Acclimatization of the oscillatoria ( Oscillatoria agardhii ) in alkaline lakes of various mineralization

. The article presents the results of a study on the adaptation of Oscillatoria agardhii to the water of lakes of various mineralization. It has been established that cyanobacteria develops in the range of mineralization from 2 to 50 g/l. The optimum mineralization was in the range of 2-21 g/l. The pH of the waters in which the development of cyanobacteria was observed varied from 6.5 to 9.2. The temperature optimum of growth was observed in the range of 25-40 °C. Principal component analysis revealed a trend in increasing cell density, coinciding with the greatest number of short trichomes, which coincided with a trend in trace elements and compounds in the direction from Na to Ca. In all the studied lakes, the vast majority of elements and compounds were found to exceed the MPC for fishery water bodies, which should be taken into account when introducing new types of aquaculture into highly mineralized water bodies.


Introduction
Blue-green algae of the Oscillatoriaceae family are characterized by wide euryhaline.The reservoirs of the Southern Trans-Urals are rich in lakes with high mineralization.At the same time, they are little used in terms of fish farming and aquaculture, since mineralization from 10 to 25 and more than 35 g/l is transitional and unsuitable for the development of many aquatic organisms.One of the euryhaline species of algae, Oscillatoria agardhii, is cultivated in artificial conditions.The aim of our work was to study the development of Oscillatoria agardhii in lakes of various mineralization.

Materials and methods
Water samples were taken from 15 lakes with salinity from 1 to 50 g/l [1].Salt concentration was measured with a WZ-212 (RHS-28ATC) refractometer in the range of 0-50% with a resolution of 0.1% and an accuracy of ±0.2%.The pH of water taken from highly mineralized lakes was determined with a PH-009 meter.Oscillatoria agardhii culture was used in the experiments.The nutrient medium for culture per 500 ml of water consisted of: a solution of potassium nitrate (KNO 3 ) -20 ml, a solution of ammonium phosphate ((NH 4 )2HPO 4 ) -1 ml, a solution of iron sulfate (FeSO 4 ) -0.1 ml, a solution of magnesium sulfate ( MgSO₄) -1 ml, potassium sulfate solution (K2SO4) -5 ml, NaHCO3 -1 g, NaCl -10 g.A 10 ml culture inoculum was added to a 0.5 L sample of water from each lake and cultivated for 1 month [2 ].Throughout the study, the number of Oscillatoria agardhii cells was counted by microscopy by visual counting on a Levenhuk D2L NG monocular microscope in a field of view of 280 μm 2 with a WF16x eyepiece and a 4x objective.The concentration of elements and compounds in water was determined by capillary electrophoresis on the Kapel 103-R system, GK Lumeks, Russia [3,4].Calculations and graphical constructions were performed in the PAST package [5].

Results and Discussion
Before the culture was introduced into the water from highly mineralized lakes, the features of the development of oscillatories were studied under different types of illumination, mineralization, and in containers of different volumes (Table 1).The largest growth rates were observed in a 0.5-liter container, which is due to its better light transmission compared to a 3-liter container.The optimal level of mineralization was found in the range of 21-35‰, where the number of cells was 31-41 copies per field of view.Optimal temperatures are in the range of 32-40°C.At temperatures below 27°C, a decrease in the number of cells was observed.In addition to the control, the highest development values were observed in Lake Spornoe 3, where, on the 5th day of development, the culture reached a maximum number of 40 cells per field of view, after which a slight decrease in cell density was observed.A similar growth dynamics was observed in lakes Lineyskoye, Khomutinino 4, and Khomutinino 3, with the corresponding abundance peaks on the 5th day of development at 23, 19, and 10 cells per field of view.In Lake Kulikovo, the maximum abundance was detected on the 3rd day, and in Lake Kayasan, on the 1st day.In Lake Lafetnoye, as well as in the control medium, the maximum number was detected on the 12th day after the introduction of the inoculum, during the first 10 days there was a gradual increase in the number of cells.The shortest cell trichomes were observed in lakes Khomutinino 4 and Khomutinino 3; also, trichomes from algae from lakes Lafetnoe and Bolshie Kultaiki accounted for half the length of trichomes from their length in the control (Figure 1).In lakes Kayasan, Lineyskoe and Kamyshnoe, trichomes were characterized by a wide range of lengths.It should be noted that Lake Spornoe 3, where the maximum values of the number of cells were revealed, differed in the values of mineralization of 12 ‰.The mineralization of other lakes where high growth rates were revealed (Lineyskoye, Khomutinino 4, Khomutinino 3, Kayasan, Lafetnoye, Kulikovo) ranged from 2-21 ‰.At the same time, some development of algae was also observed in lakes with mineralization indices of 30 and 50 ‰.In Lake Bolshiye Kultayki with the lowest pH values (6.5), some of the lowest values of cell numbers were revealed, while this number of cells was recorded throughout the entire developmental exposure stage.In Lake Spornoe 3, with the highest cell numbers, the pH was 6.9.The highest pH values of 9.2 were found in lakes Okunevo 5 and Lafetnoye, which differed in medium and high cell density values.In general, Oscillatoria agardhii showed a wide euryhaline adaptability and the ability to develop both in fresh and salt lakes.Also, this algae can develop in the pH range from neutral to alkaline waters.The highest rates of algae growth are observed when water temperatures warm up above 25-26 °C and up to 40 °C.Thus, consideration of the toxic properties of Oscillatoria agardhii in fresh water should be revised taking into account its high euryhaline adaptability [6,7,8].

Conclusion
The study of the hydrochemical composition of water in the lakes used for the cultivation of Oscillatoria agardhii showed the following results (Table 3).Lake Khomutinino 4, where the highest algae growth was observed, was characterized by average concentrations of compounds and chemical elements.At the same time, this is the only body of water where F was detected.In Lake Chesnokovo, where the lowest values of algae growth were detected, the highest concentrations of NO 3 and Ca were recorded from all the studied lakes.In lakes Kayasan, Kulikovo, Khomutinino 3, and Gorkoye, with average values of algae development, hydrochemical parameters differed greatly.Lake Kayasan was distinguished by the highest values of Na, Cl and SO 4 .Lake Gorkoe has the highest Mg values.And in Lake Khomutinino 3, the highest concentrations of PO 4 were found.Since, after the hydrochemical analysis of water, it was not possible to establish the predisposition of the algae to any trace elements, an analysis of the data was carried out in a multidimensional space using the principal components (Figure 2).Principal component analysis revealed a trend in the location of lakes Gorkoe -Chesnokovo -Khomutinino 4 -Kulikovo -Kayasan -Khomutinino 3, which coincided with the trend of trace elements and compounds from Na to Ca.In this trend of the hydrochemical composition of water, two opposite poles were mineralization and pH as opposed to Cl.In general, it should be concluded that algae gravitate towards the main pool of microelements in the direction of increasing mineralization and pH.For all elements and compounds, except for Ca, exceedances of MPC for fishery reservoirs were revealed [9].At the same time, the excesses in F and NH 3 were by 3 orders, in PO 4 -by 2-3 orders of magnitude, in Mg, Cl, NO 3 -by 1-2 orders, in Na, K, Sr -by 1 order.And only for SO 4 the excesses were at times.

Fig. 1 .
Density and size of cells (Oscillatoria agardhii) in various lakes.

Table 1 .
Breeding Oscillatoria (Oscillatoria agardhii) culture in various parameters of an artificial nutrient medium.

Table 2 .
Dynamics of the number of oscillatoria (Oscillatoria agardhii) in water from natural reservoirs.