Bacterial diversity in an arctic lake: a freshwater SAR11 cluster

We used molecular techniques to assess the phylogenetlc afflnlty of cultured and uncultured m~croorganis~ns from Toolik Lake, an ol~gotrophic lake In a r c t ~c Alaska USA The phylogenetlc positions of cloned cultures of bacteria were determined by sequence analysls of PCR ampl~fled ribosomal RNA genes The Toollk Lake bacterial isolates showed a high degree of slmllarlty, 0 94 to 0 99, to a wlde variety of phyla that are well represented in the ribosomal RNA database The occurrence of species normally associated with a terrestrial habltat (Arthrobacter globiforn~is and B ~~r k h o l d e n a solanacearum) or a more nutrient-rich environment (Cytophaga aquatills and Zoogloea r a m ~y e r a ) suggests a particle-associated origln for these cell types consistent with the fact that w e used an unflltered sample In contrast, the analysls of rRNA genes cloned from a complex natural DNA community indlcated the predominance of beta-proteobacteria closely related to the rRNA hamology group I1 pseudomonads Alcalrgenes eutrophus and Pseudomonaspickett~l However, 2 of therRNA g e n e clones are deeply branching relatives (s~rnllarity = 0 88) of the alpha-proteobacteria SARI 1 cluster, previously detected only In marine environments Thls finding lndlcates a widespread aquatic dlstnbutlon for thls recently descnbed group KEY WORDS: Bactel-]a 1 6 s rRNA. Arctic. SARll