Influence of Sulfide and Temperature on Species Composition and Community Structure of Hot Spring Microbial Mats

Abstract

In solfataric fields in southwestern Iceland, neutral and sulfide-rich hot springs are characterized by thick bacterial mats at 60 to 80°C that are white or yellow from precipitated sulfur (sulfur mats). In low-sulfide hot springs in the same area, grey or pink streamers are formed at 80 to 90°C, and a Chloroflexus mat is formed at 65 to 70°C. We have studied the microbial diversity of one sulfur mat (high-sulfide) hot spring and one Chloroflexus mat (low-sulfide) hot spring by cloning and sequencing of small-subunit rRNA genes obtained by PCR amplification from mat DNA. Using 98% sequence identity as a cutoff value, a total of 14 bacterial operational taxonomic units (OTUs) and 5 archaeal OTUs were detected in the sulfur mat; 18 bacterial OTUs were detected in the Chloroflexus mat. Although representatives of novel divisions were found, the majority of the sequences were >95% related to currently known sequences. The molecular diversity analysis showed that Chloroflexus was the dominant mat organism in the low-sulfide spring (1 mg liter ؊1 ) below 70°C, whereas Aquificales were dominant in the high-sulfide spring (12 mg liter ؊1 ) at the same temperature. Comparison of the present data to published data indicated that there is a relationship between mat type and composition of Aquificales on the one hand and temperature and sulfide concentration on the other hand.Sulfide-rich hot springs with neutral or alkaline pH are relatively rare in most geothermal areas in the world. However, these types of hot springs are rather common in Iceland due to high ground water level and climatic conditions, i.e., from melting snow and rain. Bacteria that thrive in such springs often form long streamers or mats, but the appearance of the mats and the types of bacteria in them seem to vary depending on the sulfide concentration, pH, temperature, and other chemical and physical factors (6,7,10,11,12,20,33). Many Icelandic hot springs have sulfide concentrations as high as 30 mg liter Ϫ1 and, under such conditions, thick bacterial mats which can be spectacularly white or bright yellow from precipitated sulfur are formed.The diversity of many microbial ecosystems has now been studied with different molecular methods, such as analysis of small-subunit (SSU) rRNA by sequencing, denaturing gradient gel electrophoresis, or restriction fragment length polymorphism analyses. These studies show that the diversity of microbial ecosystems is typically 100 to 1,000 times greater than that shown by cultivation alone (14,15,22,23,30,31). The sequencing of rRNA genes from environmental samples is very informative, since it provides information on both the phylogenetic relationship and the population structure of the microbial community. With increased understanding of the role and importance of microbes in many ecosystems, the benefit of microbial diversity studies is being recognized. The practical value of these methods is already widespread, as they can be used to study the performance of wastewater treatment plants (27), monitor changes upo...

Sulfurihydrogenibium subterraneum gen. nov., sp. nov., from a subsurface hot aquifer

“…Phylogenetic analysis indicated that strain HGMK1 T is most closely related to the uncultivated environmental clones SRI-40 (Skirnisdottir et al, 2000) and NAK-14 (Yamamoto et al, 1998), but distantly related to the cultivated strains P. guaymasensis EX-H2 T , P. marina EX-H1 T (Götz et al, 2002) and Hydrogenothermus marinus VM1 T (Stöhr et al, 2001). P. marina EX-H1 T and P. guaymasensis EX-H2 T were respectively isolated from deep-sea hydrothermal vent sulfide structures in the EPR (9uN) and the Guaymas Basin (Götz et al, 2002).…”

“…The most similar rDNA sequences were those from the environmental clones SRI-40 (97?5 %) (Skirnisdottir et al, 2000) and NAK-14 (97?5 %) (Yamamoto et al, 1998), respectively obtained from Icelandic and Japanese hot spring microbial mats (Fig. 1), and from the cultivated strains Persephonella guaymasensis EX-H2 T (91?1 %) and Persephonella marina EX-H1 T (90?6 %) (Götz et al, 2002) ( Fig.…”

“…Culture-resistant phylotypes of thermophiles within the order Aquificales are potentially prevalent in microbial communities occurring in a certain temperature range (50-90 uC) in habitats in global terrestrial hot spring environments such as in Yellowstone National Park (Hugenholtz et al, 1998;Reysenbach et al, 1994Reysenbach et al, , 2000a, Iceland (Skirnisdottir et al, 2000;Takacs et al, 2001) and Japan (Yamamoto et al, 1998), in subterranean hot springs (Marteinsson et al, 2001) and even in deep-sea hydrothermal vent systems (Reysenbach et al, 2000b). These phylotypes form a clade, probably corresponding to a novel family, that is separate from the HydrogenobaculumAquifex-Hydrogenobacter-Thermocrinis lineage (family Aquificaceae) within the order Aquificales (Takai et al, 2002).…”

Caldisericum exile gen. nov., sp. nov., an anaerobic, thermophilic, filamentous bacterium of a novel bacterial phylum, Caldiserica phyl. nov., originally called the candidate phylum OP5, and description of Caldisericaceae fam. nov., Caldisericales ord. nov. and Caldisericia classis nov.

“…The candidate phylum OP5 was represented originally by environmental clone sequences retrieved from the Obsidian Pool in Yellowstone National Park (Hugenholtz et al, 1998a) and indicated an independent phylum-level lineage in the domain Bacteria (Hugenholtz et al, 1998a, b;Rappé & Giovannoni, 2003). Since then, environmental clone sequences belonging to this phylum have been detected in various environments (Dojka et al, 1998;Humayoun et al, 2003;Inagaki et al, 2006;Kaksonen et al, 2004;Ley et al, 2006;Skirnisdottir et al, 2000;Teske et al, 2002). Strain AZM16c01 T was the first cultivable isolate accommodated in OP5.…”

Persephonella hydrogeniphila sp. nov., a novel thermophilic, hydrogen-oxidizing bacterium from a deep-sea hydrothermal vent chimney

“…The last lineage largely consisted of a number of previously uncultivated environmental rDNA clones obtained from global terrestrial hot-spring environments such as in Yellowstone National Park (Hugenholtz et al, 1998;Reysenbach et al, 2000a), Iceland (Skirnisdottir et al, 2000;Takacs et al, 2001) and Japan (Yamamoto et al, 1998), and in subterranean hot springs (Marteinsson et al, 2001), and even in deep-sea hydrothermal vent systems (Reysenbach et al, 2000b, c). Recently, however, several representative strains of this lineage such as Hydrogenothermus (Stöhr et al, 2001), Persephonella (Reysenbach et al, 2000a;Götz et al, 2002) and a potentially new genus of strains (Takai et al, 2002) have been successfully isolated from shallow and deep marine hydrothermal vent environments and from a subsurface hot aquifer environment.…”