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Review of preprint

Title: Predation increases prey fitness via transgenerational priming, by Silvia Kost et.al

Reviewed by: Viduthalai Rasheedkhan Regina*, Samantha Quah, Matthew Hao, Hashmath Fatimah, Hana Marican, and Minqi Lim

*Presented and led the review

Summary:

The authors have presented evidence for transgenerational bacterial memory induced by exposure to specific stress (priming), in the presented case, with predator grazing. The experimental results support their hypothesis. However, bacterial memory has been shown before and the difference between transgenerational priming and transgenerational memory is not obvious.

Major comments:

Results:

Page 10: Predation increases fitness via the formation of multicellular clusters – The authors suggest that since 3 days of co-culture increases fitness in un-exposed strains there might be a secondary mechanism in play. However, considering E. coli has a short generation time (roughly 20 minutes) and 3 days of culturing can go through roughly 200 generations, 3 days of co-culture can also be considered as evolution in short term. Also, mono-evolved strains have been evolving in the said medium for several generations (18+3 days) compared to the ancestor strain. A possible secondary mechanism that originate from evolving in the said medium can be tested by including the ancestor train in the ‘experienced setting’ experiment.

Discussion:

Page 11,12: Bacterial memory within individual cells has been demonstrated with B. subtilis responding to blue light, and in P. aeruginosa forming biofilms in specific surfaces. Based on these and the current experiments, the authors suggest that ‘adaptive transgenerational learning’ in bacteria and their mechanisms needs further investigation. It doesn’t help understand the differences between the discussed phenomenon, but wonder if the terminologies, memory, priming, adaptive learning all in essence explains the same phenomenon. If this is not these should be explicitly defined in the introduction or in the discussion section. The authors discussed intergenerational transmission in eukaryotic systems, however this can be attributed to epigenetic modifications, which are not reported or limited in bacteria. Perhaps they could speculate on a possible mechanism that is applicable to the phenomena described, or if this is a process of selection of genetic variants rather than intergenerational transmission.

Minor comments:

Introduction:

The introduction is very detailed however appears to be lengthy. Most relevant background starts within the third paragraph starting (page 4), “However, not only eukaryotic organisms, but also microbial systems….. While the phenomenon of transgenerational priming in eukaryotic organisms are relent, limiting the information about eukaryotic systems would help make the introduction more focused.

Pager 5: Cross-protection and anticipation – explanation of these phenomenon are useful but were not discussed later with the results from the study. The authors can consider removing or shortening these if it helps shorten the introduction.

The last paragraph summarising the research carried out in this manuscript with the hypothesis, methods used and the overall results is useful and give a good picture of what is in the ms.

Methods:

The explanation of experimental methods with the Fig. 1 is useful.

Page 6,7: Evolution experiment – “5% of each culture was individually transferred into fresh medium.” Assuming that the 5% is volume (5ml/100ml), where the density of T. thermophila cells were quantified? Did they stay the same or they changed over the course of the evolution? Presumably, if the no. of T. thermopile reduced over generations this will have an impact on the evolution of the bacteria as less stress would be imposed to the evolved bacteria. 

How was the fitness calculated? In the figures, Fig. 2 and 3 fitness is represented as ‘Fitness (h^-1)’. What measurement went into calculating the fitness? Malthusian paramether needs an explanation and why 0 hrs and 24 hrs were used for the calculations as 24 hours might be part of the declining phase of the growth curve.

Competing interests

The author declares that they have no competing interests.