World's largest oligotrophic Lake Baikal: Concerns about cyanobacterial blooms and potential microcystin producers along the littoral zone.

Toxic cyanobacterial blooms are great challenge for water safety globally. Previous studies mainly focused on this issue in eutrophic lakes, but associated knowledge in oligotrophic lakes is quite scarce. Lake Baikal is the world's largest oligotrophic lake, containing about 20 % of world's available freshwater. In this study, sites grouped in the east (E1-E2), west (W1-W6), and southwest (SW1-SW3) located in the littoral zone of Lake Baikal, were sampled. The target genes of 16S rRNA and mcyE in cyanobacteria, potential microcystin producers, microcystin-producing Microcystis and Dolichospermum, were quantitatively detected in collected surface water samples, and the highest target gene abundance was observed at the site where the highest water temperature (WT) and total nitrogen (TN) were recorded (P<0.05). The WT showed a strong positive correlation with the target gene abundance, possibly via promoting the growth of cyanobacteria, potential microcystin producers or toxic strain proportion. The strong positive correlation between TN and absolute mcyE gene abundance of potential microcystin producers was also shown, and it was likely that its production is related to N availability. These findings suggested that the potential risk of cyanobacterial blooms and microcystin producers for water safety should not be ignored in the world's largest oligotrophic Lake Baikal, and WT and TN could be as pivotal factors to affect the potential risk. Consequently, it is vitally necessary for water authorities to take suitable action to cope with this challenge in hot spot littoral region of increased water temperature and nitrogen in a large oligotrophic lake.