Abstract
To characterize high-temperature cellulolytic microbial communities, two lignocellulosic substrates, ammonia fiber-explosion-treated corn stover and aspen shavings, were incubated at average temperatures of 77 and 85°C in the sediment and water column of Great Boiling Spring, Nevada. Comparison of 109,941 quality-filtered 16S rRNA gene pyrosequences (pyrotags) from eight enrichments to 37,057 quality-filtered pyrotags from corresponding natural samples revealed distinct enriched communities dominated by phylotypes related to cellulolytic and hemicellulolytic Thermotoga and Dictyoglomus, cellulolytic and sugar-fermenting Desulfurococcales, and sugar-fermenting and hydrogenotrophic Archaeoglobales. Minor enriched populations included close relatives of hydrogenotrophic Thermodesulfobacteria, the candidate bacterial phylum OP9, and candidate archaeal groups C2 and DHVE3. Enrichment temperature was the major factor influencing community composition, with a negative correlation between temperature and richness, followed by lignocellulosic substrate composition. This study establishes the importance of these groups in the natural degradation of lignocellulose at high temperatures and suggests that a substantial portion of the diversity of thermophiles contributing to consortial cellulolysis may be contained within lineages that have representatives in pure culture.
Highlights
Growing human populations and expanding industrialization have led to an increasing global demand upon finite supplies of fossil fuels, prompting growing interest in alternative fuel sources
Two sites (Site 85 and Site 77) along the perimeter of Great Boiling Spring (GBS) were selected for lignocellulosic substrate incubation and sample collection (Table 1, Figure 1)
The microbial communities enriched on the lignocellulose were compared with aggregate samples created in silico to represent the natural communities of GBS at each site
Summary
Growing human populations and expanding industrialization have led to an increasing global demand upon finite supplies of fossil fuels, prompting growing interest in alternative fuel sources. Current bioethanol production methods, considered ‘‘first-generation’’ biofuel technology, rely on fermentable sugars from plants traditionally utilized as food crops, so their production directly competes with the supply of food for human populations [2,3,4] and contribute to a range of coincident environmental concerns such as soil erosion, loss of biodiversity, and impact on water resources [5,6,7]. Thermostable cellulases offer several potential benefits to mitigate the high costs of enzymatic saccharification of lignocellulose. They tend to have much greater activity at their optimal temperature than those from mesophilic organisms because each 10uC increase in reaction temperature increases enzymatic rates two- to three-fold [10]. Thermostable enzymes are resistant to denaturation from other factors and highly stable for long-term storage, lengthening their shelf life and operational life during lignocellulose digestion [10,12]
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