*2.8. Terpenoids*

Terpenoids known as isoprenoids are structurally diverse metabolites found in many natural sources. This class of compounds displays a wide sector of important pharmacological entities that confirmed by several preclinical and clinical studies [89,90]. Only two terpenoidals were isolated from the co-cultures of marine fungi–bacteria (one compound, 50%) and bacteria–bacteria (one compound, 50%).

#### 2.8.1. Terpenoids Derived from the Co-Cultures of Marine Fungi and Bacteria

The production of the bacterial sesquiterpene pentalenic acid (**141**) (Figure 27) might be attributed to the competition relationship between marine fungus *A. fumigatus* MR2012 isolated from a Red Sea sediment in Hurghada, Egypt and terrestrial bacterium *S. leeuwenhoekii* C58 collected from the hyper-arid soil of Laguna de Chaxa Salar de Atacama, Chile, in which *S. leeuwenhoekii* C58 suppressed the production of *A. fumigatus* MR2012 and enhanced the production of **141 [37]**. This suggested that *S. leeuwenhoekii* C58 appeared to activate the cryptic biosynthetic gene clusters to construct a defense mechanism based on the chemical signals generated by the competitive fungus, *A. fumigatus* MR2012. Thus, the bacterial strain was capable of suppressing the biosynthesis of the fungus metabolites that were present in the axenic cultures.

**Figure 27.** Chemical structures of **141**.

2.8.2. Terpenoids Derived from the Co-Cultures of Di fferent Marine Bacteria

A diterpene lobocompactol (**142**) (Figure 28) was isolated from the co-culture of marine actinomycete *Streptomyces cinnabarinus* PK209 collected from the seaweed rhizosphere, obtained at a depth of 10 m along the coast of Korea and its competitor *Alteromonas* sp. KNS-16. Its productivity was increased 10.4-fold higher than that of the pure culture of PK209 [91]. Moreover, its antifouling activities were recently confirmed against primary fouling organisms, including diatoms, bacteria, and macroalgae zoospores. In order to further determine whether **142** was a non-toxic antifoulant, the therapeutic rate (LC50/EC50) was used to evaluate its toxicity, the LC50/EC50 of **142** was more than that of **15**, indicating that the metabolite **142** was a non-toxic antifoulant. Thus, this compound could be valuable as an antifouling agen<sup>t</sup> in both antifouling coating industry and marine ecology.

**Figure 28.** Chemical structures of **142**.
