Satoshi Imura

Comparative phylogenetic analyses of Halomonas variabilis and related organisms based on 16S rRNA, gyrB and ectBC gene sequences.

Halomonas variabilis and phylogenetically related organisms were isolated from various habitats such as Antarctic terrain and saline ponds, deep-sea sediment, deep-sea waters affected by hydrothermal plumes, and hydrothermal vent fluids. Ten strains were selected for physiological and phylogenetic characterization in detail. All of those strains were found to be piezotolerant and psychrotolerant, as well as euryhaline halophilic or halotolerant. Their stress tolerance may facilitate their wide occurrence, even in so-called extreme environments. The 16S rDNA-based phylogenetic relationship was complemented by analyses of the DNA gyrase subunit B gene (gyrB) and genes involved in the synthesis of the major compatible solute, ectoine: diaminobutyric acid aminotransferase gene (ectB) and ectoine synthase gene (ectC). The phylogenetic relationships of H. variabilis and related organisms were very similar in terms of 16S rDNA, gyrB, and ectB. The ectC-based tree was inconsistent with the other phylogenetic trees. For that reason, ectC was inferred to derive from horizontal transfer.

Phytoplankton blooms under dim and cold conditions in freshwater lakes of East Antarctica

The seasonal variations of limnological (water temperature, light availability, turbidity, and chlorophyll a concentration) parameters were recorded continuously from January 2004 to February 2005 at two freshwater lakes: Oyako-ike and Hotoke-ike, Sôya Coast, East Antarctica. Water was in a liquid phase throughout the year, with temperatures ranging from 0 to 10°C. The maximum photosynthetically active radiation in Lake Oyako-ike was 23.16xa0molxa0m−2xa0day−1 (at 3.8xa0m) and Hotoke-ike was 53.01xa0molxa0m−2xa0day−1 (at 2.2xa0m) in summer, and chlorophyll a concentration ranged from ca. 0.5 to 2.5xa0μgxa0L−1 (Oyako-ike) and from ca. 0.1 to 0.8xa0μgxa0L−1 (Hotoke-ike) during the study period. Increase in chlorophyll a fluorescence occurred under dim-light conditions when the lakes were covered with ice in spring and autumn, but the signals were minimum in ice-free summer in both the lakes. During spring and summer, as a result of decreasing snow cover, the chlorophyll a concentration similarly decreased when PAR was relatively high, following periods of heavy winds. The autumnal and spring increase occurred under different PAR levels (ca. 20-fold and 90-fold stronger, respectively, in autumn in both the lakes). Differences in the autumn and spring increases suggest that the spring algal community is more shade-adapted than the autumn algal community. Antarctic phytoplankton appears especially adapted to low-light levels and inhibited by strong light regimes.

Depth distribution of euryhaline halophilic bacteria in Suribati Ike, a meromictic lake in East Antarctica

Euryhaline halophiles grow over a wide range of salinity, from <3% NaCl (seawater equivalent) to >15% NaCl and even saturation level (about 30% NaCl). Several species of euryhaline halophiles occur worldwide, especially in marine environments and also in aquatic and terrestrial habitats of the Antarctic ice-free areas. A biogeographic view of Antarctic halophiles is that their migration among lakes on land is more difficult than in marine setting. Ponds and lakes on land may thus serve as “islands” which facilitate the selection and separation of unique species. We isolated euryhaline halophiles from the saline lake, Suribati Ike, near Syowa Station and placed them into seven groups, each demonstrating a clear depth-related distribution. Six of the seven groups probably represent new species of the genera Halomonas and Marinobacter. This result suggests that Antarctic saline lakes exhibit high selectivity of unique euryhaline halophiles and possibly of other microbial groups.

In situ photochemical activity of the phytobenthic communities in two Antarctic lakes

Photochemical activity of phytobenthic communities in two freshwater lakes in East Antarctica was estimated using a submersible pulse-amplitude modulation (PAM) chlorophyll fluorometer, to answer the following questions: (1) Are the communities under bright summer photosynthetically active radiation (PAR) photosynthetically active? (2) If active, which community shows the most active signals? (3) Where is the most productive part (or depth) in the lake? Our limnological measurements indicated the two lakes were ultra-oligotrophic. Diving observations revealed that the phytobenthos of the lakes was moss-dominated which had different life-forms (moss shoots in shallow depths of both lakes, moss-pillars in the shallow lake, pinnacle moss-microbial complex community in the deeper lake). In addition, various mat-forming microbial communities inhabited the lake beds. In situ measurements of photochemical parameters indicated that shoots of mosses living just below the littoral slope, and the apical part of the moss pillars, had the highest photosynthetic activity in open water summer conditions, but mat-forming microbial communities and the other moss-microbial complex communities, showed rather lower activity. Most of the mat-forming phytobenthos surface also showed positive photosynthetic activity, but there were some cases of negligible signals in the shallow depth. This suggests that the photosynthetic activities of mat-forming communities in the shallow water were suppressed by strong ambient light in summer.

Plant Communities at Dronning Maud Land

Studies on vegetation in Dronning Maud Land have been performed for many years and most detailed results have been mainly published by Japanese Antarctic Research Expedition (JARE; e.g. Matsuda 1963,1968; Akiyama 1967; Nakanishi 1977; Kanda 1981,1986a,b; Newton et al. 1994). This chapter provides a new overview on vegetation research with aspects on their environmental constraints and focuses on moss, lichen and algal communities with different regional aspects in a wider area and their effects on vegetation development.

Psychroflexus lacisalsi sp. nov., a moderate halophilic bacterium isolated from a hypersaline lake (Hunazoko-Ike) in Antarctica.

A novel Gram-negative, aerobic, moderate halophilic, and psychrotolerant bacterium, designated as strain H7T, was isolated from a hypersaline lake located in Skarvsnes, Antarctica. Cells were filaments with varying lengths. Coccoid bodies developed in old cultures. Growth occurred with 0.5–15% (w/v) NaCl (optimum, 5.8–7.0%), at pH 6.0–10.0 (optimum, pH 7.0–8.0), and at 10–28°C (optimum, 25°C). The strain had a G+C content of 34.9 mol%, which is within the range of 32–36 mol% reported for the genus Psychroflexus. Chemotaxonomic data (major respiratory quinone: MK-6; major fatty acids: aC15:0, iC16:0 3-OH, and aC15: 1 A) supported the classification of strain H7T within the genus Psychroflexus. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain H7T should be assigned to the genus Psychroflexus and has a homology with Psychroflexus salinarum (98.2%), P. sediminis (96.1%), P. torquis (95.2%), P. tropicus (95.8%), and P. gondwanense (92.2%). Strain H7 is not identified as P. salinarum because that DNA-DNA hybridization data were 8.5% between strain H7T and P. salinarum. The combination of phylogenetic analysis, DNA-DNA hybridization data, phenotypic characteristics, and chemotaxonomic differences supported the view that strain H7T represents a novel species of the genus Psychroflexus. The name Psychroflexus lacisalsi is proposed, and the type strain is H7T (=JCM 16231T =KACC 14089T).

Methane efflux from bubbles suspended in ice‐covered lakes in Syowa Oasis, East Antarctica

[1]xa0This is the first estimation of methane efflux from bubbles in lake ice in Antarctica. Bubbles suspended in shallow ice in 20 lakes were observed as part of the operations of the 45th Japanese Antarctic Research Expedition in ice-free rocky areas along the eastern coast of Lutzow-Holm Bay (Syowa Oasis) in East Antarctica in 2004. Anomalous methane concentrations in bubbles suspended in lake ice and anomalous dissolved methane concentrations in lake water were frequently found. Methane concentrations in bubbles varied of 5 orders of magnitude, from 1.9 ppmv to 18% vol/vol. A procedure that makes estimations of methane flux from ice bubbles possible has been developed, on the basis of a relationship between bubble-density distribution, brightness observed by digital photographs, and methane concentration in bubbles. Such a procedure applied to Lake Oyako Ike in the Skarvsnes area, where the maximum methane concentration was observed, suggests that total bubble volume is about 0.6% of ice volume and the mass of methane in bubbles in the lake is about 74 kg. Almost all gases in bubbles are released to the atmosphere in the early ice melt season (a period of a few weeks in December and January). By applying area fraction frequency distributions to methane concentration ranges for 20 lakes surveyed, extrapolation to the whole Syowa Oasis, including 110 lakes, would give a provisional estimate of total emission of about 2 tons-CH4/yr.

Time machine: Ancient life on Earth and in the cosmos

The discovery more than 30 years ago of the unique superlong anabiosis phenomenon (deep sleep/dormancy) for ancient microorganisms buried in Antarctic ice deposits created the experimental and theoretical basis for the fields of cryomicrobiology and astrobiology related to searching for life or its evidence in the universe. This discovery is of special interest in light of the upcoming International Polar Year (IPY 2007–2008) and the creation of the U.S. Subglacial Antarctic Lake Environments program (http://salepo.tamu.edu/us_sale). n nAbysov et al. [1977, 1978] discovered superlong anabiosis for microorganisms in deep Antarctic ice cores above Lake Vostok when his group found and revived ancient microbes frozen for more than 500,000 years (Figure 1). Previously, only science fiction writers had contemplated a deep sleep/dormancy phenomenon that might allow humans to postpone their deaths by freezing and thus travel in time into the future.

Air-lake exchange of methane during the open water season in Syowa Oasis, East Antarctica

[1]xa0Dissolved methane (DM) concentrations were measured in 17 lakes as part of the operations of the 45th Japanese Antarctic Research Expedition in ice-free rocky areas along the eastern coast of Lutzow-Holm Bay (Syowa Oasis) in East Antarctica in the summer of 2003–2004. DM at the surfaces of 14 lakes ranged from the atmospheric equilibrium concentration (about 4 nmol L−1 for freshwater) to 385 nmol L−1. Relatively low DM of less than 50 nmol L−1 were observed in about 60% of the lakes. Many of the lakes (area fraction of 85%) were supersaturated and are thus sources of methane to the atmosphere. The exchange coefficient was calculated using wind speed data at Syowa Station. Area fraction frequency distributions with four surface DM ranges were applied to all lakes at Syowa Oasis (110 lakes, total lake area of 9 km2). Extrapolation to the whole Syowa Oasis gives an estimate of total emission of about 1 t CH4 yr−1. This is the first estimation of methane flux from the surfaces of thawed lakes to the atmosphere in Antarctica. Since a methane efflux of about 2 t CH4 yr−1 was estimated in our previous study from frozen bubbles in lake ice, a total amount of 3 t CH4 yr−1 would be released to the atmosphere from the lakes during the ice melting season (December–January) at Syowa Oasis.