title: Effects of Exogenous Yeast and Bacteria on the Microbial Population Dynamics and Outcomes of Olive Fermentations.
abstract: In this study, we examined Sicilian-style green olive fermentations upon the addition ofSaccharomyces cerevisiaeUCDFST 09-448 and/orPichia kudriazeviiUCDFST09-427 or the lactic acid bacteria (LAB)Lactobacillus plantarumAJ11R andLeuconostoc pseudomesenteroidesBGM3R. Olives containingS. cerevisiaeUCDFST 09-448, a strain able to hydrolyze pectin, but notP. kudriazeviiUCDFST 09-427, a nonpectinolytic strain, exhibited excessive tissue damage within 4 weeks. DNA sequencing of fungal internal transcribed spacer (ITS) regions and comparisons to a yeast-specific ITS sequence database remarkably showed that neitherS. cerevisiaeUCDFST 09-448 norP. kudriazeviiUCDFST 09-427 resulted in significant changes to yeast species diversity. Instead,Candida boidiniiconstituted the majority (>90%) of the total yeast present, independent of whetherS. cerevisiaeorP. kudriazeviiwas added. By comparison,Lactobacillusspecies were enriched in olives inoculated with potential starter LABL. plantarumAJ11R andL. pseudomesenteroidesBGM3R according to community 16S rRNA gene sequence analysis. The bacterial diversity of those olives was significantly reduced and resembled control fermentations incubated for a longer period of time. Importantly, microbial populations were highly dynamic at the strain level, as indicated by the large variations in AJ11R and BGM3R cell numbers over time and reductions in the numbers of yeast isolates expressing polygalacturonase activity. These findings show the distinct effects of exogenous spoilage and starter microbes on indigenous communities in plant-based food fermentations that result in very different impacts on product quality.IMPORTANCEFood fermentations are subject to tremendous selective pressures resulting in the growth and persistence of a limited number of bacterial and fungal taxa. Although these foods are vulnerable to spoilage by unintended contamination of certain microorganisms, or alternatively, can be improved by the deliberate addition of starter culture microbes that accelerate or beneficially modify product outcomes, the impact of either of those microbial additions on community dynamics within the fermentations is not well understood at strain-specific or global scales. Herein, we show how exogenous spoilage yeast or starter lactic acid bacteria confer very different effects on microbial numbers and diversity in olive fermentations. Introduced microbes have long-lasting consequences and result in changes that are apparent even when levels of those inoculants and their major enzymatic activities decline. This work has direct implications for understanding bacterial and fungal invasions of microbial habitats resulting in pivotal changes to community structure and function.
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Zaragoza
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Zachary
authors.initials: Z
authors.lastname: Bendiks
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Tyler
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Kable
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Williams
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Yelizaveta
authors.initials: Y
authors.lastname: Luchkovska
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Elaine
authors.initials: E
authors.lastname: Chow
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Kyria
authors.initials: K
authors.lastname: Boundy-Mills
authors.affiliation: Department of Food Science & Technology, University of California, Davis, California, USA.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Marco
keywords: Lactobacillus; Saccharomyces; fermentation; microbiota; pectinases; resilient; spoilage