The Study On Production Of Sulfur Metabolites In Marine Microalgae

In seawater, Dimethylsulfide (DMS) is the enzyme cleavage of the algal metabolite dimethylsulfoniopropionate (DMSP). Methanethiol is also produced by the breakdown product of DMSP. Dimethylsulfide is the most abundant volatile biogenetic sulfur compound in the ocean,its oxidation is considered to play significant roles in the natural sulphur cycle and has a potential influence on Earth’s climate. Therefore, the study of marine microalgae release DMSP, DMS and acrylic marine organisms beneficial to measure the position and role in the marine sulfur cycle.In the present dissertation,at first,we choose the coastal waters of china as the study area that is affected seriously by human activities.The production of DMS and acrylic acid in the case of adding various concentrations of DMSPd, and the production rate of DMS and acrylic are measured at different growth stages, and further analysis the ratios of DMS/AA and AA/(DMSP+AA) in the whole growth cycle, and the the DMSP degradation mechanism is initial interpreted;then,we focus on the unit biomass of DMS, DMSP and AA in 22 marine algae during the growth stages by laboratory culture experiment,and then measure and summarize the contribution of marine microalgae production capacity of DMSP,DMS and AA differences on marine sulfur cycle; and finally by measuring two kinds of marine microalgae in different nitrogen and phosphorus under the conditions of the specific growth conditions, and thus the production and release of DMSP、DMS and AA provide reference data. The main conclusions are as follows:1. Studies on DMSP degradation in marine algae(1) In the whole growth cycle of three marine algae cultures, the main degradation pathways of DMSP is the methylation way,and the degradation rates of DMSP are higher in the exponential growth phase and in the stationary growth phase. In the slow growth stage and in the senescent stage degradation rates of DMSP show a slightly decreasing trend.(2) At different growth stages of three microalgae,when DMSPd is added,the production of DMS and acrylic increases in parallel with the time,and with the addition of exogenous DMSPd into a batch culture.(3)Ratios AA/(DMSP+AA) of the three algae have similar variations in the part of the growth stage. AA/(DMSP+AA) is inversely proportional to the added DMSPd concentration,that is,with the increase of concentration of exogenous DMSPd, AA/(DMSP+AA) ratios decrease gradually. Ratios of DMS/AA in three marine algae are different, DMS/AA increase with concentration of exogenous DMSPd in the exponential growth stage and in the stationary stage and decrease in the senescent stage. DMS/(DMSP+AA) as a whole with the increase of concentration of exogenous DMSPd presents a trend of reducing after the first rise.2. Study on DMS, DMSP and AA production in marine algae(1)Studies show that the concentration of DMS、DMSP and AA in the single cell in different growth cycle show the same trend:the maximum production of DMS/cell appears in the stationary stage or in the senescent stage; the maximum production of DMSP/cell and AA/cell appear in the exponential growth stage and in the stationary stage,and then decline in the senescent stage.(2) twenty two marine algae can product DMS, DMSP and AA,but,different units of microalgae biomass release DMS, DMSP and acrylic as well as differences between distinct strains, which may be related to the growth environment and the ability to adapt to the environment.(3) During the whole growth period,different microalgae have the different ratios of DMS/AA, in the whole,DMS/AA increases with abundance in the exponential growth phase. In general,AA/(DMSP+AA) decline in the stationary stage,then rise in the senescent stage.The ratios of DMS/ (DMSP+AA) have similar variations in the part of the growth stage,the maximum appears in the stationary stage or in the senescent stage.3. Study on sulfur metabolites and carbon parameters on different ratio of nitrogen to phosphorus(1)At different growth stages, the trends of DMS, DMSP and AA have a certain regularity.In the exponential growth phase, the concentration of the three parameters increases with the cell density.On different ratio of nitrogen to phosphorus,the maximum values of DMSPp, DMS and acrylic acid are found in the N:P 16:1, the maximum valueof DMSPd appears in N:P 40:1.(2) Under the condition of different nitrogen and phosphorus ratio,DMSP degradation pathway changes differently.The conversion rate of DMS/AA increases in the exponential growth,and keeps at high level in the stable phase.When the nitrogen and phosphorus ratio is 16:1,it reaches the maximum value; AA/(DMSP+AA) ratio in the slow growth stage decreased, then increased with cell density, in the stable phase stability to peak, in the late stable growth phase, ratio drops rapidly.N:P ratios are 16:1 and 40:1, DMSP degradation percentage is higher;DMS/(DMSP+AA) increases with the density of algae, and reaches the maximum value in the stable phase, DMS/ (DMSP+AA) maximum value appears in N:P 16:1.(3) During the cultivation,the pH、DIC、pCO2 all changed significantly and regularly with the growth and decadency of the algae dioxide system of seawater.The pH begin to rise,and then decrease,DIC initially decreases rapidly,and is followed by an upward trend,the change of pCO2 and DIC show similar patterns.when N:P is 16:1, Phaeocystis sp. pH reaches to the maximum value, while DIC and pCO2 is the smallest value.(4)Taking N:P=4:1 as the example to discuss the relationship between DMSP, DMS, AA and pCO2. We can find that DMSPp, DMSPd and pCO2 have no correlation, while DMS, AA and pCO2 show a negative correlation.