qiime2导入测序文件失败

今天在把测序数据导入qiime2时报错，提示“文件内有“含多个g”序列不能导入”，求指导

这是运行的代码

qiime tools import --type 'FeatureData[Sequence]' --input-path otus.fa --output-path rep-seqs.qza

运行结果及报错内容

There was a problem importing otus.fa:

  otus.fa is not a(n) DNAFASTAFormat file:

  Invalid character 'g' at position 6 on line 650 (does not match IUPAC characters for a DNA sequence).

各位帮忙看一下吧