Institute for Inorganic and Analyticial Chemistry, Department for Bioorganic Analytics, Friedrich Schiller University Jena, Jena, Germany.
PLoS One. 2011;6(6):e21032. doi: 10.1371/journal.pone.0021032. Epub 2011 Jun 17.
Interactions of planktonic bacteria with primary producers such as diatoms have great impact on plankton population dynamics. Several studies described the detrimental effect of certain bacteria on diatoms but the biochemical nature and the regulation mechanism involved in the production of the active compounds remained often elusive. Here, we investigated the interactions of the algicidal bacterium Kordia algicida with the marine diatoms Skeletonema costatum, Thalassiosira weissflogii, Phaeodactylum tricornutum, and Chaetoceros didymus. Algicidal activity was only observed towards the first three of the tested diatom species while C. didymus proved to be not susceptible. The cell free filtrate and the >30 kDa fraction of stationary K. algicida cultures is fully active, suggesting a secreted algicidal principle. The active supernatant from bacterial cultures exhibited high protease activity and inhibition experiments proved that these enzymes are involved in the observed algicidal action of the bacteria. Protease mediated interactions are not controlled by the presence of the alga but dependent on the cell density of the K. algicida culture. We show that protease release is triggered by cell free bacterial filtrates suggesting a quorum sensing dependent excretion mechanism of the algicidal protein. The K. algicida / algae interactions in the plankton are thus host specific and under the control of previously unidentified factors.
浮游细菌与硅藻等初级生产者的相互作用对浮游种群动态有很大影响。有几项研究描述了某些细菌对硅藻的有害影响，但产生活性化合物的生化性质和调节机制仍然难以捉摸。在这里，我们研究了杀藻细菌 Kordia algicida 与海洋硅藻 Skeletonema costatum、Thalassiosira weissflogii、Phaeodactylum tricornutum 和 Chaetoceros didymus 的相互作用。杀藻活性仅观察到在前三种测试的硅藻物种中，而 C. didymus 则不易受影响。静止 K. algicida 培养物的无细胞滤液和>30 kDa 级分是完全有效的，表明存在分泌的杀藻原理。细菌培养物的活性上清液表现出高蛋白酶活性，抑制实验证明这些酶参与了细菌的观察到的杀藻作用。蛋白酶介导的相互作用不受藻类的存在控制，而是依赖于 K. algicida 培养物的细胞密度。我们表明，蛋白酶释放是由无细胞细菌滤液触发的，这表明杀藻蛋白的群体感应依赖性排泄机制。因此，K. algicida/藻类在浮游生物中的相互作用是宿主特异性的，并受先前未识别的因素控制。
