Delivering Beneficial Microorganisms for Corals: Rotifers as Carriers of Probiotic Bacteria.

Juliana M Assis,Raquel S Peixoto,Rafael F Valle,Igor Taveira,Adam Barno,Lone Høj,Rayssa Vieira,David G Bourne,Gustavo Duarte,Fernanda Abreu,Helena M D Villela

doi:10.3389/fmicb.2020.608506

Abstract

The use of Beneficial Microorganisms for Corals (BMCs) to increase the resistance of corals to environmental stress has proven to be effective in laboratory trials. Because direct inoculation of BMCs in larger tanks or in the field can be challenging, a delivery mechanism is needed for efficient transmission of the BMC consortium. Packaged delivery mechanisms have been successfully used to transmit probiotics to other organisms, including humans, lobsters, and fish. Here, we tested a method for utilizing rotifers of the species Brachionus plicatilis for delivery of BMCs to corals of the species Pocillopora damicornis. Epifluorescence microscopy combined with a live/dead cell staining assay was used to evaluate the viability of the BMCs and monitor their in vivo uptake by the rotifers. The rotifers efficiently ingested BMCs, which accumulated in the digestive system and on the body surface after 10 min of interaction. Scanning electron microscopy confirmed the adherence of BMCs to the rotifer surfaces. BMC-enriched rotifers were actively ingested by P. damicornis corals, indicating that this is a promising technique for administering coral probiotics in situ. Studies to track the delivery of probiotics through carriers such as B. plicatilis, and the provision or establishment of beneficial traits in corals are the next proof-of-concept research priorities.

Highlights

Coral reefs are increasingly impacted by global climate change, which raises the mean sea surface temperature (SST) and the incidence of marine heatwaves (Hughes et al, 2018)
The LIVE/DEAD bacterial assay was used to demonstrate that the members of the Beneficial Microorganisms for Corals (BMCs) consortium, containing five strains of Pseudoalteromonas spp., one of C. marina, and one of H. taeanensis (Supplementary Table 1), were viable prior to addition to the rotifer cultures (Figure 3)
We aimed to alter the internal microbiome of B. plicatilis to use this species of rotifer as a possible vector for delivery of specific beneficial bacteria to corals

Summary

Introduction

Coral reefs are increasingly impacted by global climate change, which raises the mean sea surface temperature (SST) and the incidence of marine heatwaves (Hughes et al, 2018). One promising approach is the manipulation of different coralassociated microbes to increase host resistance and resilience to stressors (Peixoto et al, 2017; National Academies of Sciences and Medicine, 2019). This strategy relies on key host– microbiome symbiotic relationships that can be exploited to increase the fitness of the coral holobiont (Peixoto et al, 2017; Pita et al, 2018; Wilkins et al, 2019). Taxonomic composition, and metabolic pathways of microbial communities associated with corals have been determined (Rohwer et al, 2001; Bourne and Munn, 2005; Sánchez-Quinto and Falcón, 2019), the selection and use of specific microorganisms as probiotics for corals on an ecologically relevant scale is a relatively new field of research (Teplitski and Ritchie, 2009; Santos et al, 2015; Peixoto et al, 2017; Damjanovic et al, 2019; Rosado et al, 2019)

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