Macro-algae microbiomes

Effects of global climate change on maro-algae microbiomes.

Global climate change includes rising temperatures and increased pCO2 concentrations in the ocean, with potential deleterious impacts on marine organisms.  We are investigating the effect of global climate stress on the host associated microbiome and the water column microbiome. The two macro-algae tested under experimental conditions, to date,  are giant kelp and Rodoliths, both of which are found off the Californian coast.

In the macrocystis experiment, we investigated the independent and combined effects of increased temperature and partial pressure of carbon dioxide (pCO2). The water and kelp microbiome responded differently to each of the climate stressors. In the water microbiome, each condition caused an increase in a distinct microbial order, whereas the kelp microbiome exhibited a reduction in the dominant kelp-associated order, Alteromondales. The water column microbiomes were most disrupted by elevated pCO2 whereas, the kelp microbiome was most influenced by elevated temperature. Kelp growth was negatively associated with elevated temperature, and the kelp microbiome showed an increase Flavobacteriales, alginate degrading enzymes and sulfated polysaccharides. In contrast, kelp growth was positively associated with the combination of high temperature and high pCO2 ‘future conditions’, with an increase Planctomycetales and Rhodobacteriales. Therefore, the water and kelp microbiomes acted as distinct communities, where the kelp was stabilizing the microbiome under changing pCO2 conditions, but lost control at high temperature. Under future conditions, the kelp and the microbiome potentially reached a new equilibrium, where the kelp grew rapidly and the commensal microbes responded to an increase in mucus production.
Read more about the result in a paper by Minich et al 2017 Plos one.

In a second experiment we investgated a temperate Coralline red algae rhodoliths (Corallinales, Rhodophyta). These organisms are photosynthesizers, calcifiers, and ecosystem engineers, and it is important to understand how these organisms and the microbiome will be affected by ocean acidification. With our collaborates from the Edwards macro-algae lab, we compared responses in photosynthetic capacity, calcium carbonate production, and associated microbiome using, respectively, carbon uptake and decalcification assays, and whole shotgun sequencing metagenomic analysis. The rhodolith microbiome remained stable, resembling a healthy holobiont, and physiological responses of the algae were still positive, with increased photosynthetic activity, and no  calcium carbonate loss. High pCO2 affected microbial abundance and diversity in the biofilm of dead rhodolith calcareous skeletons and in seawater. Nevertheless, the decreasing proportion of live rhodolith tissue measured under high pCO2 suggests that it might have reduced calcareous skeleton production, with an impact on growth. The deep microbial sequencing of seawater, coralline skeleton and rhodolith holobiont  suggests that OA-like conditions affected microbial community structure and function, which may then affect microbe-mediated processes in marine rhodolith bed ecosystems. Our results extend the scarce comprehension of microbes associated with rhodoliths beds and their reaction in more acidic oceans.