Enhancement of astaxanthin production from food waste by Phaffia rhodozyma screened by flow cytometry and feed application potential

Astaxanthin is widely used in food, aquaculture, cosmetics, and pharmaceuticals due to its strong antioxidant activity and coloring ability, but its production from Phaffia rhodozyma remains the main challenge due to the high fermentation cost and low content of carotenoid. In this study, the production of carotenoids from food waste (FW) by a P. rhodozyma mutant was investigated. P. rhodozyma mutant screened by UV mutagenesis and flow cytometry could stably produce high carotenoids at 25°C, with carotenoid production (32.9 mg/L) and content (6.7 mg/g), respectively, increasing by 31.6% and 32.3% compared with 25 mg/L and 5.1 mg/g of wild strain. Interestingly, the carotenoid production reached 192.6 mg/L by feeding wet FW, which was 21% higher than batch culture. The 373 g vacuum freeze-dried products were obtained from the fermentation of 1 kg FW by P. rhodozyma, which contained 784 mg carotenoids and 111 mg astaxanthin. The protein, total amino acids, and essential amino acids content of the fermentation products were 36.6%, 40.5%, and 18.2% (w/w), respectively, and lysine-added fermentation products had the potential of high-quality protein feed source. This study provides insights for the high-throughput screening of mutants, astaxanthin production, and the development of the feed potential of FW.

Improved Bio-Synthesis of 2,5-bis(hydroxymethyl)furan by Burkholderia contaminans NJPI-15 With Co-substrate

Upgrading of biomass derived 5-hydroxymethylfurfural (HMF) has attracted considerable interest recently. A new highly HMF-tolerant strain of Burkholderia contaminans NJPI-15 was isolated in this study, and the biocatalytic reduction of HMF into 2,5-bis(hydroxymethyl)furan (BHMF) using whole cells was reported. Co-substrate was applied to improve the BHMF yield and selectivity of this strain as well as HMF-tolerant level. The catalytic capacity of the cells can be substantially improved by Mn²⁺ ion. The strain exhibited good catalytic performance at a pH range of 6.0–9.0 and a temperature range of 25°C–35°C. In addition, 100 mM HMF could be reduced to BHMF by the B. contaminans NJPI-15 resting cells in presence of 70 mM glutamine and 30 mM sucrose, with a yield of 95%. In the fed-batch strategy, 656 mM BHMF was obtained within 48 h, giving a yield of 93.7%. The reported utilization of HMF to produce BHMF is a promising industrially sound biocatalytic process.

Enhanced O-succinyl-l-homoserine production by recombinant Escherichia coli ΔIJBB*TrcmetL/pTrc-metAfbr -Trc-thrAfbr -yjeH via multilevel fermentation optimization

AIMS

Constructing a strain with high yield of O-succinyl-l-homoserine (OSH) and improving the titre through multilevel fermentation optimization.

METHODS AND RESULTS

OSH high-yielding strain was first constructed by deleting the thrB gene to block the threonine biosynthesis. Single-factor experiment was carried out, where a Plackett-Burman design was used to screen out three factors (glucose, yeast and threonine) from the original 11 factors that affected the titre of OSH. The Box-Behnken response surface method was used to optimize the fermentation conditions. Through gene editing and medium optimization, the titre of OSH increased from 7·20 to 8·70 g l^-1 in 500 ml flask. Furthermore, the fermentation process and fed-batch fermentation conditions including pH, temperature, feeding strategy and feeding medium were investigated and optimized. Under the optimal conditions, the titre of OSH reached 102·5 g l^-1 , which is 5·6 times higher than before (15·6 g l^-1 ).

CONCLUSIONS

O-succinyl-l-homoserine fermentation process was established and the combination of response surface methodology and metabolic pathway analysis effectively improved the titre of OSH.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, the titre of OSH reached the needs for industrial production and the metabolic pathway of OSH was demonstrated for further optimization.

Efficient androst-1,4-diene-3,17-dione production by co-expressing 3-ketosteroid-Δ1 -dehydrogenase and catalase in Bacillus subtilis

AIMS

3-ketosteroid-Δ¹ -dehydrogenase (KSDD), a flavin adenine dinucleotide (FAD)-dependent enzyme involved in sterol metabolism, specifically catalyses the conversion of androst-4-ene-3,17-dione (AD) to androst-1,4-diene-3,17-dione (ADD). However, the low KSDD activity and the toxic effects of hydrogen peroxide (H₂ O₂ ) generated during the biotransformation of AD to ADD with FAD regeneration hinder its application on AD conversion. The aim of this work was to improve KSDD activity and eliminate the toxic effects of the generated H₂ O₂ to enhance ADD production.

METHODS AND RESULTS

The ksdd gene obtained from Mycobacterium neoaurum JC-12 was codon-optimized to increase its expression level in Bacillus subtilis, and the KSDD activity reached 12·3 U mg^-1 , which was sevenfold of that of codon-unoptimized gene. To improve AD conversion, catalase was co-expressed with KSDD in B. subtilis 168/pMA5-ksdd^opt -katA to eliminate the toxic effects of H₂ O₂ generated during AD conversion. Finally, under optimized bioconversion conditions, fed-batch strategy was carried out and the ADD yield improved to 8·76 g l^-1 .

CONCLUSIONS

This work demonstrates the potential to improve enzyme activity by codon-optimization and eliminate the toxic effects of H₂ O₂ by co-expressing catalase.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study showed the highest ADD productivity ever reported and provides a promising strain for efficient ADD production in the pharmaceutical industry.