Mechanism of synergistic DNA damage induced by caffeic acid phenethyl ester (CAPE) and Cu(II): Competitive binding between CAPE and DNA with Cu(II)/Cu(I).

Caffeic acid phenethyl ester (CAPE) is an active polyphenol of propolis from honeybee hives, and exhibits antioxidant and interesting pharmacological activities. However, in this study, we found that in the presence of Cu(II), CAPE exhibited pro-oxidative rather than antioxidant effect: synergistic DNA damage was induced by the combination of CAPE and Cu(II) together as measured by strand breakage in plasmid DNA and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation, which is dependent on the molar ratio of CAPE:Cu(II). Production of Cu(I) and H2O2 from the redox reaction between CAPE and Cu(II), and subsequent OH formation was found to be responsible for the synergistic DNA damage. DNA sequencing investigations provided more direct evidence that CAPE/Cu(II) caused preferential cleavage at guanine, thymine and cytosine residues. Interestingly, we found there are competitive binding between CAPE and DNA with Cu(II)/Cu(I), which changed the redox activity of Cu(II)/Cu(I), via complementary applications of different analytical methods. The observed DNA damage was mainly attributed to the formation of DNA-Cu(II)/Cu(I) complexes, which is still redox active and initiated the redox reaction near the binding site between copper and DNA. Based on these data, we proposed that the synergistic DNA damage induced by CAPE/Cu(II) might be due to the competitive binding between CAPE and DNA with Cu, and site-specific production of OH near the binding site of copper with DNA. Our findings may have broad biological implications for future research on the pro-oxidative effects of phenolic compounds in the presence of transition metals.

Paraburkholderia caffeinitolerans sp. nov., a caffeine degrading species isolated from a tea plantation soil sample.

A Gram-stain negative, facultatively anaerobic, non-sporulating, non-motile and rod-shaped bacterium, designated CF3T, was isolated from a tea plantation soil sample and its taxonomic position was determined using polyphasic taxonomy. Strain CF3T displayed optimum growth at 25 °C, pH 5.0 and in the presence of 0-1 % NaCl. Comparative phylogenetic analysis of the 16S rRNA, recA and gyrB gene sequences showed that the isolate belongs to the genus Paraburkholderia, showing high levels of similarity with respect to Paraburkholderia oxyphila OX-01T (98.3, 95 and 93 %, respectively) and Paraburkholderia sacchari IPT101T (98.2, 95 and 95 %, respectively). The predominant ubiquinone was determined to be Q-8, and the polar lipids are phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified amino-phospholipid, three unidentified amino-lipids and three unidentified polar lipids. The major fatty acids were found to be C16:0, C17:0 cyclo, summed feature 8 (C18:1 ω7c and/or C18:1 ω6c) and summed feature 3 (C16:1 ω7c and/or C16:1 ω6c). The DNA G+C content was found to be 63.8 mol% and the DNA-DNA relatedness values between strain CF3T and its two close relatives P. oxyphila OX-01T and P. sacchari IPT101T was 41 and 40 %, respectively. Based on phylogenetic analysis, phenotypic and genotypic data, it is concluded that the isolate represents a novel species of the genus Paraburkholderia, for which the name Paraburkholderia caffeinitolerans sp. nov. is proposed. The type strain is CF3T (= LMG 28688T = CGMCC 1.15105T).