Zhaoling Cai

Nisin Production by Lactococcus Lactis Subsp. lactis under Nutritional Limitation in Fed-Batch Culture

Nisin production was improved under nutritional limitation in fed-batch culture of Lactococcus lactis. Nisin titre reached 3887 IU ml−1 by a slow feeding of sucrose and 4131 IU ml−1 by slow feeding of nitrogen source, which were, respectively, 64% and 74% above the values in batch culture.

Improvement of nisin production in pH feed-back controlled, fed-batch culture by Lactococcus lactis subsp. lactis

Nisin production by Lactococcus lactis subsp. lactisin fed-batch culture was doubled by using a pH feed-back controlled method. Sucrose concentration was controlled at 10 g l−1 giving 5010 IU nisin ml−1 compared to 2660 IU nisin ml−1 in batch culture.

Effect of iron stress, light stress, and nitrogen source on physiological aspects of marine red tide alga

Abstract Effect of iron (Fe) stress, light stress, and nitrogen (N) source on physiological aspects of the marine red tide alga Heterosigma akashiwo was investigated in batch cultures. Cellular chlorophyll and carotenoid contents increased under low light stress and decreased under iron stress. A specific pigment was induced under light stress. Nitrate reductase and nitrite reductase activities of nitrate-grown cells decreased under iron and light stress, while those of ammonium-grown cells were negligible. The cell density and the growth rate decreased under Fe stress, and this decrease can be aggravated by light stress. Compared with ammonium-grown cells, nitrate-grown cells showed an increase in the cell density and the growth rate. Intracellular C:N ratios indicated that the Fe-stress effect on nitrate or ammonium did not specifically involve in the nitrate assimilatory pathway, and light stress would aggravate the Fe-stress effect.

Some physiological and biochemical changes in marine eukaryotic red tide alga Heterosigma akashiwo during the alleviation from iron limitation

Some physiological and biochemical changes in the marine eukaryotic red tide alga Heterosigma akashiwo (Hada) were investigated during the alleviation from iron limitation. Chlorophyll a/carotenoid ratio increases as a result of iron alleviation. In vivo absorption spectra of iron-limited cells showed a chlorophyll (Chl) absorption peak at 630 nm, 2 nm blue-shiftied from the normal position. Low-temperature fluorescence emission spectra of the cells have one prominent Chl emission peak at 685 nm. The cells showed a decrease in fluorescence yield from 685 nm band during alleviation from iron limitation. Low-temperature fluorescence excitation spectra and room-temperature fluorescence spectra indicated an efficient excitation energy transfer in the cells alleviated from iron limitation. Photosynthetic efficiency and carbohydrate content per cell increased after alleviation from iron limitation. Total protein decreased in iron-limited cells, while iron deficiency induced the appearance of specific soluble proteins (17 and 55 kDa)

MECHANISMS OF PROTEIN FOULING IN MICROFILTRATION. II. ADSORPTION AND DEPOSITION OF PROTEINS ON MICROFILTRATION MEMBRANES

Adsorption and deposition of proteins in/on membranes were two main mechanisms of protein fouling in microfiltration. To distinguish the two mechanisms, adsorption and deposition were studied under both static and filtration conditions. The results demonstrated that under static conditions, adsorption had an equilibrium and the equilibrium amount of adsorption was almost constant even in solutions with different concentrations. The maximum adsorption occurred at isoelectric point pH value, and the amount of protein absorbed was similar to that of monolayer type adsorption. In actual microfiltration, adsorption and deposition of proteins occur simultaneously and the adsorption has an equilibrium with adsorption values similar to that of static adsorption. The amount of protein that deposited onto the membranes was simply proportional to filtration volume of the solution. The result can be described by a mathematical model.

Regulation of CO2 on heterocyst differentiation and nitrate uptake in the cyanobacterium Anabaena sp PCC 7120

Aims:  The aim of the present investigation was to study the effects of different inorganic carbon and nitrogen sources on nitrate uptake and heterocyst differentiation in the culture of cyanobacterium Anabaena sp. PCC 7120.

Mechanisms of protein fouling in microfiltration. I. Determination of proteins fouled on microfiltration membranes

Protein fouling is one of the critical factors governing the effectiveness of many microfiltration processes. Although mechanisms have been proposed, direct correlation between protein amount fouled on membranes and filtration behavior is required. We developed a simple method to measure proteins on microfiltration membranes. The protein-fouled membranes were stained by amido black 10B first, then destained to remove excess dye not bound to protein. Finally, the dye associated with the protein on the membranes was eluted with 0.1 N NaOH. Three membranes (mixed esters of cellulose nitrate and acetate membrane, Durapore GVWP membrane, and nuclear-pore membrane) were examined by blotting, adsorbing, and depositing bovine serum albumin on them. The absorbency of the eluted solutions was measured at 620 nm. The absorbency of the eluted solutions was independent of staining time and eluting time, but decreased with prolonged destaining time. The results showed a good linear relationship between the absorbency and amount of protein on membranes in all conditions examined. Three other proteins were also examined and the results showed that different proteins have different slopes. These results indicate that the method could be used to quantify proteins fouled on membrane.