Abstract
Planktonic sulfur oxidizers are important constituents of ecosystems in stratified water bodies, and contribute to sulfide detoxification. In contrast to marine environments, taxonomic identities of major planktonic sulfur oxidizers in freshwater lakes still remain largely unknown. Bacterioplankton community structure was analyzed in a stratified freshwater lake, Lake Mizugaki in Japan. In the clone libraries of 16S rRNA gene, clones very closely related to a sulfur oxidizer isolated from this lake, Sulfuritalea hydrogenivorans, were detected in deep anoxic water, and occupied up to 12.5% in each library of different water depth. Assemblages of planktonic sulfur oxidizers were specifically analyzed by constructing clone libraries of genes involved in sulfur oxidation, aprA, dsrA, soxB and sqr. In the libraries, clones related to betaproteobacteria were detected with high frequencies, including the close relatives of Sulfuritalea hydrogenivorans.
Highlights
As one of major effects of global warming on aquatic environments, enhanced stratification of water columns causes various secondary effects on ecosystems [1,2,3]
These clones were very closely related to the Sulfuritalea hydrogenivorans sk43HT, with sequence identities greater than 98%
The results of 16S rRNA cloning analysis targeting all bacteria suggested that Sulfuritalea hydrogenivorans (OTU_r55) was one of major planktonic bacteria in this lake, and its relative abundance in the bacterial community was greater in anoxic zones (Table 1, Fig. 1)
Summary
As one of major effects of global warming on aquatic environments, enhanced stratification of water columns causes various secondary effects on ecosystems [1,2,3]. In the developed anoxic zones, activities of anaerobic microorganisms generate reduced substances which further affect biotic and abiotic environments. One of these reduced substances, sulfide originated from sulfate reduction has high toxicity and can causes serious damage to various organisms. As to sulfide detoxification by chemolithotrophs in stratified marine environments, several key sulfur oxidizers were recently identified [4,5,6]. They all belong to the phylum Proteobacteria, and are classified as either gammaproteobacteria or epsilonproteobacteria. General freshwater environments are characterized by lower concentrations of sulfate and sulfide in comparison to marine environments, understanding sulfur cycles in freshwater has great importance from the aspect of water resource management since quality of available freshwater has a direct influence on human activities
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