Background Twelve populations of the bacterium, Escherichia coli, adapted to a simple, glucose-limited, laboratory environment over 10,000 generations. As a consequence, these populations tended to lose functionality on alternative resources. I examined whether these populations in turn became inferior competitors in four alternative environments. These experiments are among the first to quantify and compare dimensions of the fundamental and realized niches. Results Three clones were isolated from each of the twelve populations after 10,000 generations of evolution. Direct competition between these clones and the ancestor in the selective environment revealed average fitness improvements of ~50%. When grown in the wells of Biolog plates, however, evolved clones grew 25% worse on average than the ancestor on a variety of different carbon sources. Next, I competed each evolved population versus the ancestor in four foreign environments (10-fold higher and lower glucose concentration, added bile salts, and dilute LB media). Surprisingly, nearly all populations were more fit than the ancestor in each foreign environment, though the margin of improvement was least in the most different environment. Most populations also evolved increased sensitivity to novobiocin. Conclusions Reduced functionality on numerous carbon sources suggested that the fundamental niche of twelve E. coli populations had narrowed after adapting to a specific laboratory environment. However, in spite of these results, the same populations were competitively superior in four novel environments. These findings suggest that adaptation to certain dimensions of the environment may compensate for other functional losses and apparently enhance the realized niche.

Background Laboratory experiments under controlled conditions during thousands of generations are useful tools to assess the processes underlying bacterial evolution. As a result of these experiments, the way in which the traits change in time is obtained. Under these conditions, the bacteria E. coli shows a parallel increase in cell volume and fitness. Results To explain this pattern it is required to consider organismic and population contributions. For this purpose we incorporate relevant information concerning bacterial structure, composition and transformations in a minimal modular model. In the short time scale, the model reproduces the physiological responses of the traits to changes in nutrient concentration. The decay of unused catabolic functions, found experimentally, is introduced in the model using simple population genetics. The resulting curves representing the evolution of volume and fitness in time are in good agreement with those obtained experimentally. Conclusions This study draws attention on physiology when studying evolution. Moreover, minimal modular models appear to be an adequate strategy to unite these barely related disciplines of biology.

,The data presents the antimicrobial susceptibility testing results in three separate files: 1) third generation cephalosporin resistant E. coli isolates obtained on cefotaxime supplemented media; 2) extended spectrum beta-lactamase (ESBL) producing E. coli, and 3) ESBL-producing Klebsiella, Enterobacter and Citrobacter species obtained on chromogenic media. The data was generated as part of a research project that evaluated the impact of tylosin supplementation of feedlot cattle on the dynamics of antimicrobial resistant fecal bacteria. The study was a longitudinal design with periodic sampling of fecal samples from individual animals over the entire feeding period. Two publications from the project, one describing the study design in detail, and the other specifically reporting on these data, are linked to the database.,Resources in this dataset:,

Background Experimental populations of Escherichia coli have evolved for 20,000 generations in a uniform environment. Their rate of improvement, as measured in competitions with the ancestor in that environment, has declined substantially over this period. This deceleration has been interpreted as the bacteria approaching a peak or plateau in a fitness landscape. Alternatively, this deceleration might be caused by non-transitive competitive interactions, in particular such that the measured advantage of later genotypes relative to earlier ones would be greater if they competed directly. Results To distinguish these two hypotheses, we performed a large set of competitions using one of the evolved lines. Twenty-one samples obtained at 1,000-generation intervals each competed against five genetically marked clones isolated at 5,000-generation intervals, with three-fold replication. The pattern of relative fitness values for these 315 pairwise competitions was compared with expectations under transitive and non-transitive models, the latter structured to produce the observed deceleration in fitness relative to the ancestor. In general, the relative fitness of later and earlier generations measured by direct competition agrees well with the fitness inferred from separately competing each against the ancestor. These data thus support the transitive model. Conclusion Non-transitive competitive interactions were not a major feature of evolution in this population. Instead, the pronounced deceleration in its rate of fitness improvement indicates that the population early on incorporated most of those mutations that provided the greatest gains, and subsequently relied on beneficial mutations that were fewer in number, smaller in effect, or both.

,A requirement of any foodborne pathogen testing method is that it only detects live bacteria. Ethidium monoazide (EMA) and propidium monoazide (PMA) are dyes that penetrate the membranes of dead cells and form cross-linkages in the DNA, which prevents its amplification in PCR. This study investigated whether treatment with EMA or PMA would inhibit sequencing of DNA from dead Escherichia coli. Range finding experiments with qPCR were conducted to determine the optimal concentrations of EMA and PMA needed to inhibit amplification of DNA from dead cells while not influencing live cells. An EMA concentration that differentiated between live and dead cells could not be established. However, a PMA concentration of 25 µM effectively prevented qPCR amplification of DNA from dead E. coli while not impacting the amplification of live E. coli DNA. Sequencing experiments were conducted with PMA-treated live, untreated live, PMA-treated dead, and untreated dead E. coli. There were no significant differences in the detection of virulence genes of interest between the PMA-treated live, untreated live, and untreated dead E. coli. However, no DNA sequencing data was obtained from the PMA-treated dead E. coli. These results suggest that PMA could be incorporated into sample preparation methods prior to sequencing to selectively detect live cells of foodborne pathogens.,

,Foodborne pathogens are a significant cause of illness and infection with Shiga toxin-producing Escherichia coli (STEC) has the potential to produce life-threatening complications. The current methods to identify STEC in meat involve culture-based, molecular, and proteomic assays and take at least four days to complete. This time could be reduced by using long-read whole genome sequencing to identify foodborne pathogens. Therefore, the goal of this project was to evaluate using long-read sequencing to detect STEC in ground beef. The objectives of the project included: establishing optimal sequencing parameters, determining the limit of detection of all STEC virulence genes of interest in pure cultures and spiked ground beef, and evaluating selective sequencing to enhance STEC detection in ground beef. Sequencing libraries were run on Oxford Nanopore Technologies’ MinION sequencer. Optimal sequencing output was obtained using the default parameters in MinKNOW, except for setting the minimum read length to 1 kb. All genes of interest (eae, stx1, stx2, fliC, wzx, wzy, rrsC) were detected in DNA extracted from STEC pure cultures within 1 hour of sequencing, and 30X coverage was obtained within 2 hours. All virulence genes were confidently detected in STEC DNA quantities as low as 12.5 ng. In STEC inoculated ground beef, software-controlled selective sequencing improved virulence gene detection; however, several virulence genes were not detected due to high bovine DNA concentrations in the samples. Growth enrichment of inoculated meat samples in mTSB resulted in a 100-fold increase in virulence gene detection as compared to the unenriched samples. The results of this project suggest that further development of long-read sequencing protocols may result in a faster, less labor-intensive method to detect STEC in ground beef. The sequencing data from this project has been uploaded.,

,Biological soil amendments are an essential input in organic lettuce production. However, these BSAs can introduce or transfer pathogens like Escherichia coli O157:H7 to lettuce in pre-harvest environments. This study evaluated the effect of BSAs on survival of non-pathogenic and pathogenic E. coli in soils and transfer to lettuce. Romaine lettuce was grown with controlled light, temperature, and relative humidity. Soil was amended (side-dressed) with either heat treated poultry pellets (HTPP), HTPP with corn steep liquor (CSL), seabird guano (SBG), SBG with CSL, or left unamended (UA). Soils were co-inoculated with non-pathogenic, rifampicin-resistant E. coli TVS 353 and two chloramphenicol-resistant E. coli O157:H7 isolates (100 mL of 106 CFU/mL). E. coli survival over 28 days was evaluated. On day 28, Romaine lettuce was harvested, and presence of E. coli was determined.,

This data set includes information on collections of fecal samples from wild gulls (Larus spp.) at seven locations in Alaska, USA. Samples were screened for carbapenemase producing Escherichia coli (E. coli) and tested for resistance to multiple antibiotics.