Response of bacterial colonization in Nematostella vectensis to development, environment and biogeography

Abstract

The establishment of host-bacterial colonization during development is a fundamental process influencing the fitness of many organisms, but the factors controlling community membership and influencing the establishment of the microbial ecosystem during development are poorly understood. The starlet sea anemone Nematostella vectensis serves as a cnidarian model organism due to the availability of laboratory cultures and its high tolerance for broad ranges of salinity and temperature. Here, we show that the anemone's epithelia are colonized by diverse bacterial communities and that the composition of its microbiota is tightly coupled to host development. Environmental variations led to robust adjustments in the microbial composition while still maintaining the ontogenetic core signature. In addition, analysis of bacterial communities of Nematostella polyps from five different populations revealed a strong correlation between host biogeography and bacterial diversity despite years of laboratory culturing. These observed variations in fine-scale community composition following environmental change and for individuals from different geographic origins could represent the microbiome's contribution to host acclimation and potentially adaptation, respectively, and thereby contribute to the maintenance of homeostasis due to environmental changes.

Temperature and Water Quality-Related Patterns in Sediment-Associated Symbiodinium Communities Impact Symbiont Uptake and Fitness of Juveniles in the Genus Acropora

“…A predisposition for acquiring certain Symbiodinium types is supported by the acquisition of clade C symbionts in offshore sediment treatments when their comparative availability in offshore sediments was low, potentially signifying the presence of recognition mechanisms, consistent with findings that clade C ultimately dominates adult communities of these corals (Abrego et al, 2009). A bipartite system, involving both genetic and environmental contributions to the structuring of symbiont communities, has also been observed in closely-related Nematostella-bacterial partnerships (Mortzfeld et al, 2015). Knowledge of the environmental availability of symbionts, in conjunction with an understanding of the genetic mechanisms regulating symbiont uptake by the host, are therefore required to predict the potential for differential selection of Symbiodinium to affect coral health.…”

“…More rapid rates of infection in juveniles exposed to Rib and Davies (central offshore) sediment treatments may reflect an increased capacity of A3, C15, and C to infect and proliferate within coral juveniles. The presence of A3, both when dominant or at background levels of abundance, also strongly impacted F v /F m in juveniles and provides corroborative support that numerically rare background symbionts contribute to changes in the photophysiological performance of their hosts (Erwin et al, 2012;Hoadley et al, 2015;Karim et al, 2015;Mortzfeld et al, 2015). Lower F v /F m values in juveniles that acquired symbionts from offshore sediments and spikes in chlorophyll fluorescence may indicate that the symbionts acquired were adapted to higher light environments (due to increased sediment particle size or decreased turbidity) and a stress response (Shapiro et al, 2016), respectively.…”

“…Symbiodinium communities in juveniles varied through time, although it is unclear whether patterns reflected changes associated with juvenile development or dynamics among Symbiodinium types. Similar fine-scale successional patterns over short time-scales (1-2 weeks) in bacterial communities have been tied to developmental (including immunological) remodeling in Nematostella, amphibians and insects (Mortzfeld et al, 2015). Lack of change in relevant symbiont availability within the sediments from the start to the end of the experiment indicates that lack of symbionts available for infection was not the underlying reason, but does suggest that active selection by the host or competition among symbionts was driving temporal changes in community structure.…”

“…Even fine-scale changes in the relative abundances of some types may translate to large scale impacts at the colony level (Cunning et al, 2015a;Quigley et al, 2016). For example, small shifts in bacterial community composition in Nematostella resulted in changes to host fitness, potentially caused by variation in the immune responses elicited by different symbionts under different selective pressures (Mortzfeld et al, 2015). Alternatively, the early acquisition of certain types may have led to greater longterm juvenile survival.…”

Using Nematostella vectensis to Study the Interactions between Genome, Epigenome, and Bacteria in a Changing Environment

“…In N. vectensis bacterial colonization is characterized by a stable associated bacterial community, which is dynamic but highly conserved in response to host development. Nevertheless, environmental changes induce a robust tuning of bacterial colonization (Mortzfeld et al, 2015), e.g., by the increase of rare bacterial species. In addition, analysis of bacterial communities of Nematostella polyps from five different populations revealed a strong correlation between host biogeography and bacterial diversity ( Figure 2D).…”