Copper alters the physiology of tomato rhizospheric isolates of Papiliotrema laurentii

In horticulture copper sulphate is utilized for the inhibition of phytopathogenic fungi. However, copper tends to accumulate in soil with a concomitant effect on soil quality and microbial diversity. As part of the biological diversity of soil and the rhizosphere, yeasts have been relatively less characterized than bacteria or filamentous fungi. In this work, we analyzed the presence of yeasts in the rhizosphere of tomato plants and the effect of copper in fungal biological activities of agronomical and ecological interest. Yeasts isolates that were selected for their higher copper resistance were all identified molecularly as Papiliotrema laurentii. Results show that all were capable of auxin production, and that copper has a detrimental effect on it. In contrast, ammonification was mainly increased by the metal. Copper also inhibits the growth of the yeasts on D-xylose, cellobiose and phenolic acids, suggesting a negative consequence on the recycling of lignocellulosic degradation products. Laccase and catechol oxidase activities were increased by the metal in P. laurentii. Altogether, results presented in this report indicate that P. laurentii presents properties of ecological and agronomical interest. The effect of the metal highlights the importance of the analysis of the consequence of copper utilization as fungicide on microbial activities. At the same time, the variability in the yeast response to copper suggests the concern of not only the characterization of biotechnological properties of a specific strain, but also the effect of copper on them.