Remoção de nitratos de águas em biorreatores com suporte de sabugo de milho e espuma de poliuretano

A presença de nitrato em corpos d’água pode causar danos ambientais e, se consumido, ao ser humano. Estudos mostram que biorreatores preenchidos com suportes orgânicos são eficientes na remoção de nitratos de águas de drenagem agrícola, que são ricas em nutrientes. Este trabalho teve como objetivo avaliar a remoção de nitratos em biorreator de leito fixo preenchido com dois tipos de meio suporte: R1 (Reator 1), com pedaços de sabugo de milho, e R2 (Reator 2), com pedaços de sabugo de milho e Mini Biobobs®. Os reatores foram alimentados com água de drenagem agrícola enriquecida com 20 mg.L-1 de N-NO3 e operados com tempos de detenção hidráulica (TDH) de 96, 48, 24 e 16 horas. Observou-se que, com exceção dos ensaios com TDH = 16 h, todos os demais apresentaram efluente com concentração de N-NO3 abaixo de 10 mg.L-1, que atende aos padrões exigidos pela legislação brasileiras para potabilidade de água para consumo humano. Através da técnica de NMP constatou-se a presença de bactérias desnitrificantes em ambos os reatores, comprovando a remoção do nitrato pelo processo de desnitrificação heterotrófica. Pode-se concluir que os reatores estudados são eficientes na remoção de nitratos de águas.

Evidence of Horizontal Transfer of Symbiotic Genes from a Bradyrhizobium japonicum Inoculant Strain to Indigenous Diazotrophs Sinorhizobium (Ensifer) fredii and Bradyrhizobium elkanii in a Brazilian Savannah Soil

The importance of horizontal gene transfer (HGT) in the evolution and speciation of bacteria has been emphasized; however, most studies have focused on genes clustered in pathogenesis and very few on symbiosis islands. Both soybean (Glycine max [L.] Merrill) and compatible Bradyrhizobium japonicum and Bradyrhizobium elkanii strains are exotic to Brazil and have been massively introduced in the country since the early 1960s, occupying today about 45% of the cropped land. For the past 10 years, our group has obtained several isolates showing high diversity in morphological, physiological, genetic, and symbiotic properties in relation to the putative parental inoculant strains. In this study, parental strains and putative natural variants isolated from field-grown soybean nodules were genetically characterized in relation to conserved genes (by repetitive extragenic palindromic PCR using REP and BOX A1R primers, PCR-restriction fragment length polymorphism, and sequencing of the 16SrRNA genes), nodulation, and N(2)-fixation genes (PCR-RFLP and sequencing of nodY-nodA, nodC, and nifH genes). Both genetic variability due to adaptation to the stressful environmental conditions of the Brazilian Cerrados and HGT events were confirmed. One strain (S 127) was identified as an indigenous B. elkanii strain that acquired a nodC gene from the inoculant B. japonicum. Another one (CPAC 402) was identified as an indigenous Sinorhizobium (Ensifer) fredii strain that received the whole symbiotic island from the B. japonicum inoculant strain and maintained an extra copy of the original nifH gene. The results highlight the strategies that bacteria may commonly use to obtain ecological advantages, such as the acquisition of genes to establish effective symbioses with an exotic host legume

Proteomic profiling of <it>Rhizobium tropici</it> PRF 81: identification of conserved and specific responses to heat stress

Abstract Background Rhizobium tropici strain PRF 81 (= SEMIA 4080) has been used in commercial inoculants for application to common-bean crops in Brazil since 1998, due to its high efficiency in fixing nitrogen, competitiveness against indigenous rhizobial populations and capacity to adapt to stressful tropical conditions, representing a key alternative to application of N-fertilizers. The objective of our study was to obtain an overview of adaptive responses to heat stress of strain PRF 81, by analyzing differentially expressed proteins when the bacterium is grown at 28°C and 35°C. Results Two-dimensional gel electrophoresis (2DE) revealed up-regulation of fifty-nine spots that were identified by MALDI-TOF/TOF-TOF. Differentially expressed proteins were associated with the functional COG categories of metabolism, cellular processes and signaling, information storage and processing. Among the up-regulated proteins, we found some related to conserved heat responses, such as molecular chaperones DnaK and GroEL, and other related proteins, such as translation factors EF-Tu, EF-G, EF-Ts and IF2. Interestingly, several oxidative stress-responsive proteins were also up-regulated, and these results reveal the diversity of adaptation mechanisms presented by this thermotolerant strain, suggesting a cross-talk between heat and oxidative stresses. Conclusions Our data provide valuable protein-expression information relevant to the ongoing genome sequencing of strain PRF 81, and contributes to our still-poor knowledge of the molecular determinants of the thermotolerance exhibited by R. tropici species.</p

A simple, economical and reproducible protein extraction protocol for proteomics studies of soybean roots

Sample preparation is a critical step in two-dimensional gel electrophoresis (2-DE) of plant tissues. Here we describe a phenol/SDS procedure that, although greatly simplified, produced well-resolved and reproducible 2-DE profiles of protein extracts from soybean [Glycine max (L.) Merril] roots. Extractions were made in three replicates using both the original and simplified procedure. To evaluate the quality of the extracted proteins, ten spots were randomly selected and identified by mass spectrometry (MS). The 2-DE gels were equally well resolved, with no streaks or smears, and no significant differences were observed in protein yield, reproducibility, resolution or number of spots. Mass spectra of the ten selected spots were compared with database entries and allowed high-quality identification of proteins. The simplified protocol described here presents considerable savings of time and reagents without compromising the quality of 2-DE protein profiles and compatibility with MS analysis, and may facilitate the progress of proteomics studies of legume-rhizobia interactions