ORIGINAL PAPER Bioremediation of dry olive-mill residue removes inhibition of growth induced by this waste in tomato plants M. Garcı ´a-Sa´nchez • A. Paradiso • I. Garcı ´a-Romera • E. Aranda • M. C. de Pinto Received: 6 August 2012 / Revised: 15 October 2012 / Accepted: 25 December 2012 / Published online: 8 February 2013 Ó Islamic Azad University (IAU) 2013 Abstract The disposal of dry olive-mill residue, the waste product from olive oil production, is a serious environmental issue. Dry olive-mill residue, being rich in organic and inorganic nutrients, could be used as fertilizer; however, it contains phenolic compounds that can inhibit plant growth. In order to clarify whether bioremediation of this waste could be a valuable strategy for its reuse, the effect of aqueous extract of dry olive-mill residue, untreated or bioremediated by the saprobe fungi Coriol- opsis rigida and Penicillium chrysogenum-10, has been analyzed in relation to some physiological parameters of tomato plants. The data show that aqueous dry olive-mill residue significantly reduces the biomass of roots and shoots. In particular, it causes a dramatic reduction in root length, area, and volume as well as in the number of root tips. At an early stage, aqueous dry olive-mill residue also reduces the content of chlorophyll a and b and the effi- ciency of PS II. The inhibition of growth seems to be due to the increase in phenolic compounds that induce oxidative stress. Interestingly, when plants are treated with aqueous dry olive-mill residue bioremediated by saprobe fungi a decrease in phenolic content and an alleviation of oxidative stress occur. In conclusion, the results show that biore- mediation of aqueous dry olive-mill residue is a useful tool to remove most of the inhibiting effects of this waste on plant growth. Keywords Oxidative stress  Phenolics  Reactive oxygen species  Saprobe fungi Introduction Olive oil production is one of the most important agro- industrial activities in the Mediterranean region. In addi- tion to oil, this activity produces large quantities of waste whose disposal represents a serious environmental prob- lem. Two-phase centrifugation, one of the most widely used olive-mill extraction systems, generates a wet waste product commonly called ‘‘alpeorujo’’. A second centri- fugation of alpeorujo results in an extra oil yield and a new by-product that is dried and extracted with solvents, pro- ducing a final solid waste called dry olive-mill residue (DOR). Due to its high organic and inorganic nutrient content, DOR has great potential as fertilizer (Sampedro et al. 2007a). However, DOR also contains phytotoxic compounds capable of inhibiting the growth of microor- ganisms and thus germination and growth of plants (Sampedro et al. 2004; Saparrat et al. 2010). Therefore, before being applied to agricultural soils as an organic fertilizer, DOR needs to be remediated. Optimal removal of bio-recalcitrant phenols from DOR can be achieved using a well-designed sequential treatment consisting of various chemical, physical, and biological processes (Aranda et al. 2007). Bioremediation with saprobe fungi represents one of the most promising approaches for DOR detoxification (Sampedro et al. 2004, 2007a). Saprobe fungi are known to be capable of degrading a wide variety of pollutants, including phenolic compounds, which are the main M. Garcı ´a-Sa´nchez  I. Garcı ´a-Romera  E. Aranda Department of Soil Microbiology and Symbiotic Systems, Estacio´n Experimental Del Zaidı ´n (EEZ), Consejo Superior de Investigaciones Cientı ´ficas (CSIC), Prof. Albareda 1 Apdo. 419, 18008 Granada, Spain A. Paradiso  M. C. de Pinto (&) Department of Biology, University of Bari Aldo Moro, Via Orabona 4, 70125 Bari, Italy e-mail: mariaconcetta.depinto@uniba.it 123 Int. J. Environ. Sci. Technol. (2014) 11:21–32 DOI 10.1007/s13762-012-0170-3