Regulation of scytophycin accumulation in cultures of Scytonema ocellatum. II. Nutrient requirements

Scytodecamide from the Cultured Scytonema sp. UIC 10036 Expands the Chemical and Genetic Diversity of Cyanobactins

Cyanobactins are a large family of cyanobacterial ribosomally synthesized and post-translationally modified peptides (RiPPs) often associated with biological activities, such as cytotoxicity, antiviral, and antimalarial activities. They are traditionally described as cyclic molecules containing heterocyclized amino acids. However, this definition has been recently challenged by the discovery of short, linear cyanobactins containing three to five amino acids as well as cyanobactins containing no heterocyclized residues. Herein we report the discovery of scytodecamide (1) from the freshwater cyanobacterium Scytonema sp. UIC 10036. Structural elucidation based on mass spectrometry, 1D and 2D NMR spectroscopy, and Marfey's method revealed 1 to be a linear decapeptide with an N-terminal N-methylation and a C-terminal amidation. The genome of Scytonema sp. UIC 10036 was sequenced, and bioinformatic analysis revealed a cyanobactin-like biosynthetic gene cluster consistent with the structure of 1. The discovery of 1 as a novel linear peptide containing an N-terminal N-methylation and a C-terminal amidation expands the chemical and genetic diversity of the cyanobactin family of compounds.

The impact of culture conditions on growth and metabolomic profiles of freshwater cyanobacteria

Cultured cyanobacteria produce secondary metabolites with a wide range of biological activities and are an important source of natural products. In the context of secondary metabolite discovery, microbial culture conditions are expected to support optimum growth, induce maximum chemical diversity, and be suitable for the majority of cyanobacterial strains. We investigated the effect of nitrate and phosphate on biomass production and metabolomic profiles of three filamentous freshwater cyanobacterial strains: cf. Oscillatoria sp. UIC 10045, Scytonema sp. UIC 10036, and Nostoc sp. UIC 10110. A standardized inoculation procedure allowed for the assessment of cell mass production. Dried cyanobacterial cell mass was extracted and analyzed by liquid chromatography coupled with high resolution mass spectrometry (UPLC-HRMS), followed by comparative metabolomics analysis using XCMS Online. Results showed that low nitrate media significantly reduced cell mass production for all three strains. Low nitrate also induced production of primary metabolites (heterocyst glycolipids) in strains UIC 10036 and UIC 10110. Changes in phosphate levels affected each strain differently. Strain UIC 10110 showed a significant increase in production of merocyclophane C when cultivated in low phosphate, while strain UIC 10036 displayed higher production of tolytoxin under high phosphate. Additionally, these experiments led to the identification of a potentially new peptide produced by strain UIC 10036.

Nutrients and pH regulate algicide accumulation in cultures of the cyanobacterium Oscillatoria laetevirens

• The change in algicide synthesis in response to nutrients and pH in axenic cultures of the planktonic cyanobacterium, Oscillatoria laetevirens is reported. • Analytical and bioassay techniques were used to determine the effects of nitrogen (N), sulpher (S), phosphorus (P), magnesium (Mg²⁺ ), calcium (Ca²⁺ ) and hydrogen (H⁺ ) on Oscillatoria laetevirens growth, secondary metabolite accumulation and minimum inhibitory concentration in culture filtrates. • Growth and secondary metabolite production were affected by nutrient addition. High algicide production, which was not dependent on optimal growth, correlated with deficiences of magnesium and phosphate, and high pH. Algicidal activity in the culture medium was not detected following organic nitrogen addition while optimal growth was sustained; however, ammonia reduced biomass yield but did not affect algicide formation. The differential algicide concentration inside the cells and in the culture medium indicated secretion by an efflux mechanism rather than leakage from aging cells. • Algicide production by Oscillatoria laetevirens was negatively regulated by both phosphate and magnesium, and by pH. The interactive influence of nutrients and allelopathy is discussed in species succession and dominance in the maintenance of freshwater blooms.

Regulation of scytophycin accumulation in cultures of Scytonema ocellatum. II. Nutrient requirements

The effects of optimal sources and concentrations of major nutrients (supplying N, S, P, K+, Na+, Ca2+, Mg2+, and inorganic carbon) and organic buffers on growth and secondary metabolite accumulation in Scytonema ocellatum strain FF-66-3 were determined. Nitrate, phosphate, magnesium, and sulfur had no specific stimulatory or inhibitory effects on scytophycin accumulation within the range of concentrations that supported optimal growth. Calcium concentrations greater than those required for growth (0.1 mM) stimulated scytophycin accumulation. Sodium carbonate concentrations in excess of 0.25 mM strongly inhibited growth. Ammonium (2.5 mM) inhibited both growth and product formation. 3-[N-Morpholino]propanesulfonic acid at 3-5 mM effectively controlled pH and facilitated both growth and product formation.