Economical production of poly(ε-l-lysine) and poly(l-diaminopropionic acid) using cane molasses and hydrolysate of streptomyces cells by Streptomyces albulus PD-1

Preparation of Hydrolyzed Sugarcane Molasses as a Low-Cost Medium for the Mass Production of Probiotic Lactobacillus paracasei ssp. paracasei F19

In this study, sugarcane molasses (SCM) was pre-treated in a low-cost fermentation medium to produce probiotic biomass of Lactobacillus paracasei ssp. paracasei F19 (LPPF19) with the combination of dilution, centrifugation, and acid hydrolysis (5 molar sulfuric acid, 60 °C/2 h). Microtox analysis, inductively coupled mass spectrometry (ICP-MS), and high-performance liquid chromatography (HPLC) were used to measure the effects of SCM pretreatment on the fermentation process. The results showed that the hydrolysis of sucrose into glucose and fructose was 98%, which represented an increase of 44.4% in the initial glucose content (fermentation-limiting sugar), and harmful heavy metals, such as arsenic, cadmium, and lead, were reduced by 50.3, 60.0, and 64.3%, respectively. After pretreatment, with the supplementation of only yeast extract and salts (Na, K, Mg, and Mn), a biomass of 9.58 log CFU/mL was achieved, approximately ten times higher than that for the control medium used (MRS/DeMan, Rogosa, and Sharpe). The cost reduction achieved compared to this commercial medium was 68.7% in the laboratory and 78.9% on an industrial scale. This work demonstrated that SCM could be used in a cheaper and more effective alternative fermentation to produce LPPF19.

Recent advances in microbial ε-poly-L-lysine fermentation and its diverse applications

The naturally occurring homo-polyamide biopolymer, ε-poly-L-lysine (ε-PL) consists of 25-35 L-lysine residues with amide linkages between α-carboxyl groups and ε-amino groups. ɛ-PL exhibits several useful properties because of its unusual structure, such as biodegradability, water solubility, no human toxicity, and broad-spectrum antibacterial activities; it is widely applied in the fields of food, medicine, clinical chemistry and electronics. However, current industrial production of ε-PL is only performed in a few countries. Based on an analysis of the physiological characteristics of ε-PL fermentation, current advances that enhance ε-PL fermentation, from strain improvement to product isolation are systematically reviewed, focusing on: (1) elucidating the metabolic pathway and regulatory mechanism of ε-PL synthesis; (2) enhancing biosynthetic performance through mutagenesis, fermentation optimization and metabolic engineering; and (3) understanding and improving the biological activity and functional properties of ε-PL. Finally, perspectives on engineering and exploiting ε-PL as a source material for the production of various advanced materials are also discussed, providing scientific guidelines for researchers to further improve the ε-PL fermentation process.

Biotechnological production and application of epsilon-poly-L-lysine (ε-PL): biosynthesis and its metabolic regulation

Epsilon-poly-L-lysine (ε-PL) is an unusual biopolymer composed of L-lysine produced by several microorganisms, especially by the genus Streptomyces. Due to its excellent antimicrobial activity, good water solubility, high safety, and biodegradable nature, ε-PL with a GRAS status has been widely used in food and pharmaceutical industries. In the past years, studies have focused on the biotechnological production of ɛ-PL, the biosynthetic mechanism of microbial ɛ-PL, and its application. To provide new perspectives from recent advances, the review introduced the methods for the isolation of ɛ-PL producing strains and the biosynthetic mechanism of microbial ɛ-PL. We summarized the strategies for the improvement of ɛ-PL producing strains, including physical and chemical mutagenesis, ribosome engineering and gene engineering, and compared the different metabolic regulation strategies for improving ɛ-PL production, including medium optimization, nutrient supply, pH control, and dissolved oxygen control. Then, the downstream purification methods of ɛ-PL and its recent applications in food and medicine industries were introduced. Finally, we also proposed the potential challenges and the perspectives for the production of ε-PL.

Epsilon-poly-L-lysine: Recent Advances in Biomanufacturing and Applications

ε-poly-L-lysine (ε-PL) is a naturally occurring poly(amino acid) of varying polymerization degree, which possesses excellent antimicrobial activity and has been widely used in food and pharmaceutical industries. To provide new perspectives from recent advances, this review compares several conventional and advanced strategies for the discovery of wild strains and development of high-producing strains, including isolation and culture-based traditional methods as well as genome mining and directed evolution. We also summarize process engineering approaches for improving production, including optimization of environmental conditions and utilization of industrial waste. Then, efficient downstream purification methods are described, including their drawbacks, followed by the brief introductions of proposed antimicrobial mechanisms of ε-PL and its recent applications. Finally, we discuss persistent challenges and future perspectives for the commercialization of ε-PL.

Efficient production of ε-poly-l-lysine using cassava starch and fish meal by Streptomyces albulus FQC-24

ε-Poly-l-lysine (ε-PL) is used as a natural food preservative which consists of l-lysine units connected. However, due to the expensive culture medium, the production cost of ε-PL remains high. In this study, cheap raw materials cassava starch (CS) and fish meal (FM) were employed by S. albulus FQC-24 for ε-PL production. In the single factor experiment, the maximum ε-PL production reached 0.97 g/L at 60 g/L CS and 15 g/L FM. The results of screening experiments by Plackett-Burman design showed that three main components affecting ε-PL production were CS, FM, and (NH₄)₂SO₄. And the standardized effects of CS, FM, and (NH₄)₂SO₄ were 0.13, -0.22, and -0.2, respectively. The optimum fermentation medium developed by response surface methodology for ε-PL production contained (g/L) CS, 67.56; FM, 14.70 and (NH₄)₂SO₄, 5.41. Under the optimum conditions, the ε-PL production was achieved 1.30 g/L, with 34.02% higher than that before optimization. Moreover, ε-PL productions of batch and fed-batch fermentation in a 7-L fermentor were improved to 2.13 and 17.17 g/L respectively, which increased by 0.64 and 12.2 times compared with the shake flask culture. The results indicated that FM and CS are promising substrates for the efficient production of ε-PL.

Microalgal feedstock for the production of omega-3 fatty acid ethyl esters and ɛ-polylysine

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Microalgal omega-3 fatty acids can be an alternative for fish based omega-3 fatty acids.

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Potassium carbonate is the efficient catalyst for the ethyl ester production.

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ɛ-polylysine can be produced from the spent biomass after transesterification.

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Co-production of two products could be the promising bio-refinery approach.

Microalgal omega-3 fatty acids are considered as an efficient alternative for fish-based omega-3 fatty acids. Ethyl esters derived from omega-3 fatty acids are being considered as the drug for hypertriglyceridemia. In this study, omega-3 fatty acids rich Chlorella sp. was utilized for the transesterification for the ethyl ester production using a potassium carbonate alkaline catalyst. At the optimized conditions of transesterification, 86.2% ethyl ester yield was achieved with solvent to algae ratio (20 mL/g), water addition (45 %), catalyst (4 %), temperature (75°C), and reaction time (60 min). Additionally, the acid-hydrolysed spent biomass was used for the production of ɛ-polylysine by fermentation using Streptomyces sp. as fermentative organism. The maximum yield of 1.78 g/L was achieved after 90 h fermentation. This study established a biorefinery approach where two highly valuable compounds could be produced from the Chlorella sp. by transesterification followed by fermentation.

Process optimization for mass production of 2,3-butanediol by Bacillus subtilis CS13

BACKGROUND

Bacillus subtilis CS13 was previously isolated for 2,3-butanediol (2,3-BD) and poly-γ-glutamic acid (γ-PGA) co-production. When culturing this strain without L-glutamic acid in the medium, 2,3-BD is the main metabolic product. 2,3-BD is an important substance and fuel with applications in the chemical, food, and pharmaceutical industries. However, the yield and productivity for the B. subtilis strain should be improved for more efficient production of 2,3-BD.

RESULTS

The medium composition, which contained 281.1 g/L sucrose, 21.9 g/L ammonium citrate, and 3.6 g/L MgSO₄·7H₂O, was optimized by response surface methodology for 2,3-BD production using B. subtilis CS13. The maximum amount of 2,3-BD (125.5 ± 3.1 g/L) was obtained from the optimized medium after 96 h. The highest concentration and productivity of 2,3-BD were achieved simultaneously at an agitation speed of 500 rpm and aeration rate of 2 L/min in the batch cultures. A total of 132.4 ± 4.4 g/L 2,3-BD was obtained with a productivity of 2.45 ± 0.08 g/L/h and yield of 0.45 g_2,3-BD/g_sucrose by fed-batch fermentation. The meso-2,3-BD/2,3-BD ratio of the 2,3-BD produced by B. subtilis CS13 was 92.1%. Furthermore, 89.6 ± 2.8 g/L 2,3-BD with a productivity of 2.13 ± 0.07 g/L/h and yield of 0.42 g_2,3-BD/g_sugar was achieved using molasses as a carbon source.

CONCLUSIONS

The production of 2,3-BD by B. subtilis CS13 showed a higher concentration, productivity, and yield compared to the reported generally recognized as safe 2,3-BD producers. These results suggest that B. subtilis CS13 is a promising strain for industrial-scale production of 2,3-BD.

Continuous Self-Cycling Fermentation Leads to Economical Lycopene Production by Saccharomyces cerevisiae

The economic feasibility and waste treatment problem are challenges to the industrialization of lycopene production from Saccharomyces cerevisiae. In this study, fermentation wastewater, biomass residue, and residual D-galactose are recycled for lycopene production. Results show that when fresh water is totally replaced by wastewater, lycopene titer attains 1.21 ± 0.02 g/L, which is 14.2% higher than the fresh water group (P < 0.05). An 80% replacement ratio of yeast extract by biomass residue causes no significant difference to lycopene production while 100% replacement ratio significantly lowers lycopene titer compared with the yeast extract group. Then, a novel fermentation medium containing wastewater and biomass residue with supplementing 3 g/L yeast extract and D-galactose is used for lycopene production. Lycopene titer increases 22.4% than the traditional fermentation in shake flasks (P < 0.05). Continuous self-cycling strategy using wastewater and biomass residue was tested in shake flasks. The mean lycopene titer of the first five recycles shows no significant difference with the start batch. Scaling up to 70 L fermenter, the mean lycopene titer attains 5.88 ± 0.15 g/L in three recycles, which is 22.25% higher than the start batch (P < 0.05). Economic analysis shows that the lowest unite product cost is achieved when four recycles are accomplished, which is 29.6% lower than the traditional fermentation while the chemical oxygen demand decreases 64.0%. Our study shows that continuous self-cycling fermentation process for lycopene production is feasible for the first time. The comprehensive utilization of wastewater and biomass residue from lycopene production by S. cerevisiae and achievement of high lycopene titer will hopefully accelerate industrialization of microbial production of lycopene.

High-level production of poly-γ-glutamic acid from untreated molasses by Bacillus siamensis IR10

Background

Poly-γ-glutamic acid (γ-PGA) is a promising biopolymer and has been applied in many fields. Bacillus siamensis SB1001 was a newly isolated poly-γ-glutamic acid producer with sucrose as its optimal carbon source. To improve the utilization of carbon source, and then molasses can be effectively used for γ-PGA production, ⁶⁰cobalt gamma rays was used to mutate the genes of B. siamensis SB1001.

Results

Bacillus siamensis IR10 was screened for the production of γ-PGA from untreated molasses. In batch fermentation, 17.86 ± 0.97 g/L γ-PGA was obtained after 15 h, which is 52.51% higher than that of its parent strain. Fed-batch fermentation was performed to further improve the yield of γ-PGA with untreated molasses, yielding 41.40 ± 2.01 g/L of γ-PGA with a productivity of 1.73 ± 0.08 g/L/h. An average γ-PGA productivity of 1.85 g/L/h was achieved in the repeated fed-batch fermentation. This is the first report of such a high γ-PGA productivity. The analysis of the enzyme activities showed that they were affected by the carbon sources, enhanced ICDH and GDH, and decreased ODHC, which are important for γ-PGA production.

Conclusion

These results suggest that untreated molasses can be used for economical and industrial-scale production of γ-PGA by B. siamensis IR10.

Economical production of androstenedione and 9α-hydroxyandrostenedione using untreated cane molasses by recombinant mycobacteria

Production of androstenedione (AD) and 9α-hydroxyandrostenedione (9α-OH-AD) by recombinant mycobacteria using untreated cane molasses and hydrolysate of mycobacterial cells (HMC) was investigated for the first time. B-vitamins feeding experiment and reverse transcription-PCR analysis showed that propionyl-CoA carboxylase (PCC) plays an important role in the phytosterol biotransformation of mycobacteria. The respective AD and 9α-OH-AD conversion ratios were increased by 2.91 and 1.48 times through coexpression of PCC and NADH dehydrogenase. The highest conversion ratios of AD and 9α-OH-AD obtained by using a co-feeding strategy of cane molasses and HMC reached 96.38% and 95.04%, respectively, and the total costs of carbon and nitrogen sources for the culture medium were reduced by 29.89% and 49.49%, respectively. Taking the results together, untreated cane molasses and HMC can be used for the economical production of steroidal pharmaceutical precursors by mycobacteria. This study offers an economical and green strategy for steroidal pharmaceutical precursor production.

Discovery of a Short-Chain ε-Poly-l-lysine and Its Highly Efficient Production via Synthetase Swap Strategy

ε-Poly-l-lysine (ε-PL) is a natural antimicrobial cationic peptide, which is generally recognized as safe for use as a food preservative. To date, the production capacity of strains that produce low-molecular weight ε-PL remains very low and thus unsuitable for industrial production. Here, we report a new low-molecular weight ε-PL-producing Kitasatospora aureofaciens strain. The ε-PL synthase gene of this strain was cloned into a high ε-PL-producing Streptomyces albulus strain. The resulting recombinant strain efficiently produced ε-PL with a molecular weight of 1.3-2.3 kDa and yielded of 23.6 g/L following fed-batch fermentation in a 5 L bioreactor. In addition, circular dichroism spectra showed that this ε-PL takes on a conformation similar to an antiparallel pleated-sheet. Moreover, it demonstrated better antimicrobial activity against yeast compared to the 3.2-4.5 kDa ε-PL. This study provides a highly efficient strategy for production of the low-molecular weight ε-PL, which helps to expand its potential applications.

Development of a strategy for the production of docosahexaenoic acid by Schizochytrium sp. from cane molasses and algae-residue

The aim of this work was to reduce the algae-residue emission and make use of cane molasses as fermentation materials for docosahexaenoic acid (DHA) fermentaion by Schizochytrium sp., which further could cut the cost of DHA production. Algae-residue and cane molasses were respectively used as nitrogen and carbon sources to replace yeast extract and glucose. A significant DHA yield of 18.58 g/L was obtained using algae-residue, while cane molasses could not be used well as sole carbon source due to the presence of undesirable substance. A two-stage culture strategy with glucose followed by pretreated cane molasses as carbon source was developed, resulting in a final DHA yield of 15.22 g/L. This study therefore offers an economical and green strategy for DHA production by Schizochytrium sp.

Chlamydomonas sp. as dynamic biorefinery feedstock for the production of methyl ester and ɛ-polylysine

An integrated production of methyl ester and ɛ-polylysine from Chlamydomonas sp. was studied using biorefinery approach. The harvesting efficiency of Chlamydomonas sp. was increased up to 92% by treatment with a flocculant FeCl₃ at 100 mg/L for 30 min. The DMC (dimethyl carbonate) mediated enzyme catalyzed in-situ transesterification of Chlamydomonas sp. yielded the maximum methyl ester of 92% under optimized conditions. The valued-added product ɛ-polylysine was produced from hydrolysate obtained from the spent biomass of Chlamydomonas sp. using Streptomyces sp. The key components of sugar and MgSO₄ used for ɛ-polysine production were optimized whereby the maximum ɛ-polylysine production was achieved at 50 g/L sugar and 0.3 g/L MgSO₄. The ɛ-polylysine production was further enhanced by supplementation of important amino acids (lysine and aspartate) and TCA cycle intermediates (citric acid and α-ketoglutaric acid). The maximum ɛ-polylysine production of 2.24 g/L was found with 4 mM citric acid supplementation after 110 h.

Development of a method for the valorization of fermentation wastewater and algal-residue extract in docosahexaenoic acid production by Schizochytrium sp

Fermentation wastewater (FW) and algal residue are major by-products of docosahexaenoic acid (DHA) fermentations utilizing Schizochytrium sp. In order to reduce production costs and environmental pollution, we explored the application of FW and algal-residue extract (AE) for DHA production. Components analysis showed that FW and AE contained some mineral elements and protein residues, respectively. When they were used for DHA fermentation, results showed that 20% replacement of fresh water by FW and 80% replacement of yeast extract nitrogen by AE reached DHA content of 22.23 g/L and 27.10 g/L, respectively. Furthermore, a novel medium that utilizes a mixture of FW and AE was applied for DHA fermentation, whereby the final DHA yield reached 28.45 g/L, 24.56% higher than conventional medium. The strategy of valorizing fermentation waste provides a new method for reducing the costs and reducing environmental pollution of microbial fermentations.

Improving α, ω-dodecanedioic acid productivity from n-dodecane and hydrolysate of Candida cells by membrane integrated repeated batch fermentation

The aim of the present study is to develop an effective production process for α, ω-dodecanedioic acid (DC₁₂) biosynthesis using n-dodecane and hydrolysate of Candida cells as substrates by membrane integrated repeated batch fermentation. Cells and n-dodecane were simultaneously recycled during the filtration of fermentation broth (FB) with a 150 kDa ceramic membrane under a cross-flow velocity of 4 m/s and a trans-membrane pressure of 0.2 MPa, and it was also revealed that the cells in the broth could alleviate the membrane fouling during the FB filtration. Moreover, the hydrolysate of the collected cells could be successfully used as a nitrogen source to replace 50% yeast extract for decreasing the DC₁₂ production cost. With repeated-batch culture in a membrane bioreactor, the maximal DC₁₂ productivity could be enhanced by 57.8% compared with the batch culture, meanwhile n-dodecane and cells could be recovered and used for the next fermentation cycle.

An integrated bio-process for production of functional biomolecules utilizing raw and by-products from dairy and sugarcane industries

The study investigated an integrated bioprocessing of raw and by-products from sugarcane and dairy industries for production of non-digestible prebiotic and functional ingredients. The low-priced feedstock, whey, molasses, table sugar, jaggery, etc., were subjected to transglucosylation reactions catalyzed by dextransucrase from Leuconostoc mesenteroides MTCC 10508. HPLC analysis approximated production of about 11-14 g L^-1 trisaccharide i.e. 2-α-D-glucopyranosyl-lactose (4-galactosyl-kojibiose) from the feedstock prepared from table sugar, jaggery, cane molasses and liquid whey, containing about 30 g L^-1 sucrose and lactose each. The trisaccharide was hydrolysed into the prebiotic disaccharide, kojibiose, by employing recombinant β-galactosidase from Escherichia coli. The enzyme β-galactosidase achieved about 90% conversion of 2-α-D-glucopyranosyl-lactose into kojibiose. The D-fructose generated by catalytic reactions of dextransucrase was targeted for catalytic transformation into rare sugar, D-allulose (or D-psicose), by treating the samples with Smt3-D-psicose 3-epimerase. The catalytic reactions resulted in the conversion of ~ 25% D-fructose to D-allulose. These bioactive compounds are known to exert a plethora of benefits to human health, and therefore, are preferred ingredients for making functional foods.

Production of chemicals and proteins using biomass-derived substrates from a Streptomyces host

Bioproduction using microbes from biomass feedstocks is of interest in regards to environmental problems and cost reduction. Streptomyces as an industrial microorganism plays an important role in the production of useful secondary metabolites for various applications. This strain also secretes a wide range of extracellular enzymes which degrade various biopolymers in nature, and it consumes these degrading substrates as nutrients. Hence, Streptomyces can be employed as a cell factory for the conversion of biomass-derived substrates into various products. This review focuses on the following two points: (1) Streptomyces as a producer of enzymes for degrading biomass-derived polysaccharides and polymers; and, (2) wild-type and engineered strains of Streptomyces as a host for chemical production from biomass-derived substrates.

Enhancement of ε-poly-L-lysine synthesis in Streptomyces by exogenous glutathione

Our previous work indicated that the vigor of Streptomyces decreased at the later stage of ε-poly-L-lysine (ε-PL) fermentation. In this study, we observed that the level of reactive oxygen species (ROS) in vivo increased sharply after 24 h, and the addition of an antioxidant glutathione (GSH) before this increase in ROS stimulated ε-PL synthesis in shake-flask fermentation. The enhancement of ε-PL production by GSH was further verified in batch and fed-batch fermentations. On a 5-l fermenter scale, the highest increasement was 68.8% in batch fermentation and the highest ε-PL level was 46.5 g l^- 1 in fed-batch fermentation. The RT-qPCR analysis showed that the transcriptional level of the catalase gene was down-regulated, and the decrease in cell activity was alleviated by the addition of GSH. The results revealed that exogenous antioxidant might maintain the cell vigor by reducing the excess ROS which provided a novel approach to regulate ε-PL synthesis.

Production of ε-poly-lysine by Streptomyces albulus PD-1 via solid-state fermentation

The aim of this study was to produce ε-poly-lysine (ε-PL) by Streptomyces albulus PD-1 through solid-state fermentation (SSF) using agro-industrial residues. Maximum ε-PL production (86.62mg/g substrate) was obtained a mixed substrate of rapeseed cake and wheat bran (2:1, w/w) supplemented with glucose (4%, w/w), (NH₄)₂SO₄ (3%, w/w), with an initial moisture content of 65%, initial pH of 7.0 and inoculum size of 13% v/w, incubated at 30°C for 8days. The results of scanning electron microscopy indicated that the filamentous thallus could penetrate the substrate surface. Moreover, repeated-batch SSF was successfully conducted 8 times using 10% substrate as seeds for the next fermentation cycle, and the results suggest that repeated-batch SSF is more efficient because of the shortened lag phase. To the best of our knowledge, this is the first report on ε-PL production using the SSF process.

A novel approach of integrated bioprocessing of cane molasses for production of prebiotic and functional bioproducts

In this work, the sugar industry by-product cane molasses was investigated as feedstock for acceptor reactions by dextransucrase from Leuconostoc mesenteroides MTCC 10508, leading to the biosynthesis of oligosaccharides. The starch industry corn fiber residue was used as a source for acceptor molecules, maltose, in the reaction. Production of approximately 124g oligosaccharides (DP3-DP6) per kg of fresh molasses was achieved. Further, cane molasses based medium was demonstrated as a sole carbon source for L. mesenteroides growth and dextransucrase production. d-Fructose released by dextransucrase activity as processing by-product was transformed into the functional monosaccharide with zero caloric value, d-psicose, by inducing its epimerization. Quantitative analysis approximated 37g d-psicose per kg of fresh molasses. Thus, the study established a novel approach of integrated bioprocessing of cane molasses into prebiotic and functional food additives.

Economic process to co-produce poly(ε-l-lysine) and poly(l-diaminopropionic acid) by a pH and dissolved oxygen control strategy

This study tended to apply biorefinery of indigenous microbes to the fermentation of target-product generation through a novel control strategy. A novel strategy for co-producing two valuable homopoly(amino acid)s, poly(ε-l-lysine) (ε-PL) and poly(l-diaminopropionic acid) (PDAP), was developed by controlling pH and dissolved oxygen concentrations in Streptomyces albulus PD-1 fermentation. The production of ε-PL and PDAP got 29.4 and 9.6gL(-1), respectively, via fed-batch cultivation in a 5L bioreactor. What is more, the highest production yield (21.8%) of similar production systems was achieved by using this novel strategy. To consider the economic-feasibility, large-scale production in a 1t fermentor was also implemented, which would increase the gross profit of 54,243.5USD from one fed-batch bioprocess. This type of fermentation, which produces multiple commercial products from a unified process is attractive, because it will improve the utilization rate of raw materials, enhance production value and enrich product variety.

Production of validamycin A from hemicellulose hydrolysate by Streptomyces hygroscopicus 5008

Validamycin A (VAL-A) is an important agricultural antibiotic produced by Streptomyces hygroscopicus 5008, which uses starch as carbon source occupying about 20% of total production cost. To reduce the medium cost, corncob hydrolysate - a hemicellulose hydrolysate was applied as a low-cost substrate to VAL-A fermentation. It was found that three major sugars in corncob hydrolysate including d-glucose, d-xylose and l-arabinose could all be utilized by S. hygroscopicus 5008 to produce VAL-A while d-xylose was the main contributor. A higher VAL-A production titer from d-xylose was achieved by using a genetically engineered strain TC03 derived from S. hygroscopicus 5008, which resulted in 1.27-fold improvement of VAL-A production from the medium containing 13% (v/v) corncob hydrolysate compared to that by its original strain. A medium cost analysis was done and compared with previous reports. This work indicates a great potential of the hemicellulose hydrolysate as substrate for antibiotic fermentation.