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Marine flavobacterium <i>Tenacibaculum discolor</i> sv11 has been proven to be a promising producer of bioactive nitrogen-containing heterocycles. A chemical investigation of <i>T.</i> <i>discolor</i> sv11 revealed seven new heterocycles, including the six new imidazolium-containing alkaloids discolins C-H (<b>1</b>–<b>6</b>) and one pyridinium-containing alkaloid dispyridine A (<b>7</b>). The molecular structure of each compound was elucidated by analysis of NMR and HR-ESI-MS data. Furthermore, enzymatic decarboxylation of tryptophan and tyrosine to tryptamine and tyramine catalyzed by the decarboxylase DisA was investigated using in vivo and in vitro experiments. The antimicrobial activity of the isolated compounds (<b>1</b>–<b>7</b>) was evaluated. Discolin C and E (<b>1</b> and <b>3</b>) exhibited moderate activity against Gram-positive <i>Bacillus subtilis</i> DSM10, <i>Mycobacterium smegmatis</i> ATCC607, <i>Listeria monocytogenes</i> DSM20600 and <i>Staphylococcus aureus</i> ATCC25923, with MIC values ranging from 4 μg/mL to 32 μg/mL.