Correction to: Engineering the synthetic β-alanine pathway in Komagataella phaffii for conversion of methanol into 3-hydroxypropionic acid

Correction to: Microb Cell Fact (2023) 22:237

https://doi.org/10.1186/s12934-023-02241-9

In the original version of this article [1], the promoters used to control the expression of the ydfG gene (P_POR1 and P_PDC1) in strains PpCβ10 and PpCβ20 were inadvertently swapped. Consequently, the correct genetic constructs are as follows: The ydfG gene was expressed under the control of the weak P_PDC1 in strain PpCβ10 (and thereby in all PpCβ10-derived strains), whereas the medium strength P_POR1 was used in strain PpCβ20 (and thereby in all PpCβ20-derived strains).

While the data from experiments performed with each of these strains are not affected by this correction and the fundamental conclusions of the study remain valid, the following statements, as well as Fig. 3; Table 3, have been corrected in this erratum.

Page no. 1 of the original publication under section Abstract, subsection Results, fifth sentence should be replaced by “The addition of a second copy of the panD gene and selection of a medium strength promoter to drive expression of the ydfG gene in the PpCβ21 strain resulted in an additional increase in the final 3-HP titer (1.2 g l^− 1)”.

Page no. 4 of the original publication under section The expression of panD, yhxA and ydfG genes in K. phaffii generates a 3‑HP‑producing strain, the end of the last sentence of the first paragraph should read as follows “…, namely the moderate strength mitochondrial porin (POR1) promoter, obtaining the PpCβ20 strain, and the weak pyruvate decarboxylase (PDC1) promoter, obtaining the PpCβ10 strain”.

Similarly, in the second paragraph of the same section (Page 4), the third sentence should be “The heterologous expression of panD, yhxA and ydfG genes resulted in 0.93 ± 0.03 g l^− 1 of 3-HP after 48 h of cultivation when the weak P_PDC1 was used to control the expression of the ydfG gene (PpCβ10 strain), whereas a slightly but significantly higher titer (p-value < 0.05), 1.04 ± 0.01 g l^− 1 3-HP, was obtained with the P_POR1 driving the expression of this gene (PpCβ20 strain)”.

Page no. 5 of the original publication under section Improving 3‑HP production by optimizing the flux through the β‑alanine synthetic pathway, the last three sentences need to be rephrased as follows: “These results indicate that higher expression levels of the ydfG gene (i.e., under the control of P_POR1) seem to be beneficial in terms of 3-HP production. These results point at the final step of the pathway, which catalyzes the NADPH-dependent reduction of the malonic semialdehyde to 3-HP, as a critical rate-limiting reaction. Notably, the increase in the flux through the β-alanine pathway enabled by the insertion of an additional copy of the panD gene under the strong AOX1 promoter combined with the expression of the ydfG gene under the control of the medium-strength POR1 promoter did not further exacerbate the limitation of NADPH equivalents for anabolism/cell growth on methanol in small scale cultures (Fig. 3).”

Page 5 of the original publication Fig. 3 should be corrected to the following Fig. 3, in which the promoters used for ydfG expression (in orange) are correctly assigned to the corresponding strain.

Fig. 3

Global product yields (Y_P/S) calculated for the base strains constructed in this study. The key heterologous enzymes expressed in each strain are depicted in the left side of the graph. One colored arrow corresponds to one copy of the related expression cassette (blue for PAND_Tc, purple for BAPAT_Bc, and orange for YDFG_Ec). Promoters selected to drive expression of every transcriptional unit are mentioned above the arrows. On the right side, the grey bars show the average product yield (g g^− 1), and the black dots represent the averaged endpoint OD₆₀₀. The error bars show the standard deviation, and the asterisk sign indicates a significant difference in global 3-HP yields between the strains indicated in brackets (p-values < 0.05)

Page no. 6 of the original publication under section Evaluating the impact of the β-alanine pathway on cell growth kinetics, the fourth sentence needs to be changed as follows: “Interestingly, higher levels of the NADPH-consuming YDFG_Ec enzyme of the β-alanine pathway (i.e., ydfG gene expressed under the control of P_POR1, strain PpCβ20) proved to be beneficial, both in terms of 3-HP production and in µ_max reduction (referred to the µ_max of the wild type strain), which was less pronounced (µ_max reduction from 0.14 h^− 1 to 0.11 h^− 1) than that observed for strain PpCβ10 (µ_max reduction from 0.14 h^− 1 to 0.09 h^− 1).”

Page no. 11 of the original publication, Table 3 should be modified as follows:

Table 3 List of plasmids and strains used in this study

Finally, upon publication of this article [1], it was brought to our attention that in Table S1 from Additional file 1, we utilized a mechanistic P/O value of 2.5 for mitochondrial NADH oxidation in our stoichiometric analysis of both the Malonyl-CoA and the β-alanine pathways towards 3-HP using different carbon sources, indicating that 2.5 ATP are obtained per oxygen atom reduced by the respiratory chain. This value was chosen based on historical estimations found in several earlier reports [2]. However, other studies suggest a lower theoretical P/O ratio of 1.5 for Saccharomyces cerevisiae as more realistic [3], which has also been used in K. phaffii genome-scale models for validation of phenotypic predictions [4, 5]. Accordingly, Table S1 from Additional file 1 should be modified as follows:

Table S1 Stoichiometric analysis of the main metabolic pathways towards 3-HP using different carbon sources

Importantly, the stoichiometric calculations considering a theoretical P/O value of 1.5 do not alter the resulting stoichiometries for 3-HP production from glucose and methanol. Consequently, the original publication’s conclusion that the β-alanine pathway is more energetically efficient than the malonyl-CoA pathway for producing one molecule of 3-HP from three molecules of methanol still holds true.