Diversity And Abundance Of Ammonia-oxidizing Archaea And Bacteria In The Summer Sea Ice From The Prydz Bay,Antarctica

Sea ice plays an important role in the global ecosystem, and its area can reach13%of the global area in the winter. The sea-ice microbial communities mostly consist of many planktonic organisms, including viruses, bacteria, algae, protists, zooplankton and small metazoa. Bacteria and Archaea perform the first and rate-limiting step of chemoautotrophic nitrification, ammonia oxidation in marine environment. Recently, more evidences suggest that active nitrification and denitrification occurring in the sea ice. However, the knowledge about the ecological function of bacteria and archaea dwelled in sea ice, involved in the process the nitrification, is still limited. Using16S rRNA and ammonia monooxygenase-subunit (amoA) gene as molecular markers, the diversity and abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in top, middle and bottom section of sea ice were analyzed.The bacterial16S rRNA gene clones were grouped into three distinct major lineages of Bacteria (a, y-Proteobacteria and Cytophaga-Flavobacterium-Bacteroide division) by clone library analysis of sea ice. Most sequences were related to cultured bacterial isolates from the marine environment, especially arctic and antarctic sea ice samples with higher similarity. The member of CFB division was not detected in the bottom section of sea ice, and the bacterial diversity in the water was higher than that in the ice. Betaproteobacterial16S rRNA and amoA genes clone libraries were composed exclusively of Nitrosospira-like genes in sea ice and seawater.Archaea were detected with universal16S rRNA and amoA genes primer sets in bottom section of sea ice and seawater samples. All archaeal16S rRNA gene clones obtained from the bottom section of sea ice were grouped within Marine Group I Crenarchaeota. While the archaeal clones from the seawater were belong to Marine Group I Crenarchaeota, Marine Group II and III of Euryarchaeote. The sequences of crenarchaeal amoA gene obtained from the bottom section of sea ice were affiliated with Crenarchaeota group I. The copy number of16S rRNA and amoA gene was analyzed by QPCR. The copy number of bacterial16S rRNA gene in the sea ice was2.9×106-3.8×107/μg DNA, and the copy number in the middle of sea ice was the highest. The copy number of bacterial amoA gene was1.3-5×104/μg DNA, and the copy number of the bottom section of sea ice was the highest. The copy number of archaeal16S rRNA and amoA gene was5×103-2.4×104/μg DNA and1.8×103-1.7×105/μg DNA, respectively. The abundance of archaeal16S rRNA and amoA gene in the middle of sea ice was the highest.The ratio of archaeal amoA to16S rRNA gene abundance was0.32-7.1, suggesting that ammonia-oxidizing Crenarchaeota are active contributors to the ammonia oxidation in sea ice and only part of the Crenarchaeota contain amoA gene.Fluorescence in situ hybridization was applied to determine the proportions of Bacteria and Archaea. Bacteria were detected0.92×105-1.22×106cells/cm3in sea ice. The percentage of Bacteria in the bottom section of sea ice was more than56%. The number of Archaea in sea ice was between0-5.33×10cells/cm. Crenarchaeota were approximately more abundant in middle section of sea ice. The percentage of Crenarchaeotai in bottom section of sea ice and seawater was0-25%. Our data suggest that the ammonia oxidation of AOA was higher than AOB, and only part of the Crenarchaeota were ammonia oxidizing archaea.