Pentoses Used in Cultures of Synechococcus nidulans and Spirulina paracas: Evaluation of Effects in Growth and in Content of Proteins and Carbohydrates

Abstract The biological assimilation of the sugars present in lignocellulosic residues has gained prominence since these residues are the most abundant and economic residues in nature. Thus, the objective of this work was to determine whether the use of D-xylose and L-arabinose as sources of carbon in Synechococcus nidulans and Spirulina paracas cultures affects the growth and production of proteins and carbohydrates. Kinetic growth parameters, pentose consumption, protein content and carbohydrates were evaluated. Synechococcus nidulans and Spirulina paracas consumed all concentrations of pentose used. The highest cellular concentration (1.37 g.L-1) and the highest protein productivity (54 mg.L-1.d-1) were obtained for Spirulina paracas, which was submitted to the addition of 38.33 mg.L-1 D-xylose and 1.79 mg.L-1 L-arabinose. The use of pentose promoted the accumulation of proteins for the studied microalgae. This is one of the first works to report protein bioaccumulation as a result of pentose addition.

Production optimization, purification, expression, and characterization of a novel α-L-arabinofuranosidase from Paenibacillus polymyxa

Background: α-L-Arabinofuranosidase (EC 3.2.1.55) catalyzes the hydrolysis of terminal α-L-1,2-, -1,3-, and -1,5- arabinofuranosyl residues in arabinose-containing polymers, and hence, it plays an important role in hemicellulose degradation. Herein, the bacterium Paenibacillus polymyxa, which secretes arabinofuranosidase with high activity, was selected for enzyme production, purification, and characterization. Results: Medium components and cultural conditions were optimized by the response surface method using shake flask cultures. Arabinofuranosidase production reached 25.2 U/mL under optimized conditions, which were pH 7.5, 28°C, and a basic medium supplemented with 1.5 g/L mannitol and 3.5 g/L soymeal. Furthermore, the arabinofuranosidase secreted by P. polymyxa, named as PpAFase-1, was partially purified from the supernatant using a DEAE Sepharose Fast Flow column and a hydroxyapatite column. The approximate molecular mass of the purified PpAFase-1 was determined as 56.8 kDa by SDS-PAGE. Protein identification by mass spectrometry analysis showed that the deduced amino acid sequence had significant similarity to the glycosyl hydrolase family 51. The deduced gene of 1515 bp was cloned and expressed in Escherichia coli BL21 (DE3) cells. Purified recombinant PpAFase-1 was active toward p-nitrophenyl-α-L-arabinofuranoside (pNPAraf). The Km and kcat values toward pNPAraf were 0.81 mM and 53.2 s−1 , respectively. When wheat arabinoxylan and oat spelt xylan were used as substrates, PpAFase-1 showed poor efficiency. However, a synergistic effect was observed when PpAFase-1 was combined with xylanase from Thermomyces lanuginosus. Conclusion: A novel GH51 enzyme PpAFase-1 was cloned from the genome of P. polymyxa and expressed in E. coli. This enzyme may be suitable for hemicellulose degradation on an industrial scale.

Biohydrogen production by Thermoanaerobacterium thermosaccharolyticum KKU-ED1: Culture conditions optimization using mixed xylose/arabinose as substrate

Background: Biological hydrogen production by microorganisms can be divided into two main categories i.e. photosynthetic organisms that produce hydrogen using light as energy source and anaerobic bacteria that produce hydrogen via dark fermentation. Dark fermentative hydrogen production by anaerobic bacteria has the advantages of a higher HPR without illumination and of the capability to convert various kinds of substrate. Results: Thermophilic hydrogen producer was isolated from elephant dung and identified as Thermoanaerobacterium thermosaccharolyticum KKU-ED1 by 16S rRNA gene analysis, which was further used to produce hydrogen from mixed pentose sugar i.e., xylose/arabinose. The optimum conditions for hydrogen production from mixed xylose/arabinose by KKU-ED1 were a 1:1 xylose/arabinose mixture at the total concentration of 5 g/L, initial pH of 6.5 and temperature of 55ºC. Under the optimum conditions, hydrogen from sugar derived from acid-hydrolyzed sugarcane bagasse at a reducing sugar concentration were achieved. Soluble metabolite product (SMP) was predominantly acetic acid indicating the acetate-type fermentation. Conclusions: The strain KKU-ED1 appeared to be a suitable candidate for thermophilic fermentative hydrogen production from hemicellulosic fraction of lignocellulosic materials due to its ability to use various types of carbon sources.