Hisayoshi Terai

Biodegradation of photosynthetically produced extracellular organic carbon from intertidal benthic algae

14C-labeled extracellular products of a natural microphytobenthic community and two species of benthic diatoms (Nitzschia hybridaeformis and Amphora coffeaeformis) were fractionated into extracellular dissolved organic carbon (14C-EDOC), organic carbon extracted with EDTA (14C-EDTA-extractable OC) and extracellular polymeric substances (14C-EPS). The biodegradation of this labeled extracellular organic carbon by bacteria in sediments was examined to determine the processes of enzymatic degradation of photosynthetically-produced extracellular organic carbon from microphytobenthos in an intertidal flat ecosystem. In addition, primary production as well as extracellular enzyme activities (beta- and alpha-glucosidase) were measured to evaluate the possible relationship between organic carbon production and microbiological degradation at the Isshiki intertidal flat in Mikawa Bay, Japan. With all three 14C-fractions extracted from a natural microphytobenthic assemblage and two species of benthic diatoms, more than 50% of the added substrates were mineralized within 24 h by the bacterial community in sediments. At that time, the percentage of high-molecular-weight compounds (>5 K MW) to total MW compounds of 14C-EDTA-extractable OC and 14C-EPS fractions decreased within 24 h from 50.9 to 6.6% and 74.5 to 11.1%, respectively. In situ, beta- and alpha-glucosidase activity in sediment was higher than in the seawater column (at a depth of 1 m), though the photosynthetic production of microphytobenthos was equal to that of phytoplankton. Based on our previous studies that microphytobenthos produced much more extracellular products than phytoplankton, it is assumed from these results that carbon flowing into the microbial loop through the mediation of enzymatic degradation of extracellular products in a benthic system exceeds that in the overlying water column.

Seasonal variation in primary production of microphytobenthos at the Isshiki intertidal flat in Mikawa Bay

Abstract Seasonal variations in photosynthetic rates by microphytobenthos and phytoplankton at the Isshiki tidal flat in Mikawa Bay were measured with a 14C combustion method. In addition, diurnal variations in the photosynthetic rate and photosynthesis versus irradiance (P-I) curves were obtained through in situ incubation. The photosynthetic rate of microphytobenthos (annual average, 13.9 ± 6.4 mg C m−2 h−1) did not show a remarkable change, and they maintained a higher production rate than phytoplankton (annual average 9.0 ± 5.1 mg C m−2 h−1) throughout the year. The P-I curves from in situ experiments showed that the photosynthetic activity of microphytobenthos at the laboratory irradiance (250 μE m−2 s−1) was 56% of that at the maximum irradiance (1200 μE m−2 s−1) in situ. In the in situ experiments, the chlorophyll a concentration, photosynthetic rate, and activity of microphytobenthos varied greatly throughout the day, influenced by tidal submersion/emersion and daylight. From an analysis of these results, it is considered that microphytobenthos contributed greatly to primary production in this ecosystem throughout the year by adapting suitably to intertidal environments.

Relationships between electron transport rates determined by pulse amplitude modulated (PAM) chlorophyll fluorescence and photosynthetic rates by traditional and common methods in natural freshwater phytoplankton

The relationships between the electron transport rate (ETR) measured by pulse amplitude modulated (PAM) fluorometer and the rate of O 2 production and 14 C fixation by traditional and most common methods were estimated in natural phytoplankton communities to determine the molar ratio of oxygen produced and carbon fixation per electron transported. The observations were carried out in Lake Biwa, Japan approximately once a month for a year. A remarkable linear relationship was observed between the rate of O 2 production and C fixation to ETR at low-to-medium irradiances during the sampling period, but not at higher irradiances. The annual average O 2 production/ETR and C fixation/ETR ratios at low-to-medium irradiances were 0.117 and 0.095, respectively, and the photosynthetic quotient (O 2 production/C fixation) calculated from the two ratios was 1.23, which is the most common value as the photosynthetic quotient. The same was true for cultured algal species. These results indicate that the O 2 production/ETR and C fixation/ETR ratios are reliable values at low-to-medium irradiances, and that PAM measurements can be used to quantify primary production rates based on traditional methods using the ratios. However, it must be noted that the determination of the average O 2 production/ETR and C fixation/ETR ratios in a natural phytoplankton community requires long-term observation because those ratios change seasonally over a certain range.

Studies on phosphorylation coupled with denitrification and aerobic respiration inPseudomonas denitrificans

Formation of ATP during aerobic respiration and denitrification was determined inPseudomonas denitrificans.In the intact cell system, the ATP formation associated with denitrification was almost the same as that associated with aerobic respiration when lactate was used as an electron donor. The ATP formation was inhibited by KCN, NaN3 and DNP. No phosphate uptake occurred when NH2OH, DMPD or TMPD was used as an electron donor, although the production of N2O, N2 or NO from nitrite was accelerated under anaerobic conditions.In the cell-free system, the ATP formation was also demonstrated using an ATP trapping system and lactate as a substrate. The effects of inhibitors were almost the same as those observed with the intact cells. DMPD or TMPD together with ascorbate promoted the ATP formation during aerobic oxidation by the cell-free system whereas no stimulation of ATP formation was detected during denitrification.

Behavior of hydroxylamine and nitrous oxide in the stratified brackish Lake Nakaumi, Japan

Ammonia, nitrite, nitrate, hydroxylamine (NH20H), and nitrous oxide (N20) are components ofthe nitrogen cycle that are formed and transformed by aquatic microbial processes. Previously we studied denitrification (SEIKE et al. 1986a, 1986b ), nitrification (SEIKE et al. 1986b, 1997), the behavior of nitrate (SEIKE et al. 1990) and nitrous oxide (S EN GA et al. 200 l, 2002, 2006, HIROTA et al. 2007) in brackish Lake Nakaumi, Japan. Microbes produce N20 as a by-product of nitrification and as an intermediate during denitrification (YoH et al. 1990, SENGA et al. 2002). VINCENT et al. (1981) found an extreme accumulation ofN20 in the saline bottom waters of Lake Vanda, Antarctica. Ihey reported that this N20 was produced by a narrow band of nitrifiers lying well above oxycline. YoH (1992) indicated that the shift in N20 production-consumption balance during denitrification was responsible for a wide variation in N20 accumulation level. However, it is difficult to determine the relative importance o f nitrification and denitrification in N20 production. Hydroxylamine has been recognized as an intermediate in the nitrogen cycles, such as the oxidation of ammonia to nitrite by microorganisms in aquatic and sedimentary systems. Furthermore, NH20H is often described as an intermediate for producing N20. SuTKA et al. (2006) demonstrated N20 production from NH20H by an ammonia oxidizer anda methane oxidizer. Nitrous oxide is a greenhouse gas associated with the reduction of ozone in the stratosphere. Hence, NH20H is an important nitrogen species, not only for understanding the nitrogen cycle, but also for claritying the mechanism ofN20 production. We developed a new and simple method for the determination ofNH20H in environmental water samples such as rivers and lakes using hypochlorite, followed by its gas chromatographic detection (SEIKE et al. 2004). In this study, we used the method modified for brackish water samples. Vertical profiles of hydroxylamine and nitrous oxide were investigated at a dredged area (15.5 m depth) in the stratified brackish Lake Nakaumi, Japan. Ihree pattems on the profiles of hydroxylamine aml/or nitrous oxide were observed at the boundary layer of oxidation-reduction.

Production of extracellular organic carbon in the total primary production by freshwater benthic algae at the littoral zone and inflow river of Lake Biwa

In general, a high proportion of benthic algae flora consists of diatoms belonging to the pennates (Ro uN o et al. 1990). One o f the conspicuous characteristic of diatoms is the production of an adhesive extracellular secretion. This mucilaginous substance is secreted from the raphe and/or mucilage pores of diatoms to the outside ofthe cell, covering it in various forms such as stalks, tubes, apical pads, adhering films and fibrils (HOAGLA;-..;o et al. 1993). These secretions are highly hydrated, carbohydrate-rich substances containing extracellular polymeric substances (EPS) consisting mainly of acidic polysaccharides that may be carboxylated and/or su1fated to varying degrees. Various functions have been proposed for benthic algae secretions in aquatic ecosystems, including protection against rapid changes in enhabited environments, sessile adhesion, motility, stabilization of sediments, and adsorption of dissolved organic matter and metals (DECHO 1990, HOAGLAI\D et ai. 1993, MILLER et al. 1996 ). Moreover, from the viewpoint o f food webs in inshore ecosystems, the extracellular organic carbon produced by benthic algae p1ays an important role as an organic carbon source for heterotrophic organisms (DECHO & LOPEZ 1993, KAWAMURA et al. 1998, GOTO et al. 200 l). Recent studies have shown that the production 1evel of extracellular organic matter by marine microphytobenthos is much higher than that ofmarine phytoplankton, ranging from about 30-80% o f total primary production (GOTO et al. 1999, MIDDELBURG et al. 2000, SMITH & UNDERWOOD 2000, WOLFSTEIN et al. 2002). In addition, GoTo et al. (1999) found that mos t of the extracel1ular organic matter produced by benthic diatoms inhabiting an intertidal flat was made up of colloidal organic carbon (EDTA-extractable organic carbon) containing 41-53% EPS. Although extracellular organic matter containing EPS is considered to p1ay various important ro1es in inshore ecosystems, as mentioned above, the production level o f extracellu1ar organic matter an d EPS by benthic algae in freshwater ecosystems such as rivers and lakes has yet to be clarified. Therefore, in this study, we elucidated the ratio of each organic carbon fraction to the carbon photoassimilated by cu1tured freshwater benthic a1gae and benthic alga1 communities in comparison to phytoplankton in natural fresh waters.

Generation of particulate iron and DOC consumption by heterotrophic iron oxidation bacteria in spring waters.

愛知県知多半島には,赤水を溶出する湧水が多くあり,特に鵜の池の土手に位置する井戸水の周囲には多量の赤土が堆積している。この井戸水(最大深度140cm)について1998年から1999年に調査した結果,溶存酸素の鉛直分布において,2mgL-1以下に急激に減少する深度で,溶存有機炭素(DOC)の極小値が出現し,かつ懸濁態鉄の極大値が観測された。この深度付近の層には検鏡の結果,多量の従属栄養の鉄細菌であるLeptothrix sp.が認められた。室内実験から,従属栄養性鉄細菌の増殖に伴い溶存態鉄の減少に対応し懸濁態鉄の生成とDOC消費が確認できた。さらに愛知県内の赤水が溶出する他の湧水についても,従属栄養性鉄細菌の増殖に対応したDOC消費と溶存態・懸濁態鉄の増減を求め,従属栄養性鉄細菌(KK-2)による懸濁態鉄の生成速度は0.61ngCFU-1d-1が得られた。KK-2は高月院(豊田市)より分離したもので,この地点で春・夏期に認められる赤水は微生物による懸濁態鉄の生成であると示唆された。また,DOC画分(分子量(MW):<5,000)とDOCに結合した溶存態鉄の画分(MW:5,000～100,000)を主として分離細菌が消費していると考えられた。