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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

One of the most cultivated and consumed vegetables in Brazil is the common bean, Phaseolus vulgaris L. The symbiosis of this plant species with nitrogen-fixing bacteria that are adapted to the stresses commonly found in tropical soils can increase production. The aim of this study was to evaluate the symbiotic effectiveness of bacterial strains from soils under different land uses in the Amazon region. Further, rhizobia tolerance to acidity and aluminium and the involvement of some possible physiological mechanisms of such tolerance were also investigated. In assessing the efficiency of biological nitrogen fixation, inoculation with strains UFLA04-195, UFLA04-173 and UFLA04-202, belonging to the genus Rhizobium, resulted in greater plant growth, higher shoot nitrogen content and good nodulation compared to the inoculation with the strain CIAT 899 (R. tropici), and to the mineral nitrogen control or Burkholderia fungorum strains that nodulated or not bean plants. These efficient strains grew better at pH 5.0 than at pH 6.0 or pH 6.9; they also tolerated up to 1 mmol l(-1) of Al(3+) and showed an increased production of exopolysaccharides where the growing rates were less (pH 6.0 and pH 6.9). With respect to aluminium, the highest production of EPS produced greater tolerance to this element. Taken together, these results indicate that the strains evaluated in this study were tolerant to acidity and aluminium; they appeared to have developed resistance mechanisms such as EPS production and a resistant cell outer membrane (indicated by resistance to polymyxin and methyl violet). As these strains also gave increased yields of the host species, further studies on whether to recommend these strains as inoculants are already underway.

Several processes that promote plant growth were investigated in endophytic and symbiotic bacteria isolated from cowpea and siratro nodules and also in bacterial strains recommended for the inoculation of cowpea beans. The processes verified in 31 strains were: antagonism against phytopathogenic fungi, free-living biological nitrogen fixation, solubilization of insoluble phosphates and indole acetic acid (IAA) production. The resistance to antibiotics was also assessed. Sequencing of the partial 16S rRNA gene was performed and the strains were identified as belonging to different genera. Eight strains, including some identified as Burkholderia fungorum, fixed nitrogen in the free-living state. Eighteen strains exhibited potential to solubilize calcium phosphate, and 13 strains could solubilize aluminum phosphate. High levels of IAA production were recorded with L-tryptophan addition for the strain UFLA04-321 (42.3 μg mL⁻¹). Strains highly efficient in symbiosis with cowpea bean, including strains already approved as inoculants showed the ability to perform other processes that promote plant growth. Besides, these strains exhibited resistance to several antibiotics. The ability of the nitrogen-fixing bacteria to perform other processes and their adaptation to environmental conditions add value to these strains, which could lead to improved inoculants for plant growth and environmental quality.

Anthracnose, caused by Colletotrichum sublineolum, is one of the most important diseases of sorghum in Brazil. This fungus showed conidial dimorphism when cultivated on solid or in liquid media. In solid media only falcate conidia were produced, whereas in liquid media the conidia were of variable size, but mostly oval. Wild strains, differentiated by their α and β esterase electrophoretic profiles, were assessed. The effect of different culture media on the production of both conidial types was evaluated. Unlike that of oval conidia, the production of falcate conidia was light‐dependent. Some strains failed to produce falcate conidia in solid media, but all produced oval conidia in all the liquid media. The falcate conidia were uninucleate, but oval conidia contained one to three nuclei, although most were uninucleate. Both types of conidia induced symptoms in inoculable sorghum plants under controlled conditions. Both oval and falcate conidia produced mutants after exposure to UV light, and hyphal anastomoses occurred in crosses between mutant conidia carriers of complementary markers. The production of these oval conidia in C. sublineolum is an alternative to pathogenicity tests and genetic studies, especially for strains that sporulate poorly in solid culture media.

Keywords RESUMOPantoea ananatis . Palavras-chave:

Resumo -O objetivo deste trabalho foi avaliar a tolerância de estirpes de Cupriavidus necator a zinco, cádmio, cobre e chumbo, além de determinar a eficiência simbiótica das estirpes mais tolerantes em associação a espécies leguminosas com potencial para revegetação. A tolerância foi testada em meio LB, suplementado com 2,5; 5,0; 7,5; 10; 12,5 . pudica e M. caesalpiniifolia e as estirpes UFLA01-659 e UFLA02-71, selecionadas na avaliação de eficiência simbiótica. A estirpe UFLA02-71 proporcionou incrementos de matéria seca da parte aérea de 870% em M. caesalpiniifolia, enquanto que UFLA01-659 proporcionou 885% em M. pudica e 924% em L. leucocephala. As estirpes UFLA01-659 e UFLA02-71, além da alta tolerância a metais pesados, apresentaram eficiência em fixar nitrogênio, em simbiose com essas leguminosas, em solos com rizóbios nativos capazes de nodulá-las, e devem ser avaliadas quanto ao seu potencial de utilização em programas de recuperação de áreas degradadas.Termos para indexação: áreas degradadas, β-proteobactéria, fixação biológica de nitrogênio, metais pesados, revegetação. Symbiotic efficiency of Cupriavidus necator strains tolerant to zinc, cadmium, copper and leadAbstract -The objective of this work was to evaluate the tolerance of Cupriavidus necator strains to zinc, cadmium, copper and lead, as well as to determine the symbiotic efficiency of the most tolerant ones in legume species suited for use in revegetation. Tolerance was evaluated in LB medium supplemented with 2.5, 5.0, 7.5, 10, 12.5 and 15 mmol L -1 of ZnSO 4 .7H 2 O, CdSO 4 .8H 2 O, CuSO 4 .5H 2 O and PbCl 2 , respectively, in comparison to a control without metal. The symbiotic efficiency of the four C. necator most metal-tolerant strains (UFLA02-71, UFLA02-73, UFLA01-659 and UFLA01-663) was determined, and these strains were inoculated in the species: Leucaena leucocephala, Enterolobium contortisiliquum, Acacia mangium, Mimosa caesalpiniifolia, M. pudica, M. pigra and M. acutistipula. Leucaena leucocephala, M. pudica and M. caesalpiniifolia and the strains UFLA02-71 and UFLA01-659, which presented the high symbiotic efficiency, were evaluated in pots with soil. UFLA02-71 provided increments of 870% in shoot dry matter of M. caesalpiniifolia, and UFLA01-659 provided 885% in M. pudica and 924% in L. leucocephala. These strains should be assessed for potential use in programs to restore degraded areas, since they showed high efficiency in nitrogen fixation and were competitive with indigenous rhizobia populations, besides being highly tolerant to heavy metals.Index terms: degraded areas, β-proteobacteria, biological nitrogen fixation, heavy metals, revegetation. IntroduçãoA recuperação das áreas degradadas pela atividade de mineração deve ser realizada para acelerar a sucessão natural. Com este propósito, a revegetação tem sido a principal prática para recompor e proteger o solo, evitar a poluição das águas e promover o retorno da biota edáfica. Para implantar a revegetação,

A semi-selective agar medium to detect the presence of Xanthomonas axonopodis pv. malvacearum in naturally infected cotton seed. Fitopatologia Brasileira 30: 489-496. 2005. ABSTRACTA semi-selective agar medium was developed for detection of Xanthomonas axonopodis pv. malvacearum (Xam) in cotton (Gossypium hirsutum) seed. The basic medium was peptone-sucrose-agar (PSA). Criteria for the semi-selective medium were the typical colony characters of Xam and its pathogenicity on cotton. Several systemic fungicides and antibiotics in different concentrations were tested alone or in combination with others. The final composition of the semi-selective agar medium was established after several attempts in order to inhibit most of the fungal and bacterial saprophytes and favour the development of Xam. It contained PSA + cyclohexamide, cephalexin, pencycuron, triadimenol and tolylfluanid. The bacteria were recovered from naturally infected seeds by the direct plating of 2,000 surface disinfected seeds on the semi-selective medium. The recovery of the pathogen from naturally infected leaf tissues and in dilution plating, on semiselective medium and on nutrient agar, were comparable. Among the three detection methods tested, the semi-selective medium was found to be the most reliable and quantifiable. Degree of severity of angular leaf spot in the field was not always correlated with the level of infection in the seed. This is the first report of a semi-selective agar medium to detect the presence of Xam in naturally infected cotton seed.Additional keywords: Gossypium hirsutum, black arm of cotton, angular leaf spot. RESUMOMeio semi-selectivo para detectar a presença de Xanthomonas axonopodis pv. malvacearum em sementes de algodoeiro naturalmente infetadas Um meio de cultura semi-seletivo foi desenvolvido para detectar Xanthomonas axonopodis pv. malvacearum (Xam) em sementes do algodoeiro (Gossypium hirsutum). O meio básico foi peptona-sacarose-ágar (PSA). Os critérios para o meio semi-seletivo foram; as características típicas das colônias de Xam e sua patogenicidade em algodoeiro. Vários fungicidas sistêmicos e antibióticos foram testados sozinhos ou em combinação com outros em diferentes concentrações. A composição final do meio semi-seletivo foi estabelecida após várias tentativas no sentido de inibir a maioria dos fungos e bactérias saprofíticas e favorecer o desenvolvimento de Xam. O meio contém: PSA + ciclohexamida, cefalexina, pencycuron, triadimenol e tolylfluanid. A bactéria foi recuperada de sementes naturalmente infetadas através do plaqueamento direto de 2.000 sementes externamente desinfestadas em meio semi-seletivo. A recuperação do patógeno de tecidos homogenizados da folha infetada e a recuperação em plaqueamento por diluição, em meio semi-seletivo e em agar nutriente, foram comparáveis. Entre os três métodos de detecção, o meio semi-seletivo foi o mais preciso e confiável. O nível da severidade de infecção em campo não era sempre correlacionado com o nível de infecção nas sementes. Este é o primeiro relato d...