Ecological Adaptability of Bacillus to Extreme Oligotrophy in the Cuatro Cienegas Basin
The genus Bacillus is known for its ability to colonize diverse environments and to take up a wide variety of resources. Both properties are linked to its spore-forming life history strategy and to its high number of rrn operon copies per genome. Experimental evidence has postulated a relationship between the number of copies of the rrn operon and the availability of environmental phosphorus. Generally, aquatic bacteria isolated from oligotrophic environments have few rrn operon copies and other adaptations that decrease cellular phosphorus demand. The Cuatro Cienegas Basin (CCB) is an aquatic ecosystem with extreme oligotrophy and with high diversity of Bacillus strains. For this reason, we explored the variation of the rrn operon copy number in different Bacillus lineages and their physiological implications during growth under oligotrophic conditions. Unexpectedly, the Bacillus from the CCB has a high variation in the number of rrn operon copies despite the extreme phosphorus limitation in this environment. In addition, these bacilli showed different ecological responses reflected in the heterogeneity of their growth dynamics. This heterogeneity seems to be a response to the low availability of nutrients and the competitive cost represented by a high number of rrn operon copies. Interestingly, the cellular stoichiometry and protein content during growth dynamics of these Bacillus are not consistent with the growth rate hypothesis. The ecological adaptability of the genus Bacillus to the oligotrophy of the CCB appears to be due to its high heterogeneity in the number of copies of the rrn operon, its cellular stoichiometry, and its ecophysiological adaptations.
KeywordsAquatic bacteria Bacillus Growth Rate Hypothesis Phosphorus rrn operon
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