a b s t r a c tIn the present work bacteria associated with milk kefir grains from several Brazilian States, Canada and the United States of America under traditional conditions have, for the first time, been studied using a combination of pheno-and genotypic methods. Conventional culturing was performed and a total of 270 isolates were obtained from all samples. Isolates were identified using biochemical tests and partial sequence analysis of 16S rDNA. Denaturing gradient gel electrophoresis (DGGE) of partially amplified 16S rDNA followed by sequencing of the most intense bands showed that the dominant bacterium was Lactobacillus kefiri. PCR-DGGE revealed the presence of Gluconobacter japonicus and Lactobacillus uvarum which were no isolated. Conventional isolation revealed the presence of L. helveticus, L. kefiri and Acetobacter syzygii not identified among the sequenced DGGE bands. This study is the first to report the presence of Lactobacillus satsumensis and Acetobacter syzygii in milk kefir grains.
Brucella spp. are facultative intracellular pathogens that have the ability to survive and multiply in professional and non-professional phagocytes, and cause abortion in domestic animals and undulant fever in humans. Several species are recognized within the genus Brucella and this classification is mainly based on the difference in pathogenicity and in host preference. Brucella strains may occur as either smooth or rough, expressing smooth LPS (S-LPS) or rough LPS (R-LPS) as major surface antigen. This bacterium possesses an unconventional non-endotoxic lipopolysaccharide that confers resistance to anti-microbial attacks and modulates the host immune response. The strains that are pathogenic for humans (B. abortus, B. suis, B. melitensis) carry a smooth LPS involved in the virulence of these bacteria. The LPS O-chain protects the bacteria from cellular cationic peptides, oxygen metabolites and complement-mediated lysis and it is a key molecule for Brucella survival and replication in the host. Here, we review i) Brucella LPS structure; ii) Brucella genome, iii) genes involved in LPS biosynthesis; iv) the interaction between LPS and innate immunity.
SUMMARYThe process of biological nitrogen fixation (BNF), performed by symbiotic nitrogen fixing bacteria with legume species, commonly known as α and β rhizobia, provides high sustainability for the ecosystems. Its management as a biotechnology is well succeeded for improving crop yields. A remarkable example of this success is the inoculation of Brazilian soybeans with Bradyrhizobium strains. Rhizobia produce a wide diversity of chemical structures of exopolysaccharides (EPS). Although the role of EPS is relatively well studied in the process of BNF, their economic and environmental potential is not yet explored. These EPS are mostly species-specific heteropolysaccharides, which can vary according to the composition of sugars, their linkages in a single subunit, the repeating unit size and the degree of polymerization. Studies have showed that the EPS produced by rhizobia play an important role in the invasion process, infection threads formation, bacteroid and nodule development and plant defense response. These EPS also confer protection to these bacteria when exposed to environmental stresses. In general, strains of rhizobia that produce greater amounts of EPS are more tolerant to adverse conditions when compared with strains that produce less. Moreover, it is known that the EPS produced by microorganisms are widely used in various industrial activities. These compounds, also called biopolymers, provide a valid alternative for the commonly used in food industry through the development of products with identical properties or with better rheological characteristics, which can be used for new applications. The microbial EPS are also able to increase the adhesion of soil particles favoring the mechanical stability of aggregates, increasing levels of water retention and air flows in this environment. Due to the importance of EPS, in this review we discuss the role of these compounds in the process of BNF, in the adaptation of rhizobia to environmental stresses and in the process of soil aggregation. The possible applications of these biopolymers in industry are also discussed.Index terms: Exopolysaccharides, nodules, environmental stress, soil aggregation, rhizobia.
RESUMO: EXOPOLISSACARÍDEOS PRODUZIDOS POR BACTÉRIAS FIXADORAS DE NITROGÊNIO SIMBIÓTICAS DE LEGUMINOSAE O processo de fixação biológica de nitrogênio (FBN), realizado por bactérias fixadoras de
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