I am treating E. coli at different AgNO3 concentrations in order to follow bacteria kinetic growth. The slope of the bacterial growth curve continuously decreased with increasing AgNO3 concentration. At low concentrations, the growth of bacteria was delayed and at higher concentrations, growth was completely inhibited.
My question is related to why bacteria are not reaching the same Max. OD600 after long-term silver exposure for concentration below MIC. Assuming that the stationary phase is often due to a growth-limiting factor such as the depletion of an essential nutrient, I would expect that all the curves reached the same OD600 at a certain point after bacteria re-growing. I was thinking one possible explanation could be that AgNO3 is inducing the expression of new genes required for survival under stress (e.g, high AgNO3 concentration, lack of nutrients or toxic byproducts).
Thank you in advance,
Cami
You are asking a very sophisticated and interesting question. Undoubtedly AgNO3 is inducing expression of some new genes, any stress response of any sort is highly likely to do so. Whether that is the reason you don't get slow but high density growth is certainly a reasonable hypothesis, growth of the cells may be self limiting in such situations. But it is also possible that cells are lysing you are releasing toxic products into the medium.
Hi Camilo Sanchez Velasquez , a year ago we worked on a project where we found that silver ions initiate a hormetic effect in bacteria, where cell proliferates at sub-lethal doses. I agree, it could be a stress response. We also saw an increased biofilm formation and lower ROS induction at sub-lethal doses. Its really interesting.
You can check the following link:
https://www.sciencedirect.com/science/article/abs/pii/S0956713520306848
Good luck.
Silver nitrate has a substantial impact on metabolism in E. coli so it is likely that even at sub-lethal doses its metabolism is simply less efficient and a lower OD is attained.
Article Deciphering molecular mechanism of silver by integrated omic...
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