OPTIMIZATION OF FERMENTATION MEDIUM FOR ACETOIN PRODUCTION BYBacillus subtilisSF4-3 USING STATISTICAL METHODS

Multilevel systemic engineering of Bacillus licheniformis for efficient production of acetoin from lignocellulosic hydrolysates

Bio-refining lignocellulosic resource offers a renewable and sustainable approach for producing biofuels and biochemicals. However, the conversion efficiency of lignocellulosic resource is still challenging due to the intrinsic inefficiency in co-utilization of xylose and glucose. In this study, the industrial bacterium Bacillus licheniformis was engineered for biorefining lignocellulosic resource to produce acetoin. First, adaptive evolution was conducted to improve acetoin tolerance, leading to a 19.6 % increase in acetoin production. Then, ARTP mutagenesis and 60Co-γ irradiation was carried out to enhance the production of acetoin, obtaining 73.0 g/L acetoin from glucose. Further, xylose uptake and xylose utilization pathway were rewired to facilitate the co-utilization of xylose and glucose, enabling the production of 60.6 g/L acetoin from glucose and xylose mixtures. Finally, this efficient cell factory was utilized for acetoin production from lignocellulosic hydrolysates with the highest titer of 68.3 g/L in fed-batch fermentation. This strategy described here holds great applied potential in the biorefinery of lignocellulose for the efficient synthesis of high-value chemicals.

Optimization of the fermentation media and growth conditions of Bacillus velezensis BHZ-29 using a Plackett-Burman design experiment combined with response surface methodology

Introduction

Bacillus velezensis occurs extensively in the soil environment. It produces a range of antimicrobial compounds that play an important role in the field of biological control. However, during the actual application process it is often affected by factors such as the medium formulation and fermentation conditions, and therefore biocontrol measures often do not achieve their expected outcomes.

Methods

In this study, the B. velezensis BHZ-29 strain was used as the research object. The carbon and nitrogen sources, and inorganic salts that affect the number of viable bacteria and antibacterial potency of B. velezensis BHZ-29, were screened by a single factor test. A Plackett-Burman design experiment was conducted to determine the significant factors affecting the number of viable bacteria and antibacterial potency, and a Box-Behnken design experiment was used to obtain the optimal growth of B. velezensis BHZ-29. The medium formula that produced the highest number of viable bacteria and most antibacterial substances was determined. The initial pH, temperature, amount of inoculant, liquid volume, shaking speed, and culture time were determined by a single factor test. The factors that had a significant influence on the number of viable bacteria of B. velezensis BHZ-29 were selected by an orthogonal test. A Box-Behnken design experiment was conducted to obtain the optimal fermentation conditions, and highest number of viable bacteria and antibacterial titer.

Results

Molasses, peptone, and magnesium sulfate had significant effects on the viable count and antibacterial titer of B. velezensis BHZ-29. The viable count of B. velezensis BHZ-29 increased from 7.83 × 109 to 2.17 × 1010 CFU/mL, and the antibacterial titer increased from 111.67 to 153.13 mm/mL when the optimal media were used. The optimal fermentation conditions for B. velezensis BHZ-29 were as follows: temperature 25.57°C, pH 7.23, culture time 95.90 h, rotation speed 160 rpm, amount of inoculant 2%, and liquid volume 100 ml. After the optimization of fermentation conditions, the number of viable bacteria increased to 3.39 × 1010 CFU/mL, and the bacteriostatic titer increased to 158.85 mm/ml.The plant height and leaf number of cotton plants treated with BHZ-29 fermentation broth were higher than those of cotton inoculated with Verticillium dahliae. The number of bacteria was 1.15 × 107 CFU/g, and the number of fungi was 1.60 × 105 spores/g. The disease index of the cotton seedlings treated with the optimized fermentation broth was 2.2, and a control effect of 93.8% was achieved. B. velezensis BHZ-29 could reduce the disease index of cotton Verticillium wilt and had a controlling effect on the disease. The best effect was achieved in the treatment group with an inoculation concentration of 2 × 108 CFU/ml, the disease index was 14.50, and a control effect of 84.18% was achieved.

Discussion

The fermentation process parameters of the number of viable bacteria and antibacterial titer by strain B. velezensis BHZ-29 were optimized to lay a foundation for the practical production and application of strain B. velezensis BHZ-29 in agriculture.

Optimization of medium composition of Lactobacillus plantarum Y44 using Plackett-Burman and Box-Behnken designs

The biomass of Lactobacillus strains depends on the culture media and culture conditions. The purpose of this study was to optimize the culture medium composition and culture conditions of Lactobacillus plantarum Y44 to improve its biomass. The utilization of different carbon sources and nitrogen sources by L. plantarum Y44 was assessed by single factor experiment to screen out the economical carbon and nitrogen sources for L. plantarum Y44 growth. Through optimization experiments, the optimized culture medium for L. plantarum Y44 growth consists of soybean peptone 44.1 g/L, yeast extract 22.1 g/L, sucrose 35.6 g/L, hydrogen diamine citrate 2 g/L, anhydrous sodium acetate 8.5 g/L, dipotassium hydrogen phosphate 4 g/L, Tween-80 2 mL/L, manganese sulfate 0.25 g/L, and magnesium sulfate 0.58 g/L, and the initial pH 6.7. The concentration of viable bacteria cells of L. plantarum Y44 culturing in the optimized medium at 37 °C for 16 h was up to 3.363 × 1010 CFU/mL, as 6.11 times higher than that in the MRS medium.

Screening and Selection of a New Medium for Diosgenin Production via Microbial Biocatalysis of Fusarium sp

Steroidal saponins are widely used as starting precursors and medical intermediates for the semi-/total-synthesis of hundreds of steroidal drugs. One such steroidal saponin is diosgenin, which has attracted significant attention due to the huge market demand in the pharmaceutical industry. Due to water waste and severe environmental pollution, the traditional diosgenin production process based on direct acid hydrolysis is no longer used. In this study, to develop a submerged fermentation (SmF) medium for clean diosgenin production via efficient microbial biocatalysis, the Box-Behnken design (BBD) in combination with the Plackett-Burman design (PBD) was used to determine the medium compositions for Fusarium strains. Three components (wheat bran, phosphate, and Tween-80) were determined as significant factors by the PBD. Using the BBD, the three significant factors were further optimized, and the optimum values were determined for maximal diosgenin production. With 21.16 g/L of wheat bran, 9.60 g/L of phosphate, and 1.97 g/L of Tween-80, the diosgenin yield was 2.28%, i.e., 3.17 mg/L/h. The experimental values agreed with the predicted values, representing a significant increase in diosgenin production compared to its production using the basic SmF medium. For the first time, we reported the development of a new medium for Fusarium strains to produce diosgenin via microbial biocatalysis of the root of Dioscorea zingiberensis C. H. Wright (DZW). A simple-composition, low-cost, and high-efficiency medium was developed for the first time for the SmF of Fusarium strains. The medium is considered useful for large-scale SmF and may be applicable to other fungi. This study lays a solid foundation for diosgenin production in an acid-free and wastewater-free way. It may also provide fundamental support for producing other value-added products via microbial biocatalysis of low-value materials by endophytic fungi.

Identification and Antihypertension Study of Novel Angiotensin I-Converting Enzyme Inhibitory Peptides from the Skirt of Chlamys farreri Fermented with Bacillus natto

The aim of this study was to isolate the angiotensin I-converting enzyme (ACE) inhibitory peptides from the skirt of Chlamys farreri fermented with Bacillus natto and to explore the antihypertension effect through in vivo studies. ACE inhibitory peptides were purified from the fermentation mixture by ultrafiltration, gel filtration chromatography, and reversed-phase high-performance liquid chromatography sequentially. The amino acids' sequence of the five novel ACE inhibitory peptides were identified by liquid chromatography-tandem mass spectrometry. Animal experiments demonstrated that the novel ACE inhibitory peptides significantly reduced the blood pressure in spontaneously hypertensive rats after a single or long-time treatment. Potential mechanisms were explored, and the results indicated that the novel peptides could regulate the renal renin-angiotensin system, improve vascular remodeling, inhibit myocardial fibrosis, and rebalance the gut microbial dysbiosis. Our results suggest that the fermentation products of the Chlamys farreri skirt by B. natto are potential sources of active peptides processing antihypertension activities.

Optimization of process variables for acetoin production in a bioreactor using Taguchi orthogonal array design

Microbial production of acetoin is eco-friendly and inexpensive when compared with its synthetic methods of production. In the present findings, bioproduction of acetoin in a typical bioreactor was discussed with a view to ascertain the seemingly comparative advantage of bioreactor system over shake flask, and more importantly, to confirm that corn steep liquor can indeed adequately be used as a replacement for other organic nitrogen sources. Taguchi design was statistically used to optimized the fermentation process which resulted in a 3-fold increase in molar yield (83%) corresponding to a six-fold increase in acetoin concentration (63.43 g/L), as compared to a similar study conducted in a shake flask. Although agitation rate was observed to be the most controlling, the bioreactor may underperform at agitation rate greater than 300 rpm. The optimum parameters for acetoin production in this study were 300 rpm agitation, 1.5 slpm aeration, 2 days fermentation time, and pH 6.5. The results show that the commercial production of acetoin can be envisioned using a biological approach that may be of economic advantage.

Biovalorization of glucose in four culture media and effect of the nitrogen source on fermentative alcohols production by Escherichia coli

Glucose is one of the most abundant monosaccharides and the easiest carbon source to be consumed by bacteria. In this study, four culture media (LB, M9, M63 and MOPS) were supplemented with glucose at three different concentrations (4, 12.5 and 25 g/L) in the presence of a genetically modified strain of Escherichia coli with the purpose of selecting the most suitable culture medium to obtain ABD (acetoin (A) and 2,3-butanediol (2,3-BD)). The selected medium was M9, the cheapest culture medium, since the ABD yields obtained fermenting 12.5 and 25 g/L of glucose in M9 culture medium at 37°C, atmospheric pressure, initial pH 6.5, 100 rpm and 10% (v/v) of inoculum were similar compared to the ABD yields obtained using M63 and LB culture media. The influence of nitrogen on ABD yield was tested adding sodium nitrate (NaNO₃) or urea ((NH₂)₂CO) to M9 culture medium at three different nitrogen concentrations (2.5, 5.0 and 7.0 g N/L). Adding urea (7.0 g N/L) to M9 supplemented with 25 g/L of glucose improved by 23% the ABD yield at 96 h compared to M9 without urea, reaching a value of 27.2% (g ABD/g glucose). In contrast, the use of NaNO₃ had no significant effect on the ABD yield.

Optimization of the culture condition of Bacillus mucilaginous using Agaricus bisporus industrial wastewater by Plackett-Burman combined with Box-Behnken response surface method

In the present study, conditions for Bacillus mucilaginous fermentation using Agaricus bisporus wastewater as culture medium were optimized. We analyzed the total number of living B. mucilaginous in the fermentation broth using multispectral imaging flow cytometry. Single-factor experiments were carried out, where a Plackett–Burman design was used to screen out three factors from the original six factors of processing wastewater solubility, initial pH, inoculum size, liquid volume, culture temperature, and rotation speed that affected the total number of viable B. mucilaginous. The Box–Behnken response surface method was used to optimize interactions between the three main factors and predict optimal fermentation conditions. Factors significantly affecting the total number of viable B. mucilaginous, including shaking speed, culturing temperature, and initial pH, were investigated. The optimum conditions for B. mucilaginous fermentation in A. bisporus wastewater were a rotational speed of 195 rpm, culture temperature of 29 °C, initial pH of 6.5, solubility of 0.5%, 8% inoculation volume, and 90 mL liquid volume in a 250 mL flask, culture time of 48 h. Under these conditions, the concentration of total viable bacteria reached 2.16 ± 0.02 × 10⁸ Obj/mL, which meets the national standard. A. bisporus wastewater can be used for the cultivation of B. mucilaginous.