Abstract
We, the Editor and Publisher of Bioengineered have retracted the following article: Xiaocui Liu, "Effects of Methyl Donors on L-Tryptophan Fermentation," Bioengineered, 10.1080/21655979.2021.1882821.This author became unresponsive after the posting of the author's accepted manuscript version of this article and has not responded to follow up emails for over one year. Since the author has not signed the copyright agreement, Bioengineered cannot proceed with final publication and must remove the accepted author manuscript version from the website.We have been informed in our decision-making by our policy on publishing ethics and integrityandthe COPE guidelines on retractions. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as "Retracted".