The Preprint titled Production of alkanes from CO2 by engineered bacteria is about the production of long-chain alkanes for use in fuels and chemicals from CO2, which is transformed into acetate and then into alkanes from native and non-native bacteria. The title is very attractive because it presents a solution and a method in a concrete and short way, however to make it more interesting it could contain the application, which is sustainable fuel production

The aim in the abstract is clear, it has a main verb that is to demonstrate and it mentions what it is going to demonstrate, how it is going to do it and what it will be used for, it also includes a base problem for which the study is being carried out. I believe the goal can be understood by anyone with a basic understanding of organic chemistry and biology. Most of the references used in the research are from 2014 and 2016, so if it can be considered recent, however it also has other very old sources from 1981 and 1997 that could be changed. The images, graphics such as the text are correctly cited, and the references are in APA format, including the pages where the information is located.

In the introduction section is very clear what is already known on the subject, they review the known methods to produce alkanes from other compounds such as sugars derived from biomass and show us what their limitations are in the treatment of bacteria, synthesis of alkanes, aldehydes, and biofuel production, after explaining this indicates why it is necessary to find out a new way of producing alkanes from CO2 and why it cannot be done with the same bacteria, so clearly delineate the research question and invite the reader to find out the method by which the problem posed can be solved. The study presents a diagram that summarizes the entire process, therefore the selection of topics is clear. The variables are correctly exposed, which are the options for bacteria to absorb CO2 and convert to acetate, the evaluation of the best bacteria through sensors and finally obtaining alkane. The methods are based on previous studies but through the sensor they developed they verify that the product is suitable, however I consider that it is necessary to expose more about the manufacture of the sensor so that the study can be replicated, it is also necessary that the sources are presented where the materials are obtained and the conditions to which the bacteria must be conserved.

The results are presented in order according to the procedure and complemented by the two graphs that show the trend of the data and the gap between the parameters studied. The data is presented with a maximum of 3 significant figures, therefore they are easy to understand and expose. It should have more subtitles to organize and find information easier and more categories. The statistically significant results are summarized at the end of the text and in the corresponding graphs, however the most significant results should be summarized in a text box.

The discussion of the results has well-defined comparisons with other similar processes already studied, and uses them only as references or justifications for the project, therefore, discussed from different angles, and are placed in the text without being overinterpreted. I think that you should better organize the information in the discussion according to the steps of the procedure because you discuss the production of acetate by acetogen A. woodii at the end of the discussion, when it should be at the beginning because it is the first step to start the production of alkanes.

Finally, the conclusions respond to the three main objectives of the study, that is, it creates a method to detect the best strain of bacteria for the production of alkanes, in this case the luminescence and fluorescence sensors, it also divides the process into the production of acetate and the production of alkanes, responding to the objective of improving the production of alkanes from CO2 and presents the applications in the industry of chemical products and fuels, however in this last part it does not give details therefore the creative critical thinking is not so developed with respect to other fields of application. The conclusions on their part are well supported by the results found in the procedure and method. The limitations of the study are correctly presented as opportunities for future research.