Functional assessment of mycosporine‐like amino acids in Microcystis aeruginosa strain PCC 7806

Abstract

The biological role of the widespread mycosporine-like amino acids (MAAs) in cyanobacteria is under debate. Here, we have constructed and characterized two mutants impaired in MAA biosynthesis in the bloom-forming cyanobacterium Microcystis aeruginosa PCC 7806. We could identify shinorine as the sole MAA type of the strain, which is exclusively located in the extracellular matrix. Bioinformatic studies as wells as polymerase chain reaction screening revealed that the ability to produce MAAs is sporadically distributed within the genus. Growth experiments and reactive oxygen species quantification with wild-type and mutant strains did not support a role of shinorine in protection against UV or other stress conditions in M. aeruginosa PCC 7806. The shinorine content per dry weight of cells as well as transcription of the mys gene cluster was not significantly elevated in response to UV-A, UV-B or any other stress condition tested. Remarkably, both mutants exhibited pronounced morphological changes compared with the wild type. We observed an increased accumulation and an enhanced hydrophobicity of the extracellular matrix. Our study suggests that MAAs in Microcystis play a negligible role in protection against UV radiation but might be a strain-specific trait involved in extracellular matrix formation and cell-cell interaction.

Heterologous Production of Cyanobacterial Mycosporine-Like Amino Acids Mycosporine-Ornithine and Mycosporine-Lysine in Escherichia coli

“…2), N. punctiforme ATCC 29133, A. halophytica, Actinosynnema mirum DSM 43827, and Microcystis aeruginosa sp. PCC 7806 (19,21,(23)(24)(25). Several MAA-like compounds contain a second amino acid residue attached to the 1 position of mycosporine-glycine.…”

“…Several MAA-like compounds contain a second amino acid residue attached to the 1 position of mycosporine-glycine. Shinorine contains a serine residue at this position, whose attachment is catalyzed by an NRPS-like protein (Ava_3855) in A. variabilis or a D-AlaϪD-Ala ligase in N. punctiforme (NpF5597) and M. aeruginosa (MysD) (19,21,25). In all organisms described, MAA synthase genes are organized collinearly with the proposed biosynthesis pathway, with the exception of NpF5597 in N. punctiforme, which is transcribed in the direction opposite to the mycosporine-glycine biosynthesis genes (Fig.…”

Comparative Profiling and Discovery of Novel Glycosylated Mycosporine-Like Amino Acids in Two Strains of the Cyanobacterium Scytonema cf. crispum

“…Next, MysC, an enzyme belonging to the ATP-grasp superfamily, attaches glycine to 4-DG, forming mycosporine-glycine. The three genes (mysABC) present in both Anabaena variabilis ATCC 29413 (Ava_3856 to Ava_3858) and Nostoc punctiforme ATCC 29133 (NpR5598 to NpR5600) are thought to be essential for mycosporine-glycine biosynthesis, while additional genes are required to produce a range of MAA analogues (21). The final step involved in the biosynthesis of the common MAA shinorine can occur via two distinct enzymes, which catalyze functionally identical reactions via the addition of serine to mycosporine-glycine.…”

“…Alternatively, a DAla-D-Ala ligase (NpF5597; MysD) may add serine to mycosporine-glycine to form shinorine, as occurs in N. punctiforme ATCC 29133 and Aphanothece halophytica. The genes involved in this pathway are located within so-called "Nostoc-type" mys clusters (21)(22)(23). However, the genes responsible for the formation of many other MAA analogues have yet to be identified.…”

The sedoheptulose 7-phosphate cyclases and their emerging roles in biology and ecology

“…22, 28, 41, 42 In the cyanobacterium Microcystis aeruginosa , shinorine was found in the slime layer, where it appears to have a primary structural role in the sheath and a limited role in UV protection. 43 Stronger evidence for MAAs primarily acting as sunscreen exist in other cyanobacteria, e.g., A. variabilis , where shinorine production is directly linked to UV exposure. 27, 42 However, MAAs may still have multiple functions in those cyanobacteria, possibly observed only under stressful conditions (e.g., sulfate deficiency, salt shock, and UV exposure).…”