Biotechnological Production of Organic Acids from Renewable Resources

Fumaric acid production by Rhizopus species from acid hydrolysate of oil palm empty fruit bunches

The hemicellulosic fraction of lignocellulosic biomass is a very important material, due to the significant concentration of pentoses present in its composition and that can be used sustainably in biotechnological processes such as the production of fumaric acid. Research efforts are currently being promoted for the proper disposal and valorization of empty fruit bunches (EFB) from oil palm. In this work, seventeen Rhizopus species were evaluated in a fermentation medium with EFB hydrolyzate, without detoxification, as a carbon source for fumaric acid production. Rhizopus circicans 1475 and Rhizopus 3271 achieved productions of 5.65 g.L-1 and 5.25 g.L-1 of fumaric acid at 30 °C, 120 rpm for 96 h, respectively. The percentage of consumed sugars, mainly pentoses, was 24.88% and 34.02% for R. circicans 1475 and R 3271, respectively. Soy peptone and ammonium sulfate were evaluated as nitrogen sources, where soy peptone stimulated the formation of biomass pellets while ammonium sulfate produced mycelia and clamps.

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.

The antimicrobial and bioactive properties of lactobionic acid

Lactobionic acid (LBA) is a bioactive molecule that has generated keen interest in different industries. However, its future application in the food area is one of the most promising. Chemically, it is a polyhydroxy acid formed by the union of two molecules (galactose and gluconic acid) linked by an ether-bond, showing many interesting and unusual properties due to its structure and composition, although it is traditionally known in the food industry for its chelating, moisturizing, gelling, and antioxidant properties. There has been much research into the production of LBA, either by microbial fermentation or biocatalytic approaches such as enzymatic synthesis, but its use in foodstuffs, to produce new functional products and to evaluate its antimicrobial activity against food-borne pathogens, is a relatively new topic that has attracted the interest of the international research community recently. Furthermore, in spite of the potential of LBA, it has been approved only by the US Food and Drug Administration, and for its use as the salt form, but the publication of new comprehensive studies, able to agglutinate all the new food-related LBA research results, could disseminate knowledge about this compound and have an influence on its current regulation status. The aim of the present review is to describe the most recent advances and research on its antimicrobial potential, as well as summarizing the significant aspects that make LBA a promising bioactive compound for the food sector. © 2022 Society of Chemical Industry.

Engineering Zymomonas mobilis for the Production of Xylonic Acid from Sugarcane Bagasse Hydrolysate

Sugarcane bagasse is an agricultural residue rich in xylose, which may be used as a feedstock for the production of high-value-added chemicals, such as xylonic acid, an organic acid listed as one of the top 30 value-added chemicals on a NREL report. Here, Zymomonas mobilis was engineered for the first time to produce xylonic acid from sugarcane bagasse hydrolysate. Seven coding genes for xylose dehydrogenase (XDH) were tested. The expression of XDH gene from Paraburkholderia xenovorans allowed the highest production of xylonic acid (26.17 ± 0.58 g L-1) from 50 g L-1 xylose in shake flasks, with a productivity of 1.85 ± 0.06 g L-1 h-1 and a yield of 1.04 ± 0.04 gAX/gX. Deletion of the xylose reductase gene further increased the production of xylonic acid to 56.44 ± 1.93 g L-1 from 54.27 ± 0.26 g L-1 xylose in a bioreactor. Strain performance was also evaluated in sugarcane bagasse hydrolysate as a cheap feedstock, which resulted in the production of 11.13 g L-1 xylonic acid from 10 g L-1 xylose. The results show that Z. mobilis may be regarded as a potential platform for the production of organic acids from cheap lignocellulosic biomass in the context of biorefineries.

In-situ muconic acid extraction reveals sugar consumption bottleneck in a xylose-utilizing Saccharomyces cerevisiae strain

Background

The current shift from a fossil-resource based economy to a more sustainable, bio-based economy requires development of alternative production routes based on utilization of biomass for the many chemicals that are currently produced from petroleum. Muconic acid is an attractive platform chemical for the bio-based economy because it can be converted in chemicals with wide industrial applicability, such as adipic and terephthalic acid, and because its two double bonds offer great versatility for chemical modification.

Results

We have constructed a yeast cell factory converting glucose and xylose into muconic acid without formation of ethanol. We consecutively eliminated feedback inhibition in the shikimate pathway, inserted the heterologous pathway for muconic acid biosynthesis from 3-dehydroshikimate (DHS) by co-expression of DHS dehydratase from P. anserina, protocatechuic acid (PCA) decarboxylase (PCAD) from K. pneumoniae and oxygen-consuming catechol 1,2-dioxygenase (CDO) from C. albicans, eliminated ethanol production by deletion of the three PDC genes and minimized PCA production by enhancing PCAD overexpression and production of its co-factor. The yeast pitching rate was increased to lower high biomass formation caused by the compulsory aerobic conditions. Maximal titers of 4 g/L, 4.5 g/L and 3.8 g/L muconic acid were reached with glucose, xylose, and a mixture, respectively. The use of an elevated initial sugar level, resulting in muconic acid titers above 2.5 g/L, caused stuck fermentations with incomplete utilization of the sugar. Application of polypropylene glycol 4000 (PPG) as solvent for in situ product removal during the fermentation shows that this is not due to toxicity by the muconic acid produced.

Conclusions

This work has developed an industrial yeast strain able to produce muconic acid from glucose and also with great efficiency from xylose, without any ethanol production, minimal production of PCA and reaching the highest titers in batch fermentation reported up to now. Utilization of higher sugar levels remained conspicuously incomplete. Since this was not due to product inhibition by muconic acid or to loss of viability, an unknown, possibly metabolic bottleneck apparently arises during muconic acid fermentation with high sugar levels and blocks further sugar utilization.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01594-3.

Whey Utilization: Sustainable Uses and Environmental Approach

The dairy industry produces large amounts of whey as a by- or co-product, which has led to considerable environmental problems due to its high organic matter content. Over the past decades, possibilities of more environmentally and economically efficient whey utilisation have been studied, primarily to convert unwanted end products into a valuable raw material. Sustainable whey management is mostly oriented to biotechnological and food applications for the development of value-added products such as whey powders, whey proteins, functional food and beverages, edible films and coatings, lactic acid and other biochemicals, bioplastic, biofuels and similar valuable bioproducts. This paper provides an overview of the sustainable utilization of whey and its constituents, considering new refining approaches and integrated processes to convert whey, or lactose and whey proteins to high value-added whey-based products.

Bioconversion of Fish Discards through the Production of Lactic Acid Bacteria and Metabolites: Sustainable Application of Fish Peptones in Nutritive Fermentation Media

In the current work, we study the capacity of 30 peptones obtained by enzyme proteolysis of ten discarded fish species (hake, megrim, red scorpionfish, pouting, mackerel, gurnard, blue whiting, Atlantic horse mackerel, grenadier, and boarfish) to support the growth and metabolite production of four lactic acid bacteria (LAB) of probiotic and technological importance. Batch fermentations of Lactobacillus plantarum, L. brevis, L. casei, and Leuconostoc mesenteroides in most of the media formulated with fish peptones (87% of the cases) led to similar growths (quantified as dry-weight biomass and viable cells) and metabolites (mainly lactic acid) than in commercial control broth (MRS). Comparisons among cultures were performed by means of the parameters obtained from the mathematical fittings of experimental kinetics to the logistic equation. Modelling among experimental and predicted data from each bioproduction was generally accurate. A simple economic assessment demonstrated the profitability achieved when MRS is substituted by media formulated with fish discards: a 3-4-fold reduction of costs for LAB biomass, viable cells formation, and lactic and acetic acid production. Thus, these fish peptones are promising alternatives to the expensive commercial peptones as well as a possible solution to valorize discarded fish biomasses and by-products.

Biotechnological Valorization of Food Marine Wastes: Microbial Productions on Peptones Obtained from Aquaculture By-Products

Based on a biotechnological strategy, in the present work several peptones are produced from the Alcalase hydrolysis (0.1-0.2% v/w, 56-64 °C, pH 8.27-8.98, 3 h) and thermal processing (105 °C, 60 min) of wastes generated from the industrial processing of turbot, salmon, trout, seabream and seabass. These peptones were included (in the range of 2.6-11 g/L of soluble protein) as main source of organic nitrogen (protein substrates) in low-cost media for the culture of lactic acid bacteria (LAB), marine probiotic bacteria (MPB) and ubiquitous Gram+ bacteria. In most cases, batch fermentations conducted in aquaculture peptone media led to the best growth, metabolic productions and yields. Nevertheless, no significant differences between aquaculture peptones and commercial media were generally observed. Kinetic parameters from a logistic equation and used for cultures modeling were applied with the purpose of comparing the bioproduction outcomes. In economical terms, the validity of the aquaculture peptones as substitutives of the peptones (meat extract, casitone, etc.) from commercial media was also compared. The decreasing of the costs for LAB bioproductions ranged between 3-4 times and the growth costs of MPB and Gram+ bacteria were improved more than 70 and 15 times, respectively, in relation to those found in control commercial media.

Genome shuffling improved acid-tolerance and succinic acid production of Actinobacillus succinogenes

Succinic acid is widely applied to chemical, pharmaceutical, food, and agricultural industries. With the rapid development of these industries, a great demand of succinic acid is required. The acid-tolerance and succinic acid production of Actinobacillus succinogenes strain were improved by using genome shuffling. Results showed that one modified strain AS-F32, with the best acid resistance and the highest succinic acid production, was obtained after 3 cycles of genome shuffling. The minimum growth pH of AS-F32 was 3.5, and the acid production and cell dry weight were 5.1 and 4.8 g/L in flask, improved 2.6 and 1.85 times over the start strain As-R2. Furthermore, the succinic acid yield of As-32 was 31.2 g/L and the dry cell weight was increased 44.4% by maintaining pH 4.8 with 7.0 M NH₄OH in 5 L bioreactor, increased 1.1 times than the original strain As-R2.

Bacillus coagulans MA-13: a promising thermophilic and cellulolytic strain for the production of lactic acid from lignocellulosic hydrolysate

BACKGROUND

The transition from a petroleum-based economy towards more sustainable bioprocesses for the production of fuels and chemicals (circular economy) is necessary to alleviate the impact of anthropic activities on the global ecosystem. Lignocellulosic biomass-derived sugars are suitable alternative feedstocks that can be fermented or biochemically converted to value-added products. An example is lactic acid, which is an essential chemical for the production of polylactic acid, a biodegradable bioplastic. However, lactic acid is still mainly produced by Lactobacillus species via fermentation of starch-containing materials, the use of which competes with the supply of food and feed.

RESULTS

A thermophilic and cellulolytic lactic acid producer was isolated from bean processing waste and was identified as a new strain of Bacillus coagulans, named MA-13. This bacterium fermented lignocellulose-derived sugars to lactic acid at 55 °C and pH 5.5. Moreover, it was found to be a robust strain able to tolerate high concentrations of hydrolysate obtained from wheat straw pre-treated by acid-catalysed (pre-)hydrolysis and steam explosion, especially when cultivated in controlled bioreactor conditions. Indeed, unlike what was observed in microscale cultivations (complete growth inhibition at hydrolysate concentrations above 50%), B. coagulans MA-13 was able to grow and ferment in 95% hydrolysate-containing bioreactor fermentations. This bacterium was also found to secrete soluble thermophilic cellulases, which could be produced at low temperature (37 °C), still retaining an optimal operational activity at 50 °C.

CONCLUSIONS

The above-mentioned features make B. coagulans MA-13 an appealing starting point for future development of a consolidated bioprocess for production of lactic acid from lignocellulosic biomass, after further strain development by genetic and evolutionary engineering. Its optimal temperature and pH of growth match with the operational conditions of fungal enzymes hitherto employed for the depolymerisation of lignocellulosic biomasses to fermentable sugars. Moreover, the robustness of B. coagulans MA-13 is a desirable trait, given the presence of microbial growth inhibitors in the pre-treated biomass hydrolysate.