accessibility by masking and unmasking stably expressed components that are essential in host interaction and survival

Further evidence to justify reassignment of Mycoplasma mycoides subspecies mycoides Large Colony type to Mycoplasma mycoides subspecies capri

Analysis, using the polymerase chain reaction (PCR), restriction enzyme endonuclease analysis (REA), protein profile patterns, random amplification of polymorphic DNA (RAPD) fingerprinting, 16S rRNA gene sequencing and antisera growth inhibition tests, of 22 strains of Mycoplasma mycoides subsp. mycoides Large Colony type (MmmLC) and eight strains of M. mycoides subsp. capri (Mmc) are presented, along with a summary of comparative data from the literature for over 100 strains, all of which supports the reclassification of the MmmLC and Mmc strains into the single subspecies, M. mycoides subspecies capri

Reconstruction of Transcription Control Networks in Mollicutes by High-Throughput Identification of Promoters

Bacteria of the class Mollicutes have significantly reduced genomes and gene expression control systems. They are also efficient pathogens that can colonize a broad range of hosts including plants and animals. Despite their simplicity, Mollicutes demonstrate complex transcriptional responses to various conditions, which contradicts their reduction in gene expression regulation mechanisms. We analyzed the conservation and distribution of transcription regulators across the 50 Mollicutes species. The majority of the transcription factors regulate transport and metabolism, and there are four transcription factors that demonstrate significant conservation across the analyzed bacteria. These factors include repressors of chaperone HrcA, cell cycle regulator MraZ and two regulators with unclear function from the WhiA and YebC/PmpR families. We then used three representative species of the major clades of Mollicutes (Acholeplasma laidlawii, Spiroplasma melliferum and Mycoplasma gallisepticum) to perform promoters mapping and activity quantitation. We revealed that Mollicutes evolved towards a promoter architecture simplification that correlates with a diminishing role of transcription regulation and an increase in transcriptional noise. Using the identified operons structure and a comparative genomics approach, we reconstructed the transcription control networks for these three species. The organization of the networks reflects the adaptation of bacteria to specific conditions and hosts