The main objective of this work is the study of the phylogeny, evolution and ecological importance of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, the activity of which represents one of the most important and studied mechanisms used by plant growth–promoting microorganisms. The ACC deaminase gene and its regulatory elements presence in completely sequenced organisms was verified by multiple searches in diverse databases, and based on the data obtained a comprehensive analysis was conducted. Strain habitat, origin and ACC deaminase activity were taken into account when analyzing the results. In order to unveil ACC deaminase origin, evolution and relationships with other closely related pyridoxal phosphate (PLP) dependent enzymes a phylogenetic analysis was also performed. The data obtained show that ACC deaminase is mostly prevalent in some Bacteria, Fungi and members of Stramenopiles. Contrary to previous reports, we show that ACC deaminase genes are predominantly vertically inherited in various bacterial and fungal classes. Still, results suggest a considerable degree of horizontal gene transfer events, including interkingdom transfer events. A model for ACC deaminase origin and evolution is also proposed. This study also confirms the previous reports suggesting that the Lrp-like regulatory protein AcdR is a common mechanism regulating ACC deaminase expression in Proteobacteria, however, we also show that other regulatory mechanisms may be present in some Proteobacteria and other bacterial phyla. In this study we provide a more complete view of the role for ACC deaminase than was previously available. The results show that ACC deaminase may not only be related to plant growth promotion abilities, but may also play multiple roles in microorganism's developmental processes. Hence, exploring the origin and functioning of this enzyme may be the key in a variety of important agricultural and biotechnological applications.

Frequent applications of copper (Cu)-based fungicides on vines causes the accumulation of this metal in vineyard soils, which can cause toxicity in young vines. However, liming may reduce these toxic effects. The present study aimed to evaluate the effects of Cu toxicity on the root anatomy of young vines and the alleviation of Cu toxicity by lime applications to contaminated sandy soil. The treatments consisted of the addition of lime (0.0, 1.5 and 3.0 Mg ha(-1)) and two Cu concentrations (0 and 50 mg kg(-1)) to Typic Hapludalf soil. Young vines 'Niágara Branca' (Vitis labrusca L.) were obtained by micropropagation and cultivated for 70 days. The young vines grown with Cu and without liming presented a disorganized root structure; reduced root cap size; increased diameter (47%), cortex area (128%), vascular cylinder area (93%), and number of cortical layers and cells containing phenolic compounds (132%); and reduced root (41%), stem (44%) and leaf dry mass (21%) and height increase (55%). Moreover, Cu exposure reduced Ca concentrations (13%) and increased Cu concentrations (371%) in the roots. Liming, primarily with the highest tested dose, increased the soil pH (from 4.4 to 5.4-6.1), decreased the Cu concentration in the soil (extracted by CaCl2), increased the calcium (Ca) and magnesium (Mg) uptake by plants, prevented root anatomical changes and benefited young vine growth in soil with higher Cu concentrations.

Microbial solubilisation of low soluble inorganic phosphates is an important process contributing for the phosphorus available to plants in tropical soils. This study evaluates the ability of inoculant strains for tropical legumes to solubilise inorganic phosphates of low solubility that are found in tropical soils. Seven strains of Leguminosae nodulating bacteria (LNB) were compared with one another and with a non-nodulating positive control, Burkholderia cepacia (LMG 1222T). Four of the strains are used as inoculants for cowpeas (Vigna unguiculata) (Bradyrhizobium sp. UFLA 03-84; Bradyrhizobium elkani INPA 03-11B and Bradyrhizobium japonicum BR3267) or for common beans (Phaseolus vulgaris) (Rhizobium tropici CIAT 899T). Rhizobium etli UFLA 02-100 and Rhizobium leguminosarum 316C10a are also efficient nodulators of beans and Cupriavidus taiwanensis LMG 19424T nodulates on Mimosa pudica. Two experiments, with solid and liquid media, were performed to determine whether the strains were able to solubilise CaHPO4, Al(H2PO4)3 or FePO4.2H2O. On solid GELP medium none of the strains dissolved FePO4.2H2O, but LMG 1222, UFLA 03-84 and CIAT 899 solubilised CaHPO4 particularly well. These strains, along with LMG 19424 and BR 3267, were also able to increase the solubility of Al(H2PO4)3. In liquid GELP medium, LMG 1222 solubilised all phosphate sources, but no legume nodulating strain could increase the solubility of Al(H2PO4)3. The strains CIAT 899 and UFLA 02-100 were the only legume nodulating bacteria able to solubilise the other phosphate sources in liquid media, dissolving both CaHPO4 and FePO4.2H2O. There was a negative correlation between the pH of the culture medium and the concentration of soluble phosphate when the phosphorus source was CaHPO4 or FePO4.2H2O. The contribution of these strains to increasing the phosphorus nutrition of legumes and non-legume plant species should be investigated further by in vivo experiments.