Samples are organically (Org) and PARP inhibitor conventionally grown baby spinach (Spi), romaine lettuce (Rom), red leaf lettuce (Red), iceberg lettuce (Ice), and green leaf lettuce (Gre) and include intact and surface sterilized (S) subsamples. Community similarity is determined from Jaccard similarity scores followed by nonmetric multidimensional

scaling (A) or UPGMA dendrogram construction (B). Analyses are run on subsamples of 1507 sequences from each sample, and show the mean outcome of 1000 individual subsampling runs. Comparing the culture dependent and culture independent approaches A paradigm in microbial ecology is that culture-based techniques only recover 1-10% click here of the true bacterial diversity within an environment [29, 30] and that molecular surveys of bacterial communities yield dramatically different results than traditional culture approaches. Comparing GSI-IX the number of different isolated bacterial species (31 total) obtained in this study to the overall number of OTUs (634 total) obtained from pyrosequencing would initially seem to confirm this concept. However, many of the proportionally dominant taxa identified by the pyrosequencing approach were actually represented by isolates (Tables  2 and 3). A similar outcome has been reported for Arabidopsis thaliana, in that

many of the endophytic populations detected by pyrosequencing were related to culturable Urease species [31]. In the current study, Pseudomonas spp. were the most prevalent taxa in the majority of samples according to the molecular approach, and strains of Pseudomonas were isolated from all but two samples (surface sterilized iceberg lettuce). Other taxa that were proportionally dominant in some samples according to community sequencing included Flavobacterium, Stenotrophomonas, Serratia, Erwinia, Xanthomonas, and Pantoea; all of which were also obtained as isolates, often from samples that showed higher proportions of that taxa in the sequence collection.

Our culture approach was by no means exhaustive (just two media types, and only selecting colonies that appeared to be abundant based on morphology), suggesting that compared to other environmental samples it may be relatively easy to isolate the more dominant members of some plant-associated bacterial communities, or at least those associated with salad produce. A notable exception was Ralstonia which, while absent from nine samples, was the most abundant sequence type detected in six samples but was not obtained as an isolate. Species of Ralstonia are typically capable of growth on TSA, but colonies are commonly small [32] so may have not been chosen during our isolate selection. Ralstonia was, however, one of the few taxa to show significant differences between samples, being present in greater proportions in surface sterilized and/or conventionally grown samples.