Study On Growth Conditions And Biochemical Compositions Of Marine Benthic Diatoms

The growth conditions and biochemical compositions of 4 marine benthic diatoms isolated from coastal seawater of Dalian were researched.Combined with the results of bait-experimentation,an estimable applied benthic diatoms,Nitzschia sp.,was chosen to be researched further to establish a good foundation of potential as food for aquaculture and application value and a large-scale-high-density cultivation.The results in detail were stated as follows:The specific growth rate of 4 benthic diatoms could maximat when the temperature was15～25℃,light intensity was 1500～55001x,salinity was 25～40 and initial pH was 7.5～9.0.Most of the main biochemical compositions would achieve maximum under the optimum conditions.It was advantageous for the chlorophyll under the low light,but disadvantageous for the intra-and extracellular polysaccharide except Nitzschia sp..Initial pH had unconspicuous influence on the chlorophyll of all the kinds and the intracellular polysaccharide of Navicula.corymbosa and Amphora.coffeaeformis.Nitzschia sp.would grow well when the concentrations of CO(NH₂)₂-N,KH₂PO₄-P,Na₂SiO₃-Si,C₆H₅O₇Fe-Fe were 4.64,1.14,22.95,0.33～0.49 mg/L,respectively,and the cell density increased to 1.66 times compared with original conditions.The proportion of nutrition element was N:P:Si:Fe=24.64:1.14:22.95:0.33～0.49.The absorptivity of Nitzschia sp.on different kinds of nitrogen sources was different, arrangement sequence as follows:CO(NH₂)₂＞NH₄Cl≥NaNO₃.The specific growth rate was high when the concentrations of nitrogen sources were 12.32～36.96mg/L;Using NaNO₃ and CO(NH₂)₂ were more favorable for the synthesise of chlorophyll a than NH₄Cl,but NH₄Cl and CO(NH₂)₂ were more favorable for the protein than NaNO₃.The synthesise of protein would be restrained when the concentrations of nitrogen sources were below 12.32mg/L.The intra-and extracellular polysaccharide was influenced obviously by NaNO₃.The total fat contents reduced with the increasing NaNO₃-N and CO(NH₂)₂-N concentrations,but presented high-low-high changed curves with NH₄Cl-N concentrations.The absorptivity of Nitzschia sp.on KH₂PO₄ was little higher than NaH₂PO₄.The absorptivity of nitrogen and phosphorus was the highest near the optimum phosphorus sources.KH₂PO₄ was more favorable for the synthesise of chlorophyll a and total fat than NaH₂PO₄,but NaH₂PO₄ was more favorable for the synthesise of protein,and both of them had no influence on intra-and extracellular polysaccharide.The main biochemical compositions could achieve maximum near the optimum silicon and iron sources except that the chlorophyll a was unconspicuous influenced by iron concentrations and the extracellular polysaccharide contents increased with the increasing concentrations of silicon.The conditions of simultaneous determinations of oxalic,tartaric,formic,pyruvic, malic,ascorbic,acetic,maleic,citric,succinic,fumaric acid by reversed-phase HPLC in 12 minutes had been studied,by use of Agilent 1200 HPLC and ODS C₁₈(φ5μm,4.6×250 mm)-column,with 0.5%(NH₄)₂HPO₄-H₃PO₄(pH=2.4)as mobile phase,by UV detector at 214nm,with flow rate of 1.0mL/min.Using 2%HPO₃ as extractant with ultrasonic-assisted extraction would extract the molecular weight organic acids effectively,among the extract methods of 80%ethanol,2%HPO₃ and 2%H₃PO₃.Ten kinds of organic acids were detected in three microalgae cells and the culture medium of Navicula,corymbosa except succinic acid, and nine kinds were detected in culture medium of Nitzschia sp.and Chlorella sp.except citric and succinic acid.The contents of organic acids differed from different kinds.