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Major research achievements of the Lab over the last decade:

 

ecadal trends have been revealed in bacterioplankton dynamics in Sevastopol bay (SW Crimea, the Black Sea) after examining complete time series including both published (1966 to 1988) and our own (since 1990s) data on bacterial abundance (BA). Three distinct periods have been recognized: (i) a significant increase in the average annual BA owing to growing levels of pollution and eutrophication of the waters since late 1960s till late 1980s, especially after building a stone mole at the entrance to the bay, which reduced water exchange rates sufficiently; (ii) elevated but highly variable values since early 1990s till early 2000s (the ecosystem ‘deregulation’); (iii) stable decrease in the values and their variability over the post-perestroika period of economical depression, providing an evidence that the bay capacity for recovery was not exhausted before the USSR collapse.

 

easonal dynamics and spatial patterns of bacterioplankton abundances in Sevastopol bay (SW Crimea, the Black Sea) have been studied as a function of hydrometeorological (air and water temperature, prevailing winds, sea level variations, open sea-bay water exchange, the Black river discharge), anthropogenic (pollution, emergency evacuation of water from a storage reservoir) and biological (phytoplankton development) factors. Additional hydrological and hydrochemical variables (water salinity, pH, alkalinity, density, transparency, soluble oxygen, PO43-, NO3-, NO2, NH43+, SiO32-) have been used in multiple discriminant analysis for zoning the bay waters and revealing three significantly different provinces.

 

henotyping of the Black Sea pico- and nanophytoplankton from coastal and open waters has been first performed by flow cytometric approach. The analysis of cells clusters on the cytograms was based on average cell size and pigment content (Chl a, PE and their ratio) as variables for phenotype classification (CA and DA in StatSoft Statistica 6.0). The distribution of phenotypes was shown to correlate well with light and temperature conditions, nutrient and pollutant concentrations. Rare phenotypes can potentially be used as markers of the water trophic status.   

 

revision of the current paradigm of the energy flow in aquatic ecosystems (and, in particular, microplankton) is required as the latter is based on a few false assumptions, namely: (i) the energy flow is coupled exceptionally to trophic processes (“trophic energy flow”); (ii) aerobic respiration is the only catabolic process in the oxic water column; (iii) intracellular metabolism is the only source of heat energy dissipated by water sample. There is a considerable gap in the data on in situ physiological activity of planktonic microorganisms, which is filled with indirect estimates of their metabolic rates approximated from material flows (like production). This prevalent approach provides no valuable information on the real metabolic rate but produces its fallacious estimates as the net growth efficiency (K2) is not actually measured in the same experiment. Applying nanocalorimetry in the field of hydrobiology looks promising as a highly sensitive method for measuring directly the heat dissipation by native microplankton, without any cell pre-concentration. Modern knowledge of the viral loop, physiology of ultramicrobacteria, and bacteria-mediated extracellular hydrolysis of biopolymers have to be taken into account to calculate detailed energy budget of microplankton.

 

nalysis of historical and modern data on respiration (R), production (P) and net growth efficiency (K2) of bacterioplankton in Sevastopol bay has revealed a weaker R-P dependence comparing with the classical models by Del Giorgio and Cole (1998). Searching for valid fundamental relationships between R, P and K2 looks reasonable only if both trophic and pollution statuses of the waters are considered equally important.  

 

 novel approach was proposed and tested in a pilot study for measuring energy budget of aquatic viral loop, which was based on multi-cycle re-filtrations of native seawater sample through a 0.2-um membrane for controlling MOI, and subsequent direct calorimetry of the hosts (picoplankton) concentrated on the membrane. Depressed biomass production and yield of virus-like particles were detected on the membrane by a radioisotopic method and microscopic observations, that provided evidence of virus-induced cell lysis. Elevated heat flow by the sample indicated an increase in the total metabolism. Cell-specific heat flux seemed to be higher in the infected cells.  

 

ignificant changes in species composition of the tintinnid community were observed over 2000s. Species number decreased from 20 to 17. Some native species were changed to invasive ones.

 

ew prospectives have been revealed for applying the microcalorimetric approach as a tool for measuring directly the energy flows in pelagic microbial communities and, in particular, the microbial and viral loops. The first data on the picoplankton heat flux (2-75 fW cell-1), entropy production rate (0,3-0,7 J m-3 h-1 К-1) and dissipation function (2-5 ´ 10-4 h-1 К-1) were obtained for a number of marine and hypersaline ecosystems for further inter-ecosystem comparisons.

 

t was surprisingly found that plankton femtofraction (FF, <0,2 µm) produced more heat per seawater volume (48 ± 24 (95% CI) μW l-1) than picofraction (25 ± 14 μW l-1). Consequently, two hypotheses were tested, which defined the heat source in FF either as (i) metabolism of ultramicrobacteria, the only living component in the fraction besides the non-metabolizing virioplankton which are unable to produce heat; or (ii) extracellular chemical processes in aquatic environments. It was experimentally showed that both sources contributed to the overall heat flow by FF but the non-living component was responsible for the bulk of it. Hydrolysis of high molecular weight organic substances dissolved in seawater, associated with bacterial extracellular enzyme activity, is considered the most probable source of the heat. If so, microcalorimetry has great prospective in aquatic microbial ecology and biochemistry as a powerful unspecific analytical method.

 

n natural bacterioplankton assemblage, biovolume- and biosurface-specific heat fluxes insignificantly increased with decreasing average cell size from 0.75 ± 0.12 to 0.13 ± 0.04 um3, to give indirect evidence that at least a part of the ultramicrobacterial pool are cells with high volume-specific metabolic rate.

 

he maximum biosurface-specific metabolic rate measured for the natural bacteria proved to be close to those averaged for actively growing aquatic protozoans at 1.3 × 1015 mol O2 um2 h1 (equivalent to 2 × 1013 W um2 for purely aerobic metabolism), as calculated from published data. The latter does not depend on the cell volume (r2 < 0.001, n = 58) over the size range from 102 um3 (smallest flagellates) to 108 um3 (largest sarcodines), supplying illustrative evidence for Rubner’s law. Marine bacteria (101 um3) appear to fit this law and extend its scale by 2 orders of magnitude.

 

hotocalorimetry has rarely been employed to investigate the processes in photosynthesis. The possibility of detecting light emission as fluorescence and thermal dissipation in chlorophytic microalga Dunaliella maritima was examined by this method when complemented by simultaneous oxygen polarographic measurements. The results showed that under acute light stress, the net heat flow was sharply positive (exothermic) while the oxygen polarographic sensor indicated oxygen evolution in the light. Energy balances to correct for the imbalance in the response to incident radiant light and to convert the oxygen evolution to energy values by the oxycaloric equivalent for glucose (–470 kJ mol–1 O2) revealed an extra source (15.5 ± 3.3 (SE) and 9.4 ± 3.2 pW per cell for the control and treated cells, respectively) of heat which was thought to be due mainly to nonphotochemical quenching (NPQ).

 

customised photomicrocalorimeter module has been improved using light-emitting diodes (LEDs).

 

he photocalorimetric method was shown to be highly promising for quantifying both the photosynthesis and respiration of marine phytoplankton and probing the phenomena like photoinhibition and non-photochemical quenching on the global scale.