*2.3. Cyanobacterial Species Have Lowest Secondary Metabolite Biosynthetic Gene Clusters*

A total of 770 secondary metabolite BGCs were found in 103 cyanobacterial species (Table S2). Species-wise comparative analysis revealed that 29 cyanobacterial species have at least two-digit numbers of secondary metabolites BGCs in their genomes (Figure 6). Among cyanobacterial species, *Cylindrospermum stagnale* (Csg) and *Prochlorococcus marinus* MIT 9303 (Pmf) have the highest number of secondary metabolite BGCs (23 BGCs in each), followed by *Nostoc* sp. CENA543 (Noe) (18 BGCs) and 17 BGCs each in *Nostocales cyanobacterium* HT-58-2 (Ncn) and *P. marinus* MIT 9313 (Pmt) (Figure 6). Comparative analysis of secondary metabolite BGCs revealed that cyanobacterial species have the lowest number of secondary metabolite BGCs in their genomes compared to *Bacillus* species, mycobacterial species and *Streptomyces* species (Table 2). On average, seven secondary metabolite BGCs were found in cyanobacterial species compared to nine in *Bacillus* species, 15 in mycobacterial species and 30 in *Streptomyces* species (Table 2). This indicates that *Streptomyces* species dominate the production of secondary metabolites and this is the reason why more than 80% of the antibiotics that are in use today are in fact sourced from *Streptomyces* species [64].

**Figure 6.** Comparative analysis of secondary metabolite biosynthetic gene clusters (BGCs) in cyanobacterial species. Species with a two-digit number of secondary metabolite BGCs are shown in the figure. The species names with respect to their codes can be found in Table S1. Detailed information on each of the species' secondary metabolite BGCs is presented in Table S2.
