Biocontrol potential of actinobacteria against Pantoea ananatis, the causal agent of maize white spot disease.

Pantoea ananatis is the causal agent of maize white spot, a foliar disease responsible for significant maize yield reduction worldwide, especially in Brazil. In general, the maize foliar diseases control involves the adoption of resistant genotypes and pesticides application. However, the use of agrochemicals can significantly cause increase production costs, damage to human health and negative environmental impacts. In this sense, the use of biological control agents has been considered among the most promising eco-friendly technologies for sustainable agriculture. Actinobacteria, particularly of Streptomyces genus, has been widely recognized as agroindustrially important microorganism due to its potential in producing diverse range of secondary metabolites, including antibiotics and enzymes. Thus, the aim of this work is to characterize and to evaluate the potential of soil actinobacteria for P. ananatis control. We observed that 59 actinobacteria strains (85%) exhibited proteolytic or chitinolytic activity. Only the strains Streptomyces pseudovenezuelae ACSL 470, that also exhibited high proteolytic activity, S. novaecaesareae ACSL 432 and S. laculatispora ACP 35 demonstrated high or moderate antagonist activity in vitro against P. ananatis. Temporal analysis of metabolites produced by these strains growth in different liquid media indicated greater antibacterial activity at 72 h. In this condition, chromatographic and mass spectrometry analysis revealed that S. pseudovenezuelae ACSL 470 strain produced neomycin, an aminoglycoside antibiotic that displayed high bactericidal activity in vitro against P. ananatis. This is the first report of actinobacteria acting as potential microbial antagonists for P. ananatis control. Further studies are needed to determine the control efficacy of maize white spot disease by Streptomyces strains or their metabolites in greenhouse and field conditions.

Ecology and identification of environmental fungi and metabolic processes involved in the biodeterioration of Brazilian soapstone historical monuments.

This study aimed to evaluate the action of organic acids produced by the fungal population associated with the biodeterioration process of the Twelve Prophets of Aleijadinho, a set of soapstone sculptures in Congonhas, state of Minas Gerais, Brazil. For this, samples of fungi were obtained from the surface of each of the 12 outdoor stone sculptures that comprise the set of Prophets. The identification of the colonizing filamentous fungi was performed by classical microbiology and molecular methods. Some species of filamentous fungi-dependent cultivation were detected, and the presence of species Aspergillus versicolor, Curvularia lunata, Epicoccum nigrum, Penicillium citrinum and Pseudocercospora norchiensis indicated a connection with the excretion of organic acids. The acids produced by each of these fungal species were analysed quantitatively by chromatographic methods, revealing potential biodeterioration by the action of acidic metabolites excreted in the stone. SIGNIFICANCE AND IMPACT OF THE STUDY: Minas Gerais, Brazil, is vulnerable to the activities of mineral extraction industries, posing an imminent risk to United Nations Educational, Scientific and Cultural Organization (UNESCO) recognized cities, e.g. Congonhas. Many of these municipalities hold many soapstone religious sculptures and historical monuments. Consequently, soapstone is susceptible to filamentous fungi attack causing irreversible biodeterioration. Despite the concern related to nondestructive sampling of 18th century sculptures, in this study, we have discussed the factors that lead to biodeterioration of soapstone due to organic acid excretion by the fungi that damage the stone, thereby providing an insight in conserving and preserving the soapstone monuments.