meridional exchange. Using additional experiments to test the effect of deepening of major ocean gateways in the Maastrichtian, we demonstrate that the geometry of these gateways likely had a considerable impact on ocean circulation. We further compare sim ulated circulation results with compilations of ε records and show Nd that simulated changes in Late Cretaceous ocean circulation are reasonably consistent with inferences from this proxy. In our simulations, consistency with the geologic history of major ocean gateways and absence of shift in areas of deep- water formation suggest that the Late Cretaceous trend in ε values in the Atlantic and southern Nd Indian Oceans was caused by the subsidence of volcanic provinces and opening of the Atlantic and Southern Oceans rather than changes in deep-water formation areas and/or reversal of deep-water fluxes. However, the compl exity in interpreting Late Cretaceous ε values underscores the need for new records as well as specific Nd ε modeling to better discriminate between the various plausible theories of ocean circulation change during Nd this period.

Lai, Y.-W., Ridone, P., Peralta, G., Tanaka, M.M., Baker, M.A.B., 2020. Evolution of the stator elements of rotary prokaryote motors. Journal of Bacteriology 202, e00557-19.

http://jb.asm.org/content/202/3/e00557-19.abstract The bacterial flagellar motor is driven by an ion flux that is converted to torque by motor-attendant complexes known as stators. The dynamics of stator assembly around the motor in response to external stimuli have been the subject of much recent research, but less is known about the evolutionary origins of stator complexes and how they select for specific ions. Here, we review the latest structural and biochemical data for the stator complexes and compare these with other ion transporters and microbial motors to examine possible evolutionary origins of the stator complex.

Lam, B.R., Barge, L.M., Noell, A.C., Nealson, K.H., 2019. Detecting endogenous microbial metabolism and differentiating between abiotic and biotic signals observed by bioelectrochemical systems in soils. Astrobiology 20, 39-52.

https://doi.org/10.1089/ast.2018.1892 Unambiguous detection of chemical and physical signatures of microbial life on Mars or other solar system bodies requires differentiation between signals produced by biotic and abiotic processes; instruments aimed at generalized in situ extant life detection would therefore increase the science return of a life-detection mission. Here, we investigate Bioelectrochemical Systems (BES) as a technique to measure microbial metabolism (which produces electrical current and redox changes) and distinguish between potential abiotic and biotic responses in environmental samples. Samples from inhabited niches should contain everything necessary to produce current, that is, catalysts (microorganisms) and fuel (nutrients). BES can also probe for inactive organisms in less energetically rich areas by adding a fuel to drive metabolism. A commercial potting soil and a Mars simulant soil were inoculated in the anodic chamber of microbial fuel cells, and current was monitored over time. Addition of a fuel (electron donor) source was tested for metabolic stimulation of endogenous microbes. Redox reactions between Mars simulant soil and the introduced electron donor (lactate) produced false-positive results, emphasizing the importance of careful interpretation of signals obtained. The addition of lactate to both soils resulted in enhanced biologically produced current, allowing stimulation and detection of dormant microbes. Our results demonstrate that BES provide an approach to detect metabolism in samples without prior knowledge of the organisms present, and that thorough electrochemical analyses and experimental design are necessary to determine if signals are biotic.

Lang, S.Q., Brazelton, W.J., 2020. Habitability of the marine serpentinite subsurface: a case study of the Lost City hydrothermal field. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, 20180429.

https://doi.org/10.1098/rsta.2018.0429