J. Cynan Ellis-Evans

Bio: J. Cynan Ellis-Evans is an academic researcher from British Antarctic Survey. The author has contributed to research in topics: Phytoplankton & Plankton. The author has an hindex of 15, co-authored 17 publications receiving 950 citations. Previous affiliations of J. Cynan Ellis-Evans include Natural Environment Research Council.

Physical, chemical and biological processes in Lake Vostok and other Antarctic subglacial lakes

Abstract: Over 70 lakes have now been identified beneath the Antarctic ice sheet. Although water from none of the lakes has been sampled directly, analysis of lake ice frozen (accreted) to the underside of the ice sheet above Lake Vostok, the largest of these lakes, has allowed inferences to be made on lake water chemistry and has revealed small quantities of microbes. These findings suggest that Lake Vostok is an extreme, yet viable, environment for life. All subglacial lakes are subject to high pressure (∼350 atmospheres), low temperatures (about -3 °C) and permanent darkness. Any microbes present must therefore use chemical sources to power biological processes. Importantly, dissolved oxygen is available at least at the lake surface, from equilibration with air hydrates released from melting basal glacier ice. Microbes found in Lake Vostok's accreted ice are relatively modern, but the probability of ancient lake-floor sediments leads to a possibility of a very old biota at the base of subglacial lakes.

Temperature dependence of inorganic nitrogen uptake: Reduced affinity for nitrate at suboptimal temperatures in both algae and bacteria

Abstract: Nitrate utilization and ammonium utilization were studied by using three algal isolates, six bacterial isolates, and a range of temperatures in chemostat and batch cultures. We quantified affinities for both substrates by determining specific affinities (specific affinity = maximum growth rate/half-saturation constant) based on estimates of kinetic parameters obtained from chemostat experiments. At suboptimal temperatures, the residual concentrations of nitrate in batch cultures and the steady-state concentrations of nitrate in chemostat cultures both increased. The specific affinity for nitrate was strongly dependent on temperature (Q10 ≈ 3, where Q10 is the proportional change with a 10°C temperature increase) and consistently decreased at temperatures below the optimum temperature. In contrast, the steady-state concentrations of ammonium remained relatively constant over the same temperature range, and the specific affinity for ammonium exhibited no clear temperature dependence. This is the first time that a consistent effect of low temperature on affinity for nitrate has been identified for psychrophilic, mesophilic, and thermophilic bacteria and algae. The different responses of nitrate uptake and ammonium uptake to temperature imply that there is increasing dependence on ammonium as an inorganic nitrogen source at low temperatures.

The hydrochemistry of Lake Vostok and the potential for life in Antarctic subglacial lakes

Abstract: Our understanding of Lake Vostok, the huge subglacial lake beneath the East Antarctic Ice Sheet, has improved recently through the identification of key physical and chemical interactions between the ice sheet and the lake. The north of the lake, where the overlying ice sheet is thickest, is characterized by subglacial melting, whereas freezing of lake water occurs in the south, resulting in ∼210 m of ice accretion to the underside of the ice sheet. The accreted ice contains lower concentrations of the impurities normally found in glacier ice, suggesting a net transfer of material from meltwater into the lake. The small numbers of microbes found so far within the accreted ice have DNA profiles similar to those of contemporary surface microbes. Microbiologists expect, however, that Lake Vostok, and other subglacial lakes, will harbour unique species, particularly within the deeper waters and associated sediments. The extreme environments of subglacial lakes are characterized by high pressures, low temperatures, permanent darkness, limited nutrient availability, and oxygen concentrations that are derived from the ice that provides the meltwater. Copyright © 2002 John Wiley & Sons, Ltd.

The dynamics of heterotrophic nanoflagellates and bacterioplankton in a large ultra-oligotrophic Antarctic lake

Abstract: The abundance of both heterotrophic nanoflagellates (HNAN) and bacterioplankton in a large (9km2) ultraoligotrophic Antarctic lake (Crooked Lake) were investigated from December 1992 until November 1993. HNAN abundance peaked in spring, summer and autumn, falling to lowest numbers during the winter. Numbers ranged between 0 and 50.9×104 l−1. Bacterioplankton abundance was highest during the late summer and then fell progressively towards winter and autumn (range 1.19–4.46×106 l−1) In contrast to numbers, mean cell volumes (MCV) of the bacteria reached their highest in spring, and consequently highest bacterial biomass occurred at this time. MCV ranged between 0.052 and 0.224μm3. Bacterial production measurements following the incorporation of [3H] thymidine into DNA and [14C] leucine into protein using a doubling-labelling procedure were undertaken in January, June, August, October and November. Rates varied between 2.8 and 52 ng C l1 h1. On occasions, a significant difference in production rates based on the uptake of leucine and thymidine was observed, suggesting unbalanced growth. Highest rates of production coincided with times of high dissolved organic carbon levels in the water column and lowest production with low levels of DOC. HNAN grazing rates were measured by following the uptake of fluorescently labelled bacteria and averaged 4.8 bacterial cells individual1 day1 at 2 and 4°C. Specific growth rates (h1) ranged around 0.00070–0.00077 in both the field and laboratory, giving doubling times of 37.3 and 41.0 days, respectively. These low rates of grazing and growth indicate that there is no adaptation to low temperatures in these freshwater protists. Based on these data, the gross production efficiency is 24%. HNAN removed between 0.1 and 9.7% of bacterial production per day.

Ammonia oxidation kinetics determine niche separation of nitrifying Archaea and Bacteria

Abstract: The discovery of ammonia oxidation by mesophilic and thermophilic Crenarchaeota and the widespread distribution of these organisms in marine and terrestrial environments indicated an important role for them in the global nitrogen cycle. However, very little is known about their physiology or their contribution to nitrification. Here we report oligotrophic ammonia oxidation kinetics and cellular characteristics of the mesophilic crenarchaeon 'Candidatus Nitrosopumilus maritimus' strain SCM1. Unlike characterized ammonia-oxidizing bacteria, SCM1 is adapted to life under extreme nutrient limitation, sustaining high specific oxidation rates at ammonium concentrations found in open oceans. Its half-saturation constant (K(m) = 133 nM total ammonium) and substrate threshold (

Antarctic Sea Ice--a Habitat for Extremophiles

Abstract: The pack ice of Earth's polar oceans appears to be frozen white desert, devoid of life. However, beneath the snow lies a unique habitat for a group of bacteria and microscopic plants and animals that are encased in an ice matrix at low temperatures and light levels, with the only liquid being pockets of concentrated brines. Survival in these conditions requires a complex suite of physiological and metabolic adaptations, but sea-ice organisms thrive in the ice, and their prolific growth ensures they play a fundamental role in polar ecosystems. Apart from their ecological importance, the bacterial and algae species found in sea ice have become the focus for novel biotechnology, as well as being considered proxies for possible life forms on ice-covered extraterrestrial bodies.

A global pattern of thermal adaptation in marine phytoplankton.

Abstract: Rising ocean temperatures will alter the productivity and composition of marine phytoplankton communities, thereby affecting global biogeochemical cycles Predicting the effects of future ocean warming on biogeochemical cycles depends critically on understanding how existing global temperature variation affects phytoplankton Here we show that variation in phytoplankton temperature optima over 150 degrees of latitude is well explained by a gradient in mean ocean temperature An eco-evolutionary model predicts a similar relationship, suggesting that this pattern is the result of evolutionary adaptation Using mechanistic species distribution models, we find that rising temperatures this century will cause poleward shifts in species' thermal niches and a sharp decline in tropical phytoplankton diversity in the absence of an evolutionary response

Temperature and substrates as interactive limiting factors for marine heterotrophic bacteria

Abstract: Active heterotrophic bacterial communities exist in all marine environments, and although their growth rates or respiratory rates may be limited by the interaction of low substrate concentrations with temperatures near their lower limit for growth, temperature and substrate con- centrations are rarely considered together as limiting factors. Moreover, attempts to evaluate meta- bolic limits by both temperature and substrate concentration have sometimes led to confusing con- clusions, because, while we can measure dissolved organic carbon (DOC) concentrations in natural waters, much of it is not readily available to heterotrophic bacteria. In spite of this procedural limita- tion, it can be helpful to regard temperature and substrate concentration as potential limiting factors that interact. In temperate ocean surface waters and estuarine waters, where bacterial growth is often reduced in winter, growth and respiration may be increased experimentally either by raising the tem- perature or by increasing organic substrate concentrations, providing indirect evidence that the lim- itation is an effect of temperature on substrate uptake or assimilation. Experimental work with bac- terial isolates also has shown a temperature-substrate interaction. In permanently cold polar waters, most heterotrophic bacteria appear to be living at temperatures well below their optima for growth. Nevertheless, bacteria in permanently cold surface waters can achieve activity rates in summer that are as high as those in temperate waters. In sea ice, rates of bacterial production are most often low, even though concentrations of substrates, including free amino acids, are sometimes much higher than they are in seawater. This suggests that at sea ice temperatures heterotrophic bacteria have low- ered ability to take up or utilize organic substrates.

Adaptation and Acclimation of Photosynthetic Microorganisms to Permanently Cold Environments

Abstract: Persistently cold environments constitute one of our world's largest ecosystems, and microorganisms dominate the biomass and metabolic activity in these extreme environments. The stress of low temperatures on life is exacerbated in organisms that rely on photoautrophic production of organic carbon and energy sources. Phototrophic organisms must coordinate temperature-independent reactions of light absorption and photochemistry with temperature-dependent processes of electron transport and utilization of energy sources through growth and metabolism. Despite this conundrum, phototrophic microorganisms thrive in all cold ecosystems described and (together with chemoautrophs) provide the base of autotrophic production in low-temperature food webs. Psychrophilic (organisms with a requirement for low growth temperatures) and psychrotolerant (organisms tolerant of low growth temperatures) photoautotrophs rely on low-temperature acclimative and adaptive strategies that have been described for other low-temperature-adapted heterotrophic organisms, such as cold-active proteins and maintenance of membrane fluidity. In addition, photoautrophic organisms possess other strategies to balance the absorption of light and the transduction of light energy to stored chemical energy products (NADPH and ATP) with downstream consumption of photosynthetically derived energy products at low temperatures. Lastly, differential adaptive and acclimative mechanisms exist in phototrophic microorganisms residing in low-temperature environments that are exposed to constant low-light environments versus high-light- and high-UV-exposed phototrophic assemblages.