Biology subjects

Deignan, L. K.

Publications and source records attributed to Deignan, L. K..

3 recordsLinked to original sources

bioRxiv2026

Successful coral microbiome transplant from high to low heat tolerant corals requires antibiotic pretreatment

Microbiome transplantation, used to treat human disease, can enhance thermal and pathogen resilience in bleaching-susceptible corals via coral microbiome transplantation (CMT), though success is donor- and recipient-dependent. In this study, less thermally tolerant Pachyseris speciosa fragments were exposed to ciprofloxacin or an antibiotic cocktail for 24 h, then received CMT from the thermally tolerant Acropora millepora from Singapore's turbid reef system. Alpha diversity increased only in antibiotic-treated, CMT fragments, demonstrating that antibiotic-induced dysbiosis enhanced bacterial uptake. Coral microbiome assemblage shifted significantly at 1 and 10 d, regardless of antibiotic treatment or Acropora inoculum. Antibiotic-induced dysbiosis did not enhance uptake of donor's core ASVs (e.g., Endozoicomonas spp.). However, early uptake favoured potential pathogens like Vibrio spp., while longer inoculation allowed for uptake of unculturable environmental taxa. Our approach of using antibiotic pretreatment followed by whole microbiome transplant parallels human faecal microbiota transplantation to restore gut health.

microbiology↗

bioRxiv2026

Contact- and diffusion-based allelopathic interaction of a seaweed with coral holobionts

Shifts from coral-dominated to macroalgal-dominated reef systems have become increasingly common in many coastal regions worldwide. Coral-macroalgal interactions have been shown to be generally detrimental to coral health, with macroalgal allelopathic compounds able to exert serious and even lethal effects on coral at various stages of growth and development. Previous studies have shown that the coral-associated microbial communities play important roles in coral health and mitigating external environmental stress, including macroalgal contact stress. However, it remains unclear whether changes in the coral microbiome have an influence on the Symbiodiniaceae community composition, and if such changes subsequently affect coral health. In this study, we examined changes in both the coral microbiome and the Symbiodiniaceae communities of two Singaporean coral species (Pocillopora acuta and Merulina ampliata) when exposed to both direct and water-mediated macroalgal contact with Lobophora sp. This was investigated using 16S rRNA gene amplicon sequencing to characterize the coral microbiome, and ITS2 variable region sequencing to profile the Symbiodiniaceae communities. Although no significant differences were observed for the coral microbiomes and Symbiodiniaceae communities at both alpha-and beta- diversity levels between control and macroalgal contact treated fragments within each coral species, inter-colony variations in responses to macroalgal contact were observed for both the coral microbiome and Symbiodiniaceae communities of M. ampliata. These results suggest that coral colonies vary in the mechanisms that allow mitigation of the effects of macroalgal contact, and in their resilience to macroalgal-induced stress.

ecology↗

bioRxiv2026

A beneficial megaplasmid transforms an opportunistic bacterial pathogen to benefit coral by extending their thermal range

Resilient turbid coral reefs, found 1{degrees} north of the equator, experience fewer and less intense bleaching events despite being situated within the worlds busiest shipping port in highly urbanised Singapore. We hypothesised that bacteria within the coral holobiont play a role in maintaining coral diversity within this extreme environment by conferring traits that enhance host tolerance. Eleven Pseudovibrio isolates, whose genomes differ by only four SNPs, were isolated from the scleractinian coral Pachyseris speciosa. A [~]490 kbp megaplasmid (pCJH) was found in 7 of the 11 Pseudovibrio isolates. This study identified an opportunistic Pseudovibrio sp. pathogen of P. speciosa, accelerating bleaching disease. However, presence of the megaplasmid alters the ecological strategy of Pseudovibrio sp. toward mutualism, delaying coral bleaching. The megaplasmid enhances Pseudovibrios host colonisation and establishment of symbiosis through increased attachment and extends its bioactive genetic potential, but reduces fecundity. The Pseudovibrio genomes and megaplasmid encode several diffusible antibiotic biosynthetic gene clusters and contact-dependent inhibition mechanisms, with both types of inhibitory activity shown against local (i.e. P. speciosa) and type-strain Vibrio spp. Interaction analyses in experimentally heat-stressed corals revealed negative associations between Pseudovibrio and Vibrio ASVs corresponding to these cultured isolates. They also showed increased coral thermal tolerance by a full degree (1{degrees}C) when it is associated with the megaplasmid-bearing strain. Together, these findings support the Coral Probiotic Hypothesis that bacteria enhance coral resilience through chemical defense and identifies additional aspects to this symbiosis by a mobile genetic element which could play an important role in coral reef resilience.

microbiology↗