Neuroactive compounds produced by bacteria from the marine sponge Halichondria panicea: activation of the neuronal NMDA receptor.

Previous studies revealed that the marine sponge Halichondria panicea habors symbiotic- and commensalic bacteria (Althoff et al., 1998. Marine Biol. 130, 529-536). In the present study the hypothesis was tested whether some of those bacteria synthesize neuroactive compounds. For the first time the effect of bacterial bioactive compounds on the neuronal ionotropic glutamate receptors [iGluR], subtype N-methyl-d-aspartate (NMDA) receptor, was checked. In cortical neurons from rats as cell system the supernatant of two bacterial cultures isolated from H. panicea proved to agonize the NMDA receptor. The response of the NMDA receptor to the bioactive compounds was determined by measuring the intracellular Ca(2+) level. The supernatants of cultures 697 and 698 were found to upregulate the intracellular Ca(2+) level. To validate the specificity of the effects, inhibition studies with Memantine and d-AP5 were performed. The two bacteria were identified by polymerase chain reaction-amplification of the 16S rDNA genes and subsequent sequencing; they displayed highest identity to Antarcticum vesiculatum and to Psychroserpens burtonensis, respectively. Based on these data first experimental evidence is presented indicating that bacteria associated with sponges display neuroactivity by agonizing the NMDA receptor.