Abundance and Diversity of RuBisCO Genes Responsible for CO2 Fixation in Arid Soils of Northwest China

ABSTRACTArid soils where water and nutrients are scarce occupy over 30% of the Earth's total surface. However, the microbial autotrophy in the harsh environments remains largely unexplored. In this study, the abundance and diversity of autotrophic bacteria were investigated, by quantifying and profiling the large subunit genes of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) form I (cbbL) responsible for CO2 fixation, in the arid soils under three typical plant types (Haloxylon ammodendron, Cleistogenes chinensis, and Reaumuria soongorica) in Northwest China. The bacterial communities in the soils were also characterized using the 16S rRNA gene. Abundance of red-like autotrophic bacteria ranged from 3.94 × 105 to 1.51 × 106 copies g−1 dry soil and those of green-like autotrophic bacteria ranged from 1.15 × 106 to 2.08 × 106 copies g−1 dry soil. Abundance of both red- and green-like autotrophic bacteria did not significantly differ among the soils under different plant types. The autotrophic bacteria identified with the cbbL gene primer were mainly affiliated with Alphaproteobacteria, Betaproteobacteria and an uncultured bacterial group, which were not detected in the 16S rRNA library. In addition, 25.9% and 8.1% of the 16S rRNA genes were affiliated with Cyanobacteria in the soils under H. ammodendron and R. soongorica, respectively. However, no Cyanobacteria-affiliated cbbL genes were detected in the same soils. The results suggested that microbial autotrophic CO2 fixation might be significant in the carbon cycling of arid soils, which warrants further exploration.