Towards enhancing coral heat tolerance: a \u201cmicrobiome transplantation\u201d treatment using inoculations of homogenized coral tissues

Roman Schroeder,Tipwimon Rattanawongwan,Talisa Doering,Marlene Wall,Ute Hentschel,Anna Roik,Lalita Putchim

doi:10.1186/s40168-021-01053-6

Roman Schroeder, Tipwimon Rattanawongwan + Show 5 more

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https://doi.org/10.1186/s40168-021-01053-6

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Abstract

BackgroundMicrobiome manipulation could enhance heat tolerance and help corals survive the pressures of ocean warming. We conducted coral microbiome transplantation (CMT) experiments using the reef-building corals, Pocillopora and Porites, and investigated whether this technique can benefit coral heat resistance while modifying the bacterial microbiome. Initially, heat-tolerant donors were identified in the wild. We then used fresh homogenates made from coral donor tissues to inoculate conspecific, heat-susceptible recipients and documented their bleaching responses and microbiomes by 16S rRNA gene metabarcoding.ResultsRecipients of both coral species bleached at lower rates compared to the control group when exposed to short-term heat stress (34 °C). One hundred twelve (Pocillopora sp.) and sixteen (Porites sp.) donor-specific bacterial species were identified in the microbiomes of recipients indicating transmission of bacteria. The amplicon sequence variants of the majority of these transmitted bacteria belonged to known, putatively symbiotic bacterial taxa of corals and were linked to the observed beneficial effect on the coral stress response. Microbiome dynamics in our experiments support the notion that microbiome community evenness and dominance of one or few bacterial species, rather than host-species identity, were drivers for microbiome stability in a holobiont context.ConclusionsOur results suggest that coral recipients likely favor the uptake of putative bacterial symbionts, recommending to include these taxonomic groups in future coral probiotics screening efforts. Our study suggests a scenario where these donor-specific bacterial symbionts might have been more efficient in supporting the recipients to resist heat stress compared to the native symbionts present in the control group. These findings urgently call for further experimental investigation of the mechanisms of action underlying the beneficial effect of CMT and for field-based long-term studies testing the persistence of the effect.AsHw_a2eZumNFLCqTFt1FJVideo abstract

Highlights

Reef-building corals are subjected to heat stress due to ocean warming
We present the results from two coral microbiome transplantation experiments with the underlying concept of using a fresh tissue homogenate of heat-tolerant donors from the wild, containing living microbiome communities, for the inoculation of heat-sensitive conspecifics to enhance their resilience under ocean warming (Fig. 1)
Approaches that investigate the probiotic potential of microbiome manipulation, such as several previous coral probiotic studies [30, 31, 67] and the coral microbiome transplantation (CMT) concept developed in our study (Fig. 1), are founded on the hypothesis that exposure of the holobiont to beneficial bacterial consortia can be applied to increase health and resilience

Summary

Introduction

Reef-building corals are subjected to heat stress due to ocean warming. Frequent heatwaves induce coral bleaching, the disruption of the symbiosis between the coral host and its dinoflagellate symbionts. Coral bleaching events that entail high mortality have increased over the last decades and are expected to intensify [1], which calls for interventions that can enhance coral resilience One such concept is “assisted evolution,” encompassing selective breeding of corals and the manipulation of coral-associated microbiome communities, like dinoflagellate symbionts and bacteria [2]. While we know that coral holobiont functioning relies on the supply of fixed carbon and several essential amino acids by dinoflagellate symbionts [7, 8], the roles of other holobiont members are still widely elusive [9] Among all those other holobiont members, coral-associated bacterial communities (in the following “the microbiome”) have been studied and characterized for the past two decades [10,11,12,13,14] and we learned that they likely support diverse metabolic processes of the holobiont [8, 15,16,17]. We used fresh homogenates made from coral donor tissues to inoculate conspecific, heat-susceptible recipients and documented their bleaching responses and microbiomes by 16S rRNA gene metabarcoding

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