Some more interesting findings! I just wanted to highlight a few things I found interesting while reading.
Microbes are well-recognized members of the coral holobiont. However, little is known about the short-term dynamics of mucus-associated microbial communities under natural conditions and after disturbances, and how these dynamics relate to the host’s health. Here we examined the natural...
www.nature.com
In this article they note that
"The SML (Surface Mucus Layer) is particularly important for the biology of corals not only as a habitat for a distinctive suite of coral-associated microbes but also due to its nutritional, protective and cleansing roles (Brown and Bythell, 2005). Consisting of polymeric glycoproteins and lipids (Bythell and Wild, 2011), coral mucus provides a nutritious medium on which a diverse assemblage of microbes thrives, many of which are highly host specific (Rohwer et al., 2002). Although coral mucus is in constant contact with the adjacent seawater, their prevalent microbial communities exhibit almost no overlap (Rohwer et al., 2001, 2002; Frias-Lopez et al., 2002). Furthermore, it has been hypothesized that the microbial community in the coral SML operates as a defense barrier and therefore protects the coral against invasive microbes either because of the production of antimicrobial substances or simply because of the occupation of this interface niche (Rohwer et al., 2002; Reshef et al., 2006; Rosenberg et al., 2007; Shnit-Orland and Kushmaro, 2009)."
These researchers note that the mucus layer of the corals act as a protective barrier, and that the coral most likely curates specific bacteria with specific properties to exploit and protect itself.
"Antibiotic-treated colonies exhibited no visible signs of health deterioration during the 8 days of aquaria incubation. Control colonies, in contrast, were negatively affected, as half (n=3) of them showed bleaching and necrosis during the incubation period (Figure 1b). Prokaryotic abundance in mucus of the colonies was highly variable, with an average of 3.9±4.5 × 105 cells ml−1 before the experiment (n=12). After 24 h of incubation with antibiotics (n=6), prokaryotic abundance was only 5.4±4.6 × 104 cells ml−1 (Figure 3) representing a reduction to 14% of the original in situ abundance (rANOVA, P<0.001; Tukey HSD, P<0.01, see Supplementary Table S7). There was no apparent change in the overall alpha diversity of the coral mucus community (Table 1) concomitant with this reduction. This low abundance remained relatively constant until the end of the incubation period. In contrast, prokaryotic abundance in mucus of control colonies (n=6) remained relatively high (4.1±1.7 × 105 cells ml−1 at 24 h) throughout the entire incubation period (see Figure 3 and Supplementary Table S7), accompanied with a significant increase in alpha diversity (rANOVA, P<0.001; Tukey HSD, P<0.01; see Supplementary Table S8–S10) compared with the original in situ alpha diversity.Once coral colonies were brought back to the reef they exhibited health response patterns opposite to those observed in the aquaria incubation (Figure 1b). Within the first 3 days, all antibiotic-treated colonies (n=6) showed rapid health deterioration and exhibited clear signs of bleaching, with only two surviving the following weeks. Non-treated corals, in contrast, recovered from aquarium incubations within 28 days of re-introduction to the natural reef environment (Figure 1b)... Initially, during the aquarium incubation, both groups diverged from the natural community typical of new mucus layers on healthy corals. After being deployed back on the reef, antibiotic-treated corals exhibited a major change in their community assembly within the first 24 h becoming more similar to that found in sediments and in aged mucus layers. Within the next days, their community became similar to the one of aged mucus layers and of unhealthy-looking colonies such as the control group during the aquaria incubation. This shift in the prokaryotic community happened concomitantly with an increase in bleaching and mortality. After 28 days, the only two surviving colonies harbored a community similar to that in new mucus. The control group, however, after suffering of necrosis and bleaching during aquarium incubation, rapidly regained a prokaryotic community similar to the original one and concurrently exhibited again a healthy appearance (Figure 4).
A jab against the use of antibiotics. This is an interesting find, with all the talks about the use antibiotics lately I think this would pique the interest of many. While in the closed aquarium system, the use of antibiotics was found to be quite useful during this short period of 8 days, however, upon their reintroduction to their wild habitat the antibiotic treated corals fared much worse than the control group which was not treated with antibiotics.
Antibiotic use could have potentially killed off certain bacteria with antiseptic properties which would've opened up the coral to secondary infections once reintroduced to the wild.
The implications of this could potentially become prevalent in our own closed systems as well.
Imagine someone who has an established system that has never/rarely treats with antibiotics, they then purchase from a vendor that heavily treats their corals with antibiotics the result could be increased mortality! This is just a thought, perhaps instead of relying on antibiotics, we should focus our research towards combating these pathogenic microbes with other probiotic microbes in the hopes for a more natural way to approach our issues. This could also provide much more long-term success too!
"Out of the prokaryotic families responsible for the divergence among treatment groups (SIMPER, Supplementary Table S13), Endozoicimonaceae was dominant in mucus (relative abundance up to 80%) of corals in their natural environment (Supplementary Figure S8). However, it decreased in relative abundance once corals suffered from bleaching and necrosis when kept in the aquaria but also in the reef. Within 24 h after re-introduction to the reef, the mucus of antibiotic-treated corals became dominated by Verrucomicrobiaceae (35.9%±20.2%) and Vibrionaceae (13.5%±14.7%). Within the next days, Rhodobacteraceae, Oceanospirillaceae, Vibrionaceae, Flammeovirgaceae, Verrucomicrobiaceae and Colwelliaceae dominated the mucus of antibiotic-treated colonies. Mucus of the control group became evenly colonized by various prokaryotic families such as Verrucomicrobiaceae, Vibrionaceae, Rhodobacteraceae, Alteromonadaceae, Colwelliaceae, Pelagibacteraceae and Synechococceae (Supplementary Figure S8). Archaea did not contribute to significant community variation and showed very low relative abundance in mucus throughout the disturbance experiment (overall 1.25%±4.28%) with the exception of two samples collected at the end of the antibiotic treatment (34.33% and 17.48%, respectively; Supplementary Figure S11)."
Endozoicimonaceae!!!!! Could these be our superheroes??? Here is another recent paper discussing Endozoicimonaceae.
Endozoicomonas are prevalent, abundant bacterial associates of marine animals, including corals. Their role in holobiont health and functioning, however, remains poorly understood. To identify potential interactions within the coral holobiont, we characterized the novel isolate Endozoicomonas...
www.nature.com
"Endozoicomonas 6c has a large genome size, high metabolic diversity, and is culturable. Together with the existence of free-living stages of bacteria in the genus Endozoicomonas [35], this suggests that no genome streamlining has occurred [32], and that Endozoicomonas 6c is not an obligate, fully host-restricted coral-bacterial symbiont."
"The novel E. marisrubri 6c appears to be less similar to E. acroporae, an Endozoicomonasisolated from an unknown species of Acropora collected from the coast of southern Taiwan [52], and is placed in a separate clade of Endozoicomonas by phylogenomic analysis (Fig. 2A). This observation suggests complex patterns of host-symbiont species co-diversification, geographical adaptation (i.e., Acropora hosts might harbor geographically distinct Endozoicomonas, as previously proposed for the coral genus Stylophora [9]), and/or could reflect environmental acquisition of Endozoicomonas, as suggested previously [9, 13]."
"at present we do not know the exact location of E. marisrubri 6c in the coral host. Characterization of their particular niche within the intact symbiosis will help further elucidate their roles, functionality, and interactome in the coral holobiont."
"The differential expression of genes associated with amino acid metabolism suggests that E. marisrubri 6c may have responded to amino acids and their precursors in the host tissue extract (refer to Fig. 4A and Supplementary Table S6a). While further studies in hospite are required, this suggests that E. marisrubri 6c may be able to respond to changes in holobiont amino acid availability. Amino acids contribute to a “currency” of interactions within a holobiont regulated by nitrogen limitation [18, 105,106,107]. For instance, Symbiodiniaceae may translocate a fraction of the amino acids they metabolize to the host [108,109,110,111,112]. Further, bacteria have been proposed as sources and sinks of amino acids within the coral holobiont [13, 37, 86], and use amino acids as cues to locate and “home in” on a suitable host with which to establish symbiosis [113, 114]."
"The increase in abundance of proteins related to B vitamin biosynthesis by E. marisrubri 6c in response to host tissue extract is of particular interest. Animals and most algae, including dinoflagellates, are auxotrophic for B vitamins, and must therefore acquire them from their diet or bacterial symbionts [37, 115,116,117,118,119]. Endozoicomonas, including E. marisrubri6c, harbor biosynthetic gene clusters for different B vitamins [13, 14], and the clusters for vitamin B1 and B6 biosynthesis are present across all screened genomes (Fig. 2B). Therefore, it may well be possible that Endozoicomonas contribute to both the coral host’s and algal symbionts’ metabolic requirement for B vitamins, which in the specific case of E. marisrubri6c includes vitamins B1, B6, and potentially B7 (as reflected in biotin synthase bioB protein abundance trending upwards in the proteome; Supplementary Results and Discussion, Supplementary Table S6b). These B vitamins are essential coenzymes involved in basic cellular processes. These include energy production and central metabolism, in particular carbon assimilation, respiration, and primary carbohydrate metabolism (vitamin B1), amino acid metabolism (vitamin B6), carboxylases involved in fatty acid biosynthesis, gluconeogenesis, amino acid and fatty acid degradation (vitamin B7), and osmolyte and antioxidant production (vitamin B1) [118, 120, 121]. Vitamin B1 is known as a component of stress responses of autotrophs, in particular in the context of plant disease resistance, stress tolerance, and crop yield [120]."
"In this study we cannot currently quantify vitamin B production, discriminate whether E. marisrubri 6c (or other Endozoicomonas) channels its entire vitamin B pool into its own metabolic processes, or whether translocation to the host and/or algal symbiont compartment occurs"
Endozoicomonas bacteria are emerging as extremely diverse and flexible symbionts of numerous marine hosts inhabiting oceans worldwide. Their hosts range from simple invertebrate species, such as sponges and corals, to complex vertebrates, such as fish. ...
www.ncbi.nlm.nih.gov
Another paper discussing Endozoicimonaceae.
"Although no quantitative methods have been applied to Endozoicomonas, trends in cell abundance have been inferred from SSU rRNA gene sequence abundances. These studies have linked the abundance of Endozoicomonas to the abundance of its coral host. For example, when the fungid coral Ctenactis echinatagrew in its preferred Red Sea habitat, Endozoicomonas symbionts were more abundant than in habitats of degraded quality (Roder et al. 2015). Moreover, reduced abundances of the corals Acropora millepora and Porites cylindrica near carbon dioxide seeps in Papua New Guinea coincided with a 50 % reduction in Endozoicomonas symbionts (Morrow et al. 2015). Anthropogenic pollution can similarly decrease the abundance of Endozoicomonas bacteria. Near the large Red Sea city of Jeddah, the corals P. verrucosa and Acropora hemprichii contained a lower proportion of Endozoicomonas compared to corals further afield (Ziegler et al. 2016). In addition, bleaching of the coral A. millepora on the Great Barrier Reef induced a shift from Endozoicomonas-like symbionts to a Vibrio-dominated community (Bourne et al. 2008). Lesioned P. astreoides colonies also contained reduced Endozoicomonas sequence abundances, compared to non-lesioned colonies (Meyer et al. 2014). These studies suggest that Endozoicomonas bacteria are part of a healthy coral microbiome and reductions in their abundance may indicate unfavourable environmental conditions."
"In addition to nutrient cycling, Endozoicomonas-related members may also play a role in regulating bacterial colonization of the animal host via the production of bioactive secondary metabolites or probiotic mechanisms, such as competitive exclusion of pathogenic bacteria (Bayer et al. 2013b; Jessen et al. 2013; Rua et al. 2014; Morrow et al. 2015). Moreover, the loss of Endozoicomonas is often characteristic of corals with lesions, signs of disease, or if they are living in eutrophicated, warm, or acidic environments. Therefore, the abundance of Endozoicomonas seems to be linked with healthy colonies of diverse coral species (Morrow et al. 2012; Bayer et al. 2013b; Roder et al. 2015; Morrow et al. 2015; Ziegler et al. 2016)."
"Importantly, Neave, Michell, Apprill and Voolstra (Endozoicomonas genomes reveals functional adaptation and plasticity in bacterial strains symbiotically associated with diverse marine hosts, Submitted) comparatively analysed the genomes of E. elysicola, E. montiporae, E. numazuensis, and four newly sequenced Endozoicomonas strains from the Red Sea corals S. pistillata, P. verrucosa, and Acropora humilis and found a high proportion of transposable elements in the Endozoicomonas genomes, further implying that Endozoicomonas use these elements to rapidly evolve to new hosts or niches. In addition, the Endozoicomonas genomes were enriched for carbon sugar transport and protein secretion, suggesting that they contribute to carbohydrate cycling and delivery to their host organism (Neave, Michell, Apprill and Voolstra, Endozoicomonas genomes reveals functional adaptation and plasticity in bacterial strains symbiotically associated with diverse marine hosts, Submitted). The common denominator among Endozoicomonas genome projects is the high incidence of transposable elements incorporated into their genomes, possibly allowing for rapid adaptation."
Another paper on
Endozoicomonas.
The coral-associated Endozoicomonas are dominant bacteria in the coral holobiont. Their relative abundance usually decreases with heat-induced coral bleaching and is proposed to be positively correlated with Symbiodiniaceae abundance. It remains unclear whether this phenomenon of decreased...
www.frontiersin.org
"Our results contradict the hypothesis, and demonstrate that the abundance of
Endozoicomonas is not dependent on Symbiodiniaceae density."
"Overall, bacterial communities differed between coral and seawater samples (ANOSIM, R = 0.907, p < 0.001; Supplementary Figure S4A). Regarding order-level variation in the bacterial composition between all coral and seawater samples, Altermonadales and Rhodobacterales were dominant (29.2 and 27.0% of the relative abundance, respectively) in seawater samples, whereas Oceanospirillales was dominant in coral samples (59.3%; Supplementary Figure S4B). In addition, 98.3% of Oceanospirillales sequences in coral samples belonged to Endozoicomonas."
"This study demonstrated that the abundance of total bacteria and Endozoicomonas is stable and high in living bleached corals for 3 months."
"Many studies have shown that Symbiodiniaceae and Endozoicomonas abundances decrease during coral bleaching, but these corals were all under heat stress (Bourne et al., 2008; Bayer et al., 2013; Neave et al., 2017; Supplementary Figures S6, S7)."
"Symbiodiniaceae and Endozoicomonas were found to be independent on two previous occasions. Shiu et al. (2017) reported high densities of Symbiodiniaceae but a low abundance of Endozoicomonasunder cold stress, and Pogoreutz et al. (2018) showed low densities of Symbiodiniaceae but a high relative Endozoicomonas abundance under excessive nutrient treatment. A decrease in Endozoicomonas is therefore suggested to occur when corals are under temperature stress, either hot or cold, regardless of whether the coral is bleached. It is therefore suggested that the majority of Endozoicomonas strains are sensitive to temperature stress outside this optimal range."
Another interesting paper about the bacterial communities of coral mucus.
The role of microorganisms in coral health, disease, and nutrition has been demonstrated in various studies. Environmental factors including pH, temperature, and dissolved oxygen also play crucial roles in maintaining sustainable coral ecosystems. However, how geographical and environmental...
www.mdpi.com
