Sanja Tomšić

Live diatoms facing Ag nanoparticles: surface enhanced Raman scattering of bulk cylindrotheca closterium pennate diatoms and of the single cells

A comprehensive exploratory SERS experiment in conjunction with conventional Raman spectroscopy was conducted to investigate the interface between the silver nanoparticles (AgNPs) and the lightly silicified Cylindrotheca closterium diatoms in vivo both in the bulk cells culture and at the single cell level. The SERS chemisorption mechanism was found dependent on the NPs type and size as the SERS signal showed different signature for different NPs, the common SERS feature being the absence of the conventional Raman signal of carotenoids when microalgae are excited with the 532 nm line. SERS results suggest that the (pre)resonance Raman effect observed in bulk diatoms is no longer dominant in the case of SERS in bulk solution. Detection of polyunsaturated fatty acids was achieved together with specific SERS evidence of carotenoids and chlorophylls. The results are a prerequisite for the further exploration the diatoms fluctuant contribution to the SERS outcome of natural seawater.

Methyl mercury inhibits short-circuit current and Cl- influx across isolated epipodite of European lobster (Homarus gammarus).

The effect of methyl mercuric chloride (MeHg) on short-circuit current (I(SC)) was studied in the isolated perfused epipodite preparation from the branchial chamber of European lobster (Homarus gammarus) acclimated to dilute seawater. When applied at the apical surface, 0.2, 1.0 and 3.0 microM MeHg depressed I(SC) by a 26%, 81% and 98%, respectively. The half-maximal inhibitory concentration (IC(50)) of apically applied MeHg was 0.6 microM. Basolaterally added MeHg (3.0 microM) had no effect on I(SC), whereas addition of the specific Na(+),K(+)-ATPase inhibitor ouabain (1.5 mM) reduced I(SC) by approximately 90%. Ouabain effects were reversible, and I(SC) fully recovered upon removal of ouabain. The MeHg-induced block of I(SC) was partially reversed by the reducing agent, 1,4-dithiothreitol, suggesting that the formation of S-Hg-S bridges is important in the inhibitory mechanism. A significant reduction of I(SC) and conductance occurred when low Na(+) and Cl(-) salines were substituted. Furthermore, in the low Na(+) saline, J(Cl)(A-->B) fluxes were reduced by about 50%. In the highly conductive epipodite epithelium, coupling of Na(+) and Cl(-) fluxes was suggested. The effects of MeHg on I(SC) in the lobster epipodite are attributed to inhibition of an apical Cl(-) influx.

Growth and Gonad Changes in Stony Sea Urchin, Paracentrotus Lividus (Lamark, 1816) Fed Artificially Formulated Feed and Benthic Macrophyte Diet

This study reported the efficiency of artificially formulated feed and benthic macrophyte diet on growth and gonad development of cultured stony sea urchin, Paracentrotus lividus (Lamark, 1816). An initial sample of 720 individual urchins was gathered in coastal area of SE Adriatic, near Dubrovnik, Croatia and for the purposes of the experiment, was held in a flow-through system. Sea urchin were fed four test diets A, B, C and D. Diet A consisted of seaweeds collected in the natural habitat of sampled sea urchin, artificial diets B, C, and D contained a different ratio of ingredients. The feed mixtures differed in respect to corn meal content; B (22%), C (30%) and D (35%) as well as the distribution of fish meal content; B (15%), C (5%) and D (0%). Prior to the commencement of feeding, sea urchins in all groups were starved for 15 days. During the period of starvation, recorded total urchin weight, gonadosomatic index (GSI) and gonad weight values for all experimental groups, showed a declining trend except in the control group, where they stayed the same. After 30 days, the declining trend of morphometric values was recorded for treatment A and the control group. During the two months of the intensive feeding conditions in the regimes with artificially prepared feed, B, C and D a growing trend was recorded for all morphometric values, and it was particularly evident in the treatment C. In the last month of the experiment, a significant decline in the GSI and gonad weight values were observed for the groups, A and the control. The differences among the artificially formulated feeds expressed through increase of GSI and gonad mass values revealed that the best among them was artificial feed C whose variance in consistence of essential nutritional components fits between prepared feeds B and D. Based on the results of our study we conclude that the artificially formulated feed is adequate food for sea urchins in a controlled environment, especially when it contains a smaller animal protein component (510%) and a larger share of plant components (over 90%).