Highly effective, regiospecific reduction of chalcone by cyanobacteria leads to the formation of dihydrochalcone: two steps towards natural sweetness

Abstract

BackgroundChalcones are the biogenetic precursors of all known flavonoids, which play an essential role in various metabolic processes in photosynthesizing organisms. The use of whole cyanobacteria cells in a two-step, light-catalysed regioselective bio-reduction of chalcone, leading to the formation of the corresponding dihydrochalcone, is reported. The prokaryotic microalgae cyanobacteria are known to produce phenolic compounds, including flavonoids, as natural components of cells. It seems logical that organisms producing such compounds possess a suitable “enzymatic apparatus” to carry out their biotransformation. Therefore, determination of the ability of whole cells of selected cyanobacteria to carry out biocatalytic transformations of chalcone, the biogenetic precursor of all known flavonoids, was the aim of our study.ResultsChalcone was found to be converted to dihydrochalcone by all examined cyanobacterial strains; however, the effectiveness of this process depends on the strain with biotransformation yields ranging from 3% to >99%. The most effective biocatalysts are Anabaena laxa, Aphanizomenon klebahnii, Nodularia moravica, Synechocystis aquatilis (>99% yield) and Merismopedia glauca (92% yield). The strains Anabaena sp. and Chroococcus minutus transformed chalcone in more than one way, forming a few products; however, dihydrochalcone was the dominant product. The course of biotransformation shed light on the pathway of chalcone conversion, indicating that the process proceeds through the intermediate cis-chalcone. The scaled-up process, conducted on a preparative scale and by using a mini-pilot photobioreactor, fully confirmed the high effectiveness of this bioconversion. Moreover, in the case of the mini-pilot photobioreactor batch cultures, the optimization of culturing conditions allowed the shortening of the process conducted by A. klebahnii by 50% (from 8 to 4 days), maintaining its >99% yield.ConclusionsThis is the first report related to the use of whole cells of halophilic and freshwater cyanobacteria strains in a two-step, light-catalysed regioselective bio-reduction of chalcone, leading to the formation of the corresponding dihydrochalcone. The total bioconversion of chalcone in analytical, preparative, and mini-pilot scales of this process creates the possibility of its use in the food industry for the production of natural sweeteners.

Biocatalytic hydrogenation of the C=C bond in the enone unit of hydroxylated chalcones—process arising from cyanobacterial adaptations

“…The products of biotransformation were identified by HPTLC and UHPLC-UV-ESI-MS techniques similarly as it was reported for dihydrochalcone (Żyszka et al 2017a ). To examine the course of biotransformation, the products of this process were separated in HPTLC experiments, on TLC aluminium plates using a CAMAG Linomat 5 applicator (CAMAG, Muttenz, Switzerland).…”

“…All hydroxylated chalcone stock solutions were prepared in dimethyl sulfoxide (DMSO) (15 mg/mL) and sterilised by filtration prior to their addition to the medium. All stock solutions were made on the same day of use and kept in dark to prevent photodamage (Zyszka et al 2017a ). All components of the medium were purchased from Avantor Performance Materials Poland S.A. (Gliwice, Poland).…”

“…To prepare the inoculates used to initiate the experimental cultures, all tested cyanobacteria were pre-grown in standard media: MSp (ATCC 1679) medium (pH 9.5) for the halophilic strain and BG11 (ATCC 616) or Z8 medium (pH 7.0) for the freshwater strains. The cultures of the tested cyanobacteria were grown at 24 ± 1 °C with 16-h day (1000 lx light intensity) and 8-h night photoperiods, corresponding to the conditions of a long day, in 250-mL Erlenmeyer flasks containing 60 mL of each culture (Allen 1968 ; Rippka et al 1979 ; Żyszka et al 2017a ).…”

“…Screening (analytical) scale biotransformations of all hydroxylated chalcones were studied according to previously described methodology (Żyszka et al 2017a ). The cyanobacterial inoculum was added to 100-mL Erlenmeyer flasks containing 30 mL of the respective culture medium supplemented with the appropriate hydroxylated chalcone stock solution (0.13%, v / v ) to obtain a final concentration of 20 mg/L of hydroxylated chalcone.…”

Non-Conventional Yeasts as Sources of Ene-Reductases for the Bioreduction of Chalcones

“…In particular, some dihydrochalcones (achieved via bioreduction of the C=C double bond) have been found to express antioxidant, UV-protective and pro-health activities, which could be interesting for pharmaceutical and cosmetic industries [25,30]. Moreover, their sweet taste make them attractive for producing sweeteners [31,32]. In addition, the dihydrochalcone obtained from bioreduction of (E)-1,3-diphenylprop-2-en-1-one has been isolated from the leaves of Leptoderris fasciculata [33], a woody liana used in traditional medicine for the treatment of dropsy, edema, pulmonary disorders and as a laxative [34].…”