Abstract
To verify the hypothesis that cyanobacteria naturally biosynthesising polyphenolic compounds possess an active enzymatic system that enables them to transform these substances, such an ability of the biocatalytic systems of whole cells of these biota was assessed for the first time. One halophilic strain and seven freshwater strains of cyanobacteria representing four of the five taxonomic orders of Cyanophyta were examined to determine the following: (i) whether they contain polyphenols, including flavonoids; (ii) the resistance of their cultures when suppressed by the presence of exogenous hydroxychalcones—precursors of flavonoid biosynthesis and (iii) whether these photoautotrophs can transform hydroxylated chalcones. All examined strains were found to contain polyphenols and flavonoids, and the growth of their cultures was inhibited in the presence of 2′-hydroxychalcone, 2″-hydroxychalcone and 4″-hydroxychalcone. We also confirmed that the examined cyanobacteria transformed hydroxychalcones via hydrogenative bio-reduction and formed the corresponding hydroxydihydro derivatives with yields above 90% whenever the substrates were bioavailable for such a conversion. Moreover, we observed that the routes and efficiency of biohydrogenation (and hydroxylation) of chalcones were dependent on the location of the hydroxyl substituent. The final products obtained as the results of biotransformations were extracted from the media and identified by mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (1H NMR, 13C NMR, COSY, HSQC). Based on those results, we believe that the very efficient biohydrogenation of hydroxychalcones, which may easy be scaled up for biotechnological purposes, reflects the natural activity of the cyanobacterial defence system, because hydroxydihydrochalcones were less active inhibitors of the growth of cyanobacterial cultures than the corresponding substrates.
Highlights
Chalcones are a group of plant-derived compounds belonging to the flavonoid family that are synthesised through the phenylpropanoid pathway and play a vital role in different met-Appl Microbiol Biotechnol (2018) 102:7097–7111Biocatalysis represents a successful and, in many cases, outstanding substitute to standard chemical synthesis (Park et al 2009) or extraction of chalcones from plant material (Du et al 2010)
Cell-free extracts of eight strains of cyanobacteria belonging to different genera, including one halophilic strain (S. platensis) and seven freshwater strains (A. laxa, Anabaena sp., A. klebahnii, N. moravica, C. minutus, M. glauca and S. aquatilis), were evaluated for the total content of phenolics (TPC) and flavonoids (TFC)
The total phenolic content (TPC) varied from 10.23 ± 0.51 to 49.87 ± 2.49 mg/g GAE, and the total flavonoid content ranged between 1.87 ± 0.09 and 7.90 ± 0.40 mg/g QE of the extracts
Summary
Chalcones are a group of plant-derived compounds belonging to the flavonoid family that are synthesised through the phenylpropanoid pathway and play a vital role in different met-Appl Microbiol Biotechnol (2018) 102:7097–7111Biocatalysis represents a successful and, in many cases, outstanding substitute to standard chemical synthesis (Park et al 2009) or extraction of chalcones from plant material (Du et al 2010). Microbial conversion of compounds containing a three-carbon enone moiety has attracted increasing attention, with the recent rediscovery of ene-reductases from the old yellow enzyme family These flavoenzymes selectively catalyse the hydrogenation of activated C=C bonds of α,β-unsaturated carbonyl molecules in excellent yield (Fu et al 2013). Enereductases have been identified in prokaryotic microalgae, i.e. cyanobacteria (Fu et al 2013), and used for light-induced, photocatalytic reduction of C=C bonds (Koninger et al 2016) that conduces to the formation of dihydrochalcones Because of their high sweet taste, these compounds have potential applications in the food industry for the production of low-calorie, multicomponent, nontoxic and safety sweeteners of natural origin. Their UV-protective, antioxidant and health-promoting properties make dihydrochalcones of interest to the pharmaceutical and cosmetics industries (DuBois et al 1977; Winnig et al 2007)
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