A polyyne toxin produced by an antagonistic bacterium blinds and lyses a green microalga

Abstract

Microalgae are key contributors to global carbon fixation and the basis of many food webs. In nature, their growth is often supported or suppressed by other microorganisms. The bacterium Pseudomonas protegens Pf-5 arrests the growth of the green alga Chlamydomonas reinhardtii, deflagellates the alga by the cyclic lipopeptide orfamide A, and alters its morphology. Using a combination of Raman microspectroscopy, genome mining and mutational analysis, we discovered a novel polyyne toxin we name protegencin that is secreted by P. protegens and penetrates algal cells to destroy their primitive visual system, the eyespot. Together with secreted orfamide A, protegencin prevents the phototactic behavior of C. reinhardtii needed to perform optimal photosynthesis. A protegencin-deficient biosynthetic mutant of P. protegens does not affect growth or eyespot carotenoids of C. reinhardtii. Thus, protegencin acts in a direct and destructive way, and reveals at least a two-pronged molecular strategy used by algicidal bacteria.

Sequential Allylic Alcohol Formation by a Multifunctional Cytochrome P450 Monooxygenase with Rare Redox Partners

“…The initial functional assessment of cayG was based on a single crossover, which may lead to polar effects [4] . Thus, for the targeted gene deletion (approach a), we employed an improved method in which we replaced the target gene with an apramycin resistance cassette by double‐crossover knock‐in [9b] (Figure S1). As expected, the resulting cayG null mutant strain produces 2 in lieu of 1 (Figure 2A, trace b).…”

“…Protegencin F ( 11 ) has a secondary alcohol in lieu of the terminal alkyne and may be regarded as a shunt product of the multiple chain desaturations [4] . We also synthesized the CuAAC ( 12 ) [9b] and the phosphopantetheinyl‐mimicking N ‐acetyl‐cysteamine thioester (SNAC) [17] ( 13 ) derivatives of 2 (Figure S39–S43) to probe the substrate requirements of CayG.…”

Discovery of the Pseudomonas Polyyne Protegencin by a Phylogeny-Guided Study of Polyyne Biosynthetic Gene Cluster Diversity

“…Mapping the diversity of polyyne biosynthetic gene clusters through functional gene and protein phylogenies permitted the discovery of an uncharacterized Pseudomonas polyyne BGC, pgn , and metabolite, protegencin. Hotter et al ( 22 ) have recently demonstrated that this P. protegens polyyne, protegencin, acts as an algicidal toxin of the green alga Chlamydomonas reinhardtii . In parallel to these studies characterizing protegencin, Murata et al ( 23 ) identified the same polyyne biosynthetic gene cluster in the biocontrol strain P. protegens Cab57, designating the molecules produced as protegenins.…”

Thiotemplated Biosynthesis of Bacterial Polyyne Fatty Acids by a Designated Desaturase Triad

“…protegenin [5] ) from Pseudomonas protegens [6] (Figure 1A). Their versatile ecological functions in protective symbioses [1b,4b] and their involvement in plant/algal, [6b] and mushroom [7] diseases have prompted the analyses of bacterial polyyne biosynthetic gene clusters (BGCs) [6a] . These BGCs harbor conserved core genes coding for a fatty acyl‐AMP ligase, three desaturases, an acyl carrier protein (ACP), a thioesterase, and an electron transport component such as rubredoxin (Figure 1B).…”

“…Because of the high potential for bioprospecting, [9] as antifungals, [10] and for bio‐orthogonal chemistry [11] and in vivo imaging [6b,7] there is high interest in understanding the biochemical basis for microbial alkyne and polyyne formation. Although various in silico and genetic analyses have been performed, [1b,3,5,6,8a,9] bacterial polyyne fatty acid biosynthesis is still little understood.…”