From miscommunication to misinformation: Streptomyces species erroneously reported as producers of prodigiosin

attracted due to its anticancer, antibiotic, antimalarial and even 24 immunosuppressive activities (Darshan et al). On account of its promising biotechnological potential, 25 the compound has been the focus of several reviews and experimental articles. The authors of these 26 articles typically begin their discussion of prodigiosin by mentioning the names of a few bacterial 27 species that are prominent producers of prodigiosin. In recent years, one name that has consistently 28 cropped up as a prodigiosin-producer is Streptomyces coelicolor. This claim appeared in a highly cited 29 considered an authoritative review on prodigiosin. What all these reviews have in common is that 32 their statements regarding S. coelicolor as a prodigiosin-producer is incorrect. This species is in fact a 33 well-known producer of undecylprodigiosin (Tsao et al., 1985). Structurally, undecylprodigiosin differs 34 from prodigiosin by the length of its alkyl side chain; the former contains an undecyl chain while the 35 latter has a shorter pentyl group. 36 37 So how did the false notion arise that S. coelicolor is a prodigiosin-producer? Well, it originated from 38 the misleading title of a study carried out by Liu et al in 2017 (Liu et al., 2017). The title of this study is 39 "Metabolic engineering of Streptomyces coelicolor for enhanced prodigiosins (RED) production." In the 40 title, the word 'prodigiosin' is used interchangeably with 'prodiginine' resulting in misinformation. The 41 terms prodigiosin and prodiginine are not interchangeable terms, as they hold different meanings. 42Prodigiosin is the name of a chemically distinct molecule while prodiginine is the name given to the 43 family of tripyrrole compounds, of which prodigiosin is a member. Hence, a more accurate title would 44 have been, "Metabolic engineering of Streptomyces coelicolor for enhanced prodiginine (RED) 45 production." 46 47 S. coelicolor is not the only species to fall foul of this misattribution; Streptomyces griseoviridis offers 48 us yet another example. As before, the error arises from the inaccurate title of experimental work 49 carried out by Kawasaki et al (Kawasaki et al., 2008) titled, "A prodigiosin from the roseophilin 50 producer Streptomyces griseoviridis." A thorough assessment of this work in addition to a follow-on 51 study would have revealed that S. griseoviridans is a producer of prodigiosin R1 and prodigiosin R2 52 (Kawasaki et al., 2008;Kimata et al., 2018). These analogs are cyclic derivatives of prodigiosin in which 53 the alkyl side chain is linked to the terminal pyrrole moiety. This structural arrangement differs 54 markedly from the linear structure of the prodigiosin molecule.