Phylogenetic analyses of bacteria in sea ice at Cape Hallett, Antarctica

Every year, an area of sea ice forms around the continent of Antarctica that is inhabited by communities of microbes. Although the microbial component of this habitat has been postulated to play an ecologically important role in the Southern Ocean, our understanding of the diversity of Antarctic sea-ice bacteria is limited. The aim of this study was to identify bacterial components present in sea ice at Cape Hallett. Total community DNA was isolated from sea-ice cores and the 16S ribosomal RNA genes were amplified by polymerase chain reaction (PCR) using a range of universal and targeted primer sets. PCR products were de-replicated using restriction fragment length polymorphism (RFLP) and distinct RFLP types were sequenced. The major bacterial classes identified consisted of alpha-proteobacteria, gamma-proteobacteria, Cytophaga-Flavobacteria-Bacteroides group and a small number of Gram-positive species. Our findings indicate that the bacterial component of sea ice at Cape Hallett is primarily heterotrophic. Cyanobacteria and Archaea were not detected using the methods and primer sets employed in this study. However, bacteria whose 16S rDNA sequences cluster with species that encode phototrophic genes were detected in our sea-ice samples. This raised the possibility that bacterial phototrophy may occur in Antarctic sea ice.