Abstract
Thermoactinospora rubra YIM 77501T is an aerobic, Gram-positive, spore-forming and cellulose degrading thermophilic actinomycete isolated from a sandy soil sample of a volcano. Its growth temperature range is 28–60°C. The genomic sequence of this strain revealed that there are 27 cellulase genes belonging to six glycoside hydrolase families. To understand the strategy that this strain uses to utilize carbon sources such as cellulose at different temperatures, comparative transcriptomics analysis of T. rubra YIM 77501T was performed by growing it with cellulose (CMC) and without cellulose (replaced with glucose) at 30, 40, and 50°C, respectively. Transcriptomic analyses showed four cellulase genes (TrBG2, TrBG3, TrBG4, and ThrCel6B) were up-regulated at 30, 40, and 50°C. The rate of gene expression of TrBG2, TrBG3, TrBG4, and ThrCel6B were 50°C > 30°C > 40°C. One cellulase gene (TrBG1) and two cellulase genes (TrBG5 and ThrCel6A) were up-regulated only at 30 and 50°C, respectively. These up-regulated cellulase genes were cloned and expressed in Escherichia coli. The enzymatic properties of up-regulated cellulases showed a variety of responses to temperature. Special up-regulated cellulases TrBG1 and ThrCel6A displayed temperature acclimation for each growth condition. These expression patterns revealed that a hybrid strategy was used by T. rubra to utilize carbon sources at different temperatures. This study provides genomic, transcriptomics, and experimental data useful for understanding how microorganisms respond to environmental changes and their application in enhancing cellulose hydrolysis for animal feed and bioenergy production.
Highlights
Cellulose, as a main carbon source in the biosphere, is utilized by microorganisms and animals (Hungate, 1964; Batjes, 1996; Amundson, 2001)
Cultures of R2A-glucose media contained ∼10.8, 19.9, and 22.1% reads mapping to intergenic regions at 30, 40, and 50◦C, respectively (Figure S5). These results revealed that intergenic regions might play some functions in adapting to higher temperatures for strain T. rubra
To understand the strategies of carbon source acquisition, such as cellulose, in the environment at different temperatures for microorganisms, comparative transcriptomics of T. rubra grown with cellulose (CMC) and without cellulose at 30, 40, and 50◦Cwere studied
Summary
As a main carbon source in the biosphere, is utilized by microorganisms and animals (Hungate, 1964; Batjes, 1996; Amundson, 2001). Temperature is one of the most important environmental factors (Lin et al, 2016), and it may impact utilization of cellulose as a carbon source from two aspects: (1) it could affect the activity and stability of cellulases, and (2) it might be a crucial factor for inducing some cellulases under special temperatures. Some cellulases are stable only at a low temperature (Dhar et al, 2015), while some remain stable at a high temperature (Brunecky et al, 2013). Thermobifida fusca secretes thermo stable cellulolytic enzymes to degrade cellulose (Adav et al, 2011). The potential strategy of carbon source acquisition (such as cellulose) at different temperatures remains unclear for microorganisms
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