Kazuhisa Miyamoto

Biological elimination of nitric oxide and carbon dioxide from flue gas by marine microalga NOA-113 cultivated in a long tubular photobioreactor

Nitric oxide (NO) and carbon dioxide (CO2) were simultaneously eliminated from a model flue gas using a marine microalga, strain NOA-113, cultivated in a long tubular photobioreactor. About 40 mg of NO and 3.5 g of CO2 were eliminated per day in a 4-l reactor column with aeration of 300 ppm (v/v) NO and 15% (v/v) CO2 in N2 at a rate of 150 ml/min. This reactor system is thought to be suitable for evaluating NO elimination by microalgae. The effects of NO concentration, gas flow rate, and light conditions on NO elimination were investigated using this system.

Enhancement of tolerance to heavy metals and oxidative stress in Dunaliella tertiolecta by Zn-induced phytochelatin synthesis

The synthesis of phytochelatins (PCs) in a marine alga, Dunalliela tertiolecta, is strongly induced by Zn. Pretreatment of the cells with Zn enhances the tolerance toward toxic heavy metals such as Cd, Hg, Cu, Pb, and arsenate. Moreover, the pretreatment also increases the tolerance toward oxidative stress caused by hydrogen peroxide or paraquat. In vitro analysis shows that PC is a stronger scavenger of hydrogen peroxide and superoxide radical than glutathione. These results suggest that PCs inducibly synthesized by Zn treatment could play a role not only in detoxification of heavy metals but also in mitigation of oxidative stress.

H2 production from algal biomass by a mixed culture of Rhodobium marinum A-501 and Lactobacillus amylovorus

To produce hydrogen from starch accumulated in an algal biomass, we used a mixed culture of the lactic acid bacterium, Lactobacillus amylovorus, and the photosynthetic bacterium, Rhodobium marinum A-501. In this system L. amylovorus, which possesses amylase activity, utilized algal starch for lactic acid production, and R. marinum A-501 produced hydrogen in the presence of light using lactic acid as an electron donor. Algal starch accumulated in the marine green alga Dunaliella tertiolecta, and the freshwater green alga Chlamydomonas reinhardtii, was more suitable for lactic acid fermentation by L. amylovorus than an authentic starch sample. Consequently, the yields of hydrogen obtained from starch contained in D. tertiolecta and C. reinhardtii were 61% and 52%, respectively, in the mixed culture of L. amylovorus and R. marinum A-501. These values were markedly superior to those obtained using a mixed culture of Vibrio fluvialis T-522 and R. marinum A-501 described previously. The yield and production rate of hydrogen by R. marinum A-501 from the lactic acid fermentates were higher than from authentic lactic acid, suggesting that the fermentates contain a factor(s) which promotes H2 production by this bacterium.

Uptake pathway and continuous removal of nitric oxide from flue gas using microalgae

Abstract Nitric oxide (NO), a major constituent of NOx in fossil fuel flue gas, can be removed by the microalga, Dunaliella tertiolecta, in a bubble-column-type bioreactor. The uptake pathway of NO was investigated, and it was found that little NO was oxidized in the medium before its uptake by algal cells and that NO mostly permeated directly into the cells by diffusion based on the mass balance of nitrogen and the change in nitrate and nitrite concentration in the medium in batch culture. For further application of this system, it is necessary to remove NO over a long duration, and the stability of NO removal is important. NO removal rate of about 50–60% could be maintained stably for 15 days in continuous culture under the light condition. Because the consumption of nitrate was reduced by the amount of taken NO, NO rather than nitrate is preferentially utilized as a nitrogen source for cell growth. Therefore, this algal system is useful for continuous NO removal and production of algal biomass using NO as a nitrogen source.

The ATP‐binding cassette transporter subfamily C member 2 in Bombyx mori larvae is a functional receptor for Cry toxins from Bacillus thuringiensis

Bacillus thuringiensis is the most widely used biopesticide, and its Cry toxin genes are essential transgenes for the generation of insect‐resistant transgenic crops. Recent reports have suggested that ATP‐binding cassette transporter subfamily C2 (ABCC2) proteins are implicated in Cry intoxication, and that a single amino acid insertion results in high levels of resistance to Cry1 toxins. However, there is currently no available direct evidence of functional interactions between ABCC2 and Cry toxins. To address this important knowledge gap, we investigated the role of Bombyx mori ABCC2 (BmABCC2) or its mutant from a Cry1Ab‐resistant B. mori strain on Cry1A toxin action. When we expressed BmABCC2 ectopically on Sf9 cells, it served as a functional receptor, and the single amino acid insertion found in BmABCC2 from Cry1Ab‐resistant larvae resulted in lack of susceptibility to Cry1Ab and Cry1Ac. Using the same expression system, we found that Bo. mori cadherin‐like receptor (BtR175) conferred susceptibility to Cry1A toxins, albeit to a lower degree than BmABCC2. Coexpression of BtR175 and BmABCC2 resulted in the highest cell susceptibility to Cry1A, Cry1F, and even the phylogenetically distant Cry8Ca toxin, when compared with expression of either receptor alone. The susceptibility observed in the coexpressing cells and that in Bo. mori larvae are likely to be correlated, suggesting that BtR175 and BmABCC2 are important factors determining larval susceptibility. Our study demonstrates, for the first time, Cry toxin receptor functionality for ABCC2, and highlights the crucial role of this protein and cadherin in the mechanism of action of Cry toxin.

Removal of hazardous phenols by microalgae under photoautotrophic conditions

Various algae were screened for their ability to decrease the concentration of 2,4-dinitrophenol (DNP), as a model compound of hazardous phenols, under photoautotrophic conditions. Chlorella fusca var. vacuolata and Anabaena variabilis grew well and showed high DNP removal ability over the concentration range of 5 to 40 microM. Their abilities to remove various phenols were investigated. More than 90% of 40 microM o- and m-nitrophenol and DNP was removed during the cultivation period of 5 d. o-, p-Chlorophenol and 2,4-dichlorophenol could be removed, but not to a significant extent. C. fusca also removed 85% of bisphenol A, suspected to be an endocrine disrupter. It was found that microalgae would be applicable to the removal of hazardous phenols without the addition of any organic carbon sources.

Characteristics of Biological NOx Removal from Flue Gas in a Dunaliella tertiolecta Culture System

Abstract A system for the biological removal of NOx from fuel flue gas was investigated using the unicellular microalga Dunaliella tertiolecta . When nitric oxide (NO), the main component of NOx in flue gas, was supplied to the algal culture in a bioreactor with a 2-m column in the light at concentrations ranging from 25 to 500 ppm, about 65% of the NO was removed. Under these conditions, cell growth was not affected by the concentration of the NO supplied, and about 1.6% O 2 was constantly evolved by photosynthesis. About 30% of the NO was removed by the medium without cells at 2% O 2 , in which case the NO was probably photochemically oxidized by Fe 3+ present in the medium. In cell cultures without Fe 3+ , however, 65% NO removal was achieved. In the dark, on the other hand, the rate of NO removal was governed by the amount of O 2 supplied in the inlet gas, i.e. , achievement of a NO removal rate similar to that achieved in the light required the presence of O 2 at 2% or more, and NO removal did not occur without the supply of O 2 . It is thus clear that both algal cells and O 2 are essential in the reactor system. NO removal is assumed to proceed as follows: NO in the gas is first dissolved in the aqueous phase, after which it is oxidized and assimilated by the algal cells. The results of investigations under various culture conditions indicate that the dissolution of NO in the aqueous phase is the rate-limiting step in this reactor system.

Improvement of Microalgal NOx Removal in Bubble Column and Airlift Reactors

Nitric oxide (NO), a major nitrogen oxide component in fossil fuel flue gas, was removed by the green alga Dunaliella tertiolecta cultivated in bubble column and airlift reactors. As NO removal was enhanced by increasing the dissolution of NO in water, increasing the gas-liquid contact area and time was deemed as an effective method for improving NO removal. The highest level of NO removal, 96%, was achieved with a counter-flow type airlift reactor when 100 ppm NO was aerated with smaller bubbles.

Vertical tubular reactor for microalgae cultivation

SummaryVertical glass tubular reactors, 5 cm in diameter and 2.35 m high, were used to grow several species of cyanobacteria, green algae, and diatoms. The reactors were gassed with an air/CO2 mixture, to supply CO2, remove O2, and provide mixing. Most of the 10 strains tested had productivities similar to those observed with mechanically mixed reactors. The advantages of the vertical tubular reactors are their high surface to volume ratios, low shear forces, low cost, absence of wall growth, high CO2 use efficiency, and the ability to use sunlight.

Bioactivities of nostocine a produced by a freshwater cyanobacterium Nostoc spongiaeforme TISTR 8169.

A freshwater cyanobacterium, Nostoc spongiaeforme TISTR 8169, synthesizes and releases a violet pigment, nostocine A, into medium. We examined the bioactivity of nostocine A to several model organisms breeding with N. spongiaeforme in the natural environment. To microalgae, nostocine A exhibited growth inhibitory activity comparable to paraquat, and the activity tended to be stronger to green algae than to cyanobacteria. Nostocine A also exhibited strong inhibitory activity to the root elongation of barnyard grass, strong antifeedant activity to cotton ballworm, and acute toxicity to mice resulting in its classification as a dangerous poison. The results suggest that nostocine A may act as a toxin or an allelochemical to breeding organisms in nature. In a laboratory culture of N. spongiaeforme, the production of nostocine A was enhanced at higher temperature, 30 degrees C, and more intense light, 30 W/m2, than the basal conditions, 25 degrees C and 10 W/m2. Cultivation of cells with H2O2 at 1 or 2 mM also enhanced the production of nostocine A, indicating that nostocine A may be synthesized and released when the cells are exposed to oxidative stress, possibly occurring at higher temperature and more intense light. LC-MS and electron spin resonance analyses revealed that nostocine A, reduced previously by NaBH4, immediately recovered to its original form upon exposure to air and the generation of superoxide radical anions occurred at this re-oxidation step. These results suggest that the adverse effects of nostocine A on various organisms may be related to the function of nostocine A in generating toxic reactive oxygen species, which occurs in the cells of target organisms.