Microbial succession and dynamics in meromictic Mono Lake, California

Creators: Phillips, Alexandra A.; Speth, Daan R.; Miller, Laurence G.; Wang, Xingchen T.; Wu, Fenfang; Medeiros, Patricia M.; Monteverde, Danielle R.; Osburn, Magdalena R.; Berelson, William M.; Betts, Hannah L.; Wijker, Reto S.; Mullin, Sean W.; Johnson, Hope A.; Orphan, Victoria J.; Fischer, Woodward W.; Sessions, Alex L.; Geobiology Course 2017; Geobiology Course 2018

Abstract

Mono Lake is a closed-basin, hypersaline, alkaline lake located in Eastern Sierra Nevada, California, that is dominated by microbial life. This unique ecosystem offers a natural laboratory for probing microbial community responses to environmental change. In 2017, a heavy snowpack and subsequent runoff led Mono Lake to transition from annually mixed (monomictic) to indefinitely stratified (meromictic). We followed microbial succession during this limnological shift, establishing a two-year (2017–2018) water-column time series of geochemical and microbiological data. Following meromictic conditions, anoxia persisted below the chemocline and reduced compounds such as sulfide and ammonium increased in concentration from near 0 to ~400 and ~150 µM, respectively, throughout 2018. We observed significant microbial succession, with trends varying by water depth. In the epilimnion (above the chemocline), aerobic heterotrophs were displaced by phototrophic genera when a large bloom of cyanobacteria appeared in fall 2018. Bacteria in the hypolimnion (below the chemocline) had a delayed, but systematic, response reflecting colonization by sediment "seed bank" communities. Phototrophic sulfide-oxidizing bacteria appeared first in summer 2017, followed by microbes associated with anaerobic fermentation in spring 2018, and eventually sulfate-reducing taxa by fall 2018. This slow shift indicated that multi-year meromixis was required to establish a sulfate-reducing community in Mono Lake, although sulfide oxidizers thrive throughout mixing regimes. The abundant green alga Picocystis remained the dominant primary producer during the meromixis event, abundant throughout the water column including in the hypolimnion despite the absence of light and prevalence of sulfide. Our study adds to the growing literature describing microbial resistance and resilience during lake mixing events related to climatic events and environmental change.

Additional Information

© 2021 The Authors. Geobiology published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Issue Online: 21 June 2021; Version of Record online: 25 February 2021; Manuscript accepted: 08 February 2021; Manuscript revised: 18 November 2020; Manuscript received: 29 May 2020. This research was supported by the International Geobiology Course in 2017, 2018, and 2019. Funding for the course was provided by the Agouron Institute (Award #12520044) and the Simons Foundation (Award #12520045). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. We would like to thank Blake Stamps for the use of his code that was modified to generate our 16S OTU heatmaps. We also acknowledge Ronald Oremland for shipping an aliquot of Picocystis culture. We thank Sujung Lim and Grayson Chadwick for early conversations on 16S rRNA data, Usha Lingappa for her expertise on Cyanobacteria, and Aaron Martinez for his helpful dialogue on fatty acids. We are grateful to Jared Leadbetter for continuous conversations about the microbial community. We acknowledge Ashley Shade for her helpful dialogue on microbial succession in lakes. We thank Miquela Ingalls for comments and suggestions on the manuscript and her help with sample processing in the field. Additionally, we thank other field assistants: Jodi Blum, Elise Wilkes, Yonaton Goldsmith, and Barbara Ratschbacher. We would like to thank Tim Hollibaugh for use of his Seabird CTD. We thank Melissa Miller from the Oceanographic Data Facility at Scripps Institution of Oceanography for measuring nutrient concentrations and Joshua West at the University of Southern California for measuring trace metals. We acknowledge members of the Agouron International Geobiology Course from 2017 and 2018, especially students who worked directly with Mono Lake water-column samples: Katherine Fullerton, Rui Bao, Dawson Fairbanks, Michael Wells, Sergio Parra, Qingzeng Zhu, Bridget Conley, and Maria Figueroa. We thank the administrative team for the geobiology courses in 2017 and 2018, including Julie Lee and Ann Close. We also acknowledge course TAs, including Lizzy Trower, John Magyar, Eryn Eitel, and Elise Wilkes. We would like to thank the Agouron Institute and the Simons Foundation for funding the International Geobiology Course and this research. We would also like to acknowledge the Mono Lake Committee and the LA Department of Water and Power for detailed, public records on lake levels and other Mono Lake parameters. Data Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request. 16S rRNA amplicon sequencing data is available in GenBank under BioProject accession number PRJNA702881.

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