Energy accumulation and starvation tolerance of the embayment copepod Acartia steueri Smirnov (Calanoida: Acartiidae)

内湾生態系は、潮汐、陸水の流入、複雑な海底地形、人間活動の影響を直接受け、絶えず生物種の移入・消失による生態系の構造変化や、生物生産の変動が起きている。内湾域の生物多様性は、沿岸域や外洋域と比較して低く、内湾生態系において再生産を行って優占する生物種は限られている。内湾域の植物プランクトン量は、短期間のうちに急激に減少し、その後低濃度餌料環境が形成され、内湾性かいあし類は頻繁に餌不足に曝される。内湾性かいあし類は、このような変動の激しい餌環境に対して生理的な耐性メカニズムを持つことで適応し、個体群を維持しているものと考えられる。本研究は、飢餓に対する内湾性かいあし類の生理的耐性メカニズムを明らかにするために、西部北太平洋内湾に広く優占するかいあし類Acartia steueri Smirnovを対象種とし、(1)本種のエネルギー蓄積特性と、(2)飢餓状態における生物学的応答を研究した。エネルギー蓄積特性については、飽食条件および飢餓条件でそれぞれ10日間培養したA. steueriメス成体1個体あたりの前体部長、乾燥重量、生化学組成を測定した。くわえて、飽食条件のメス成体、卵、糞粒のアミノ酸量、アミノ酸の窒素同位体比を測定してアミノ酸のエネルギー収支を調べた。内湾、沿岸、外洋性かいあし類約50種の体長－体重の関係は、1つの回帰式で表されたが、本研究のA. steueriはこの回帰式から大きく乖離し、体長に比して、極端に重量が高いことが明らかとなった。60oC、24 hにおける本種の乾燥重量は、80 oC、100 oC、120oCの高温条件下で乾燥させると顕著に減少したことから、たんぱく質分子を覆う結合水が含まれていると示唆された。脂肪酸量、アミノ酸量、アミノ酸の窒素同位体比からは、卵・糞粒生産および代謝に利用した後の余剰分のアミノ酸を体内に蓄積し、脂肪酸を主とする他の生化学組成へ常時生合成することで、短期間のエネルギー蓄積を可能にすることが示唆された。飢餓条件における生物学的応答は、生残率、卵生産速度、糞粒生産速度、呼吸速度を測定した。生残率、卵生産速度、糞粒生産速度を調べるための、20日間における飢餓実験は、2日もしくは5日間、高濃度の餌料条件に曝した後、個体維持に必要な最低限の濃度条件と飢餓条件に曝す、計4条件を設定した。高濃度条件後の飢餓環境下で、A. steueriは15日間卵生産を継続し、18日以上生存した。A. steueriは、内湾性種の中で長い飢餓耐性日数を示し、飢餓環境下で卵を生産し続ける期間が長く、現場環境下における極めて低濃度の餌料環境下でも代謝・卵生産を継続し、次の好適な餌料環境が訪れるまで個体群を繋ぐことができる。飢餓条件における呼吸速度は、高濃度条件よりも1.5－3分の1、低い値を示したことから、本種は飢餓状態では呼吸量を低く保ち、エネルギーを卵生産に分配することで、長期間卵生産を継続することが明らかとなった。本研究は、A. steueriの飢餓に対する生理的な耐性メカニズムとして (1)遊離アミノ酸を利用した、短期間の速やかなエネルギー蓄積能を有すること、(2)飢餓状態における代謝や卵生産へのエネルギー分配を変化させることを解明した。このような本種の飢餓耐性は、変動が絶えず起こる、生物多様性の低い内湾生態系で個体群を維持するために必要不可欠な生存戦略であると言える。創価大

Treatment of synthetic poultry slaughterhouse wastewater using a consortium of anaerobic digestion microorganisms and purple phototrophic bacteria

As global population increases and living standards improve in developing countries, the demand for meat is increasing, resulting in the rise of highly concentrated organic waste water generated from poultry processing. An effective method for treating this wastewater is through anaerobic digestion, which converts it into biogas as an energy source using anaerobic microorganisms. However, while this process effectively removes organic carbon, nutrients suchas nitrogen and phosphorus remain in high concentrations in the effluent, necessitating second ary treatment facilities such as separate nitrification and denitrification tanks. Purple phototro phic bacteria are microorganisms that can uptake organic matter and nutrient-rich pollutants in wastewater, accumulating protein and carbohydrate in their cells. Since both anaerobic digestion and purple phototrophic bacterial processes occur under anaerobic conditions and have similar suitable environments such as pH and temperature, they can potentially be integrated into a single reactor. This study proposes a new process using a consortium of anaerobic digestion microorganisms and purple phototrophic bacteria for simultaneous treatment of organic carbon and nutrients from poultry slaughterhouse wastewater. The performance of the proposed simul taneous process was compared with that of the only-anaerobic digestion process and only-purple phototrophic bacterial process in a 19-day batch e periment at 33 ± 2oC under anaerobic conditions. Synthetic poultry slaughterhouse wastewater was used as the substrate, and anaerobic digestion sludge collected from a mesophilic anaerobic digestion plant and Rhodopseudomonas capsulata were used as the inoculums.In the simultaneous process, biogas production and organic carbon (chemical o ygen demand) removal progressed first with and without infrared light irradiation, followed by an increase in bacteriochlorophyll a concentration, an indicator of the biomass of purple phototrophic bacte ria. These results indicate that the anaerobic digestion process and purple phototrophic bacterial process functioned in a single reactor, although there was a time gap between the two processes. Despite uniform substrate input, the simultaneous process produced higher biogas (276-337 mL) than the only-anaerobic digestion process (138 mL), possibly due to degradation of some purple phototrophic bacteria biomass as feedstock for anaerobic digestion. In the simultaneous process, organic carbon removal efficiencies ranged from 40 to 81%, similar to or lower than the removal efficiency of the only-anaerobic digestion process (81%). In purple phototrophic bacteria added conditions, nitrogen removal was not confirmed, indicating low nutrient removal capability. The treatment performance of the simultaneous process can be enhanced by improving light permea bility using flat-panel reactors or granular anaerobic sludge and acclimation of purple phototro phic bacteria with highly concentrated organic wastewater before using it as an inoculum.departmental bulletin pape

浮遊性カイアシ類Acartia steueriの幼生・幼体の培養における微細藻類餌料の検討

In aquaculture and ornamental industries, copepods are recognized as preferred live feeds for marine fish larvae over commonly used organisms such as Artemia and rotifers. Marine fish larvae fed with copepods show better survival and growth. Despite obvious advantages of copepods as the live feed, their use is still limited owing to low productivity and cost-efficiency when mass cultivated. Copepods from the genus Acartia are good candidates for a live feed because their body size, swimming behavior, and biochemical composition are suitable for many marine fish larvae which have small mouth gapes. In addition, Acartia species produce dormant eggs which can be stored and hatched to feed fish larvae. Acartia steueri Smirnov is widely distributed in the coastal waters of the western Pacific Ocean, and is an essential food source for the larvae of commercially important fish in their natural habitats. Different dietary microalgae affect the egg production rate, hatching success, survival rate, growth rate, and the population growth of copepods. One of the underlying bottlenecks in the intensive cultivation of copepods is fatally low survival rate during their larval stages. Calanoid copepods including genus Acartia feed on live microalgae. In the present study, in order to clarify the favorable dietary microalgae for larvae of Acartia steueri, the nauplii individuals were fed with four mono-microalgal diets and one mixed-microalgal diet to measure their survival rate. The present study conducted two experiments. In the first experiment, the nauplii hatched within 24 hours were individually reared in 6-well plates under three diet conditions (mono-diet of Tetraselmis suecica, Rhodomonas salina and Isochrysis galbana) in April 2019. Survival rate and development stages of the copepods were measured every two days. In the second experiment, the nauplii were reared in 600 mL beakers under three diet conditions (mono-diet of T. suecica, Chaetoceros gracilis, and a mixed diet of T. suecica + C. gracilis at 1:1 carbon ratio) in April 2020. Survival rate and development stages of the copepods were measured at day 10 and day 20 during the incubation duration.In the first experiment, the survival rate at day 20 was 26.8 ± 7.2％ when fed with T. suecica, which was the highest value among the mono-microalgal diet conditions. However, only 0.6％ of individuals fed with T. suecica were developed to the adult stage (copepodid VI). In addition, the malformation at first antennas was observed from the copepodid individuals fed with T. suecica. T. suecica is well known to be rich in amino acids but with poor fatty acid content. These results might suggest that T. suecica is the favorable diet for early developmental stages (i.e. nauplii) of the copepod A. steueri, but has a nutritional problem for the later development stages of life cycle. In the second experiment, the ratio of individuals developed until adult stages was maximized under the mixed diet condition of T. suecica and C. gracilis, and this mixed diet can be considered a favorable diet for A. steueri larvae in the present study

High productivity of eicosapentaenoic acid and fucoxanthin by a marine diatom chaetoceros gracilis in a semi-continuous culture

Significantly high eicosapentaenoic acid (EPA) and fucoxanthin contents with high production rate were achieved in semi continuous culture of marine diatom. Effects of dilution rate on the production of biomass and high value biocompounds such as EPA and fucoxanthin were evaluated in semi-continuous cultures of Chaetoceros gracilis under high light condition. Cellular dry weight increased at lower dilution rate and higher light intensity conditions, and cell size strongly affected EPA and fucoxanthin contents. The smaller microalgae cells showed significantly higher (p < 0.05) value of 17.1 mg g-dw−1 fucoxanthin and 41.5% EPA content per total fatty acid compared to those observed in the larger cells. Chaetoceros gracilis can accumulate relatively higher EPA and fucoxanthin than those reported previously. In addition, maintenance of small cell size by supplying sufficient nutrients and light energy can be the key for the increase production of valuable biocompounds in C. gracilis

間欠的な曝気撹拌が海産珪藻Chaetoceros gracilis の生産性に与える影響

The demand for global fisheries protein source continues to increase with the increase of the worldʼs population, causing decrease of natural fishery resources due to the overfishing and the degradation of habitats. Under these circumstances, the fisheries industry for marine products has rapidly grown in recent decades to promote the stable production and utilization of fishery resources while managing and conserving them. Mass cultivation of microalgae is essential for efficient production of artificial seedlings of bivalves whose resources are rapidly decreasing. Diatoms can provide high utility as a primary feed because they contain a high content of fucoxanthin, a carotenoid pigment. The marine diatom, Chaetoceros gracilis which can accumulate fucoxanthin, is a promising feed for fishery products. However, marine diatoms are known as a taxonomic group in which stable cultivation is difficult, and it is necessary to establish a cultivation method that enables high-density cultivation. In previous studies, the factors involved in the growth of marine diatoms have been investigated by controlling the external environment such as light intensity, water temperature and nutrient concentration. However, the establishment of high-density cultivation for marine diatoms under each optimal environmental condition has still not been achieved. A problematic point in the high-density cultivation involves the heterogeneity of the light intensity, water temperature, and nutrient concentration in the culture tank, which limits the growth of algae. Previous studies have reported that “agitation” of the culture solution has the effect of promoting the supply of CO2, as a carbon source, and the removal of dissolved oxygen by equalizing the internal environment of the culture tank, and is essential to improve the productivity of microalgae. However, the performance of using the agitation method remain to be solved in mass culture operation. Intermittent agitation frequency is one of the solutions for low-energy cost operation. There is no previous research comparing biomass productivity per unit of agitation energy input between the same species using both continuous and intermittent agitation methods. The objective of this study was to evaluate the productivity per aeration energy under different agitation frequencies toward high-density cultivation of marine diatom C. gracilis. C. gracilis (UPMC-A0010-2) isolated from Malaysian coastal waters was semi-continuously cultured using modified Conway medium in 1.2-L bubble column reactors (n=2). The culture was conducted under stable light intensity 300 μmol m-2 s-1 (12 hours cycle of light and dark) and temperature (25oC). The dilution rates were adjusted at 0.3 d-1. The aeration rate in each reactor was set to 0.2 L min-1 (2% CO2), and aeration frequency was set to the following three conditions: (1) continuous agitation condition, (2) intermittent agitation condition once 9 every minutes, and (3) intermittent agitation condition once 18 every minutes. The cultivation period was a stationary phase of the biomass for up to 5 days, and the absorbance (750 nm) and pH of the culture, and the dry weight were measured. The biomass productivity per algal volume was equivalent to that under continuous agitation conditions even with relatively high frequency of intermittent agitation once 9 every minutes. This may be caused by the high light utilization efficiency of the cells because the cells in the culture are distributed on an average without sedimentation even after the aeration pause period without agitation. The biomass productivity per unit of agitation energy input in the intermittent agitation conditions showed a higher value than the continuous agitation condition by several times. Intermittent agitation performance can be evaluated as an environmental control technology that can maintain biomass productivity equivalent to continuous agitation conditions. The reduction of energy consumption by intermittent agitation is expected to significantly contribute to the reduction of operating costs for outdoor closed-system reactors