Abstract:In this study, Illumina high-throughput sequencing of 16S rDNA V4/V3-V4 variable regions of old and young pit-mud (PM) samples were performed. The diversity indices, NMDS clustering results, and the relative abundance of dominant phyla/genera of two variable regions were compared. The number of OTUs in V4 (264~639) were significantly lower than that of V3-V4 (459~1123). The Shannon indices of V4 in the young (2.47) and old (5.02) Wall-PM (WPM) samples were significantly lower than those of V3-V4 (3.33 and 6.46, respectively). Insignificant difference (p>0.05) was found between the young (4.98vs5.98) and old (5.64vs5.39) bottom-PM (BPM) samples. The Chao1 indices of V4 in the young BPM (2455vs1358), young WPM (1326vs504) and old BPM (3475vs1260) were significantly higher than those of V3-V4, with insignificant difference (p>0.05) in the old WPM samples (1915vs1312). The sequencing of the two variable regions had no effect on the NMDS clustering results. The heat-map clustering results showed that the relative abundance of the dominant phyla/genera for two variable regions were pretty similar, while it was easier for theV4 variable region to distinguish old BPM samples at the genus level. Compare with the V3-V4 region, the V4 variable region was more conducive to distinguishing between WPM and BPM and detecting the content of methanogen, which allows efficient analysis of the PM microbial composition. This study provided a good reference for the selection of V3-V4 and V4 regions during high-throughput sequencing of 16S rDNA.
