Microbial community structure and disposal issues of table olive wastewaters generated from the fermentation of the olive cultivar ‘Kalamon’

Table olive wastewaters (TOWW) are produced worldwide in large quantities annually and are characterized by high COD concentration, salt and phenolic content. Although microbial communities in fermentation processes have been studied extensively, a limited number of studies have been performed on the disposed brine. In this study, molecular techniques were applied to examining the dominant bacterial and fungal communities in Kalamon TOWW and the findings are discussed in relation to disposal issues of these wastewaters. Based on fluorescence in situ hybridization (FISH), the bacterial population in TOWW was estimated to be 55 ± 8 % of the total microbial population, while total fungal counts were 11.7 ± 2.6 × 10⁴ CFU mL⁻¹. The main bacterial taxon identified in Kalamon TOWW was associated, but not closely, to Microvirga subterranea, while the dominant fungal isolates were related to the genus Pichia. However, these fungal isolates warrant further investigation since they were distantly related to their closest taxonomically described relative Pichia manshurica (96.0 % similarity in ITS1-5.8S rRNA gene-ITS2 region). Based on 16S rRNA gene sequencing, at least five novel phylogenetic linkages among Bacteria were identified. No lactic acid bacteria were detected in the brine, indicating that lactic acid fermentation was completed at an early stage. Moreover, no fecal contamination threat was found since coliforms and other enteric bacteria were not identified. However, physicochemical characterization and phytoxicity tests revealed that TOWW should be considered as a wastewater of high toxicity. It appears that oligotrophy, endospore-formation, osmotolerance and polyphenol-tolerance are adaptive strategies adopted by indigenous microbiota to resist adverse environmental conditions in TOWW.