Microbial diversity in a Pacific Ocean transect from the Arctic to Antarctic circles

Microbial diversity in surface waters was examined along a similar to 15 400 km transect of the Pacific Ocean from 70 degrees N to 68 degrees S latitude between late August and early November 2003. Comparative microbial diversity was determined using terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR amplified 16S and 18S rDNA restriction digested with CfoI and MspI. Bacterial numbers and total chlorophyll were greatest at higher latitudes in both hemispheres, with a smaller peak in equatorial waters. Flow cytometry analysis indicated a strong peak in Prochlorococcus from approximately 30 degrees N to 30 degrees S. Richness at each station was relatively low, with similar to 11 prokaryotic peaks per sample and similar to 12 eukaryotic peaks per community. Overall, prokaryotic populations appeared more diverse, with 181 total terminal restriction fragments (T-RFs) generated, while eukaryotic populations produced a total of 135 T-RFs. Prokaryotic and eukaryotic similarity dendrograms revealed 4 distinct cluster groups relating to regions sub-Arctic/Arctic, temperate, tropical and sub-Antarctic/Antarctic. T-RFLP patterns suggest that microbial communities may be influenced by ambient water temperature, with mid-latitudinal and equatorial communities more similar in composition to each other than to cold water communities. Global distribution of prokaryotic communities revealed an average inter-group similarity of similar to 52 %, while eukaryotic communities showed similar to 51 % similarity, implying that Pacific planktonic communities appear to be fairly homogenous in composition. Several T-RFs were ubiquitously distributed and contributed significantly to each cluster group, while several T-RFs were observed to be endemic to particular oceanic regions. Within-group similarities of >70 % were attributed to 12-14 T-RFs and 8-11 T-RFs in prokaryotic and eukaryotic profiles, respectively, suggesting that a small number of phylogenetic groups were responsible for each cluster group.