nai

Project Progress

Molecular characterization of microbial diversity within a sulfur spring network

Sulfur springs have traditionally provided an excellent framework within which to study microbial communities in the contexts of their geochemical environments. We have investigated a sulfur spring network that has multiple discharge sites along a fault, focusing on two sites (MS4 and MS11) that were chosen based on flow rate, chemistry, and the presence of eye-visible white biofilms. Isotopic analyses of the spring waters indicate that they discharge from a common source, but MS4 receives more meteoric input, thus is more dilute. Correcting for dilution, the composition of major chemical species between both sites is comparable, dominated by sodium, calcium, and sulfide. However, the total sulfide concentration at MS11 nearly five times that of MS4.

To determine the effects of geochemical factors on population structure we used multiple methods to examine the biofilms: Phospholipid fatty acid analysis (PLFA), terminal restriction fragment length polymorphism (TRFLP), 16S rRNA gene library construction, and 16S ‘Phylochip’ microarray experiments. PLFA yielded almost no information, as both community profiles were essentially identical. TRFLP experiments indicate that the two communities are dominated by a few organisms, with MS4 having a slightly greater species richness. 16S rRNA gene libraries provided the highest resolution of variation between the two sites (~150 OTUs) and revealed considerable micro-heterogeneity. Both spring communities are dominated by sulfur-oxidizing members of Gamma- and Epsilonproteobacteria. MS4 shows a more diverse community structure than MS11, with a significant amount of Beta- and Alphaproteobacteria, while MS11 shows a greater micro-diversity of sulfur-oxidizing members.

The 16S ‘Phylochip’ provides a new method to analyze microbial diversity, providing much higher resolution and more complete insights than can be achieved via library construction and sequencing. We detected 320 OTUs and were able to corroborate the greater level of microbial diversity at MS4. Results indicate that differences in the bacterial community structures in the two spring sites may be due primarily to differences in the sulfide concentration and that this concentration difference can significantly affect total diversity levels.

{{ 1 }}

{{ 2 }}