biostudies-literatureHake KHHoward Hughes Medical InstituteNational Science Foundation (NSF)'la Caixa' Foundation ('la Caixa')Howard Hughes Medical Institute (HHMI)&apos;la Caixa&apos; FoundationNational Science Foundatione0162324https://www.ebi.ac.uk/biostudies/studies/S-EPMC11389367biostudies-literatureUnknown15(9)As the closest living relatives of animals, choanoflagellates offer insights into the ancestry of animal cell physiology. Here, we report the isolation and characterization of a colonial choanoflagellate from Mono Lake, California. The choanoflagellate forms large spherical colonies that are an order of magnitude larger than those formed by the closely related choanoflagellate <i>Salpingoeca rosetta</i>. In cultures maintained in the laboratory, the lumen of the spherical colony is filled with a branched network of extracellular matrix and colonized by bacteria, including diverse Gammaproteobacteria and Alphaproteobacteria. We propose to erect <i>Barroeca monosierra</i> gen. nov., sp. nov. Hake, Burkhardt, Richter, and King to accommodate this extremophile choanoflagellate. The physical asmBioA large colonial choanoflagellate from Mono Lake harbors live bacteria.PMC11389367DGE 1106400n/a100010434DGE 1752814Banfield JFHake KHKing NWest PTGarcia De Las Bayonas AMcDonald KRichter DJReyes-Rivera JBurkhardt PFeng CLaundon DfalseA large colonial choanoflagellate from Mono Lake harbors live bacteria.As the closest living relatives of animals, choanoflagellates offer insights into the ancestry of animal cell physiology. Here, we report the isolation and characterization of a colonial choanoflagellate from Mono Lake, California. The choanoflagellate forms large spherical colonies that are an order of magnitude larger than those formed by the closely related choanoflagellate <i>Salpingoeca rosetta</i>. In cultures maintained in the laboratory, the lumen of the spherical colony is filled with a branched network of extracellular matrix and colonized by bacteria, including diverse Gammaproteobacteria and Alphaproteobacteria. We propose to erect <i>Barroeca monosierra</i> gen. nov., sp. nov. Hake, Burkhardt, Richter, and King to accommodate this extremophile choanoflagellate. The physical as2024-01-01T00:00:00Z2024 Sep2026-06-02T22:18:57.295Z2025-04-06T12:29:32.32ZS-EPMC113893673914074310.1128/mbio.01623-24