Efficient production of lactobionic acid using genetically engineered Pseudomonas taetrolens as a whole-cell biocatalyst

Conversion of Deproteinized Cheese Whey to Lactobionate by an Engineered Neurospora crassa Strain F5

We report a novel production process for lactobionic acid (LBA) production using an engineered Neurospora crassa strain F5. The wild-type N. crassa strain produces cellobiose dehydrogenase (CDH) and uses lactose as a carbon source. N. crassa strain F5, which was constructed by deleting six out of the seven β-glucosidases in the wild type, showed a much slower lactose utilization rate and produced a much higher level of cellobiose dehydrogenase (CDH) than the wild type. Strain N. crassa F5 produced CDH and laccase simultaneously on the pretreated wheat straw with 3 µM of cycloheximide added as the laccase inducer. The deproteinized cheese whey was added directly to the shake flasks with the fungus present to achieve LBA production. Strain F5 produced about 37 g/L of LBA from 45 g/L of lactose in 27 h since deproteinized cheese whey addition. The yield of LBA from consumed lactose was about 85%, and the LBA productivity achieved was about 1.37 g/L/h.

Valorization of cheese whey to lactobionic acid by a novel strain Pseudomonas fragi and identification of enzyme involved in lactose oxidation

Background

Efficient upgrading of inferior agro-industrial resources and production of bio-based chemicals through a simple and environmentally friendly biotechnological approach is interesting Lactobionic acid is a versatile aldonic acid obtained from the oxidation of lactose. Several microorganisms have been used to produce lactobionic acid from lactose and whey. However, the lactobionic acid production titer and productivity should be further improved to compete with other methods.

Results

In this study, a new strain, Pseudomonas fragi NL20W, was screened as an outstanding biocatalyst for efficient utilization of waste whey to produce lactobionic acid. After systematic optimization of biocatalytic reactions, the lactobionic acid productivity from lactose increased from 3.01 g/L/h to 6.38 g/L/h in the flask. In batch fermentation using a 3 L bioreactor, the lactobionic acid productivity from whey powder containing 300 g/L lactose reached 3.09 g/L/h with the yield of 100%. Based on whole genome sequencing, a novel glucose dehydrogenase (GDH1) was determined as a lactose-oxidizing enzyme. Heterologous expression the enzyme GDH1 into P. putida KT2440 increased the lactobionic acid yield by 486.1%.

Conclusion

This study made significant progress both in improving lactobionic acid titer and productivity, and the lactobionic acid productivity from waste whey is superior to the ever reports. This study also revealed a new kind of aldose-oxidizing enzyme for lactose oxidation using P. fragi NL20W for the first time, which laid the foundation for further enhance lactobionic acid production by metabolic engineering.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01907-0.

Production of lactobionic acid at high salt concentrations by Acinetobacter halotolerans isolated from seaside soil

A lactobionic acid (LBA)-producing bacterium isolated from seaside soils was identified as Acinetobacter halotolerans and designated as strain KRICT-1. We determined whether KRICT-1 can produce LBA at high salt concentrations. The KRICT-1 strain grew on a nutrient broth (NB) agar plate with up to 7.0% NaCl, indicating high NaCl tolerance, and 30 °C was the optimum growth temperature for LBA production. We produced LBA using the KRICT-1 strain in NB medium containing various concentrations of NaCl. While Pseudomonas taetrolens, an efficient LBA-producing bacterium, could produce LBA with up to 5.5% NaCl, the KRICT-1 strain could produce LBA at up to 7.0% NaCl and produced more LBA than P. taetrolens with over 5.5% NaCl. We produced LBA using NB medium containing 7.0% NaCl by batch fermentation of the KRICT-1 strain in a 5 L fermenter. The LBA production titer and productivity of the KRICT-1 strain were 32.1 g/L and 0.22 g/L/h, respectively, which were approximately 1.35- and 1.38-fold higher than those (23.7 g/L and 0.16 g/L/h) obtained from flask culture. Additionally, quinoprotein glucose dehydrogenase is an LBA-producing enzyme in A. halotolerans. We demonstrated that the A. halotolerans KRICT-1 strain is appropriate for LBA production at high salt concentrations.

Efficient production of cellobionic acid using whole-cell biocatalyst of genetically modified Pseudomonas taetrolens

Pseudomonas taetrolens has previously been shown to convert cellobiose to cellobionic acid (CBA), which can potentially be used in cosmetics, food, and pharmaceutical industries. The cellobiose-oxidizing activity of the P. taetrolens strain, which expressed the homologous quinoprotein glucose dehydrogenase (GDH), was increased by approximately 50.8% compared to the original strain. Whole-cell biocatalyst (WCB) of the genetically modified P. taetrolens strain [pDSK-GDH] was prepared simply by fermentation and washing processes. Reaction conditions for the proper use of WCB, such as reaction temperature, cell density to be added, and cell harvest time for preparing WCB, were investigated. The highest CBA productivity (18.2 g/L/h) was achieved when WCB prepared in the late-exponential phase of cell culture was used at 35 °C with cell density of 10 at OD_600nm. Under these conditions, 200 g/L of cellobiose was all converted to CBA in 11 h, and the WCB of P. taetrolens [pDSK-GDH] maintained the maximum catalytic activity during at least six cycles without a significant decline in the productivity. Our results suggest that the manufacture of WCB based on genetically engineered P. taetrolens and its optimized use could be further developed as an economically viable option for the large-scale production of CBA.

Whole-cell biocatalysis using genetically modified Pseudomonas taetrolens for efficient production of maltobionic acid from pure maltose and high-maltose corn syrup

Maltobionic acid (MBA) can be applied to various fields such as food, cosmetics, and pharmaceutical industries. In this study, whole-cell biocatalysis for MBA production was performed using recombinant Pseudomonas taetrolens homologously expressing quinoprotein glucose dehydrogenase (GDH). Various reaction parameters such as temperature, cell density, and cell harvest time, were optimized for improving MBA production. Under the optimized reaction conditions using pure maltose as a substrate, the MBA production titer, yield, and productivity of whole-cell biocatalyst (WCB) were 200 g/L, 95.6%, and 18.18 g/L/h, respectively, which were the highest compared to those reported previously. Productivity, a key factor for industrial MBA production, obtained from whole-cell biocatalysis in this study, was enhanced by approximately 1.9-fold compared to that obtained in our previous work (9.52 g/L/h) using the fermentation method. Additionally, the WCB could be reused up to six times without a significant reduction in MBA productivity, indicating that the WCB is very robust. Although MBA productivity (8.33 g/L/h) obtained from high-maltose corn syrup (HMCS) as a substrate was 45.8% of that using pure maltose, HMCS can be a better substrate for commercial MBA production because its price is only 1.1% of that of pure maltose. The results of this study using a WCB to convert maltose into MBA may support the development of a potential industrial process for more economically effective MBA production in the future.

Efficient Production of Lactobionic Acid Using Escherichia coli Capable of Synthesizing Pyrroloquinoline Quinone

Lactobionic acid (LBA) is an emerging chemical that has been widely utilized in food, cosmetic, and pharmaceutical industries. We sought to produce LBA using Escherichia coli. LBA can be produced from lactose in E. coli, which is innately unable to produce LBA, by coexpressing a heterologous quinoprotein glucose dehydrogenase (GDH) and a pyrroloquinoline quinone (PQQ) synthesis gene cluster. Using a recombinant E. coli strain, we successfully produced LBA without additional supplementation of PQQ, and changing the type of heterologous GDH improved the LBA production titer and productivity. To further enhance LBA production, culture conditions, such as growth temperature and isopropyl-β-d-1-thiogalactopyranoside concentration, were optimized. Using optimized culture conditions, batch fermentation of the recombinant E. coli strain was performed using a 5 L bioreactor. After fermentation, this strain produced an LBA titer of 209.3 g/L, a yield of 100%, and a productivity of 1.45 g/L/h. To our best knowledge, this is the first study to produce LBA using heterologous GDH in an E. coli strain without any additional cofactors. Our results provide a simple method to produce LBA from lactose in a naturally non-LBA-producing bacterium and lay the groundwork for highly efficient LBA production in E. coli, which is one of the most versatile metabolite-producing bacterial hosts.

Efficient isolation of new lactobionic acid-producing microorganisms from environmental samples by colloidal calcium carbonate agar plate-based screening

Lactobionic acid (LBA) has recently emerged as an important substance in various industries, such as cosmetics, foods, and pharmaceuticals. In this study, we developed a simple, efficient, and high-throughput method for screening LBA-producing microorganisms. First, an agar plate was prepared to isolate LBA-producing microorganisms by utilizing the property of LBA to solubilize colloidal calcium carbonate (CaCO₃), resulting in the formation of a clear halo around colonies on a nutrient broth agar plate containing CaCO₃. Subsequently, LBA production from the isolated microorganisms was confirmed using high-performance liquid chromatography (HPLC). Approximately 560 colonies from soil samples in Ulsan, Korea were screened and a clear halo was observed around three colonies on the prepared LBA-screening agar plate. The culture supernatants of these three colonies were analyzed by HPLC and it was found that these strains could produce LBA from lactose. Phylogenetic analysis by comparing their 16S rRNA nucleotide sequences revealed that these strains were Pseudomonas spp. and Alcaligenes faecalis. This is the first report highlighting that A. faecalis can produce LBA. As per the aforementioned results, the LBA-screening method that we devised here is highly effective for isolating and identifying new LBA-producing microorganisms.

Isolation of new lactobionic acid-producing microorganisms and improvement of their production ability by heterologous expression of glucose dehydrogenase from Pseudomonas taetrolens

Lactobionic acid (LBA) is a specialty organic acid that is widely employed in the food, cosmetic, and pharmaceutical industries. In the present study, we screened new LBA-producing bacteria from the soil of a poultry farm. Among the 700 bacterial colonies, five that exhibited LBA-producing ability were successfully isolated. Phylogenetic analysis based on 16 S rRNA sequences identified strain 2-15 as an Acinetobacter sp., strains 3-13 and 3-15 as Pseudomonas spp., and strains 7-7 and 7-8 as Psychrobacter spp. The LBA-producing abilities of the five strains were compared in flask culture, whereupon Psychrobacter sp. 7-8 showed the highest LBA titer (203.7 g/L), LBA yield from lactose (97.3%), and LBA productivity (2.83 g/L/h). To our best knowledge, this is the first study showing that Acinetobacter and Psychrobacter spp. can produce LBA from lactose. Our results would help broaden the spectrum of workhorse bacteria available for the industrially important microbial production of LBA. In addition, we improved the LBA-production ability of the three isolated bacteria, namely Acinetobacter sp. 2-15, Pseudomonas spp. strains 3-13 and 3-15, by heterologously expressing quinoprotein glucose dehydrogenase from Pseudomonas taetrolens. In particular, the LBA-production ability of the recombinant Pseudomonas sp. 3-13 were highly improved that the LBA titer and productivity were 19.2- (205.6 vs. 10.7 g/L, respectively) and 17.8-fold (1.07 vs. 0.06 g/L/h, respectively) higher, respectively, than those of the wild-type strain. These values were almost identical to those of the wild-type Psychrobacter sp. 7-8, which showed the highest LBA productivity among the five isolated strains. This result demonstrated that the expression of lactose-oxidizing enzyme in LBA-producing microorganisms was highly effective to enhance their LBA-production ability. Our study presents a practical method to screen for efficient LBA-producing microorganisms and to improve their production ability by genetic engineering for industrial LBA production.

Identification of a lactose-oxidizing enzyme in Escherichia coli and improvement of lactobionic acid production by recombinant expression of a quinoprotein glucose dehydrogenase from Pseudomonas taetrolens

Lactobionic acid (LBA), an aldonic acid prepared by oxidation of the free aldehyde group of lactose, has been broadly used in cosmetic, food, and pharmaceutical industries. Although Escherichia coli is unable to produce LBA naturally, a wild-type E. coli strain successfully produced LBA from lactose upon pyrroloquinoline quinone (PQQ) supplementation, indicating that E. coli contains at least one lactose-oxidizing enzyme as an apo-form. By inactivating the candidate genes in the E. coli chromosome, we found that the lactose-oxidizing enzyme of E. coli was the quinoprotein glucose dehydrogenase (GCD). To improve the LBA production ability of the E. coli strain, quinoprotein glucose dehydrogenase (GDH) from Pseudomonas taetrolens was recombinantly expressed and culture conditions such as growth temperature, initial lactose concentration, PQQ concentration, and isopropyl-β-D-1-thiogalactopyranoside induction concentration were optimized. We performed batch fermentation using a 5-L bioreactor under the optimized culture conditions determined in flask culture experiments. After batch fermentation, the LBA production titer, yield, and productivity of the recombinant E. coli strain were 200 g/L, 100 %, and 1.28 g/L/h, respectively. To the best our knowledge, this is the first report to identify the lactose-oxidizing enzyme of E. coli and to produce LBA using a recombinant E. coli strain as the production host. Because E. coli is one of the most easily genetically manipulated bacteria, our result provides the groundwork to further enhance LBA production by metabolic engineering of LBA-producing E. coli.

High-level production of maltobionic acid from high-maltose corn syrup by genetically engineered Pseudomonas taetrolens

Maltobionic acid (MBA) has recently emerged as an important material in various industries. Here, we showed that quinoprotein glucose dehydrogenase (GDH) from Pseudomonas taetrolens could convert maltose into MBA by heterologously expressing this enzyme in MBA non-producing Escherichia coli. We homologously expressed GDH in P. taetrolens to improve intracellular maltose-oxidizing activity and MBA production. We optimized culture conditions, then applied these conditions to batch fermentation by recombinant P. taetrolens in a 5-L bioreactor. The MBA production, yield, and productivity of batch fermentation using high-maltose corn syrup (HMCS), an inexpensive maltose source, were 200 g/L, 95.6 %, and 6.67 g/L/h, respectively. Although the MBA productivity from HMCS was 70.1 % of that compared with pure maltose as the substrate, HMCS was a better substrate for commercial MBA production, considering the cost was 1.1 % of that of pure maltose. The present findings provide an economically feasible strategy with which to produce MBA.