Abstract
The alkaliphilic hemicellulolytic bacterium Bacillus sp. N16-5 has a broad substrate spectrum and exhibits the capacity to utilize complex carbohydrates such as galactomannan, xylan, and pectin. In the monosaccharide mixture, sequential utilization by Bacillus sp. N16-5 was observed. Glucose appeared to be its preferential monosaccharide, followed by fructose, mannose, arabinose, xylose, and galactose. Global transcription profiles of the strain were determined separately for growth on six monosaccharides (glucose, fructose, mannose, galactose, arabinose, and xylose) and four polysaccharides (galactomannan, xylan, pectin, and sodium carboxymethylcellulose) using one-color microarrays. Numerous genes potentially related to polysaccharide degradation, sugar transport, and monosaccharide metabolism were found to respond to a specific substrate. Putative gene clusters for different carbohydrates were identified according to transcriptional patterns and genome annotation. Identification and analysis of these gene clusters contributed to pathway reconstruction for carbohydrate utilization in Bacillus sp. N16-5. Several genes encoding putative sugar transporters were highly expressed during growth on specific sugars, suggesting their functional roles. Two phosphoenolpyruvate-dependent phosphotransferase systems were identified as candidate transporters for mannose and fructose, and a major facilitator superfamily transporter was identified as a candidate transporter for arabinose and xylose. Five carbohydrate uptake transporter 1 family ATP-binding cassette transporters were predicted to participate in the uptake of hemicellulose and pectin degradation products. Collectively, microarray data improved the pathway reconstruction involved in carbohydrate utilization of Bacillus sp. N16-5 and revealed that the organism precisely regulates gene transcription in response to fluctuations in energy resources.
Highlights
Due to the diminishing supply of fossil fuel sources, exploiting alternative renewable energy sources has become increasingly necessary
Our experimental data showed that the culture grew to a cell density of approximately 1.56109 cells/mL on glucose, fructose, mannose, arabinose, and xylose, grew to a cell density of nearly 2.06109 cells/mL on galactomannan, xylan, and pectin, and grew to a cell density of less than 1.06109 cells/mL on galactose and CMC
The combination of microarray data with gene neighborhood and sequence analysis has been widely used in predicting gene function and analyzing metabolic pathways involved in carbohydrate utilization [29,30,32,33,34,35]
Summary
Due to the diminishing supply of fossil fuel sources, exploiting alternative renewable energy sources has become increasingly necessary. Microorganisms employ different strategies for degrading polysaccharides and utilizing the degradation products. Aerobic fungi such as Trichoderma and Aspergillus spp. secrete a number of free enzymes, such as cellulases, hemicellulases, and ligninases, which work cooperatively to completely degrade polysaccharides into mono- and disaccharides extracellularly to allow their assimilation [8,9,10]. Due to the powerful ability to degrade crystalline cellulose, organization of the cellulosome and expression of relative enzymes on different substrates have been thoroughly examined, in some Clostridium spp. It has been found that bacteria not containing cellulosome, such as Bacillus spp., secrete extracellular enzymes to degrade polysaccharides and transport partial degradation products into the cell for subsequent processing into fermentable sugars [17,18]. Numerous extracellular and intracellular hydrolytic enzymes have been identified for this type of microorganism, how these organisms control transcription of enzymes and transport of their degradation products is not well understood [17,19]
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