User talk:SozB
I have removed your request for a citation in the lede of this article.
In general, the lede section of an article is intended to summarize the rest of the article and should not include information not found elsewhere in the article. Per WP:LEDE, the information should be sourced in the body of the article, not in the lede.
The section "Microbial sources" provides reliable sources for the statement that B12 is produced only by prokaryotes, not eukaryotes. - SummerPhDv2.0 17:52, 15 January 2018 (UTC)