Heather S Nunn Victoria Petryshyn Ronald S. Oremland Laurence G. Miller Michael R. Rosen Kohen Bauer Katherine J. Thompson Elise M. Tookmanian Anna R. Waldeck Sean J Lloyd Hope A Johnson Bradley S. Stevenson William M Berelson Frank A Corsetti John R. Spear Blake W. Stamps 2018 <div>Algal blooms in lakes are often associated with anthropogenic eutrophication; however, they can occur without the human introduction of nutrients to a lake. A rare bloom of the alga<span>&nbsp;</span><span class="named-content" data-type="genus-species">Picocystis</span><span>&nbsp;</span>sp. strain ML occurred in the spring of 2016 at Mono Lake, a hyperalkaline lake in California, which was also at the apex of a multiyear-long drought. These conditions presented a unique sampling opportunity to investigate microbiological dynamics and potential metabolic function during an intense natural algal bloom. We conducted a comprehensive molecular analysis along a depth transect near the center of the lake from the surface to a depth of 25 m in June 2016. Across sampled depths, rRNA gene sequencing revealed that<span>&nbsp;</span><span class="named-content" data-type="genus-species">Picocystis</span>-associated chloroplasts were found at 40 to 50% relative abundance, greater than values recorded previously. Despite high relative abundances of the photosynthetic oxygenic algal genus<span>&nbsp;</span><span class="named-content" data-type="genus-species">Picocystis</span>, oxygen declined below detectable limits below a depth of 15 m, corresponding with an increase in microorganisms known to be anaerobic. In contrast to previously sampled years, both metagenomic and metatranscriptomic data suggested a depletion of anaerobic sulfate-reducing microorganisms throughout the lake's water column. Transcripts associated with photosystem I and II were expressed at both 2 m and 25 m, suggesting that limited oxygen production could occur at extremely low light levels at depth within the lake. Blooms of<span>&nbsp;</span><span class="named-content" data-type="genus-species">Picocystis</span><span>&nbsp;</span>appear to correspond with a loss of microbial activity such as sulfate reduction within Mono Lake, yet microorganisms may survive within the sediment to repopulate the lake water column as the bloom subsides.</div> application/pdf 10.1128/AEM.01171-18 en American Society for Microbiology Metabolic capability and phylogenetic diversity of Mono Lake during a bloom of the eukaryotic phototroph Picocystis sp. strain ML article