Studies in the Amazon are being intensified to evaluate the alterations in the microbial communities of soils and sediments in the face of increasing deforestation and land-use changes in the region. However, since these environments present highly heterogeneous physicochemical properties, including contaminants that hinder nucleic acids isolation and downstream techniques, the development of best molecular practices is crucial. This work aimed to optimize standard protocols for DNA extraction and gene quantification by quantitative real-time PCR (qPCR) based on natural and anthropogenic soils and sediments (primary forest, pasture, Amazonian Dark Earth, and várzea, a seasonally flooded area) of the Eastern Amazon. Our modified extraction protocol increased the fluorometric DNA concentration by 48%, reaching twice the original amount for most of the pasture and várzea samples, and the 260/280 purity ratio by 15% to values between 1.8 to 2.0, considered ideal for DNA. The addition of bovine serum albumin in the qPCR reaction improved the quantification of the 16S rRNA genes of Archaea and Bacteria and its precision among technical replicates, as well as allowed their detection in previously non-amplifiable samples. It is concluded that the changes made in the protocols improved the parameters of the DNA samples and their amplification, thus increasing the reliability of microbial communities' analysis and its ecological interpretations.

Inoculants containing bacteria which promote growth in plants can increase productivity and both the economic and the environmental cost in plant crop systems. Similarly, in the flower and ornamental plant sector, the use of diazotrophic bacteria is a promising approach for improving orchid propagation from tissue culture to the ex vitro environment. We isolated diazotrophic bacteria from the roots and leaves of Cymbidium sp. The isolates were used to inoculate Cymbidium sp. plantlets during acclimatization in the nursery. After 150 days, plants were collected and their morphological and nutritional characteristics assessed. Eight bacterial strains were isolated containing traits that promote plant growth: Bacillus thuringiensis, Burkholderia cepacia, Burkholderia gladioli, Herbaspirillum frisingense, Pseudomonas stutzeri, Rhizobium cellulosilyticum, Rhizobium radiobacter, and Stenotrophomonas maltophilia. The isolated Herbaspirillum frisingense and Stenotrophomonas maltophilia increased 26 % and 29 % in dry matter in Cymbidium sp. plants, respectively, compared to the control. In addition, H. frisingense led to higher contents of N and P, by 68 % and 28 %, respectively, than those found in the control plants. These isolates, therefore, have potential for application as biostimulants and biofertilizers to promote growth and development of Cymbidium sp. during acclimatization.