Our BrdU work is a collaboration with Gabrielle Rocap.
Bacterial growth rates and population dynamics are fundamentally linked to organic matter processing. We use four general approaches to understanding the links between microbial community structure and carbon flow:
- routine measurement of thymidine incorporation into bacterial DNA
- measurement of degradation rates for specific organic compounds
- measurement of polymer hydrolysis patterns during microbial degradation
- incorporation of BrdU into DNA from specific bacterial communities
One of our research goals is the development of tools to better understand the activities of bacteria in ocean waters and sediments, and the role of specific types of bacteria in mediating important biogeochemical reactions. To this end, we have developed a techique to measure the actively growing bacterial portion of a mixed community (Evans et al., submitted to Limnology and Oceanography Methods – download this from our publications page).
There is a long-standing need in aquatic microbial ecology for phylogenetic methods that can distinguish actively-growing heterotrophic bacteria from those that comprise the total community. The method we developed (Evans et al., submitted) employs the thymidine analog bromodeoxyuridine (BrdU) to label DNA from actively-growing bacteria for subsequent antibody capture and isolation. The diversity of 16S rRNA genes in BrdU-containing DNA was compared to that of the total bacterial community using terminal restriction length polymorphism (T-RFLP) and multidimensional scaling (MDS). This relatively straightforward approach is a substantial modification of previously reported method (URBACH, E. VERGIN, K.L., GIOVANNONI, S.J. 1999. Appl. Environ. Microbiol. 65: 1207-1213) and allows a much more detailed comparison of actively-growing and total community composition. Our results from the fjords of Vancouver Island, B.C. showed that the compositions of the actively-growing and total bacterial communities are distinct. In addition, variations in the composition of the actively-growing community are correlated with environmental parameters in these fjords such as salinity. This method provides the ability to identify members of a complex population that are actively-growing, which will allow more detailed studies of environmental controls on the composition of the total bacterial community.
The image below, figure 4 from Evans et al, submitted shows the divergence between the actively growing bacteria and the total bacterial community as a function of increasing salinity. That is, at higher salinities, fewer and fewer members of the total bacterial community are growing.
