Microbial Communities Associated with Healthy and White Syndrome-Affected Echinopora lamellosa in Aquaria and Experimental Treatment with the Antibiotic Ampicillin

Abstract

Prokaryotic and ciliate communities of healthy and aquarium White Syndrome (WS)-affected coral fragments were screened using denaturing gradient gel electrophoresis (DGGE). A significant difference (R = 0.907, p < 0.001) in 16S rRNA prokaryotic diversity was found between healthy (H), sloughed tissue (ST), WS-affected (WSU) and antibiotic treated (WST) samples. Although 3 Vibrio spp were found in WS-affected samples, two of these species were eliminated following ampicillin treatment, yet lesions continued to advance, suggesting they play a minor or secondary role in the pathogenesis. The third Vibrio sp increased slightly in relative abundance in diseased samples and was abundant in non-diseased samples. Interestingly, a Tenacibaculum sp showed the greatest increase in relative abundance between healthy and WS-affected samples, demonstrating consistently high abundance across all WS-affected and treated samples, suggesting Tenacibaculum sp could be a more likely candidate for pathogenesis in this instance. In contrast to previous studies bacterial abundance did not vary significantly (ANOVA, F2, 6 = 1.000, p = 0.422) between H, ST, WSU or WST. Antimicrobial activity (assessed on Vibrio harveyi cultures) was limited in both H and WSU samples (8.1% ±8.2 and 8.0% ±2.5, respectively) and did not differ significantly (Kruskal-Wallis, χ2 (2) = 3.842, p = 0.146). A Philaster sp, a Cohnilembus sp and a Pseudokeronopsis sp. were present in all WS-affected samples, but not in healthy samples. The exact role of ciliates in WS is yet to be determined, but it is proposed that they are at least responsible for the neat lesion boundary observed in the disease.

Identification of quorum sensing-regulated Vibrio fortis as potential pathogenic bacteria for coral bleaching and the effects on the microbial shift

“…In addition, considering that the planktonic bacteria in the water could flow into the gastrovascular cavity of coral along with the filter feeding, the significantly increased abundance of Thalassobius (also detected with higher abundance in bleaching coral but with no significant difference) and Tenacibaculum in water might also affect the coral health (Figure 7). Thalassobius belonging to the family Rhodobacteraceae has been reported as a microbial bioindicator enriched in the Stony Coral Tissue Loss Disease accompanied by Vibrio (Becker et al, 2021), and has been associated with invertebrate diseases (Roder et al, 2014), while the increased abundance of Tenacibaculum was also consistent with the findings from microbial community shift in the White syndromeaffected Echinopora lamellosa in aquaria (Smith et al, 2015).…”

Antibiotics reduce Pocillopora coral‐associated bacteria diversity, decrease holobiont oxygen consumption and activate immune gene expression

“…While antibiotics treatment was successful in reducing bacterial community diversity and eliminating many transiently associated and presumably antibiotics‐susceptible bacteria, not all core bacteria were eliminated and several ASVs were observed to increase in relative abundance (Figure 3d, Table S6), despite the caveat that 16S rRNA gene amplicon sequencing data cannot distinguish whether these bacteria are still alive and metabolically active. These persistent ASVs included a single Vibrio ASV with 100% sequence similarity to the known coral pathogen V. harveyi , which could be driving the observed activation of coral immune responses through niche expansion and opportunistic infection following initial resistance to antibiotics (Luna et al, 2010; Meyer et al, 2015; Smith et al, 2015). Indeed, cultured Vibrio bacteria from Pocillopora corals have been shown to possess genomes encoding antibiotic resistance genes, virulence factors and quorum‐sensing inhibitors (Li et al, 2022; Ma et al, 2018), indicating the potential for pathogenesis following microbiome disruption.…”

“…Specifically, the positive correlation of the “lightyellow” and “orange” modules and negative correlation of the “brown” module with the antibiotics treatment indicate the existence of trade‐offs between the activation of cellular immune responses, such as interleukin signalling pathways and coagulation cascades (Poole & Weis, 2014) and cellular housekeeping functions, such as ATP production and cytoskeleton maintenance (Figures 4c,d and 5). These changes may be related to the increased relative abundance of opportunistic microbes such as Vibrio bacteria in the coral holobiont following antibiotics treatment (Figure 3d) because these bacteria are known coral pathogens (Ben‐Haim et al, 2003; Luna et al, 2010) that may possess antibiotics resistance genes and could shift to a pathogenic lifestyle following antibiotic disruption of the healthy community (Gao et al, 2021; Meyer et al, 2015; Smith et al, 2015). Prior studies implicated Alteromonas and Vibrio bacteria in driving dysbiosis following antibiotics treatment and heat stress in P. acuta and P. damicornis corals from Taiwan (Connelly et al, 2022) and while Alteromonas bacteria were reduced following the addition of ciprofloxacin in this study, several of the same key immune genes, including endoribonuclease ZC3H12B (pdam_00012426), ETS‐related transcription factor Elf‐4 (pdam_00016137) and ETS domain‐containing protein Elk‐1 (pdam_00003296), were upregulated following antibiotics treatment (Table S7).…”

Stability of a dominant sponge‐symbiont in spite of antibiotic‐induced microbiome disturbance

“…Few studies reported bacterial change in absolute numbers during dysbiosis. As one example, increases in absolute bacterial abundances were linked to disease in corals (Luna et al, 2010; Smith et al, 2015). Most other studies have so far relied on amplicon sequencing as a marker of relative community changes, although relative data alone can mask underlying community dynamics (Rao et al, 2021).…”