Impact of airborne zinc pollution on the antimicrobial activity of olive oil and the microbial metabolic profiles of Zn-contaminated soils in an Italian olive orchard

The growing of microbial resistance leads to a great interest about some natural alternatives to synthetic compounds. This study was carried out in two olive orchards (Olea europaea L., cv. Coratina) South Italy (Basilicata region), one located in a polluted area near a fertilizers factory releasing Zn and the other in a control unpolluted site, both managed with similar cultivation techniques. Olive oil samples were studied from both areas during 2014 and 2015. The soil microbiological status of the polluted and unpolluted orchards has been characterized and the antimicrobial effects of olive oils extracted from polluted plants (PP) and control plants (CP) against some phytopathogens have been explored. Results showed that the antibacterial activity of PP oil was significantly higher than CP and this could be due to the high content of some phenolic compounds elicited by air and soil Zn pollution (especially in the layer 0-20 cm). There is no detectable antifungal activity of the studied oils. The metabolic activity (both total and for each carbon substrate group), diversity and evenness of PP soil bacterial communities were significantly different from CP soil, while the effects of soil depth was negligible. The same parameters measured on soil fungal communities are lower in PP soil at 0-20 cm soil depth. The current research clarified the impact of atmospheric Zn pollution on the antimicrobial activity of olive oil and the soil microbial metabolic profiles. The bioactive substances extracted from olive oils growing in Zn-polluted area might be used as antibiotics.