Bacterial and archaeal community structure across a gradient of saline lakes in Kiritimati, Republic of Kiribati

Microbial mats, multilayered sheets of microorganisms often found in extreme environments, are increasingly gaining attention for their utility and influence on the global carbon cycle. However, our understanding of the organisms that define microbial mats and how they vary across environmental gradients remains limited, given the sparse sampling of these systems worldwide. Here we investigate a series of distinct microbial communities across a gradient of natural saline lakes on Kiritimati to define how mat communities in hypersaline lakes, where microbial mats have been previously assessed, differ from microbial communities in fresher lakes. Preliminary terminal restriction fragment length polymorphism analysis indicated that samples from the least saline lakes were statistically distinct from the most saline lake microbial communities. Results from Illumina sequencing of 16S rRNA gene amplicons support this finding and also pointed to both salinity and pH as major drivers of community variability. Alpha diversity measurements show no apparent link between salinity and microbial diversity. Extremely saline samples had both higher and lower Shannon index values, whereas lower salinity groups showed a range of Shannon index values. Our findings suggest pH may interact with salinity to influence microbial community structure and that diversity at high salinities may be controlled by both environmental and temporal factors. Greater insight into the drivers of community structure and diversity requires a deeper understanding of functional groups within brackish and brine lakes