Sakae Kudoh

DOC and its relationship to algae in bottom ice communities

The seasonal development of algal biomass and dissolved organic carbon (DOC) in bottom ice was determined for two widely separated areas of annual sea ice, Saroma-ko in northern Japan and Resolute Passage in the Canadian High Arctic, to determine the importance of DOC to estimates of primary production in sea ice communities. As algal biomass, measured either as chlorophyll a (Chl a) or particulate organic carbon (POC), increased, DOC concentrations increased to extremely high values (up to 40 mg Cl−1 DOC). The highest algal biomass and DOC concentrations were observed at Resolute under thin (4–8 cm) snow cover. Highly significant double-log linear relationships (r2 = 62–80%, p < 0.01) existed between DOC and both Chl a and POC, suggesting much of the DOC originated from the ice algae. A highly significant global relationship between DOC and POC (r2 = 74%, p<0.01) was also found when previously published data for Frobisher Bay were included, indicating substantial consistency in the relationship between DOC and algal biomass among widely separated locations and differing climatic/hydrodynamic regimes. The significance of the apparently rich production of substrates for microheterotrophic processes in the ice is unclear until the nature and origin of the DOC are better resolved. It is clear, however, that estimates of organic production in ice based only on accumulation of particulate organic material will be seriously biased if dissolved material is ignored.

Strategies of phytoplankton to perform effective photosynthesis in the North Water

Abstract During the 1999 expedition of the International North Water Polynya Study in northern Baffin Bay, the photosynthetic characteristics of phytoplankton were measured using pulse-amplitude-modulated (PAM) fluorescence methods. We focused mainly on the functioning of the diadinoxanthin cycle, which was expected to be an effective protection system of photosystems from high irradiance under low temperature. In spite of the low temperature (ca. 0°C), the diadinoxanthin cycle was very active, as monitored by the change of non-photochemical quenching of fluorescence (NPQ). The extent of NPQ became larger when phytoplankton were exposed to higher irradiance, and seemed to be in good correlation with the total amount of diadinoxanthin plus diatoxanthin, which are responsible for the diadinoxanthin cycle. The NPQ was more active in the surface phytoplankton community than in the phytoplankton living at the bottom of the euphotic zone, which had less xanthophyll pigments. These results indicate that the diadinoxanthin cycle actively drains out excess light energy as non-radiative heat and protects photosystems under high irradiance. The active NPQ reduced the effective irradiance; the effective quantum yield of photosystem II became smaller under higher irradiance. Reflecting these features, the resulting rate of photosynthesis in surface phytoplankton tended to be smaller than that of phytoplankton at the bottom of the euphotic zone. The irradiance at the onset of light saturation (Ik) was generally higher than the reported values for polar phytoplankton and ice algae, probably because of the presence of a water–water cycle and/or other metabolic pathways. Our work also shows the usefulness of PAM measurements for ecological and biochemical studies of psychrophilic phytoplankton in polar regions.

Concerted response of xanthophyll-cycle pigments in a marine diatom, Chaetoceros gracilis, to shifts in light condition

The interconversion rate of diadinoxanthin (DD) cycle under high irradiance and subsequent darkness was analyzed using the cultivated centric marine diatom, Chaetoceros gracilis Schütt. A prompt de‐epoxidation from diadinoxanthin to diatoxanthin (DT) occurred immediately after the onset of higher irradiance. The fist‐order rate constant, k, for this de‐epoxidation was 0.1–0.2 min‐1 irrespective of the irradiance. The difference in photon fluence rate lead to the difference of the final amount of DT, leaving the rate constant at almost the same value. After turning off the light, epoxidation from DT to DD occurred. The first‐order constant of epoxidation was much slower than that of de‐epoxidation: 0.005 – 0.009 min‐1. Independent of this epoxidation process, de novo synthesis of DD‐cycle pigments was also observed under the subsequent darkness. Based on these findings, a common nature of the DD‐cycle as a protection mechanism for photo‐systems was demonstrated for C. gracilis.

Photosynthetic and respiratory characteristics of an Arctic ice algal community living in low light and low temperature conditions

Abstract The massive development of the ice algal community commonly observed under first-year sea ice was studied with particular attention to photosynthetic and respiratory characteristics of ice algae at low temperature and low light conditions. Field experiments were carried out in April and May 1992 at Resolute Passage in the Canadian Arctic. Under ca. 200 cm of sea ice with a snow cover of less than 7 cm, ice algal biomass increased from 3.7 to 88.7 Chl a m −2 with growth rates increasing from 0.17 to 0.23 doublings d −1 , although the development was disturbed between 1 and 6 May. The photosynthetically active radiation (PAR) measured at the bottom of the sea ice near midday was between 8.6 and 1.5 μmol photons m −2 s −1 (1.0 and 0.1% of the surface irradiance), and the water temperature was near −1.8°C. In response to these low irradiance levels, ice algae exhibited a high α (the initial slope of the photosynthesis vs. irradiance relationship) of 0.26 μg C μg Chl a −1 h −1 (μ mol photons m −2 s −1 ) −1 . The dark respiration contributed up to 35% of the gross photosynthetic rare and was estimated to be 0.22 μg C μg Chl a −1 h −1 on average. Considering the value of α and the dark respiration rate, light compensation was estimated to be 0.8 μmol photons m −2 s −1 for the ice algal community, which was enough for ice algae to maintain the positive photosynthesis at the bottom of the sea ice at the maximum daily irradiance. Using a numerical model with these estimated parameters, we evaluated the net positive diel photosynthesis under natural environmental conditions. The numerical model also suggested that the long day length in the late spring and summer in the Arctic region allowed the algae to maintain positive net photosynthesis even after the massive development of the ice algal community.

Horizontal heterogeneity of microalgal biomass in the first-year sea ice of Saroma-ko Lagoon (Hokkaido, Japan)

The horizontal distribution of sea-ice microalgae in Saroma-ko Lagoon (Sea of Okhotsk, Hokkaido, Japan) was studied in relation to snow depth, ice thickness, salinity in the ice bottom and within-ice irradiance. Three scales of variation were considered: a 4-km transect extending from the Saromabetsu River towards the eastern inlet of the lagoon and two different sampling grids (10 x 10 m and 1 x 1 m). Diatoms, Detonula confervacea and three species of Navicula, dominated the algal assemblage. Along the transect, the taxonomic composition and percent contribution of species to the total cell volume varied. Chlorophyll a (chl a) concentration (2–119 mg m−2) was characterized by a quadratic trend, and variability in the residual stationary series showed structures of ca. 500, 100 and 70 m. Snow depth was quite uniform and ice thickness decreased as the ice-bottom salinity increased. Within-ice irradiance was minimum at mid-transect. The chl a trend was significantly related to ice thickness, which was controlled by ice-bottom salinity. Variance in the detrended chl a series was explained by ice-bottom salinity at the 70-m scale (68%). Analyses of data from the two grids did not show evidence of variation in chl a biomass at scales <20 m. In Saroma-ko Lagoon, as in southeastern Hudson Bay, ice-bottom salinity explained the meso- and small-scale patchiness of ice algae. Salinity of underlying waters probably controlled the spatial co-heterogeneity of salinity and microalgal biomass in the ice bottom.

An Application of Wastewater Treatment in a Cold Environment and Stable Lipase Production of Antarctic Basidiomycetous Yeast Mrakia blollopis

Milk fat curdle in sewage is one of the refractory materials for active sludge treatment under low temperature conditions. For the purpose of solving this problem by using a bio-remediation agent, we screened Antarctic yeasts and isolated SK-4 strain from algal mat of sediments of Naga-ike, a lake in Skarvsnes, East Antarctica. The yeast strain showed high nucleotide sequence homologies (>99.6%) to Mrakia blollopis CBS8921T in ITS and D1/D2 sequences and had two unique characteristics when applied on an active sludge; i.e., it showed a potential to use various carbon sources and to grow under vitamin-free conditions. Indeed, it showed a biochemical oxygen demand (BOD) removal rate that was 1.25-fold higher than that of the control. We considered that the improved BOD removal rate by applying SK-4 strain was based on its lipase activity and characteristics. Finally, we purified the lipase from SK-4 and found that the enzyme was quite stable under wide ranges of temperatures and pH, even in the presence of various metal ions and organic solvents. SK-4, therefore, is a promising bio-remediation agent for cleaning up unwanted milk fat curdles from dairy milk wastewater under low temperature conditions.

Photosynthetic acclimation and the estimation of temperate ice algal primary production in Saroma-ko Lagoon, Japan

Abstract Temporal changes in the sea ice environment, ice algal biomass and photosynthetic characteristics were studied at Saroma-ko Lagoon in Japan, the area where the southernmost seasonal sea ice in the northern hemisphere occurs. In 1992, the sea ice started to develop in early January and covered the entire lagoon surface in late January, when water temperatures at the center of the lagoon decreased below −1.7°C. High concentrations of ice algae in the bottom layer of the sea ice, where light levels were 0.5–2.8% of the surface irradiance, were visually confirmed in mid-February. The biomass increased in late February to a maximum of 38.25 mg Chl am−2 then suddenly decreased during stormy weather in early March. Afterwards it remained rather constant, with high values of 20–30 mg Chl am−2 until mid-March. Photosynthesis vs. light analysis revealed that ice algae in this lagoon had a low dark respiration rate of 0.024 mg C mg Chl a−1h−1 on average while the increase of photosynthesis at light levels lower than 25 μmol m−2s−1 showed gentle linear increases with increments of light intensity. However, the maximum photosynthetic rate and the efficiency of the photosynthesis at low light levels were rather low compared with values from previous studies in the polar sea ice areas. Nevertheless, in situ estimates of net diel photosynthesis and production, which were calculated with a numerical model using the photosynthetic parameters and hourly averaged light at the ice algal habitat, suggested that large positive values were expected throughout this study. In temperate sea ice areas like Saroma-ko, where there are day/night light cycles, ice algae that have a small net loss of carbon at night due to dark respiration could achieve positive photosynthesis and growth even though they do not show the efficient photosynthesis under low light as shown by polar ice algae.

Temporal and spatial patterns in the surface-water biomass of phytoplankton in the North Water

Temperature, salinity, and in vivo fluorescence of surface seawater in the North Water were recorded continuously, using a CTD+fluorometer, in August 1997, April–July 1998 and August–October 1999. The phytoplankton bloom started in the polynya on the Greenland side in April. In April and May, high phytoplankton biomass coincided with saline water on the Greenland side, while biomass was low on the Ellesmere Island (Canada) side where a deep mixed layer prevailed. High phytoplankton biomass extended over the whole polynya in June, when surface temperature increased due to solar heating and salinity decreased due to freshwater input. The initiation of the bloom was about 2 months earlier on the Greenland than the Canadian side. In July and August, phytoplankton biomass became low in the southern survey area, indicating that the phytoplankton bloom had ended. In September, relatively saline and warm water occurred in the southeastern part of the study area where, consistent with the change in water properties, high concentrations of chlorophyll a were observed again. These results imply that both the earlier start of the algal bloom in spring and the eventual increase in phytoplankton biomass in summer contribute to the high annual primary production along the Greenland side, thus influencing the structure and biological productivity of the entire North Water ecosystem.

DIMETHYLSULFONIOPROPIONATE PRODUCTION BY PSYCHROPHILIC DIATOM ISOLATES1

Dimethylsulfoniopropionate (DMSP) production by psychrophilic diatom strains, Chaetoceros sp., Navicula sp., and Nitzschia sp., were experimentally analyzed. All strains showed rapid growth (0.3–0.5 d−1) under cold culture conditions (1.7°C). DMSP concentrations (both as particulate, DMSPp, and dissolved, DMSPd) were negligible in cultures of Chaetoceros sp., whereas those for Navicula sp. and Nitzschia sp. increased toward the end of the 56‐day experiments. The ratio of DMSPp:chl a of the latter two species was approximately 5 in the early exponential growth phase and decreased slightly toward the early stationary phase. During the stationary phase, when chl a and fluorescence remained constant, the ratios in both species increased linearly by up to approximately 6.5 times the value at the start of the stationary phase. This growth‐related DMSP production by diatoms may result in the low concentrations of DMSPp observed in the early stage of diatom blooms under natural conditions.

Direct ethanol fermentation from lignocellulosic biomass by Antarctic basidiomycetous yeast Mrakia blollopis under a low temperature condition

Antarctic basidiomycetous yeast Mrakia blollopis SK-4 has unique fermentability for various sugars under a low temperature condition. Hence, this yeast was used for ethanol fermentation from glucose and also for direct ethanol fermentation (DEF) from cellulosic biomass without/with Tween 80 at 10°C. Maximally, 48.2 g/l ethanol was formed from 12% (w/v) glucose. DEF converted filter paper, Japanese cedar and Eucalyptus to 12.2 g/l, 12.5 g/l and 7.2 g/l ethanol, respectively. In the presence of 1% (v/v) Tween 80, ethanol concentration increased by about 1.1-1.6-fold compared to that without Tween 80. This is the first report on DEF using cryophilic fungi under a low temperature condition. We consider that M. blollopis SK-4 has a good potential for ethanol fermentation in cold environments.