Correction: Morón-Asensio et al. Differential Labeling of Chemically Modified Peptides and Lipids among Cyanobacteria Planktothrix and Microcystis. Microorganisms 2021, 9, 1578

The authors wish to make the following corrections to this paper [...].

The authors wish to make the following corrections to this paper [1]: We repeated the peptide analysis as well as labeling for the P. agardhii CYA126/8 mutant strain with experimentally inactivated AP synthesis (∆apnC), since, as reported, the ∆apnC mutant strain did not only stop producing anabaenopeptins (APs) but, unexpectedly, also did not contain microcystins (MCs) ( Figure S9). Thus, in comparison with the WT strain CYA126/8, it was impossible to find out whether, besides Aps, unnatural amino acids Prop-Tyr, Prop-Lys, or Phe-Az might be incorporated into the MC molecule during its synthesis and contribute to the observed labeling signal (Figure 3, Figure 4 and Table 2, Table 3).
To elucidate the possible incorporation of unnatural amino acids into the MCs strain, P. agardhii CYA126/8 ∆apnC was regrown from one single filament from the original mutant culture [2] and reanalyzed under identical conditions. Peptide analysis via LC-MS revealed that both AP 905 and AP 915 were lacking but as expected, the other peptides, i.e., aeruginosin 126A, 126B, Microviridin K, demethylated MC-RR, demethylated MC-LR, cyanopeptolin 880, and sulfated cyanopeptolin 960 were still produced (corrected Figure S9 as follows).
In addition, during the reanalysis of the ∆apnC strain peptide extract, no clear evidence for incorporation of Prop-Tyr, Prop-Lys, or Phe-Az into the MC molecules was observed (corrected Figure S9 as follows). As for M. aeruginosa (Table 1), a modified D-Asp-MC-Tyr-alkyne [M + H] 1069.5 has been predicted from the original MC molecular weight, subtracting the mass of the original AA (Htyr = 195.2), and adding the mass of the non-natural AA (Prop-Tyr = 219.2) added, but could not be unequivocally identified ( Figure S9A).
Nevertheless, some increased intensity for Prop-Tyr was observed using ALEXA488 (1.3 ± 0.4 vs. 0.7 ± 0.2, p < 0.001) and ALEXA405 (1.4 ± 0.2 vs. 0.6 ± 0.1, p < 0.05) while no increase was detected for the Prop-Lys fed cultures labeled with ALEXA405. However, since this increase in intensity was rather small, the ∆apnC mutant did not show increased ratios of ALEXA488 to autofluorescence (AF) and ALEXA405 to AF under Prop-Tyr feeding conditions (corrected Figures 3 and 4).
Thus, we conclude that the increase in ALEXA488 or ALEXA405 intensity for the P. agardhii ∆apnC mutant strain was not derived from D-Asp-MC-Tyr-alkyne [M + H] 1069.5 to a major extent. Since neither the ALEXA488 nor the ALEXA405 fluorescence to AF ratios were affected, we conclude that the signal increase from Tyr-alkyne was relatively minor.  [2]. P. agardhii was grown in the presence of (A) Prop-Tyr, (B) Prop-Lys, and (C) Phe-Az. Controls were from cells grown under identical conditions but without substrate. As expected, this mutant strain did not contain any AP molecule but the other peptide groups, i.e., aeruginosin 126A, 126B, Microviridin K, demethylated MC-RR, demethylated MC-LR, cyanopeptolin 880, and sulfated cyanopeptolin 960. Figure S9. LC-MS Base Peak Chromatograms (BPC) and Extracted Ion Chromatograms (EIC) in positive ionization mode for P. agardhii strain CYA126/8 ∆apnC mutant insertionally inactivated in AP synthesis [2]. P. agardhii was grown in the presence of (A) Prop-Tyr, (B) Prop-Lys, and (C) Phe-Az. Controls were from cells grown under identical conditions but without substrate. As expected, this mutant strain did not contain any AP molecule but the other peptide groups, i.e., aeruginosin 126A, 126B, Microviridin K, demethylated MC-RR, demethylated MC-LR, cyanopeptolin 880, and sulfated cyanopeptolin 960.

A correction of the original version follows:
In Section 3.2.1 Peptide Labeling Intensity, the fourth and fifth sentence of the fourth paragraph should read as follows: "In comparison with CYA126/8 WT, labeling intensity was found to be less reduced in the AP synthesis mutant ∆apnC, i.e., a slightly increased intensity for Prop-Tyr was observed using ALEXA488 (1.3 ± 0.4 vs. 0.7 ± 0.2, p < 0.001) and ALEXA405 (1.4 ± 0.2 vs. 0.6 ± 0.1, p < 0.05) while no increase was detected for the Prop-Lys fed cultures labeled with ALEXA405." In Section 3.2.2 Peptide Intensity/Autofluorescence Ratio, the last sentence of the second paragraph should read as follows: "The ∆apnC mutant did not show increased ratios of peptide intensity vs. AF between the treatments." In Section 3.2.2 Peptide Intensity/Autofluorescence Ratio, the fourth sentence of the fourth paragraph should read as follows: "Using ALEXA405 labeling, the ∆apnC mutant did not reveal a change in signal ratio, i.e., the median ratio varied from 1.7 (Prop-Lys), 1.9 (Prop-Tyr), and 1.7 (Control)." In Section 4 Discussion, the third paragraph should read as follows: "Currently the observed, rather moderate, Prop-Tyr labeling for the P. agardhii ∆apnC mutant strain does not support our hypothesis on Prop-Tyr incorporation during MC biosynthesis, i.e., identification of its derivation from D-Asp-MC-Tyr-alkyne [M + H] 1069.5 could not be unequivocally performed. However, since neither the ALEXA488 nor the ALEXA405 fluorescence to AF ratios were affected, we conclude that the signal increase from Tyralkyne in the ∆apnC mutant strain was generally minor." Additionally, the following tables and figures have been updated to represent the results obtained for the corrected P. agardhii ∆apnC strain analysis results. Table 2. Average (±SD) min-max green fluorescence intensity obtained for individual treatments using non-natural amino acid feeding (Phe-Az, Prop-Lys, and Prop-Tyr) and subsequent labeling by ALEXA488 using copper-catalyzed azid-alkyne cycloaddition (CuAAC). The intensity was divided by the average intensity of control filaments or cells, i.e., cells which were grown without amino acid addition but used for the chemical reaction under identical conditions. No Fluorophore indicates filaments or cells grown with amino acid addition but no subsequent labeling by the click-chemical reaction. n: number of individual filaments (Planktothrix) or cells (Microcystis, Synechocystis).   Table 3. Average (±SD) min-max blue fluorescence intensity obtained for individual treatments using non-natural amino acid feeding (Prop-Lys and Prop-Tyr) and subsequent labeling by ALEXA405 using copper-catalyzed azide-alkyne cycloaddition (CuAAC). The intensity was divided by the average intensity of control filaments or cells, i.e., cells were grown without amino acid addition but used for the chemical reaction under identical conditions. No Fluorophore indicates filaments or cells grown with amino acid addition but no subsequent labeling by the click-chemical reaction. n: number of individual filaments (Planktothrix) or cells (Microcystis, Synechocystis). . Controls were grown without amino acid addition but used for the chemical reaction under identical conditions. No Fluorophore indicates filaments or cells grown with amino acid addition but no subsequent labeling by click-chemical reaction. The gradient in coloring was defined for each strain separately using the average intensity from the control cultures. Superscripts indicate statistically significant different subgroups after overall difference was found (p < 0.05). . Controls were grown without amino acid addition but used for the chemical reaction under identical conditions. No Fluorophore indicates filaments or cells grown with amino acid addition but no subsequent labeling by click-chemical reaction. The gradient in coloring was defined for each strain separately using the average intensity from the control cultures. Superscripts indicate statistically significant different subgroups after overall difference was found (p < 0.05).
Microorganisms 2021, 9, x FOR PEER REVIEW 5 of 5 . Controls were grown without amino acid addition but used for the chemical reaction under identical conditions. No Fluorophore indicates filaments or cells grown with amino acid addition but no subsequent labeling by click-chemical reaction. The gradient in coloring was defined for each strain separately using the average intensity from the control cultures. Superscripts indicate statistically significant different subgroups after overall difference was found (p < 0.05).

Change in Supplementary Materials:
The Supplementary Materials were changed accordingly and were included as a separate document.