Bacterial communities vary across populations and tissue type in red mangroves (Rhizophora mangle. Rhizophoraceae) along an expanding front

Plant-associated microbial communities may be important sources of functional diversity and genetic variation that influence host evolution. Bacteria provide benefits for their hosts, yet in most plant systems we know little about their taxonomic composition or variation across tissues and host range. Red Mangrove (Rhizophora mangle L.) is a vital coastal plant species that is currently expanding poleward and with it, perhaps, its microbiome. We explore variability in bacterial communities across tissues, individuals, and populations. We collected samples from six sample types from 5-10 individuals at each of 3 populations and used 16S rRNA gene (iTag) sequencing to describe their bacterial communities. Core community members and dominant bacterial classes were determined for each sample type. Community beta diversity was explored using pairwise PERMANOVA of Bray-Curtis dissimilarity. Bacterial taxa associated with specific sample types were identified using Indicator Species Analysis. We describe the previously unexplored microbiome of the reproductive tissues of R. mangle. Populations and most sample types were associated with distinct communities. Bacterial communities associated with R. mangle are influenced by host geography and sample type. Our study provides a foundation for future work exploring the functional roles of these microbes and their relevance to biogeochemical cycling.