Zoomed-in version of upper left hand section of a snapshot at generation 1000.

<p>B/C = 0.62, help = 0.09. Red lines outline some cases in which nonproducers exist at the boundary between empty space and clusters of altruists. In all figures, yellow = nonproducers, green = producer, white = empty slot.</p

Two-dimensional snapshots of the 10,000 slot torus.

<p>B/C = 0.62, help = 0.14 (this “help” value was chosen, in part, as the result of unpublished experimental work on β–lactamase secretion in producer cells). a) Generation 1, b) Generation 10, c) Generation 20, d) Generation 40, e) Generation 300 and f) Generation 1000. Note that for generations 1–999, any yellow (nonproducers) cells surrounded by only yellow or by only yellow and white cells would die and be replaced the next generation.</p

Two-dimensional snapshots of the 10,000 slot torus.

<p>B/C = 0.56, help = 0.19. a) Generation 1, b) Generation 10, c) Generation 20, d) Generation 40, e) Generation 300 and f) Generation 1000. Note that for generations 1–999, any yellow (nonproducers) cells surrounded by only yellow or by only yellow and white cells would die and be replaced the next generation.</p

Oil Biodegradation and Oil-Degrading Microbial Populations in Marsh Sediments Impacted by Oil from the Deepwater Horizon Well Blowout

To study hydrocarbon biodegradation in marsh sediments impacted by Macondo oil from the <i>Deepwater Horizon</i> well blowout, we collected sediment cores 18–36 months after the accident at the marshes in Bay Jimmy (Upper Barataria Bay), Louisiana, United States. The highest concentrations of oil were found in the top 2 cm of sediment nearest the waterline at the shorelines known to have been heavily oiled. Although petroleum hydrocarbons were detectable, Macondo oil could not be identified below 8 cm in 19 of the 20 surveyed sites. At the one site where oil was detected below 8 cm, concentrations were low. Residual Macondo oil was already highly weathered at the start of the study, and the concentrations of individual saturated hydrocarbons and polycyclic aromatic hydrocarbons continued to decrease over the course of the study due to biodegradation. Desulfococcus oleovorans, Marinobacter hydrocarbonoclasticus, Mycobacterium vanbaalenii, and related mycobacteria were the most abundant oil-degrading microorganisms detected in the top 2 cm at the oiled sites. Relative populations of these taxa declined as oil concentrations declined. The diversity of the microbial community was low at heavily oiled sites compared to that of the unoiled reference sites. As oil concentrations decreased over time, microbial diversity increased and approached the diversity levels of the reference sites. These trends show that the oil continues to be biodegraded, and microbial diversity continues to increase, indicating ongoing overall ecological recovery