Phosphorus solubilizers naturally acidify rhizospheric soil and increase phosphorus availability; therefore, their evaluation may help to reduce phosphorus fertilizer use. This work aimed to evaluate the different selection methods and select inorganic phosphorus-solubilizing bacteria as potential plant-growth promoters. Bacterial isolates obtained from sugarcane roots and soil were tested using solid growth media containing bicalcium phosphate and Irecê Apatite ground rock phosphate as phosphorus sources. Seven isolates with high (3), moderate (3) and low solubilization indices (1) and the Pseudomonas fluorescens R-243 strain were tested in two liquid growth media, followed by the pH and soluble P in the solution. The same isolates, in the absence of inoculation, were tested in Leonard jars with two high-and low-solubility sources using cowpea as a test species. Forty-four days after planting aboveground dry mass, the phosphorus content and total aboveground phosphorus and substratum phosphorus contents were evaluated. The growth media affected phosphorus solubilization by the bacteria. Evaluation of liquid media was the most reliable method for analyzing bicalcic phosphorus solubilization by the bacteria not linked to pH reduction. Isolates UAGC 17, 19 and 65 should be better studied because they were the best solubilizers in culture media; however, they did not demonstrate the same efficiency when inoculated on cowpea.

Many researches have performed on gypsum application to correct high exchangeable aluminum content in acidic soils, especially in subsurface. Although, they have found increases in the exchangeable calcium and sulfur contents, exchangeable aluminum has not been decreased. The exchangeable aluminum buffering by organic matter may contribute to non-significant reduction in exchangeable acidity. The objective of this study was to evaluate the effect of mineral gypsum on the aluminum compartments of Hardsetting Ultisol and monitor the capacity of gypsum to provide exchangeable calcium and sulfur in subsurface. Increasing amounts of mineral gypsum (0, 2, 4, 6, and 8 Mg ha -1 ) were applied with broadcast at the field. The experimental design consisted of randomized block with four replicates. Aluminum compartments (Al-organic matter, Al-amorphous and Alcrystalline) were evaluated at 0 and 15 days after gypsum application and the exchangeable calcium and sulfur contents were evaluated at 0, 15, 64 and 90 days. The evaluations were performed in three different layers. Gypsum application increased the exchangeable calcium and sulfur contents in subsurface and did not reduce the exchangeable aluminum content. Al-organic matter in the surface layers decreased along the incubation time and application gypsum. Al-amorphous in the subsurface layers increased with the increased amounts of gypsum. Al-crystalline decreased as soil depth increased. The exchangeable aluminum buffering in surface layers was performed by Al-organic matter and, in subsurface, by Al-crystalline.

Sugarcane has a high demand in nitrogen, increasing costs and causing damages to the environment. It is necessary to find alternatives to reduce nitrogen fertilizers use. Diazotrophic bacteria have capacity to promote growth in grass with potential to fix N 2 and solubilize inorganic phosphate. This study aimed to evaluate bacterial community associated with different sugarcane varieties in Northeastern Brazil, select bacteria with plant growth-promoting characteristics, and identify endophytic and epiphytic bacterial lineages in sugarcane. Endophytic bacteria of leaves and roots and epiphytic bacteria of rhizoplane were isolated from three sugarcane commercial varieties and selected for their capacity to fix N 2 and solubilize inorganic phosphate. Bacterial strains from different morphological groups were isolated and a sample of 27 strains with potential for the simultaneous development of these characteristics were selected and identified. The bacterial community that interacted with sugarcane was more associated with rhizoplane and roots regions than with leaves, and had a high potential to fix N 2 and solubilize inorganic phosphate. Bacterial lineages were mainly from genera Pantoea sp. and Burkholderia sp., but there were also genera Enterobacter sp., Klebsiella sp. and Pseudomonas sp. and two lineages at the species level: Pantoea stewartii and Burkholderia cenocepacia.

This work highlighted a putative link between the physiological activity and genetic diversity of Methylobacterium species and the association with sugarcane roots and rhizoplane. In total, 40 isolates previously described as pink-pigmented facultative methylotrophic bacteria (PPFMs), were evaluated for their ability to fix nitrogen and solubilize inorganic phosphate, amylase and pectinase activity. This in vitro potential was positively correlated with the community isolated from the root tissues than those from the rhizoplane. Regarding the genomic fingerprinting, the (BOX-PCR) approach revealed a low similarity among the isolates, occurring sole 7 haplotypes harboring more than 70% of similarity among band patterns. These results revealed that the genomic fingerprinting of the isolates recovery from roots is different from the rhizoplane. Besides that, these haplotypes occurred on both sugarcane varieties. Using a phylogenetic sequencing approach based on the 16S rRNA gene, we observed a high abundance of sequences similar to Methylobacterium radiotolerans colonizing both plant tissue and sugarcane varieties were observed. Hence, it was suggested that the plant should select those Methylobacterium spp. with a high biotechnological potential to promote plant growth. Therefore, the bioprospection of specific endophytic bacterial groups comprise an important source of biotechnological potential to improve sugarcane growth and production.

During conjugation, a conjugative DNA element is transferred from a donor to a recipient cell via a connecting channel. Conjugation has clinical relevance because it is the major route for spreading antibiotic resistance and virulence genes. The conjugation process can be divided into different steps. The initial steps carried out in the donor cell culminate in the transfer of a single DNA strand (ssDNA) of the conjugative element into the recipient cell. However, stable settlement of the conjugative element in the new host requires at least two additional events: conversion of the transferred ssDNA into double-stranded DNA and inhibition of the hosts’ defence mechanisms to prevent degradation of the transferred DNA. The genes involved in this late step are historically referred to as establishment genes. The defence mechanisms of the host must be inactivated rapidly and—importantly—transiently, because prolonged inactivation would make the cell vulnerable to the attack of other foreign DNA, such as those of phages. Therefore, expression of the establishment genes in the recipient cell has to be rapid but transient. Here, we studied regulation of the establishment genes present on the four clades of the pLS20 family of conjugative plasmids harboured by different Bacillus species. Evidence is presented that two fundamentally different mechanisms regulate the establishment genes present on these plasmids. Identification of the regulatory sequences were critical in revealing the establishment regulons. Remarkably, whereas the conjugation genes involved in the early steps of the conjugation process are conserved and are located in a single large operon, the establishment genes are highly variable and organised in multiple operons. We propose that the mosaical distribution of establishment genes in multiple operons is directly related to the variability of defence genes encoded by the host bacterial chromosomes.