Abstract
Endozoicomonas, a core bacterial group in corals, may also be a coral symbiont. Endozoicomonas communities often decrease rapidly in corals under heat stress. However, how the bacteria respond to changes in temperature and coral host during heat stress is unknown. Here, we employed the cultivable, dominant species E. montiporae as a working organism to explore how Endozoicomonas responds to heat stress. We designed two experiments to clarify the extent to which E. montiporae is influenced by temperature and coral host. We detected differentially expressed protein (DEP) profiles in this bacterium at 31 and 33°C compared to 25°C by tandem mass tags-based quantitative proteome analysis. Fifty DEPs, including many heat shock proteins, were detected when the temperature changed. The expression of antioxidant defense proteins and key pyruvate synthase proteins decreased, suggesting that E. montiporae were in a physiology of stress at 33°C. Furthermore, some proteins were differentially expressed because of the heat-stress-treated coral lysate specifically, suggesting that not only heat but also heat-induced host factors can affect the protein expression of the bacterium. This study provides an in-depth analysis of how the molecular mechanisms of Endozoicomonas are affected by heat stress and coral host.
Highlights
The coral holobiont is composed of coral and various associated microorganisms, including algae, bacteria, archaea, fungi, protists, and viruses
Most proteins are functionally related to the categories in the cellular metabolic process, nitrogen compound metabolic process, and primary metabolic process according to Gene Ontology (GO) (Supplementary Figure 1)
Results of hierarchical clustering and nMDS analyses showed that the protein profiles of the E. montiporae grown for 48 h were clearly distinct from the profiles of those grown for 16 and 24 h (Figures 2B,C and Supplementary Figure 2)
Summary
The coral holobiont is composed of coral and various associated microorganisms, including algae, bacteria, archaea, fungi, protists, and viruses. When the seawater temperature increases, heat stress impacts the coral host and all of the coral microbial partners in the coral holobiont (Bourne et al, 2016). Heat-Induced Proteomes of Endozoicomonas montiporae algae, the impact of heat stress on the coral bacteria has recently received increasing attention due to these bacteria’s indispensable ecological contribution to coral hosts (Bourne et al, 2008; Mouchka et al, 2010; McDevitt-Irwin et al, 2017). Lee et al (2015) showed rapid changes in the composition of coral bacteria between coral mucus and tissue under heat stress. Shiu et al (2017) even showed that the coral bacterial community quickly changed from normal to pathogenic- or stress-associated microbiota within 12 h of a short-term heat stress experiment (30◦C), whereas the density and photosynthetic efficiency (Fv/Fm) of Symbiodiniaceae remained unchanged
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