*Review* **Culturable Microorganisms Associated with Sea Cucumbers and Microbial Natural Products**

**Lei Chen \*, Xiao-Yu Wang, Run-Ze Liu and Guang-Yu Wang \***

> Department of Bioengineering, School of Marine Science and Technology, Harbin Institute of Technology at Weihai, Weihai 264209, China; wangxiaoyu2020@stu.hit.edu.cn (X.-Y.W.); liurunze2017@stu.hit.edu.cn (R.-Z.L.) **\*** Correspondence: chenlei18@hit.edu.cn or chenleihit@163.com (L.C.); wanggy@hit.edu.cn or

wanggy18\_2007@163.com (G.-Y.W.); Tel.: +86-631-5687076 (L.C.); +86-631-5682925 (G.-Y.W.)

**Abstract:** Sea cucumbers are a class of marine invertebrates and a source of food and drug. Numerous microorganisms are associated with sea cucumbers. 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. Sea-cucumber-associated microorganisms produce diverse secondary metabolites with various biological activities, including cytotoxic, antimicrobial, enzymeinhibiting, and antiangiogenic activities. In this review, we present the current list of the 145 natural products from microorganisms associated with sea cucumbers, which include primarily polyketides, as well as alkaloids and terpenoids. These results indicate the potential of the microorganisms associated with sea cucumbers as sources of bioactive natural products.

**Keywords:** sea cucumber; bioactivity; diversity; microorganism; polyketides; alkaloids

**Citation:** Chen, L.; Wang, X.-Y.; Liu, R.-Z.; Wang, G.-Y. Culturable Microorganisms Associated with Sea Cucumbers and Microbial Natural Products. *Mar. Drugs* **2021**, *19*, 461. https://doi.org/10.3390/md19080461

Academic Editor: Khaled A. Shaaban

Received: 20 July 2021 Accepted: 13 August 2021 Published: 16 August 2021

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