Diversification of Bacterial Community Composition along a Temperature Gradient at a Thermal Spring

Abstract

To better understand the biogeography and relationship between temperature and community structure within microbial mats, the bacterial diversity of mats at a slightly alkaline, sulfide-containing hot spring was explored. Microbial mats that developed at temperatures between 75–52°C were collected from an area of approximately 1 m2 in Nakabusa, Nagano, Japan. Bacterial 16S rRNA genes from these samples were examined by terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis. T-RFLP profiles revealed 66 unique fragments (T-RFs). Based on total T-RFs observed in environmental profiles and clone libraries, a temperature effect on diversity was determined, with complexity in the community increasing as temperature decreased. The T-RF pattern indicated four distinct community assemblages related to temperature. Members of the Aquificales and particularly the sulfuroxidizing bacterium Sulfurihydrogenibium were present at all temperatures and were the dominant component of mats taken at 75–67°C. Sulfide oxidation, which persisted throughout the temperature gradient, was the presumed dominant pathway of primary production above 67°C. As temperature decreased, successive additions of anoxygenic and oxygenic phototrophs increased primary productivity, allowing for diversification of the community.

Humboldt’s spa: microbial diversity is controlled by temperature in geothermal environments

“…The dominance of Aquificae, Crenarchaeaota and Deinococcus-Thermus is consistent with previous studies of geothermal sites with temperatures above 50 1C and neutral pH (Purcell et al, 2007;Tobler and Benning, 2011;Cole et al, 2013;Hou et al, 2013;Wang et al, 2013). The Bacteria and Archaea generally observed in this study have been previously identified in other geothermal springs in Yellowstone National Park (Miller et al, 2009;Cole et al, 2013), Japan (Everroad et al, 2012), Thailand (Purcell et al, 2007) and Tibet (Yim et al, 2006;Huang et al, 2011;Hou et al, 2013;Wang et al, 2013).…”

“…Temperature effects on the species and phylum composition of microbial communities in hot springs have been reported in several studies (Yim et al, 2006;Purcell et al, 2007;Miller et al, 2009;Huang et al, 2011;Everroad et al, 2012;Cole et al, 2013;Hou et al, 2013;Wang et al, 2013). In our study, some phyla showed distinct abundance trends with pH and temperature, whereas others showed none (Supplementary Figure 8).…”

“…The lack of consensus is not surprising given the lack of statistical robustness and the possibility for site-specific effects in these studies. They may also have suffered from a focus on samples with temperatures 455 1C (Everroad et al, 2012;Cole et al, 2013;Hou et al, 2013) where the relationship is weakest. Decreasing alpha diversity with increasing temperature was most evident in our sample set from 25-65 1C, but above this the relationship flattened out compared with experimental noise (Figure 3, Supplementary Figure S1).…”

“…However, studies comparing diversity across geothermal systems remain few in number and consistent trends remain unresolved. Although some studies have noted a lack of correlation (Yim et al, 2006;Huang et al, 2011;Hou et al, 2013;Wang et al, 2013) or even a slight increase in diversity with increasing temperature (Purcell et al, 2007), others have noted a decrease in diversity with increasing temperature (Miller et al, 2009;Tobler and Benning, 2011;Everroad et al, 2012;Cole et al, 2013). Although these studies hint at underlying general patterns, they are all limited by at least one of several shortcomings: restricted methodologies that detect only the few most abundant operational taxonomic units (OTUs), such as construction of clone libraries (Yim et al, 2006;Purcell et al, 2007;Miller et al, 2009;Huang et al, 2011;Tobler and Benning, 2011;Everroad et al, 2012); low numbers of samples (o10) (Yim et al, 2006;Purcell et al, 2007;Miller et al, 2009;Tobler and Benning, 2011;Everroad et al, 2012); samples taken from a single geothermal field and therefore possibly showing site-specific trends (Yim et al, 2006;Miller et al, 2009;Everroad et al, 2012;Cole et al, 2013); or a limited temperature range (o30 1C total range) (Purcell et al, 2007;Miller et al, 2009;Everroad et al, 2012;Cole et al, 2013).…”

“…Two recent studies based on 16S rRNA gene pyrotag sequencing, the technique that assesses microbial diversity to the most depth, support the notion that extreme temperatures may restrict microbial diversity (Everroad et al, 2012;Cole et al, 2013), but other pyrotag sequencing studies with a larger number of samples and a broader temperature range do not Wang et al, 2013). The relative importance of pH versus temperature is also unknown as few studies cover wide-ranges of both temperature and pH.…”