Production of dimethylsulfide and acrylic acid from dimethylsulfoniopropionate during growth of three marine microalgae

We measured the concentrations of dimethylsulfide(DMS),acrylic acid(AA),and dimethylsulfoniopropionate(DMSP) during growth of three microalgae:Prorocentrum micans,Gephyrocapsa oceanica,and Platymonas subcordiformis.The DMSP,AA,and DMS concentrations in culture media varied significantly among algal growth stages,with the highest concentrations in the late stationary growth stage or the senescent stage.In the stationary growth stage,the average DMSP concentration per cell in P.micans(0.066 5 pmol/cell) was 1.3 times that in G.oceanica(0.049 5 pmol/cell) and 20.2 times that in P.subcordiformis(0.003 29 pmol/cell).The average concentrations of AA were0.044 6,0.026 9,and 0.003 05 pmol/cell in P.micans,G.oceanica,and P.subcordiformis,respectively,higher than the concentrations of DMS(0.272,0.497,and 0.086 2 fmol/cell,respectively).There were significant positive correlations between cell density and AA,DMSP,and DMS concentrations.The ratios of DMS/AA and AA/(DMSP+AA) in the three algae differed significantly over the growth cycle.In all three microalgae,the DMS/AA ratios were less than 25%during the growth period,suggesting that the enzymatic cleavage pathway,which generates DMS,was not the main DMSP degradation pathway.The changes in the DMS/AA ratio indicated that there was a higher rate of enzymatic breakdown of DMSP in the early growth period and a lower rate during senescence.In all three microalgae,the AA/(DMSP+AA) ratio(degradation ratio of DMSP) decreased during the exponential growth phase,and then increased.The variations in these ratios can approximately indicate the cleavage mechanism of DMSP at different stages of algal growth.