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Self-transmissible and mobilizable plasmids contribute to the emergence and spread of multidrug-resistant bacteria by enabling the horizontal transfer of acquired antibiotic resistance. The objective of this study was to capture and characterize self-transmissible and mobilizable resistance plasmids from a coastal wetland impacted by urban stormwater runoff and human wastewater during the rainy season. Four plasmids were captured, two self-transmissible and two mobilizable, using both mating and enrichment approaches. Plasmid genomes, sequenced with either Illumina or PacBio platforms, revealed representatives of incompatibility groups IncP-6, IncR, IncN3, and IncF. The plasmids ranged in size from 36 to 144 kb and encoded known resistance genes for most of the major classes of antibiotics used to treat Gram-negative infections (tetracyclines, sulfonamides, β-lactams, fluoroquinolones, aminoglycosides, and amphenicols). The mobilizable IncP-6 plasmid pLNU-11 was discovered in a strain of Citrobacter freundii enriched from the wetland sediments with tetracycline and nalidixic acid, and encodes a novel AmpC-like β-lactamase (blaWDC-1), which shares less than 62% amino acid sequence identity with the PDC class of β-lactamases found in Pseudomonas aeruginosa. Although the IncR plasmid pTRE-1611 was captured by mating wetland bacteria with P. putida KT2440 as recipient, it was found to be mobilizable rather than self-transmissible. Two self-transmissible multidrug-resistance plasmids were also captured: the small (48 kb) IncN3 plasmid pTRE-131 was captured by mating wetland bacteria with Escherichia coli HY842 where it is seemed to be maintained at nearly 240 copies per cell, while the large (144 kb) IncF plasmid pTRE-2011, which was isolated from a cefotaxime-resistant environmental strain of E. coli ST744, exists at just a single copy per cell. Furthermore, pTRE-2011 bears the globally epidemic blaCTX-M-55 extended-spectrum β-lactamase downstream of ISEcp1. Our results indicate that urban coastal wetlands are reservoirs of diverse self-transmissible and mobilizable plasmids of relevance to human health.

Food web dynamics consist of processes that affect ecosystem structure and functioning. EcoTroph (ET) is a recently developed approach and software for modeling aquatic ecosystems, articulated entirely around the trophic level concept. Here, we used ET to investigate impacts of 2 trophic controls (i.e. foraging arena and top-down controls) on marine ecosystem trophic flows and associated fishing effects. A new version of the ET model accounting for the foraging arena theory was developed. Cross impacts of the 2 trophic controls and different fishing scenarios were analyzed using a virtual ecosystem. Results showed that foraging arena controls decreased the resistance and production of an ecosystem facing increasing fishing mortality. In contrast, the inclusion of top-down controls resulted in a more resistant ecosystem, with a decrease in the kinetics of trophic flows at lower trophic levels (TLs) when the abundance of higher TLs is reduced by fishing. These 2 controls increased the interactions between TLs, and, in part, shaped fishing impacts at the ecosystem scale. Then, we applied ET to 3 real ecosystems which have been previously modeled using Ecopath with Ecosim (EwE). EcoTroph and Ecosim predictions related to changes in fishing effort were compared, and showed that accounting for trophic controls enabled EcoTroph to mimic Ecosim models, and better reflect associated changes in trophic flows. The 3 case studies exhibited different behaviors: while the pelagic ecosystem had strong foraging arena controls but no top-down controls, the other ecosystems were characterized by weaker foraging arena controls but effective top-down controls.

Sustainable exploitation of renewable resources depends on the existence of a reproductive surplus, which is determined by the balance between births, deaths, and somatic growth. The reproductive surplus differs spatially and temporally as environmental conditions vary, and even in the absence of exploitation, change is the rule and constancy is the exception. Sustainable yields may be estimated by direct experimentation, observation of natural systems, or deduction from biological understanding. Each of these approaches has limitations, and for large-scale unique resources, the only way to determine the response of the population to harvesting is by direct exploitation. To find the maximum potential yield, the resource must be overexploited at some time, or very similar resources must have been overexploited. Temporal changes in environmental conditions mean that information on sustainability collected in the past may have limited applicability in the future. The unregulated dynamic of exploiters is to push the resources to overexploitation, and even when regulated, exploiters have been very successful at modifying their behavior so that regulations are less effective than anticipated. The most successful institutions at maintaining sustainability have been small-scale community or pri

Using theoretical arguments and a computer simulation model, we have concluded that in- creased yields may be obtained from some big game populations by harvesting only once every several years. Since productivity per female increases with age in most big game populations, and since hunting shifts the age distribution towards younger animals, annual harvest may result in lowered mean produc- tivity. Periodic harvest may help prevent changes in productivity. Computer simulation suggests that yield may be increased by 10 to 20 percent by periodic harvest and that the best interval between har- vests is usually 24 years. Abstract: Using theoretical arguments and a computer simulation model, we have concluded that in- creased yields may be obtained from some big game populations by harvesting only once every several years. Since productivity per female increases with age in most big game populations, and since hunting shifts the age distribution towards younger animals, annual harvest may result in lowered mean produc- tivity. Periodic harvest may help prevent changes in productivity. Computer simulation suggests that yield may be increased by 10 to 20 percent by periodic harvest and that the best interval between har