**4. Conclusions**

Sea cucumbers have been extensively utilized in medicine in Asia for a long time, and a variety of compounds with pharmacological activities have been isolated from sea cucumbers [10]. The actual producers of these marine natural products may be seacucumber-associated microorganisms. Sea cucumbers harbor a rich and diverse assortment of microorganisms. Over the past 20 years, seventy-eight genera of bacteria belonging to 47 families in four phyla, and 29 genera of fungi belonging to 24 families in the phylum Ascomycota have been cultured from sea cucumbers. A total of 145 natural products have been isolated from sea-cucumber-associated microorganisms. These compounds are polyketides, terpenoids, alkaloids, and others, and many have been shown to have various biological activities. Sea-cucumber-associated microorganisms have grea<sup>t</sup> potential for the production and isolation of high-value bioactive compounds.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/md19080461/s1, Table S1. Microorganism genera associated with sea cucumbers.

**Author Contributions:** L.C. and G.-Y.W. conceived and designed the format of the manuscript. L.C., X.-Y.W. and R.-Z.L. analyzed the data and drafted and edited the manuscript. X.-Y.W. drew the chemical structure of compounds. L.C. and G.-Y.W. reviewed the manuscript. All the authors contributed in terms of critical reading and discussion of the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by the Discipline Construction Guide Foundation in Harbin Institute of Technology at Weihai (No. WH20150204 and No. WH20160205), and the Research Innovation Foundation in Harbin Institute of Technology at Weihai (No. 2019KYCXJJYB15).

**Conflicts of Interest:** The authors declare no conflict of interest.
