Burkholderia has only recently been recognized as a potential nitrogen-fixing symbiont of legumes, but we find that the origins of symbiosis in Burkholderia are much deeper than previously suspected. We sampled 143 symbionts from 47 native species of Mimosa across 1800 km in central Brazil and found that 98% were Burkholderia. Gene sequences defined seven distinct and divergent species complexes within the genus Burkholderia. The symbiosis-related genes formed deep Burkholderia-specific clades, each specific to a species complex, implying that these genes diverged over a long period within Burkholderia without substantial horizontal gene transfer between species complexes.

Summary• An extensive survey of nodulation in the legume genus Mimosa was undertaken in two major biomes in Brazil, the Cerrado and the Caatinga, in both of which there are high degrees of endemicity of the genus.• Nodules were collected from 67 of the 70 Mimosa spp. found. Thirteen of the species were newly reported as nodulating. Nodules were examined by light and electron microscopy, and all except for M. gatesiae had a structure typical of effective Mimosa nodules. The endosymbiotic bacteria in nodules from all of the Mimosa spp. were identified as Burkholderia via immunolabelling with an antibody against Burkholderia phymatum STM815.• Twenty of the 23 Mimosa nodules tested were shown to contain nitrogenase by immunolabelling with an antibody to the nitrogenase Fe-(nifH) protein, and using the d 15 N ( 15 N natural abundance) technique, contributions by biological N 2 fixation of up to 60% of total plant N were calculated for Caatinga Mimosa spp.• It is concluded that nodulation in Mimosa is a generic character, and that the preferred symbionts of Brazilian species are Burkholderia. This is the first study to demonstrate N 2 fixation by beta-rhizobial symbioses in the field.

RESUMO.O presente trabalho tem como objetivo avaliar a influência de diferentes sistemas de manejos, a população microbiana e sua atividade. Para tal, foram coletadas, em outubro de 2006 e março de 2007, amostras de solo na Fazenda Sereno no Município de Jaciara, Estado do Mato Grosso. Retirou-se amostras de solo na profundidade de 0-10 cm, com quatro repetições em cinco áreas com diferentes sistemas de manejos: integração lavoura-pecuária, lavoura de milho/soja, pastagens, vegetação nativa e vegetação nativa em recuperação. Para avaliar o carbono da biomassa microbiana (CBM) e a respiração microbiana (RM) foi utilizado o método do Clorofórmio Fumigação-Incubação (CFI). Já o qCO 2 foi obtido pela relação entre a RM e o CBM. As médias foram comparadas pelo teste de Scott-Knott a 5%. No decorrer das análises, pôde-se observar que as diferentes práticas agrícolas afetam fortemente o solo causando distúrbios na comunidade microbiana que podem, por sua vez, influenciar os processos biogeoquímicos que nele ocorrem. Os dados obtidos permitem, ainda, concluir que: nos sistemas Integração lavoura-pecuária e pecuária a população microbiana é influenciada pelas épocas de coletas. Nesse trabalho, no sistema Integração lavoura-pecuária a atividade microbiana é constante nas diferentes épocas de coleta e os diferentes sistemas de manejos influenciam a atividade metabólica dos microrganismos presentes no solo.Palavras-chave: microrganismos do solo, clorofórmio fumigação-incubação, bioindicadores, quociente metabólico, integração lavoura-pecuária.

The production of sweets and similar sugarcane products is an activity performed by smallholder farmers from Acorizal, Cuiabá, Jangada, Nossa Senhora do Livramento, and Santo Antônio do Leverger, in Mato Grosso. Therefore, this study aimed to assess the socioeconomic and productive aspects of rural producers (individuals and/or families) that work with the production of sweets and sugarcane derivatives in municipalities of the ‘Baixada Cuiabana’ region.  145 questionnaires were applied to rural producers in the period from March 2019 to January 2020. Among the main results, it was verified that the predominant profile is of rural producers with a low education level, with properties with a size smaller than a fiscal module (the size varies for each municipality), without DAP possession and/or access to sectorial public policies, such as PRONAF and ATER services. Furthermore, the main income source of the interviewees was the production of sweets and similar sugarcane-derived products, and the financial gain of most individuals was up to a minimum wage. Therefore, it is verified that the low education level and the absence of technical orientation might be conditioning for the permanence of farmers in situations of socioeconomic vulnerability.