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Culture dependent and independent analysis of bacterial communities associated with commercial salad leaf vegetables.

ABSTRACT: BACKGROUND: Plants harbor a diverse bacterial community, both as epiphytes on the plant surface and as endophytes within plant tissue. While some plant-associated bacteria act as plant pathogens or promote plant growth, others may be human pathogens. The aim of the current study was to determine the bacterial community composition of organic and conventionally grown leafy salad vegetables at the point of consumption using both culture-dependent and culture-independent methods. RESULTS: Total culturable bacteria on salad vegetables ranged from 8.0 × 10(3) to 5.5 × 10(8) CFU g(-1). The number of culturable endophytic bacteria from surface sterilized plants was significantly lower, ranging from 2.2 × 10(3) to 5.8 × 10(5) CFU g(-1). Cultured isolates belonged to six major bacterial phyla, and included representatives of Pseudomonas, Pantoea, Chryseobacterium, and Flavobacterium. Eleven different phyla and subphyla were identified by culture-independent pyrosequencing, with Gammaproteobacteria, Betaproteobacteria, and Bacteroidetes being the most dominant lineages. Other bacterial lineages identified (e.g. Firmicutes, Alphaproteobacteria, Acidobacteria, and Actinobacteria) typically represented less than 1% of sequences obtained. At the genus level, sequences classified as Pseudomonas were identified in all samples and this was often the most prevalent genus. Ralstonia sequences made up a greater portion of the community in surface sterilized than non-surface sterilized samples, indicating that it was largely endophytic, while Acinetobacter sequences appeared to be primarily associated with the leaf surface. Analysis of molecular variance indicated there were no significant differences in bacterial community composition between organic versus conventionally grown, or surface-sterilized versus non-sterilized leaf vegetables. While culture-independent pyrosequencing identified significantly more bacterial taxa, the dominant taxa from pyrosequence data were also detected by traditional culture-dependent methods. CONCLUSIONS: The use of pyrosequencing allowed for the identification of low abundance bacteria in leaf salad vegetables not detected by culture-dependent methods. The presence of a range of bacterial populations as endophytes presents an interesting phenomenon as these microorganisms cannot be removed by washing and are thus ingested during salad consumption.

SUBMITTER: Jackson CR

PROVIDER: S-EPMC4219373 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Culture dependent and independent analysis of bacterial communities associated with commercial salad leaf vegetables.

Jackson Colin R CR Randolph Kevin C KC Osborn Shelly L SL Tyler Heather L HL

BMC microbiology 20131201

<h4>Background</h4>Plants harbor a diverse bacterial community, both as epiphytes on the plant surface and as endophytes within plant tissue. While some plant-associated bacteria act as plant pathogens or promote plant growth, others may be human pathogens. The aim of the current study was to determine the bacterial community composition of organic and conventionally grown leafy salad vegetables at the point of consumption using both culture-dependent and culture-independent methods.<h4>Results< ...[more]

PMID: 24289725

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Project description:Fresh fruits and vegetables can harbor large and diverse populations of bacteria. However, most of the work on produce-associated bacteria has focused on a relatively small number of pathogenic bacteria and, as a result, we know far less about the overall diversity and composition of those bacterial communities found on produce and how the structure of these communities varies across produce types. Moreover, we lack a comprehensive view of the potential effects of differing farming practices on the bacterial communities to which consumers are exposed. We addressed these knowledge gaps by assessing bacterial community structure on conventional and organic analogs of eleven store-bought produce types using a culture-independent approach, 16 S rRNA gene pyrosequencing. Our results demonstrated that the fruits and vegetables harbored diverse bacterial communities, and the communities on each produce type were significantly distinct from one another. However, certain produce types (i.e., sprouts, spinach, lettuce, tomatoes, peppers, and strawberries) tended to share more similar communities as they all had high relative abundances of taxa belonging to the family Enterobacteriaceae when compared to the other produce types (i.e., apples, peaches, grapes, and mushrooms) which were dominated by taxa belonging to the Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria phyla. Although potentially driven by factors other than farming practice, we also observed significant differences in community composition between conventional and organic analogs within produce types. These differences were often attributable to distinctions in the relative abundances of Enterobacteriaceae taxa, which were generally less abundant in organically-grown produce. Taken together, our results suggest that humans are exposed to substantially different bacteria depending on the types of fresh produce they consume with differences between conventionally and organically farmed varieties contributing to this variation.

Project description:In the central plains of North America, the beetle family Silphidae comprised two subfamilies, Silphinae and Nicrophorinae, differentiated by reproductive behaviors. Silphinae, known as carrion beetles, feed on carrion and fly larvae and produce free-living larvae that receive no parental care. Adult Nicrophorinae, known as burying beetles, prepare a vertebrate carcass into a brood ball and provide biparental care to their offspring. Preparation of a brood ball involves coating the carcass in antimicrobial oral and anal secretions. These secretions contain a community of microbes, referred to as the secretion microbiome, which inhibit carcass microbe succession, preventing normal decomposition. Here, the secretion microbiomes of five species of Nicrophorinae and two species of Silphinae, both sampled from Oklahoma, with additional Nicrophorinae from Nebraska, were characterized using culture-independent analyses to understand and decipher factors shaping diversity and community structure. We identify the core secretion microbiome across Silphidae and show that, while the host subfamily, secretion type, and collection locality had no significant effect on the bacterial community alpha diversity, these factors significantly influenced bacterial community structure. Global and local tests of phylogenetic associations identified 14 genera with phylogenetic signals to the host subfamily and species. Description of the bacterial communities present in silphid secretions furthers our understanding of how these beetles interact with microbes for carcass nutrient processing. Future culture-dependent studies from silphid secretions may identify novel antimicrobials and nontoxic compounds that can act as meat preservatives or sources for antimicrobials.IMPORTANCEThe manuscript explores the secretion bacterial community of carrion and burying beetles of the central plains of North America. A core secretion microbiome of 11 genera is identified. The host subfamily, secretion type, and collection locality significantly affects the secretion microbiome. Future culture-dependent studies from silphid secretions may identify novel antimicrobials and nontoxic compounds that can act as meat preservatives or sources for antimicrobials.

Dataset Information

Culture dependent and independent analysis of bacterial communities associated with commercial salad leaf vegetables.

Publications

Culture dependent and independent analysis of bacterial communities associated with commercial salad leaf vegetables.

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