Response of the rare biosphere to environmental disturbance in a highly diverse ecosystem (Zodletone spring, OK, USA)

Within highly diverse ecosystems, the majority of bacterial taxa are present in low abundance as members of the rare biosphere. The rationale for the occurrence and maintenance of the rare biosphere, and the putative ecological role(s) and dynamics of its members within a specific ecosystem is currently debated. We hypothesized that in highly diverse ecosystems, a fraction of the rare biosphere acts as a backup system that readily responds to environmental disturbances. We tested this hypothesis by subjecting sediments from Zodletone spring, a sulfide- and sulfur-rich spring in southwestern OK, to incremental levels of salinity (1, 2, 3, 4, and 10% NaCl), or temperature (28 0 , 30 0 , 32 0 , and 70 0 C), and traced the trajectories of rare members of the community in response to these manipulations using 16S rRNA gene analysis. Our results indicate that multiple rare bacterial taxa are promoted from rare to abundant members of the community following such manipulations and that, in general, the magnitude of such recruitment is directly proportional to the severity of the applied manipulation. Rare members that are phylogenetically distinct from abundant taxa in the original sample (unique rare biosphere) played a more important role in the microbial community response to environmental disturbances, compared to rare members that are phylogenetically similar to abundant taxa in the original sample (non-unique rare biosphere). The results emphasize the dynamic nature of the rare biosphere, and highlight its complexity and non-monolithic nature. Abstract 6 Within highly diverse ecosystems, the majority of bacterial taxa are present in low abundance as 7 members of the rare biosphere. The rationale for the occurrence and maintenance of the rare 8 biosphere, and the putative ecological role(s) and dynamics of its members within a specific 9 ecosystem is currently debated. We hypothesized that in highly diverse ecosystems, a fraction of 10 the rare biosphere acts as a backup system that readily responds to environmental disturbances. 11 We tested this hypothesis by subjecting sediments from Zodletone spring, a sulfide- and sulfur-12 rich spring in southwestern OK, to incremental levels of salinity (1, 2, 3, 4, and 10% NaCl), or 13 temperature (28 0 , 30 0 , 32 0 , and 70 0 C), and traced the trajectories of rare members of the 14 community in response to these manipulations using 16S rRNA gene analysis. Our results 15 indicate that multiple rare bacterial taxa are promoted from rare to abundant members of the 16 community following such manipulations and that, in general, the magnitude of such recruitment 17 is directly proportional to the severity of the applied manipulation. Rare members that are 18 phylogenetically distinct from abundant taxa in the original sample (unique rare biosphere) 19 played a more important role in the microbial community response to environmental 20 disturbances, compared to rare members that are phylogenetically similar to abundant taxa in the 21 original sample (non-unique rare biosphere). The results emphasize the dynamic nature of the 22 rare biosphere, and highlight its complexity and non-monolithic nature.