Matter

Event Date: 
Wednesday, April 29, 2015 - 19:00 - 19:45
Institution: 
University of Southern California
Title: 

Bridging the gap between functional genes and biogeochemistry: a DMSP case study

Abstract: 

A large fraction of the surface ocean food web is active in producing and cycling both dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS).  In addition to the potential climatic significance of DMS production, the role that these compounds play in mediating ecosystem dynamics remains unknown.  An interdisciplinary dataset of biological, chemical and physical measurements was used to test current hypotheses of the role of light and carbon supply in regulating upper-ocean sulfur cycling in oligotrophic regions. Our results suggest that UV-A radiation dose plays an important role in both phytoplankton DMS production and bacterial DMSP degradation. We suggest a modified ‘bacterial switch’ hypothesis where the prevalence of different bacterial DMSP degradation pathways is regulated by a complex set of factors including carbon supply, temperature, and UV-A dose. Finally, numerical models of varying complexity were used to link genetic and enzyme data to biogeochemical rates.

Event Date: 
Wednesday, June 27, 2012 - 19:15 - 20:00
Institution: 
Faculty of Agriculture & Environment, University of Sydney, Sydney, NSW.
Title: 

Sulfur cycling in the rhizosphere: the role of sulfatase and sulfonatase diversity.

Abstract: 

Growth of healthy, high-yielding crop plants requires a stable input not only of nitrogen and phosphorus, but also of sulfur (S). Although S is naturally present in soils, it is usually bound in organic form as sulfate esters or sulfonates, which are not directly bioavailable to plants. Sulfur can be supplemented by addition of inorganic fertilizer, but most sulfate for plant nutrition is provided by microbial turnover of organically-bound sulfur. To identify the rhizosphere organisms responsible for this turnover, we focused on the key genes atsA, which encodes arylsulfatase, and asfA, which is required for aryldesulfonation. Functional T-RFLP analysis was used to analyse atsA diversity in a range of agricultural and natural soils, and clear atsA community differences associated with land use and soil/bedrock types were observed, which were mirrored in the arylsulfatase activity of the cultivable fraction of the population. Soil arylsulfatase activity is routinely assayed as a measure of soil health, but these data highlight the need for detailed studies on arylsulfatase gene diversity in the soil. Sulfonatase diversity was measured in rhizospheres of field-grown wheat plants and in a sulfate-limited Agrostis-dominated grassland, and the effect of adding sulfate in long-term or short-term treatments was tested. Functional asfA community analysis showed that desulfonation genes from both wheat and Agrostis rhizospheres were dominated by Variovorax and Polaromonas species. This distribution of taxa was also found in a cultivation-dependent analysis, and these genera appear to be key players in rhizosphere sulfonate transformations in several environments. Increasing our understanding of the rhizosphere microbes that catalyse soil organosulfur turnover will allow us to develop management practices to maximize soil sulfur availability, and minimize the costs associated with fertilization.

Syndicate content