## 1 Introduction  
Among secondary metabolites, terpenoids including the class of sesquiterpenoids represent one of the largest and most diverse groups with over 80,000 known compounds, mostly isolated from plants [1; 2; 3; 4]. Based on their number of carbon atoms, they can be divided into the subclasses of hemi- (C\({}_{5}\)), mono- (C\({}_{10}\)), sesqui- (C\({}_{15}\)), di- (C\({}_{20}\)), tri- (C\({}_{30}\)), tetra- (C\({}_{40}\)) and polytergenes (>C\({}_{40}\)) [5; 6]. In general, the terpenoid synthesis starts from the two isoprene intermediates isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are provided either by the mevalonate (MVA) pathway or by the 1-deoxy-D-xylulose 5-phosphate (DXP) pathway, also known as the 2-C-methyl-D-erythitol 4-phosphate (MEP) pathway. While the MVA pathway uses acetyl-Cenzyme A (acetylCoA) as a substrate and is predominantly found in eukaryotes (e.g., mammals, plants,and fungi), archaea and a few bacteria [7], the DXP pathway starts from glyceraldehyde-3-phosphate (GAP) and pyruvate and primarily occurs in bacteria, cyanobacteria, and green algae [8]. Starting from IPP and DMAPP, the elongation of linear premyl pyrophosphates is catalyzed by prenytransferases via head-to-tail condensations and results in C\({}_{10}\) geranyl pyrophosphate (GPP), C\({}_{15}\) farnesyl pyrophosphate (FPP), and C\({}_{20}\) geranylgeranyl pyrophosphate (GGPP). Finally, GPP is used as a precursor molecule for the synthesis of monoterpenoids, FPP for sesqui- and triterpen production, and GGPP for di- and tetraterpenoid biosynthesis. Terpenes exhibit manifold functions in plant physiology and development, including photoprotection (carotenoids), communication (e.g., ppinene), or repellant activity against predators and parasites (e.g., verbenone, \(\beta\)-caryophyllene) [9; 10; 11]. Furthermore, terpen are of commercial interest for the pharmaceutical sector due to their various bioactivities suitable for the treatment of pathogen infections, inflammation, or cancer [12; 13]. For example, the sesquiterpene farnesol shows inhibitory effects against antibiotic-resistant _Staphylococci_, not only inhibiting the growth of planktonic cells in free suspension but also suppressing biofilm formation of _Staphylococcus aureus_, _Staphylococcus epidermidis_, and _Burkholderia pseudomalilei_[14; 15; 16; 17]. In the past, these compounds were exclusively obtained from essential oils of natural plant sources, requiring complex and time-consuming downstream processing. \(\beta\)-caryophyllene, for example, was extracted from _Cannabis sativa_[18], clove basil, _Ocimum gratissimum_[19], or representatives of the plant genus _Cadia_, such as _Cadia verhenaceae_[20]. However, the application of microorganisms as heterologous hosts allows the establishment of alternative, cost-effective, and sustainable biotechnological production processes [21; 22; 23; 24; 25; 26]. As the efficiency of such processes strongly depends on the achieved production titers, metabolic engineering of the applied hosts together with the optimization of the respective secondary metabolite pathways has gained more attention in the recent past [1; 27; 28; 29; 30; 31]. So far, terpenoids were mostly produced in the heterologous hosts _Escherichia coli_ and _Saccharomyces cerevisiae_[32; 33; 34; 35; 36]. However, in recent studies, the terpene production in less common microbes such as phototrophs has also been established and optimized, as for example documented by the _Rhodobacter_-based production of \(\beta\)-farnesene, nootkatone, valencene, and amorphadiene [37; 38; 39; 40], or the production of various terpen in cyanobacteria [41].