Thanks a lot for the posts. Actually I went through all of the posts related with chimeras on the forum. None seems to be similar with mine.
My situation is the majority of merged ASVs are inferred as chimera, but they account for 19% of merged reads. If talking about the proportion of chimera reads, actually it is not that super high, but definitely not that low.
And I confirm that all the non-biological sequences such as primer and adaptors have already been removed.
High possibly it is the library preparation resulted in a relatively higher proportion of chimeras rather than inappropriate data processing.
However, in my opinion, as long as the chimera doesn’t affect the microbial composition and the sequencing is deep enough to cover most of the diversity (Chao1 and rarefaction reached a plateau), we can still go on with the analysis after removing chimera.
Besides, this data comes from a deep sequencing on 16S V4 region with an average of 86,000±25,000 reads per sample even after removing chimera reads. I suspect the signal of chimera was enlarged a lot at such a deep sequencing depth.
That’s my opinion. Would be happy to have your comments.
PS: my only concern is whether a relatively high proportion of chimera (such as 20% of reads are chimeras) would change the bacterial community? I could not find a paper discussing on this. If there is, please correct me.