13-2 Bygone Bacteria - Gloeobacterales and the Oxygenation of Earth’s Atmosphere

Session: Earth Life Sciences across the Cordillera

Presenting Author:

Authors:

Abstract:

The evolution of the first cyanobacteria over 2 billion years ago radically transformed Earth’s surface, biogeochemical processes, and capacity for complex life by enriching the atmosphere with oxygen. This critical change facilitated the development of multicellularity, aerobic respiration, and ultimately led to the rise of complex life. Oxygenic photosynthesis evolved before the Great Oxidation Event (GOE), a geologic event that occurred between 2.4 and 2.35 Gya and saw a rise in atmospheric oxygen concentrations to approximately 0.1% of modern levels. However, the specific timing of the evolution of oxygenic photosynthesis is not well constrained and remains a highly debated topic within the scientific community. The order Gloeobacterales is an early-diverging group of cyanobacteria of which only three species have been properly cultivated. Gloeobacterales are unique among oxygenic phototrophs as they share unusual traits, such as the absence of circadian clock genes, reduced photosystem units, and an alternative morphology of the light capturing phycobilisome. While many of these traits have been interpreted as ancestral traits, a lack of described species makes it difficult to ascertain whether they are truly ancestral or if they evolved within specific Gloeobacterales (e.g. via gene loss). Analysis of their genomes and physiology is critical to understanding their synonymity with ancient cyanobacteria. Based on genomic and phylogenetic observations, we identified three candidate families - Ca. Sivonenaceae, Gloeobacteraceae, and Anthocerotibacteraceae. Of these families, Sivonenaceae appears to have the most reduced photosystems, as they are lacking several accessory components of their photosynthetic systems, such as PsbL, PsbI, PsaF, PsaM, PetM, and PetN. Each family contains a unique composition of genes encoding for the phycobilisome. Thus, we predict that the structure of the phycobilisome in the Sivonenaceae will be novel relative to the other groups. We are culturing over twenty-five samples of Sivonenaceae, representing the full species diversity, and one member of the Anthocerotibacteraceae, Ca. Aurora vandensis, to collect empirical data on the physiology and genomes of these bacteria. Gaining a greater understanding of these organisms may help us better understand the evolution of oxygenic photosynthesis billions of years ago.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.