Objective This study was conducted to determine the acid resistance of microbial functional strains and to observe the response of growth curve of these strains under acid stresses, using two experimental techniques.
Method Twenty-eight functional microbial strains were incubated in 96-well microplates to study acid resistance properties via investigating their survival and growth curve under different levels of acid stress in the range of pH 7.0-2.0 with the interval of 0.5 pH unit.
Result Results showed that the acid resistance range of these functional strains varied substantially and the lower threshold ranged from 3.5 to 5.0. Those strains in the same genus and with the same function presented similar acid resistance range, while those in a different genus but having the same function or in the same genus but having different functions had substantially different acid resistance capacity. Several strains might regulate the cellular properties to adapt to acid stress after 20-30 h of exposure to low acid stress (e.g., pH 4.0 or 4.5).
Conclusion Our results suggest that investigating changes in the growth curve of microbial strains may be more precise to study their responses to environmental changes. Considering substantial variations in the acid resistance of functional strains and the inconsistence of microbial response to acid stress, functional strains with suitable acid resistance capacity should be selected according to the soil background conditions in agricultural practices.
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