On 2017 Dec 07, Martine Crasnier-Mednansky commented:

In the discussion, the author questions whether Vibrio cholerae chitin-induced natural competence and transformation would ever occur in nature because of two seemingly irreconcilable posits: (1) transport of the PTS-sugar GlcNAc causes dephosphorylation of Enzyme IIAGlc thus preventing cAMP synthesis, and (2) chitin-induced natural competence and transformation requires cAMP for transcriptional activation of TfoX-regulated genes.

To solve this issue, the author claims "GlcNAc might not be abundant next to the chitin surface". This is probably the case as cells reaching the chitin surface are most likely limited in carbon sources, a condition in Escherichia coli leading to a marked increase in cAMP (Botsford JL, 1978). Under starving conditions, the cells are probably actively synthesizing chitinases and, in its natural chitin-rich habitat, chitin colonization and degradation are most likely not subject to catabolite repression, particularly at limiting concentrations of (GlcNAc)2 for growth.

As regards natural competence and transformation, the negative effect of GlcNAc transport is far from being established by the author’s data. According to figure 4, addition of 2 mM GlcNAc does not significantly affect transformation frequency with (GlcNAc)6 as inducer of natural transformation. Furthermore, it appears the effect of GlcNAc on transformation frequency is independent of GlcNAc transport (figure 2, third panel).

Meibom KL, 2005 proposed three controlling factors for natural transformation, "the presence of chitin; increasing cell density; and nutrient limitation, growth deceleration or stress". As regards cell density, the quorum-sensing master regulator HapR is essential for natural competence, and considering utilization of GlcNAc upon growth deceleration causes an increase in cAMP, GlcNAc may actually be a good carbon source in vitro for natural transformation in the presence of chitin.

On 2017 Dec 07, Martine Crasnier-Mednansky commented:

In the discussion, the author questions whether Vibrio cholerae chitin-induced natural competence and transformation would ever occur in nature because of two seemingly irreconcilable posits: (1) transport of the PTS-sugar GlcNAc causes dephosphorylation of Enzyme IIAGlc thus preventing cAMP synthesis, and (2) chitin-induced natural competence and transformation requires cAMP for transcriptional activation of TfoX-regulated genes.

To solve this issue, the author claims "GlcNAc might not be abundant next to the chitin surface". This is probably the case as cells reaching the chitin surface are most likely limited in carbon sources, a condition in Escherichia coli leading to a marked increase in cAMP (Botsford JL, 1978). Under starving conditions, the cells are probably actively synthesizing chitinases and, in its natural chitin-rich habitat, chitin colonization and degradation are most likely not subject to catabolite repression, particularly at limiting concentrations of (GlcNAc)2 for growth.

As regards natural competence and transformation, the negative effect of GlcNAc transport is far from being established by the author’s data. According to figure 4, addition of 2 mM GlcNAc does not significantly affect transformation frequency with (GlcNAc)6 as inducer of natural transformation. Furthermore, it appears the effect of GlcNAc on transformation frequency is independent of GlcNAc transport (figure 2, third panel).

Meibom KL, 2005 proposed three controlling factors for natural transformation, "the presence of chitin; increasing cell density; and nutrient limitation, growth deceleration or stress". As regards cell density, the quorum-sensing master regulator HapR is essential for natural competence, and considering utilization of GlcNAc upon growth deceleration causes an increase in cAMP, GlcNAc may actually be a good carbon source in vitro for natural transformation in the presence of chitin.