Anderson, C. M. | Search bioRxiv

bioRxiv2019

A New Role for Telomerase in Promoting Meiotic Homolog Pairing Fidelity

We report a role for telomerase, beyond its known function of telomeric DNA end extension, in maintaining normal chromosome dynamics during meiosis in Saccharomyces cerevisiae. When telomerase at telomeres was reduced by various genetic means, increased frequencies of crossover and noncrossover recombination events occurred. To investigate the mechanism of this increased meiotic recombination, we examined the kinetics of meiosis events, and tracked the movement of chromosomes in live cells during meiotic prophase. Cytoskeletal forces acting on telomeres during meiosis have been shown to promote active chromosome motion needed to pair homologous chromosomes. Here we show that changes in telomerase interaction with telomeres using a tlc1-11 mutant result in altered meiotic motion. Specifically, reduction in telomerase at telomeres leads to a decreased frequency of high velocity chromosome pulls. In the tlc1-11 mutant, we see earlier synapsis and increased genome-wide recombination for the majority of the cells and lower gamete viability. Notably, homologous pairing is not delayed unlike other telomere binding mutants. Although synapsis initiates earlier, the overall timing of synapsis remains the same, except for a subset of cells that do not exit meiosis I. Together, these results suggest that the strong pulling component of the active chromosome motion promotes homolog pairing fidelity, likely by pulling apart improperly associated regions. Our combined observations are consistent with a model in which telomerase-mediated telomeric anchoring to the nuclear envelope helps engage and properly transmit cytoskeletal forces to chromosomes. Thus, telomerase contributes to efficient chromosome movements leading to normal gamete viability.

cell biology↗

bioRxiv2019

In Situ Electrochemical Studies of the Terrestrial Deep Subsurface Biosphere at the Sanford Underground Research Facility, South Dakota, USA

The terrestrial deep subsurface is host to significant and diverse microbial populations. However, these microbial populations remain poorly characterized, partially due to the inherent difficulty of sampling, in situ studies, and isolating of the in situ microbes. Motivated by the ability of microbes to gain energy from redox reactions at mineral interfaces, we here present in situ electrochemical colonization (ISEC) as a method to directly study microbial electron transfer activity and to enable the capture and isolation of electrochemically active microbes. We installed a potentiostatically controlled ISEC reactor containing four working electrodes 1500 m below the surface at the Sanford Underground Research Facility. The working electrodes were poised at different redox potentials, spanning anodic to cathodic, to mimic energy-yielding mineral reducing and oxidizing reactions predicted to occur at this site. We present a 16S rRNA analysis of the in situ electrode-associated microbial communities, revealing the dominance of novel bacterial lineages under cathodic conditions. We also demonstrate that the in situ electrodes can be further used for downstream electrochemical laboratory enrichment and isolation of novel strains. Using this workflow, we isolated Bacillus, Anaerospora, Comamonas, Cupriavidus, and Azonexus strains from the electrode-attached biomass. Finally, the extracellular electron transfer activity of the electrode-oxidizing Comamonas strain (isolated at -0.19 V vs. SHE and designated WE1-1D1) and the electrode-reducing Bacillus strain (isolated at +0.53 V vs. SHE and designated WE4-1A1-BC) were confirmed in electrochemical reactors. Our study highlights the utility of in situ electrodes and electrochemical enrichment workflows to shed light on microbial activity in the deep terrestrial subsurface. SIGNIFICANCEA large section of microbial life resides in the deep subsurface, but an organized effort to explore this deep biosphere has only recently begun. A detailed characterization of the resident microbes remains scientifically and technologically challenging due to difficulty in access, sampling, and emulating the complex interactions and energetic landscapes of subsurface communities with standard laboratory techniques. Here we describe an in situ approach that exploits the ability of many microbes to perform extracellular electron transfer to/from solid surfaces such as mineral interfaces in the terrestrial subsurface. By deploying and controlling the potential of in situ electrodes 4850 ft below the surface at the Sanford Underground Research Facility (South Dakota, USA), we highlight the promise of electrochemical techniques for studying active terrestrial subsurface microbial communities and enabling the isolation of electrochemically active microbes.

microbiology↗