Identification and characterization of a novel 2R,3R-Butanediol dehydrogenase from Bacillus sp. DL01

Exploring the lipids, carotenoids, and vitamins content of Rhodotorula glutinis with selenium supplementation under lipid accumulating and growth proliferation conditions

BACKGROUND

Rhodotorula glutinis, a specific type of yeast, has been recognised as a superior resource for generating selenium-enriched biomass that possesses exceptional nutritional and functional attributes. The purpose of this investigation was to assess the effect of sodium selenite at different concentrations on lipid and carotenoid synthesis, as well as the growth of R. glutinis.

METHODS

The lipid's fatty acid composition was determined using gas chromatography (GC). The vitamins were detected by high-performance liquid chromatography (HPLC). Transmission electron microscopy was used to detect the structural modification of yeast cells caused by the addition of sodium selenite to the growth medium, as well as the accumulation of elemental selenium in the yeast cells.

RESULTS

The yeast cells demonstrated the ability to endure high concentrations of sodium selenite under lipid accumulation (LAM) and growth-promoting (YPD) conditions. 25.0 mM and 30.0 mM, respectively, were published as the IC50 values for the LAM and YPD conditions. In both growth media, 1 mM sodium selenite boosted lipid synthesis. Lipid accumulation increased 26% in LAM to 11.4 g/l and 18% in YPD to 4.3 g/l. Adding 1 mM and 3 mM sodium selenite to YPD medium increased total and cellular carotenoids by 22.8% (646.7 µg/L and 32.12 µg/g) and 48.7% (783.3 µg/L and 36.43 µg/g), respectively. Palmitic acid was identified as the most abundant fatty acid in all treatments, followed by oleic acid and linoleic acid. The concentrations of water soluble vitamins (WSV) and fat soluble vitamins (FSV) were generally significantly increased after supplementation with 1.0 mM sodium selenite. TEM examination revealed a significant reduction in lipid bodies accumulation in the yeast cells when sodium selenite was added to lipid-promoting environments. This decline is accompanied by an augmentation in the formation of peroxisomes, indicating that selenium has a direct impact on the degradation of fatty acids. In addition, autophagy appears to be the primary mechanism by which selenium ions are detoxified. Additionally, intracellular organelles disintegrate, cytoplasmic vacuolization occurs, and the cell wall and plasma membrane rupture, resulting in the discharge of cytoplasmic contents, when a high concentration of sodium selenite (20.0 mM) is added. Also, the presence of numerous electron-dense granules suggests an intracellular selenium-detoxification pathway.

CONCLUSION

This study proposes the use of YPD with 1 mM sodium selenite to cultivate selenium-enriched biomass from R. glutinis. This approach leads to heightened lipid levels with higher accumulation of oleic, linoleic and linolenic acids, carotenoids, and vitamins. Hence, this biomass has the potential to be a valuable additive for animal, fish, and poultry feed. Furthermore, explain certain potential factors that indicate the impact of selenium in reducing the accumulation of lipid droplets in R. glutinis during lipogenesis, as detected through TEM examination.

Significantly enhanced specific activity of Bacillus subtilis (2,3)-butanediol dehydrogenase through computer-aided refinement of its substrate-binding pocket

(2,3)-Butanediol dehydrogenases (BDHs) are widely utilized for the stereoselective interconversion between α-hydroxy ketones and vicinal diols to produce various functional building blocks. In this study, to enhance the specific activity towards (R)-phenyl-1,2-ethanediol (1a) for 2-hydroxyacetophenone (1b), the substrate-binding pocket of a Bacillus subtilis BDH (BsBDHA) was refined through site-directed mutagenesis. Based on molecular docking simulations, 14 residues were identified and subjected to alanine scanning mutagenesis. After screening, two residues, His42 and Gly292, were singled out for partial site-saturation mutagenesis. The results revealed that BsBDHAH42A and BsBDHAG292A displayed high activities of 3.21 and 1.97 U/mg, respectively. Employing combinatorial mutagenesis, a superior mutant, BsBDHAI49L/V266L/G292A, was developed, exhibiting significantly enhanced specific activity and catalytic efficiency towards (R)-1a, achieving 14.81 U/mg and 4.47 mM-1 s-1, respectively, which were 27.4- and 55.9-fold higher than those of BsBDHA. Further substrate spectrum analysis revealed that the superior mutant displayed increased specific activities for (R)-2a-6a by 1.4- to 10.3-fold. The integration of BsBDHAI49L/V266L/G292A into a three-enzymatic cascade for the synthesis of 1b effectively elevated the yield from 58.1 to 82.4%. Molecular mechanism analysis indicated that the mutation-induced changes in intermolecular forces resulted in a higher frequency of reactive conformations for (R)-1a in BsBDHAI49L/V266L/G292A compared to BsBDHA.

Anticandidal activity of a wild Bacillus subtilis NAM against clinical isolates of pathogenic Candida albicans

Background

Resistance to antifungal medications poses a significant obstacle in combating fungal infections. The development of novel therapeutics for Candida albicans is necessary due to the increasing resistance of candidiasis to the existing medications. The utilization of biological control is seen as a more advantageous and less hazardous strategy therefore the objective of this study is to identify the antifungal properties of Bacillus subtilis against pathogenic C. albicans.

Results

We conducted a study to evaluate the antifungal properties of three bacterial isolates against the human pathogen Candida albicans. One of the bacterial isolates exhibited a potent antifungal activity against this fungal pathogen. This bacterium was identified as Bacillus subtilis based on the 16Sr RNA gene sequence. It exhibited inhibitory efficacy ranging from 33.5 to 44.4% against 15 Candida isolates. The optimal incubation duration for achieving the maximum antifungal activity was determined to be 48 h, resulting in a mean inhibition zone diameter of 29 ± 0.39 mm. The Potato Dextrose agar (PDA) medium was the best medium for the most effective antifungal activity. Incubation temperature of 25oC and medium pH value of 8.0 were the most favorable conditions for maximum antagonistic activity that resulted fungal growth inhibition of 40 ± 0.16 and 36 ± 0.94 mm respectively. Furthermore, the addition of 10.5 mg/ml of bacterial filtrate to C. albicans colonies resulted in 86.51%. decrease in the number of germinated cells. The fungal cell ultrastructural responses due to exposure to B. subtilis filtrate after 48 h were investigated using transmission electron microscopy (TEM). It revealed primary a drastic abnormality that lead to cellular disintegration including folding and lysis of the cell wall, total collapse of the yeast cells, and malformed germ tube following the exposure to the filtrate. However, the control culture treatment had a characteristic morphology of the normal fungal cells featuring a consistently dense central region, a well-organized nucleus, and a cytoplasm containing several components of the endomembrane system. The cells were surrounded by a uniform and intact cell wall.

Conclusion

The current study demonstrates a notable antifungal properties of B. subtilis against C. albicans as a result of production of bioactive components of the bacterial exudate. This finding could be a promising natural antifungal agent that could be utilized to combat C. albicans.

Mechanism of microbial production of acetoin and 2,3-butanediol optical isomers and substrate specificity of butanediol dehydrogenase

3-Hydroxybutanone (Acetoin, AC) and 2,3-butanediol (BD) are two essential four-carbon platform compounds with numerous pharmaceutical and chemical synthesis applications. AC and BD have two and three stereoisomers, respectively, while the application of the single isomer product in chemical synthesis is superior. AC and BD are glucose overflow metabolites produced by biological fermentation from a variety of microorganisms. However, the AC or BD produced by microorganisms using glucose is typically a mixture of various stereoisomers. This was discovered to be due to the simultaneous presence of multiple butanediol dehydrogenases (BDHs) in microorganisms, and AC and BD can be interconverted under BDH catalysis. In this paper, beginning with the synthesis pathways of microbial AC and BD, we review in detail the studies on the formation mechanisms of different stereoisomers of AC and BD, summarize the properties of different types of BDH that have been tabulated, and analyze the structural characteristics and affinities of different types of BDH by comparing them using literature and biological database data. Using microorganisms, recent research on the production of optically pure AC or BD was also reviewed. Limiting factors and possible solutions for chiral AC and BD production are discussed.

Structural and enzymatic characterization of Bacillus subtilis R,R-2,3-butanediol dehydrogenase

2,3-butanediol dehydrogenase (BDH, EC 1.1.1.76) also known as acetoin reductase (AR, EC 1.1.1.4) is the key enzyme converting acetoin (AC) into 2,3-butanediol (BD) and undertaking the irreversible conversion of diacetyl to acetoin in various microorganisms. The existence of three BDHs (R,R-, meso-, and S,S-BDH) product different BD isomers. Catalyzing mechanisms of meso- and S,S-BDH have been understood with the assistance of their X-ray crystal structures. However, the lack of structural data for R,R-BDH restricts the integral understanding of the catalytic mechanism of BDHs. In this study, we successfully crystallized and solved the X-ray crystal structure of Bacillus subtilis R,R-BDH. A zinc ion was found locating in the catalytic center and coordinated by Cys37, His70 and Glu152, helping to stabilize the chiral substrates observed in the predicted molecular docking model. The interaction patterns of different chiral substrates in the molecular docking model explained the react priority measured by the enzyme activity assay of R,R-BDH. Site-directed mutation experiments determined that the amino acids Cys37, Thr244, Ile268 and Lys340 are important in the catalytically active center. The structural information of R,R-BDH presented in this study accomplished the understanding of BDHs catalytic mechanism and more importantly provides useful guidance for the directional engineering of R,R-BDH to obtain high-purity monochiral BD and AC.