Investigating on the Correlation Between Some Biological Activities of Marine Sponge-Associated Bacteria Extracts and Isolated Diketopiperazines

Marine organisms have been considered as the richest sources of novel bioactive metabolites, which can be used for pharmaceutical purposes. In the last years, the interest for marine microorganisms has grown for their enormous biodiversity and for the evidence that many novel compounds isolated from marine invertebrates are really synthesized by their associated bacteria. Nevertheless, the discovery of a chemical communication Quorum sensing (QS) between bacterial cells and between bacteria and host has gained the researchers to expand the aim of their study toward the role of bacteria associated with marine invertebrates, such as marine sponge. In the present paper, we report the evaluation of biological activities of different extracts of bacteria Vibrio sp. and Bacillus sp. associated with marine sponges Dysidea avara and Ircinia variabilis, respectively. Moreover, we evaluated the biological activities of some diketopiperazines (DKPs), previously isolated, and able to activate QS mechanism. The results showed that all extracts, fractions, and DKPs showed low scavenging activity against DPPH and superoxide anion, low cytotoxic and anti-tyrosinase activities, but no antimicrobial and acetylcholinesterase inhibitory activities. One DKP [cyclo-(trans-4-hydroxy-l-prolyl-l-leucine)] has the highest alpha-glucosidase inhibitory activity even than the standard acarbose.