AUTHOR=Rudi Knut , Zhao Liping TITLE=Grand Challenges in Understanding Gut Microbes JOURNAL=Frontiers in Microbiology VOLUME=12 YEAR=2021 URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.752829 DOI=10.3389/fmicb.2021.752829 ISSN=1664-302X