PCR bias in 16S rRNA genes caused by GC content leads to insufficient detection of some abundant species in amplicon sequencing analyses of thermophilic microbial communities.

Amplicon sequencing is a widely used method for surveying biological diversity. However, the technique is disturbed by PCR bias leading to errors in community composition analyses. In this study, microbial community composition was evaluated in twenty-eight locations of hot spring water with temperatures between 87-48°C at Nakabusa Hot Springs, Japan, using amplicon sequencing analysis with the V4 region of the 16S rRNA gene. In discrepancy with the greenish color and the absorption spectra of the microbial samples, the relative abundance of amplicon sequence variants (ASVs) in the major photosynthetic organisms, Chloroflexus spp., were scarce in any sample when using the annealing temperature of 50°C in amplicon PCR. Changing the annealing temperature to 68ºC significantly improved the detection efficiency of Chloroflexus ASVs, and the obtained numbers were consistent with the presence of the photosynthetic pigments. The abundance of many other microbial ASVs was also dependent on the annealing temperature. The log ratio in the abundance of major ASVs between two annealing temperatures was correlated with the GC content of the 16S rRNA gene, suggesting that even some other major ASVs in the community are seriously affected by PCR bias due to the GC content. Combined usage of results from two different annealing temperatures, rather than a result using a single annealing temperature, seems to be a better way to obtain community structure information with less PCR bias in thermophilic organisms of high 16S rRNA GC content.