Episodic Replication in Low Carbon and Energy Terrestrial Deep Biosphere Groundwaters

The ‘deep terrestrial biosphere’ is the vast amount of subterranean life beneath the surface that plays a notable role in global nutrient cycles, while being one of the Earth’s least understood biomes.

Due to the low availability of carbon and energy, deep biosphere microbial replication is suggested to occur every 100 to 1000s of years.

The applicants recently hypothesized that deep biosphere cellular replication occurs in short periods when an energy source is available, termed ‘episodic’ (i.e., stop/start) cell division when DNA polymerases function as rapidly as in surface populations.

This study will use bioinformatics, incubation experiments with exogenous electron donors, and sequencing of single-cell transcriptomes to answer the following interrelated hypotheses: (1) Episodic replication increases with depth such that the ratio of cells with RNA transcripts coding for replication decreases compared to those that are predicted by metagenome analyses to have a replication fork; (2) replication rates of deep biosphere lineages vary according to their symbiotic growth strategies; (3) interacting host symbiont pairs have complementary metabolic profiles specifically regarding the functions for which the symbiotic partner is auxotrophic; and (4) cryptic cycling of electron donors and acceptors results in successive blooms of populations within the community.

This will answer how deep biosphere microbes replicate over such long timeframes when energy limited.