The balance between the storage of vascular plant carbon in soils, oxidation to carbon dioxide, and export via rivers affects calculations of the strength of terrestrial ecosystems as carbon sinks. The magnitude and timescale of the riverine export pathway are not well constrained. Here we use radiocarbon dating of lignin phenols to show that plant‐derived carbon carried by suspended sediment of the Mekong River is very young, having been produced within the last 18 years. Further, this plant‐derived carbon remains young during times of the year when bulk carbon varies from modern to over 3000 radiocarbon years old. Our results demonstrate that primary‐production derivatives are exported rapidly and suggest that the age of riverine lignin is similar to estimates of the residence time of terrestrial organic carbon in tropical catchments. These results are relevant for modeling predictions of the influence of the terrestrial biosphere on atmospheric carbon dioxide levels.

Background Despite the strong evidence of HPV infection as the etiological agent in a subset of oral cancer, oral α-HPV detection is rare in healthy individuals, and little is known of the existing of novel HPV types in oral cavity. Objective We determined whether novel HPV types can be isolated from oral rinse samples collected from healthy individuals. Study design We performed rolling circle amplification (RCA) coupled with degenerated PCR assay on 48 oral rinse samples to amplify novel HPV types. Full length HPV DNA was cloned using long range PCR. Quantitative type specific Taqman assays were used to determine the prevalence of novel HPV types in 158 archived oral tissue samples. Results We were able to isolate four novel human papillomavirus types. Full length HPV DNA was cloned for three of the four novel HPV types. All four HPV types belong to the genus Gammapapillomavirus (γ-PV), where HPV 171 is most closely related to HPV 169, showing 88% similarity; HPV 172 is most closely related to HPV 156, showing 70% similarity; HPV 173 is most closely related to HPV 4, showing 73% similarity; oral sample lavage (OSL) 37 is most closely related to HPV 144, showing 69% similarity. Finally, we showed that HPV 173 was rarely present in oral tissues (2/158), HPV 172 was only detected in normal oral tissues (25/76), and HPV 171 was more prevalent in malignant oral tissues (17/82 vs 10/76, p=0.21). Conclusions Novel γ-HPV types are present in oral cavity of healthy individuals.

Many graduate programs in environmental studies attempt to foster specialized knowledge and technical skills alongside interdisciplinary collaboration and integration. We discuss strategies for addressing these distinct-sometimes competing-goals in Evergreen State College's Graduate Program on the Environment. Key strategies include (1) designing an academic program that balances specialization and integration; (2) approaching course planning with a "backward design model" that focuses on teaching outcomes rather than "covering" disciplinary content; (3) designing group assignments that require collaborative and multidisciplinary research and networking among students; (4) approaching thesis projects using place-based issues or research problems/questions developed in conjunction with local or regional organizations and a clear identification of relevant communities of practice to inform the scholarly work and analysis. Finally, we address the challenge of creating equitable social dynamics in teaching teams and offer reflections based on our 30-year tradition of collaborative team-teaching at the graduate level.

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The peripheral blood mononuclear cells (PBMC) from 5 individuals immune to typhus group rickettsiae and from 13 nonimmune individuals were stimulated in vitro for 7 days with typhus group rickettsial antigen (TGRA). At the end of day 7, lysis of the natural killer (NK)-susceptible target K562 by these PBMC was determined. As controls, PBMC from both groups of donors were cultured in vitro for 7 days without antigen or were freshly isolated, and lysis of the K562 target was determined. There was no significant difference between the level of NK activity in freshly isolated PBMC from immune and nonimmune donors. PBMC from immune donors which were stimulated with antigen for 7 days exhibited significantly greater NK activity than did the control population, which was cultured for 7 days without antigen. PBMC from immune donors which were stimulated with TGRA demonstrated significantly higher NK activity than the same PBMC stimulated with antigen derived from an antigenically unrelated rickettsia, Coxiella burnetii. There was no significant difference, however, in the level of NK activity of nonimmune antigen-stimulated PBMC compared with that of the same PBMC population cultured without antigen. Most of the antigen-stimulated NK activity was mediated by Leu-ll-positive cells as determined by electronic cell sorting. The ability of TGRA to sustain the NK activity of PBMC from immune donors was abolished when the T4/Leu-3-positive population of lymphocytes was eliminated by positive or negative selection prior to antigen stimulation. The ability of TGRA to sustain the NK activity of PBMC from immune donors was also significantly decreased in the presence of antibodies against human interleukin-2. The results suggest that the activity of human NK cells can be sustained in vitro by antigen-specific T helper cells and that the effect of the T helper cell is mediated, at least in part, by interleukin-2.