Browsing by Author "Farrar, Zoe May"

Mycosporine-like Amino Acids (MAAs) are small, secondary metabolites, with the ability to absorb UV light. They are produced by cyanobacteria to act as a sunscreen. The aim of this study was to catalogue MAA genetic and chemical diversity in strains of the cyanobacterial genus Nostoc. MAAs were detected in 21 of the 68 Nostoc strains using LC/MS. Fifty four different MAAs were detected across the Nostoc strains. Glycosylated MAAs were detected in 17 of the 21 strains with hexose being the most commonly occurring sugar. Surprisingly, two structurally distinct MAAs were detected from a lichen symbiont strain, Nostoc sp. UHCC 0926. Chemical analysis detected a theoretical methylated and glycosylated variant (m/z 583, C23H39N2O15), and a suspected tri-core variant (m/z 757, C34H53N4O15) with three chromophore rings as opposed to one which is typically found. The glycosylated MAA was predicted to have a hexenimine core which was methylated and had two hexose moieties. The tri-core consisted of 2 aminohexenone cores, one on either side of a central aminohexenimine core. An 8.3 Mb draft genome sequence was obtained to identify the MAA biosynthetic gene cluster responsible for the biosynthesis of these two unusual MAAs. This resulted in the detection of two gene clusters mysA-B-C1 and mysD-C2-C3. This gene cluster organisation was compared with those of other Nostoc strains. The gene cluster organization in Nostoc sp. UHCC 0926 was unique because it was the only strain to have two gene clusters and three mysC genes despite one of the other Nostocs having the ability to produce a tri-core MAA. The strain was cultured and harvested to allow for the extraction and purification of the target MAAs. The tri-core MAA structure was confirmed by NMR. However only a putative structure for the glycosylated MAA was made. The UV absorption spectrum of the tri-core MAA had an absorption maximum at 312 nm while the glycosylated and methylated MAA had an absorption maximum at 336 nm. The investigation into the MAA production of UHCC strains expands the known chemical and genetic diversity of MAAs produced by strains of the Nostoc genus.