Marine rhizosphere: the diversity and function of the mangrove forest microbiome

Natalia Erazo, Scripps Institution of Oceanography, La Jolla, CA and Jeff S Bowman, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA

Marine rhizosphere: the diversity and function of the mangrove forest microbiome
Natalia G. Erazo1,3, Jeff S. Bowman1,2,3

1Scripps Institution of Oceanography, UC San Diego, La Jolla, California, USA
2Center for Microbiome Innovation, UC San Diego, La Jolla, California, USA
3Center for Marine Biodiversity and Conservation, UC San Diego, La Jolla, California, USA
Background/Question/Methods and Results/Conclusions
Background/Question
Mangroves support a high diversity of microorganisms present in the water column, sediments, and above and below-ground roots. The roots provide a growth surface for microbes responsible for nitrogen fixation, carbon remineralization, and defense mechanisms against pathogens. Here we examined the diversity and the microbial community within the rhizosphere in Rhizophora mangle trees and the impact of anthropogenic stress (e.g. aquaculture effluent) on the ecosystem health.
Methods and Results
In this study we used 16S and 18S rRNA amplicon sequencing, nutrients, C and N isotopes data to asses the composition and functionality of the microbial community and evaluate the impact of land use change on the root microbiome and ecosystem health. We found that the rhizosphere microbial community was very distinct from the water, bulk soil, and aerial roots. The rhizosphere community was characterized by lower diversity dominated by Deltaproteobacteria, Plantomycetes, and Bacteroidetes suggesting a more specialized community associated with methane, sulfur and nitrogen transformations. We saw a shift in the community composition in the perturbed sites to a more opportunistic and pathogenic community associated with plant-pathogen pests (e.g., Candidatus Carosnella ruddii) and necrotic diseases in bivalves (e.g., Candidatus Gracilibacteria). The perturbed rhizosphere microbial community was associated with high alpha diversity. We perceive this impact to be an expression of the “Anna Karenina principle” in the mangrove rhizosphere, wherein perturbation induces inherently unstable states that are expressed as elevated diversity.
Conclusions
The results of this study provide a deeper understanding of plant-microbe co-dependence, and of the functions of the root microbiome and adaptation to anthropogenic stress. This is necessary for further developing rhizoremediation approaches to improve mangrove forest resilience in the face of changing climate and other increasing anthropogenic stressors. We will present a detailed analysis of the principle drivers of microbial community structure in the rhizosphere and the implications for ecosystem health.