Alpha-Ketoglutaric Acid Production from a Mixture of Glycerol and Rapeseed Oil by Yarrowia lipolytica Using Different Substrate Feeding Strategies
, Ludwika Tomaszewska-Hetman, Magdalena Rakicka-Pustułka, Piotr Juszczyk and Waldemar Rymowicz
Round 1
Reviewer 1 Report
The paper entitled “Alpha-ketoglutaric acid production from a mixture of glycerol and rapeseed oil by Yarrowia lipolytica using different substrate feeding strategies” by RywiÅ„ska A. et al. describes the development of a protocol to produce KGA by using the yeast Yarrowia lipolytica. The authors have evaluated the effect of a feeding strategy based on two different substrates, namely glycerol and rapeseed oil. Although the article is well written and has a significant number of measurements, the degree of novelty is rather low. In literature there are already articles describing the use of this yeast for the production of KGA starting from rapeseed oil at different thiamine concentrations. Published results show product yields higher than those reported by the authors of this paper. Besides, the use of glycerol has also been reported and it is known that it increases the levels of pyruvic acid, which is an unwanted side-product. For these reasons, in my opinion, the rationale behind this study is unclear. The authors should stress why this double feeding strategy was chosen, what the overall advantage of the method, and what the degree of innovation compared to the state of the art. I recommend accepting this paper as long as the authors make the substantial changes required.
Author Response
We would like to thank the Reviewer for all the comments to the manuscript.
In response to the Reviewer's suggestion - “the authors should stress why this double feeding strategy was chosen, what the overall advantage of the method, and what the degree of innovation compared to the state of the art” the comment has been added in the text and in the conclusions:
page 14, line 99-101:
The proposed conditions, despite the significant share of glycerol in the substrates pool, allow for an efficient production of KGA with a low proportion of PA.
page 15, line 144-152:
Although the production parameters of KGA by Y. lipolytica yeast are higher with the use of oil than with glycerol as a carbon source, it is very difficult to conduct long-term cultivation processes using hydrophobic substrates. To respond to the industry’s needs, this work proposes a strategy for using two sources of carbon (oil and glycerol) in one production culture. Therefore, the amount of oi needed for the process was reduced and exchanged by glycerol, which seems to be of great practical importance. Finally, replacing the hydrophobic substrate with water-soluble glycerol can significantly facilitate the industrial-scale production of KGA, especially if wild strains are used in the process. It is worth noticing that the use of two substrates for KGA biosynthesis has not been investigated so far.
Reviewer 2 Report
The authors present a comprehensive study of the growth kinetics of Yarrowia lipolytica in glycerol and rapeseed oil for the production of KGA. This molecule has a lot of applications and the strategy presented here seems to show promising results in the KGA production by microorganisms. My main concern is that the data lacks of statistical significance (there are no error bars on any figure). Without the statistical analysis there is no way to support data strength and reproducibility. Also, the manuscript should be revised for grammatical errors.
Author Response
We would like to thank the Reviewer for all the comments to the manuscript.
In response to the Reviewer's suggestion “My main concern is that the data lacks of statistical significance (there are no error bars on any figure) … Also, the manuscript should be revised for grammatical errors” - error bars have been added and the work has been linguistically checked.
All the grammatical errors introduced to the manuscript have been marked yellow.
Round 2
Reviewer 1 Report
The work has been improved and can be accepted in the present form
Reviewer 2 Report
I have revised the manuscript and I am glad to see the figures now have error bars.
