High biomasses of the marine dinoflagellate Lepidodinium chlorophorum cause green seawater discolorations along Southern Brittany (NE Atlantic, France). The viscosity associated to these phenomena has been related to problems in oyster cultivation. The harmful effect of L. chlorophorum might originate from the secretion of Extracellular Polymeric Substances (EPS). To understand whether the EPS are produced by L. chlorophorum or its associated bacteria, or if they are a product of their interaction, batch cultures were performed under non-axenic and pseudo-axenic conditions for three strains. Maximum dinoflagellate cell abundances were observed in pseudo-axenic cultures. The non-sinking fraction of polymers (Soluble Extracellular Polymers, SEP), mainly composed of proteins and the exopolysaccharide sulphated galactan, slightly increased in pseudo-axenic cultures. The amount of Transparent Exopolymer Particles (TEP) per cell increased under non-axenic conditions. Despite the high concentrations of Particulate Organic Carbon (POC) measured, viscosity did not vary. These results suggest that the L. chlorophorum-bacteria interaction could have a detrimental consequence on the dinoflagellate, translating in a negative effect on L. chlorophorum growth, as well as EPS overproduction by the dinoflagellate, at concentrations that should not affect seawater viscosity.

海洋甲藻Lepidodinium chromophorum的高生物量导致布列塔尼南部（法国东北大西洋）沿岸海水变色为绿色。与这些现象相关的粘度与牡蛎养殖中的问题有关。绿藻的有害作用可能源于胞外聚合物（EPS）的分泌。为了了解 EPS 是否由绿藻或其相关细菌产生，或者它们是否是它们相互作用的产物，在非无菌和伪无菌条件下对三种菌株进行了分批培养。在伪无菌培养物中观察到最大甲藻细胞丰度。聚合物的非下沉部分（可溶性细胞外聚合物，SEP）主要由蛋白质和胞外多糖硫酸半乳聚糖组成，在伪无菌培养物中略有增加。在非无菌条件下，每个细胞的透明外聚合物颗粒（TEP）的量增加。尽管测量的颗粒有机碳 (POC) 浓度较高，但粘度没有变化。这些结果表明，在不影响海水粘度的浓度下，绿藻-细菌相互作用可能对甲藻产生有害后果，即对绿藻生长以及甲藻过量产生 EPS 产生负面影响。