Bazarsadueva1, S.V., L.D. Radnaeva1 & V.V. Taraskin1
1Baikal Institute of Nature Management of Siberian Branch of Russian Academy of Sciences, Ulan-Ude, Russia
Key words: sponges, fatty acids, biomarkers
Introduction
Understanding of the mechanisms responsible for adaptation of living organisms to changing environmental conditions has always been one of the main tasks of ecology and systematic biology. As our knowledge of the complex processes that determine evolution, speciation and species adaptation continues to grow, need to study the mechanisms underlying resistance of living organisms to stress factors becomes more and more evident (Hoffmann & Parsons, 1997). The life of organisms is limited to a specific temperature range in which, theoretically, increasing on 10°C leads to a two- to fourfold increase in the response time of metabolic processes. Numerous physical and chemical studies show that the mechanisms of survival at abnormally high temperatures include changes in the lipid components of cell membranes.
The degree of involving of lipids in the adaptation processes depends on biological features of various species, including marine and freshwater sponges (Temperature…, 1994; Velansky &
Kostetsky, 2009; Gladyshev et al., 2011).
Because of increasing anthropogenic impact on natural ecosystems, adaptations developed by various organisms have recently received growing attention from researchers, but adaptive biochemical characteristics of organisms representing taxa of lower phylogenetic ranks are still poorly studied. Sponges as a symbiotic community of various microorganisms are a unique object for such studies. During millions of years, Baikal sponges have adapted to living in a narrow temperature range from 0.5 to 11.5°C (at depths of 4 m and below).
The aim of the research is comparative analysis of the fatty acid composition of the Baikal freshwater sponge Baicalospongia bacillifera from different depth and upon a rise of temperature in its natural habitat by 6°C.
Materials and methods Field sampling
Deep water sponges B. bacilifera were collected from the depth of 750 m from Barguzin Bay (Lake Baikal) in July-August by using manned submersible “MIR” (during the International Research Expedition «MIRs on Lake Baikal», 2008-2010). Shallow sponges B. bacilifera were collected from a depth of 15 m in the southern part of Lake Baikal in August. The collected samples were stored at -18 oC for less than seven days prior to laboratory analyses.
A living sponge colony was adapted for 14 days to the artificial conditions of glass aquariums with flowing Baikal water at 10.5°C and 12-h photoperiod without additional feeding. The water to the aquariums was supplied from a homemade refrigeration unit (Glyzina et al., 2016). After adaptation, sponge samples were taken for biochemical analysis.
Sample derivatization
In laboratory, weight samples of sponges were placed into glass tubes with anhydrous methanol containing 2 M HCl. The tubes were filled with argon, then securely closed, and heated for 2 h 90 oC for complete methanolysis (Meier et al., 2006). After cooling to room temperature, the tubes were opened and the methanol was evaporated under a stream of nitrogen, and distilled water was added to reduce the solubility of the FA methyl esters formed, which subsequently were extracted with hexane.
Fatty acid analysis
Fatty acid analysis was performed using an Agilent 6890 gas chromatograph equipped with a mass-selective detector 5973 N, HP-5MS column with a thickness of 0.2 μm and helium as the mobile phase.The oven was programmed as follows: 90 °C for 4 min, 30 °C min−1 up to 165 °C, then 3 °C min−1 up to 225 °C, and kept isothermal at this final temperature for 10.5 min before cooling for the next run.
The chromatographic peaks of the methyl ester derivatives were identified by retention time and mass spectra (NIST 14.0). A standard mixture of 37 FAMEs (Supelco 37 component FAME Mix, USA) and 26 bacterial acid methyl esters (Bacterial Acid Methyl Esters CP Mix (Supelco, USA)) was chromatographed for each tenth sample.
Results
B. bacillifera is an endemic large-sized mushroom-shaped sponge that is widespread in Lake Baikal. The FA compositions of lipids from studied sponges were compared by using GC with mass spectrometry. More than 40 FAs from lipid extract of sponges were identified and main fatty acids are listed in the table 1.
Location Barguzin bay Southern part of Lake Baikal
Depth, m 745 15 aquarium
Temperature, оС 3.7 4.5 10.5
14:0 1.93 2.17 2.40
i15 1.92 0.38 0.33
16:0 4.12 7.05 12.00
i17 1.60 0.11 0.60
a17 1.42 1.14 1.45
17:0 1.39 1.53 1.8
18:0 2.41 1.45 0.51
14:1n11 4.14 0.13 0.49
16:1n7 0.34 0.12 1.13
16:1n9 2.94 1.67 0.92
17:1n8 0.12 2.2 5.35
18:1n9 18.05 16.24 25.5
18:1n7 2.60 1.81 0.14
18:1n11 0.21 0.13 0.52
20:1n9 2.17 0.34 1.23
24:1n9 3.18 3.7 2.94
18:3n3 8.22 7.12 10.3
18:2n6 2.72 2.28 6.45
22:6n3 0.15 0.22 0.12
26:3n3 18.99 14.65 10.11
Table 1. Contents of main fatty acids in Baicalospongia bacilifera, rel. % Discussion
It was revealed that deep water sponges B. bacilifera inhabiting at a depth of 750 m contain higher levels of unsaturated FAs. Structural modifications of membrane lipids are acknowledged to play a central role in the thermal adaptation of hydrobionts’ tissues, and the physical properties of the lipids are largely determined by their FA composition (Hazel 1995).
To achieve enhanced membrane fluidity hydrobionts can utilize dietderived unsaturated FAs or increase the degree of their FA unsaturation by inserting new double bonds into the existing acyl chains by using desaturase enzymes (Trueman et al. 2000; Hsieh et al. 2007). As shown previously, В. bacillifera contains a sufficient amount of eicosapentaenoic acid (Dembitskii, 1981) and their isomers, whereas the majority of other marine and freshwater sponges contain only a small amount of these compounds. In our experiments, this acid was detected only in trace amounts. The pool of polyunsaturated acids in B. bacillifera is mainly represented by demospongic acid 26:3(5, 9, 19), which contains a characteristic 5,9-diene fragment of the carbon chain. The content of this acid is reduced as the temperature increases which indicates that the sponge is depressed.
Acids 18:1n9 and 18:2n6 are the most prominent markers sensitively responding to rise in ambient temperature. Linoleic acid actively participates in the functioning of chloroplasts, so it can be assumed that the process of photosynthesis in symbiotic algae is sharply intensified as the temperature increases. The total content of polyunsaturated fatty acids in the samples decreased by 10.5 rel.% upon a 6°С temperature rise. The relative content of iso- and antheiso- branched i15:0, i17:0, ai17:0 acids which are of bacterial origin (Kaneda, 1991) are much higher in deep water sponges. Probably, the contribution of symbiotic algae in sponges’ diet at great depths at low temperature, high pressure and absolute darkness is insignificant and the contribution of symbiotic microorganisms increases.
The results of this study may be used for further research on biochemical adaptations in hydrobionts, including taxa of lower phylogenetic level. Specific features of biosynthesis and metabolism under temperature stress in sponges, which often synthesize biologically active compounds via nonstandard biosynthetic pathways, may attract the attention of many ecologists who study the problems of inland waters.
Acknowledgements
The reported work was funded by RFBR according to the research project № 18-35-00439 mol_a.
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Probability long-term forecast of the Caspian Sea's water level Mikhail Bolgov1
1Institute of water problems of RAS, Russia. 119333, Moscow, Gubkin St., 3, IWP RAS.
Keywords: Caspian Sea, water line, long-term fluctuations, probability forecast, fiducial interval, river runoff, evaporation, morphometry
In the report the method of probability prediction of level of the Caspian Sea is considered. The s hort review of methods of prediction of long-term fluctuations of level of water in the sea is provided. Stochastic models of principal components of water balance are considered (river inflow, evaporation from the water surface).
Features of morphometric dependences are discussed (the areas of the water surface from the water lеvel). Within Markov models of hydrological processes imitating and analytical approaches to modeling and pr ediction of long-term fluctuations of the water level in the sea are considered.