Produce is one of the most popular food commodities. Unfortunately, leafy greens can be a reservoir of transferable antibiotic resistance genes. We found that IncF and IncI plasmids were the most prevalent plasmid types in E. coli isolates from produce. This study highlights the importance of the rare microbiome associated with produce as a source of antibiotic resistance genes that might escape cultivation-independent detection, yet may be transferred to human pathogens or commensals.
In a field experiment, Pseudomonas cepacia J82rif and JSlrif increased sunflower emergence in the presence of the fungus Sclerotinia sclerotiorum. Pyrrolnitrin, aminopyrrolnitrin, and monochloroaminopyrrolnitrin were isolated from J82 and identified by using thin-layer chromatography, high-performance liquid chromatography, and electron impact-mass, UV, and infrared spectroscopy. In growth chamber experiments, two antibiosis-negative mutants were not different from the parent strain in protecting the seeds from the fungus.
25Produce is increasingly recognized as a reservoir of human pathogens and transferable 26 antibiotic resistance genes. This study aimed to explore methods to characterize the 27 transferable resistome of bacteria associated with produce. Mixed salad, arugula, and 28 cilantro purchased from supermarkets were analyzed by means of cultivation-and DNA-29 based methods. Before and after a nonselective enrichment step, tetracycline (tet) 30 resistant Escherichia coli were isolated and plasmids conferring tet resistance were 31 captured by exogenous plasmid isolation. Tet resistant E. coli isolates, transconjugants 32 and total community (TC)-DNA from the microbial fraction detached from leaves or after 33 enrichment were analyzed for the presence of resistance genes, class 1 integrons and 34 various plasmids by real-time PCR and PCR-Southern blot hybridization. Real-time 35 PCR primers were developed for IncI and IncF plasmids. Tet resistant E. coli isolated 36 from arugula and cilantro carried IncF, IncI1, IncN, IncHI1, IncU and IncX1 plasmids. 37 Three isolates from cilantro were positive for IncN plasmids and bla CTX-M-1 . From mixed 38 salad and cilantro, IncF, IncI1, and IncP-1β plasmids were captured exogenously. 39 Importantly, whereas direct detection of IncI and IncF plasmids in TC-DNA failed, these 40 plasmids became detectable in DNA extracted from enrichment cultures. This confirms 41 that cultivation-independent DNA-based methods are not always sufficiently sensitive to 42 detect the transferable resistome in the rare microbiome. In summary, this study 43showed that an impressive diversity of self-transmissible multiple resistance plasmids 44 was detected in bacteria associated with produce that is consumed raw, and exogenous 45 capturing into E. coli suggests that they could transfer to gut bacteria as well. 46 47 48Produce is one of the most popular food commodities. Unfortunately, leafy greens can 49 be a reservoir of transferable antibiotic resistance genes. We found that IncF and IncI 50 plasmids were the most prevalent plasmid types in E. coli isolates from produce. This 51 study highlights the importance of the rare microbiome associated with produce as a 52 source of antibiotic resistance genes that might escape cultivation-independent 53 detection, yet may be transferred to human pathogens or commensals.
Prokaryotes, EPS and Soil Microaggregation would diminish importance of EPS, the parent material richest in inorganic C resulted in a significant effect of EPS-saccharide contents on microaggregation according to the structural equation model. For the inorganic C poor site, EPS-saccharide had no observed direct effect on microaggregation. Based on our results we conclude that the availability of decomposable OM influences the prokaryotic community composition and thereby triggers EPS production whereas large contents of polyvalent cations promote the stabilizing effect of EPS on microaggregates.
We investigated the effects of substrate (cellulose or starch) and different clay contents on the production of microbial extracellular polymeric substances (EPS) and concomitant development of stable soil aggregates. Soils were incubated with different amounts of montmorillonite (+ 0.1%, + 1%, + 10%) both with and without two substrates of contrasting quality (starch and cellulose). Microbial respiration (CO2), biomass carbon (C), EPS-protein, and EPS-polysaccharide were determined over the experimental period. The diversity and compositional shifts of microbial communities (bacteria/archaea) were analysed by sequencing 16S rRNA gene fragments amplified from soil DNA. Soil aggregate size distribution was determined and geometric mean diameter calculated for aggregate formation. Aggregate stabilities were compared among 1–2-mm size fraction. Starch amendment supported a faster increase than cellulose in both respiration and microbial biomass. Microbial community structure and composition differed depending on the C substrate added. However, clay addition had a more pronounced effect on alpha diversity compared to the addition of starch or cellulose. Substrate addition resulted in an increased EPS concentration only if combined with clay addition. At high clay addition, starch resulted in higher EPS concentrations than cellulose. Where additional substrate was not provided, EPS-protein was only weakly correlated with aggregate formation and stability. The relationship became stronger with addition of substrate. Labile organic C thus clearly plays a role in aggregate formation, but increasing clay content was found to enhance aggregate stability and additionally resulted in the development of distinct microbial communities and increased EPS production.
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