## 3 Discovery of New Natural Products Using Ribosome Engineering
[PERSON] et al. isolated three new chlorinated alkaloids, inducamides A-C (**47-49**), from _Streptomyces_ sp. SNC-109-M3, a _rif_ mutant with a S442Y mutation in _rpoB_. Inducamides contain a 6-methylsalicylic acid unit and a tryptophan derivative, connected through an amide bond. Inducamide C (**49**) exhibited moderate cytotoxicity against NSCLC cell line HCC44 at 10 \(\mu\)M.  
[PERSON] et al. screened a total of 164 _rif_ mutants among 11 actinomycetes and identified one mutant TW-R50-13 with an _rpoB_ H437Y mutation [87]. Isolation of two overproduced metabolites in TW-R50-13 and their structural elucidation led to the discovery of three methylbenzene containing linear polyketides **55-57**. Using the same approach, the authors screened a total of 114 _rif_ mutants among 9 actinomycetes and identified one _Streptomyces_ strain, S55-50-5, with the identical _rpoB_ H437Y mutation [87]. This strain produced a novel isoindole-containing tetracycline polyketide isoindolinomycin (**58**) with moderate cytotoxicity against the tested tumor cell lines and antibacterial activity against _Staphylococcus aureus_. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Natural Products** & **Strain** & **Method** & **Mutation \({}^{\text{a}}\)** & **Activity** & **Year/Ref.** \\ \hline Neotechnasodiamine (**31**) & _B. subtilis_ & Rif & S487L & Antibacterial & 2004 [80] \\ Piperidamycins (**32-34**) & _S. sp. 631689 & Rif, Str, Gen & K88R & Antibacterial & 2009 [79] \\ \(\gamma\)-Actinorhodin (**35**) & _S. acidcolor_ & Rif & - b & Antibacterial & 2013 [32] \\ Mutaxanthenes (**36-40**) & _Nocardiae_ & Rif, Str & - & - & 2013 [81] \\  & FU40 AApoS8 & _Apergillus versicalo_ & & - & - & 2014 [82] \\
**41-46** & _ASpergillus versicalo_ & & Neo & - & Antitumor & 2014 [82] \\ Inducamides A-C (**47-49**) & _S. sp. SNC-109_ & Rif & X442F & - & 2014 [83] \\
**50-54** & _Penicillium pupugroenn_ & & Neo, DMSO & - & Antibacterial & 2015 [84] \\  & _S. somaliensis_ SCSIO & & Rif & R447H & Antitumor & 2015 [41] \\ Fredericamycin A (**15**) & _ZH66_ & & Rif & - & Antibacterial & 2015 [85] \\
16 secondary metabolites & _S. acidcolor_ & Rif, Str & - & Antibacterial & 2015 [85] \\
**55-57** & _S. sp. SANK_ 60404 & Rif & H447D & - & 2016 [86] \\
**58, 59** & _S. sp. SoC090715 LN-16_ & Rif & H447Y & Antibacterial & 2018 [87] \\ Cyclopentene derivatives & _S. sp. HS-NF-1046R_ & Rif & - & - & 2019 [88] \\ \hline \end{tabular}  
* The strains with the highest titer of _rpoB_ and _rpsL_ mutation. b The highest yield strain has no detected mutation within the _rpoB_ and _rpsL_ genes.  
\end{table} 
Table 4: New natural products discovered through ribosome engineering. In addition, ribosome engineering can also activate silent BGCs and discover new active compounds in other bacterial species or fungi. [PERSON] et al. [52] first introduced a rifamycin-induced _rpoB_ mutation into the _B. subtilis_ strain, which led to the production of a new aminoaccharide antibiotic 3,3'-neotrehalosadianine (**31**), for which production is silent in the wild-type strain. In a metabolomic phenotype screening of _str_ or _rif_ mutants in a rare actinomycete _Nocardiopsis_ sp. FU40 \(\Delta\)ApoS8, 311 unique metabolomic features were revealed by ultra-performance liquid chromatography ion-mobility mass spectrometry analysis [81]. This led to the isolation of five mutaxanthenes (**36-40**) with the unprecedented 12,12a-dihydro-1H-benzo(b)anthene-based scaffold in a _rif_ mutant R4. Based on these data, [PERSON] et al. suggested that activation of BGCs might be important cellular responses of certain antibiotic resistance mutations in the mutants [81]. Compounds extracted from fungi are an important source for new drug development [89; 90]. By screening and isolation of neomycin-resistant mutants in marine-derived fungi, multiple active fungal natural products **41-46** and **50-54** were isolated from _Aspergillus versicolor_ ZBY-3 or _Penicillium purpurogenum_ G59, respectively [82; 84].