The microbiology of olive mill wastes

Abstract

Olive mill wastes (OMWs) are high-strength organic effluents, which upon disposal can degrade soil and water quality, negatively affecting aquatic and terrestrial ecosystems. The main purpose of this review paper is to provide an up-to-date knowledge concerning the microbial communities identified over the past 20 years in olive mill wastes using both culture-dependent and independent approaches. A database survey of 16S rRNA gene sequences (585 records in total) obtained from olive mill waste environments revealed the dominance of members of Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Firmicutes, and Actinobacteria. Independent studies confirmed that OMW microbial communities' structure is cultivar dependent. On the other hand, the detection of fecal bacteria and other potential human pathogens in OMWs is of major concern and deserves further examination. Despite the fact that the degradation and detoxification of the olive mill wastes have been mostly investigated through the application of known bacterial and fungal species originated from other environmental sources, the biotechnological potential of indigenous microbiota should be further exploited in respect to olive mill waste bioremediation and inactivation of plant and human pathogens. The implementation of omic and metagenomic approaches will further elucidate disposal issues of olive mill wastes.

Figure 1

Distribution of bacterial phylotypes identified in olive mill waste environments.

Figure 2

Distribution within Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Firmicutes, Actinobacteria and Bacteroidetes of bacterial phylotypes identified in olive mill waste environments.

Figure 3

Distribution of fungal phylotypes identified in olive mill waste environments.

Figure 4

Schematic representation of the olive mill waste route in relation to the studies completed and the level of analysis provided. LB: Luria Bertani medium; YPG: yeast extract-peptone-glucose medium; MEA: malt extract agar; YMA: yeast-malt agar; PDA: potato dextrose agar; NA: nutrient agar; ThCl: medium 152 for Thiobacillus (ATCC); SCA: starch casein agar; AGSA: arginine glycerol salts agar; GAA: glycerol asparagine agar. Research studies, considering less than 5 isolates, are not included; CD: culture-dependent, CI: culture-independent.