Screening and characterization of antibacterial and cytotoxic marine bacteria associated with Karlodinium micrum
微小卡罗藻（Karlodinium micrum）共附生微生物抗菌与细胞毒活性

Abstract: Objective] Antibacterial and cytotoxic activities were screened for marine bacteria which have been isolated from Karlodinium micrum, in order to obtain potential strains with antibacterial and cytotoxic activities. Methods] In total 38 bacteria isolated from Karlodinium micrum were screened by agar-screening and MTT methods. The 16S rRNA genes were amplified from the genome DNA of those bacteria positive for both antibacterial and cytotoxic activities, which were cloned into pMD18-T vector for sequencing analysis. Results] Twenty-five isolates had antimicrobial activity and 5 isolates (W-14-2, W-2-2, W-12, E-8-2 and W-4) had cytotoxicity. Molecular phylogenetic analysis of marine bacteria with cytotoxicity based on 16S rRNA sequences indicated that they exhibited the highest similarity (98%, 99%, 99%, 98% and 99%, respectively) to the 16S rRNA fragments of Alteromonas alvinellae, Stappia aggregata, Pelagibaca bermudensis, Marinobacter kribbensis and Maribacter dokdonensis. Conclusion] The bacteria with bioactivity in Karlodinium micrum were abundant. We obtained five strains positive for both antibacterial and cytotoxic activities, which provide a clue to understanding the mechanism of toxin biosynthesis in Karlodinium micrum based on epiphytic and endophytic bacteria.