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Dear authors,
After a second round of revisions, the reviewers and myself consider that this work is carefully done and provides a great tool for research and teaching. I wanted to congratulate the authors for such a unique and interesting manuscript and I wanted to thank you for choosing PeerJ.
Warm regards,
Bernardo
[# PeerJ Staff Note - this decision was reviewed and approved by Konstantinos Kormas, a PeerJ Section Editor covering this Section #]
No comment
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Under the second review, no further corrections
The data from the S. cerevisiae curve are well performed and adjusted to the model. On the other hand, the comparison between the Erlenmeter and the conventional spectrophotometer show no important difference suggesting that, under certain measure interval, one could substitute the other and maintain validity of data.
Correct
The sent corrections answer the details marked in the first review.
Dear authors,
The reports from three experts have been completed and the general appreciation of this work is positive. I also find this work interesting and in accordance with PeerJ scope. The comments raised by the reviewers are positive and will certainly improve the manuscript. In the comments, I strongly suggest including more measurements side-by-side with standard spectrophotometers and providing a more robust statistical support. The data will greatly support the Erlenmeter as a tool not only for educational purposes but also for accurate research measurements. Reviewer 1 asked me to modify a bit his last comment, please attend the following line of the reviewer comment: The result essentially suggests that the duration of the so-called “lag phase” in bacterial cultures may appear to be longer because of the low sensitivity of most OD measurement methods. Please comment carefully on each assessment of the three experts.
Thank you for choosing PeerJ for this relevant paper.
All the best for your research moving forward.
**PeerJ Staff Note:** Please ensure that all review, editorial, and staff comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
Bernardo
It is a clearly written manuscript with the required elements and sections in the appropriate order and with sufficient detail for full understanding of experiments. Raw data was shared. In the field backgound in lines 64 to 69 the current wording implies that measuring OD inevitably requires sterile collection of samples. That would be inaccurate since to avoid sampling of cultures we often measure OD using the so-called nephelometric flasks (George H. Scherr (1952) A Nephelometric Technique for Large Cultures, Mycologia, 44:4, 575-577). So, rather than referring to those flasks later in the manuscript, they could be mentioned from the beginning.
Overall is a sound experimental design. However, no reason is given for the use of 466 nm wavelength, whereas the 598 nm is very close to 600 nm, the typical wavelength for OD measurements of bacterial cultures because that wavelength avoids interference by the color of the culture medium. ¿Might 466 nm had given rise to color interference? ¿Could microalgal cultures be read at 598 nm?
Valid findings, I find particularly useful the detection of early bacterial growth by turbidimetry. Nonetheless, I suggest bacterial cultures are repeated because only triplicates were run. I understand cultures are simple to do and should not be an undue burden. It could be particularly useful if they could compare the OD values of the Erlenmeter with those on nephelometric flasks. This because as I argue below it seems that the main value of the proposed Erlenmeter could be the detection of early growth rates, which to my knowledge is always overlooked because of the low sensitivity of most OD measurements. In other words, their experiments could be challenging the existence of the so-called lag phase of bacterial growth curves.
Although authors focus on highlighting that the proposed procedure avoids opening of flasks, I see as a major strength the fact that in their method the light path length is significantly increased. That enhances sensitivity, especially at the start of the growth curve, which has always been difficult to monitor in bacterial cultures. In that way, initial growth rate is revealed, as nicely seen in Fig. 5, where exponential growth is apparent form the very early time of 1-2 h. The result essentially suggests that the so-called “lag phase” in bacterial cultures may be an artifact produced by the low sensitivity of most OD measurement methods. In my opinion this result merits a re-assessment, running a larger number of bacterial cultures and not just triplicates. It could also be that authors compared those results with measurements in nephelometric flasks. This because it could give a strong argument for the superior sensitivity of their method.
In general, the work is carried out correctly. There is access to the raw data and the websites it suggests for comparative analysis.
I consider that the work has scientific rigor and that it has advantages over other designs of devices with the same purpose that have been destined for the present idea of the erlenmeter. However, I consider that it is necessary to show or add some aspects that will make the use of the device more reliable.
I suggest you try more brands of Erlenmeyer flasks.
I suggest you perform the same experiments with a yeast organism, for example S. cerevisiae.
The data displayed on the growth of microorganisms over time will have much more impact and be displayed more reliably if you display a table or graph showing the data collected from the Erlenmeter device compared to a normal spectrophotometer.
The results support the conclusion reached. However, I consider the comparison with the data obtained with a normal spectrophotometer to be important, as this will provide reliability for the choice of said system that is proposed.
N/A
The general proposal, described in this paper, is an original project to develop a new piece of equipment, with broad utility in the lab. It is clear to me that a spectrophotometer is basic lab gear, and the new application presented to this fundamental concept is well received.
I found no evident errors in redaction or orthography. The idea of this work is well transmitted.
As this technology has great potential to be used in formal research work, It will be of great educational value, to show data generated by yeast (Saccharomyces cerevisiae); one of the most common and widely used models in microbiology, for research and science teaching. This data will add strength to the principles by which the Erlenmeter works.
The principle of operation is the same as a regular spectrophotometer, but the results obtained with this new system, will be comparable to the conventional?? Please discuss a little bit further.
The mathematical model used in the data analysis, is suitable for the purpose of the paper.
Also, I consider the project attractive for starting or low budget labs; this in virtue of the "build it yourself" idea.
Original and well planted equipment development.
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