HOW DOES SALINITY SHAPE ABUNDANT AND RARE BACTERIAL SUBCOMMUNITY STRUCTURES IN ESTUARINE GROUNDWATER?

Microbial response to environmental variables is of great importance for understanding microbial acclimatization and evolution in natural environments. Studies have reported that the microbial community has a spatial shift under salinity gradient in variable environments such as lake, soil and estuary. However, it is as yet unclear if the salinity is a critical key to shape the microbial communities and diversity in pristine aquifer. Meanwhile, bacterial communities are normally composed of a few abundant and many extremely rare species. The intrinsic responds of species with different abundance are varied and have not been attracted attention before. Here, groundwater samples from the Pearl River Estuarine (PRE) pristine aquifer were collected to investigate the salinity effect on bacterial abundant and rare communities separately. The results of 16S rDNA sequencing revealed weak correlation between alpha-diversity and salinity. Under hypersaline condition, the OTUs number could be either larger than the ¾ quartile or smaller than ¼ quartile, and vice versa. Meanwhile, the entire community abundance were failed to follow salinity gradient. The dominant bacterial appeared in the whole area, whatever the salinity gradient. However, the sub rare taxa might be more sensitive to salinity and have bio-growth with salinity than their abundant counterparts. Therefore, separation between abundant and rare subcommunity could be taken in future when evaluating microbial response. Meanwhile, with altering taxonomic resolution, excluding inactive individuals, the correlation between community abundance and salinity varied from phylum to genus. It emerged therefore that many communities can be variously correlated to one or more environmental parameters. Taken together, our findings imply that combined chemical influences the spatial organization of microbial communities and that composition patterns, which may be useful for understanding biogeochemical processes and for predicting ecology evolution.