Cellodextrin and Laminaribiose ABC Transporters in
            <i>Clostridium thermocellum</i>

Nataf, Yakir; Yaron, Sima; Stahl, Frank; Lamed, Raphael; Bayer, Edward A.; Scheper, T.; Sonenshein, Abraham L.; Shoham, Yuval

doi:10.1128/jb.01190-08

Cited by 83 publications

(89 citation statements)

References 40 publications

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“…The demonstrated ability to import CB might explain, why this green microalga does not possess a hexose uptake system 17,18 . So far, only a few CB transporters have been identified belonging to the major facilitator superfamily 40 or the ATP-binding cassette transporter family 41 , and members of both are encoded by the Chlamydomonas nuclear genome (for example, UniProtKB A8J114/A8ILE4).…”

Section: Reinhardtii Internalizes Cellulose Breakdown Productsmentioning

confidence: 99%

Cellulose degradation and assimilation by the unicellular phototrophic eukaryote Chlamydomonas reinhardtii

et al. 2012

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Section: Reinhardtii Internalizes Cellulose Breakdown Productsmentioning

confidence: 99%

Cellulose degradation and assimilation by the unicellular phototrophic eukaryote Chlamydomonas reinhardtii

et al. 2012

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“…Wild-type C. thermocellum can utilize hexose sugars but not pentose sugars as fermentation substrates, despite having eight genes encoding xylanases (1). The organism has characterized ABC transporters for the uptake of cellodextrins ranging from G2 to G5 with one, CbpA, specific for cellotriose and another specific for laminaribiose (4). Understanding C. thermocellum gene regulation is of importance for improved fundamental knowledge of this industrially relevant bacterium.…”

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confidence: 99%

LacI Transcriptional Regulatory Networks in Clostridium thermocellum DSM1313

Wilson

Klingeman

Schlachter

et al. 2017

Appl Environ Microbiol

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Organisms regulate gene expression in response to the environment to coordinate metabolic reactions. Clostridium thermocellum expresses enzymes for both lignocellulose solubilization and its fermentation to produce ethanol. One LacI regulator termed GlyR3 in C. thermocellum ATCC 27405 was previously identified as a repressor of neighboring genes with repression relieved by laminaribiose (a ␤-1,3 disaccharide). To better understand the three C. thermocellum LacI regulons, deletion mutants were constructed using the genetically tractable DSM1313 strain. DSM1313 lacI genes Clo1313_2023, Clo1313_0089, and Clo1313_0396 encode homologs of GlyR1, GlyR2, and GlyR3 from strain ATCC 27405, respectively. Growth on cellobiose or pretreated switchgrass was unaffected by any of the gene deletions under controlled-pH fermentations. Global gene expression patterns from time course analyses identified glycoside hydrolase genes encoding hemicellulases, including cellulosomal enzymes, that were highly upregulated (5-to 100-fold) in the absence of each LacI regulator, suggesting that these were repressed under wild-type conditions and that relatively few genes were controlled by each regulator under the conditions tested. Clo1313_2022, encoding lichenase enzyme LicB, was derepressed in a ΔglyR1 strain. Higher expression of Clo1313_1398, which encodes the Man5A mannanase, was observed in a ΔglyR2 strain, and ␣-mannobiose was identified as a probable inducer for GlyR2-regulated genes. For the ΔglyR3 strain, upregulation of the two genes adjacent to glyR3 in the celC-glyR3-licA operon was consistent with earlier studies. Electrophoretic mobility shift assays have confirmed LacI transcription factor binding to specific regions of gene promoters. IMPORTANCE Understanding C. thermocellum gene regulation is of importance for improved fundamental knowledge of this industrially relevant bacterium. Most LacI transcription factors regulate local genomic regions; however, a small number of those genes encode global regulatory proteins with extensive regulons. This study indicates that there are small specific C. thermocellum LacI regulons. The identification of LacI repressor activity for hemicellulase gene expression is a key result of this work and will add to the small body of existing literature on the area of gene regulation in C. thermocellum.

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“…The ABC transporter, AraNPQ, from Bacillus subtilis is involved in the uptake of arabino-oligosaccharides (22). In the anaerobic bacterium Clostridium thermocellum, five sugar ABC transporters were characterized for cellodextrins (CbpB to -D), cellotriose (CbpA), and laminaribiose (Lbp) (52).…”

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The l -Arabinan Utilization System of Geobacillus stearothermophilus

et al. 2011

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Geobacillus stearothermophilus T-6 is a thermophilic soil bacterium that has a 38-kb gene cluster for the utilization of arabinan, a branched polysaccharide that is part of the plant cell wall. The bacterium encodes a unique three-component regulatory system (araPST) that includes a sugar-binding lipoprotein (AraP), a histidine sensor kinase (AraS), and a response regulator (AraT) and lies adjacent to an ATP-binding cassette (ABC) arabinose transport system (araEGH). The lipoprotein (AraP) specifically bound arabinose, and gel mobility shift experiments showed that the response regulator, AraT, binds to a 139-bp fragment corresponding to the araE promoter region. Taken together, the results showed that the araPST system appeared to sense extracellular arabinose and to activate a specific ABC transporter for arabinose (AraEGH). The promoter regions of the arabinan utilization genes contain a 14-bp inverted repeat motif resembling an operator site for the arabinose repressor, AraR. AraR was found to bind specifically to these sequences, and binding was efficiently prevented in the presence of arabinose, suggesting that arabinose is the molecular inducer of the arabinan utilization system. The expression of the arabinan utilization genes was reduced in the presence of glucose, indicating that regulation is also mediated via a catabolic repression mechanism. The cluster also encodes a second putative ABC sugar transporter (AbnEFJ) whose sugar-binding lipoprotein (AbnE) was shown to interact specifically with linear and branched arabino-oligosaccharides. The final degradation of the arabino-oligosaccharides is likely carried out by intracellular enzymes, including two ␣-L-arabinofuranosidases (AbfA and AbfB), a ␤-L-arabinopyranosidase (Abp), and an arabinanase (AbnB), all of which are encoded in the 38-kb cluster.The natural degradation of biomass from plants is a key step in the carbon cycle (53,69,79). This process is carried out mainly by microorganisms that can be found either free or as part of the digestive system in higher animals (76). The three main polysaccharides in the plant cell wall are cellulose, hemicellulose, and pectin, which are rigidified by lignin, a heterogeneous aromatic polymer (28, 60). Pectin is a complex polysaccharide and may account for up to 30% of the dry weight of the plant cell wall (46). Arabinan is a pectic polysaccharide consisting of a backbone of ␣-1,5-linked L-arabinofuranosyl units, which are further decorated mainly with ␣-1,2-and ␣-1,3-linked arabinofuranosides (46).Three general strategies are taken by the microbial world for plant cell wall degradation and can be described as follows. Anaerobic bacteria, such as Clostridium spp., have evolved unique multienzyme complexes, named cellulosomes, that integrate many cellulolytic and hemicellulolytic enzymes and mediate both the attachment of the cell to the crystalline polymer and its controlled hydrolysis (9,16,23,65). Aerobic fungi, such as Trichoderma and Aspergillus, secrete a large variety of free cellulases, hemicellulases...

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Cellodextrin and Laminaribiose ABC Transporters in Clostridium thermocellum

Cited by 83 publications

References 40 publications

Cellulose degradation and assimilation by the unicellular phototrophic eukaryote Chlamydomonas reinhardtii

Cellulose degradation and assimilation by the unicellular phototrophic eukaryote Chlamydomonas reinhardtii

LacI Transcriptional Regulatory Networks in Clostridium thermocellum DSM1313

The l -Arabinan Utilization System of Geobacillus stearothermophilus

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