Time-Resolved Visualization of Cyanotoxin Synthesis via Labeling by the Click Reaction in the Bloom-Forming Cyanobacteria Microcystis aeruginosa and Planktothrix agardhii

TL;DR

Scientists used a chemical labeling method to track the production of toxic peptides in two types of cyanobacteria over time.

Contribution

A novel method using click chemistry and fluorescent labeling to visualize cyanotoxin synthesis dynamics in live cyanobacteria.

Findings

Fluorescent labeling with Alexa Fluor 488 effectively tracked cyanopeptide synthesis in Microcystis aeruginosa and Planktothrix agardhii.

Labeling intensity correlated with chemical analysis of clickable peptides in individual cells and populations.

Intracellular distribution of the label showed heterogeneous patterns during toxin synthesis.

Abstract

In non-ribosomal peptide synthesis of cyanobacteria, promiscuous adenylation domains allow the incorporation of clickable non-natural amino acids into peptide products—namely into microcystins (MCs) or into anabaenopeptins (APs): 4-azidophenylalanine (Phe-Az), N-propargyloxy-carbonyl-L-lysine (Prop-Lys), or O-propargyl-L-tyrosine (Prop-Tyr). Subsequently, chemo-selective labeling is used to visualize the clickable cyanopeptides using Alexa Fluor 488 (A488). In this study, the time-lapse build up or decline of azide- or alkyne-modified MCs or APs was visualized during maximum growth, specifically MC biosynthesis in Microcystis aeruginosa and AP biosynthesis in Planktothrix agardhii. Throughout the time-lapse build up or decline, the A488 signal occurred with heterogeneous intracellular distribution. There was a fast increase or decrease in the A488 signal for either Prop-Tyr or Prop-Lys, while a delayed or unobservable A488 signal for Phe-Az was related to increased cell size as well as a reduction in growth and autofluorescence. The proportion of clickable MC/AP in peptide extracts as recorded by a chemical–analytical technique correlated positively with A488 labeling intensity quantified via laser-scanning confocal microscopy for individual cells or via flow cytometry at the population level. It is concluded that chemical modification of MC/AP can be used to track intracellular dynamics in biosynthesis using both analytical chemistry and high-resolution imaging.

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