Biology subjects

Case, R. J.

Publications and source records attributed to Case, R. J..

5 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↗

bioRxiv2026

Uncoupling of seagrass host selection and succession for microbial guilds in meadow chronosequence

Succession is an ecosystem building process in which a habitat and its community interact predictably by increasing diversity, habitat engineering, and ultimately reaching a climax community, where other ecological processes influence its dynamic. Key to succession is the establishment of primary producing habitat forming species, which drives niche differentiation leading to increasing diversity. Here, we use the primary colonizing and habitat forming seagrass, Halophila ovalis, to demonstrate that it drives bacterial succession in a meadow ecosystem, and its microbiome, both rhizoplane and phylloplane, are under host selection. Many of the characteristics attributed to plants for habitat modification are microbial processes such as nitrogen fixation and sulfide detoxification and succession is often extrapolated to such processes. To determine if succession (increasing diversity) or selection (reducing diversity) drives changes in diversity (16S rRNA gene) or habitat modifying processes (nifH, soxB, aprA, dsrA), molecular analysis was performed along chronosequences (as a proxy for succession) of seagrass patches. Bacterial communities were sampled within the meadow ecosystem and the microbiomes of H. ovalis (both rhizoplane and phylloplane). Genes involved in biogeochemical cycling are differentially impacted within the microbiome and meadow sediments, with only nifH under succession. All genes from all niches sampled for community analysis are under directional community trajectories, despite being subjected to distinct ecological processes, signifying that many ecological processes, including succession and host association, drive community assemblage.

ecology↗

bioRxiv2021

Global Metabolome Analysis of Dunaliella tertiolecta, Phaeobacter italicus R11 Co-cultures using Thermal Desoprtion - Comprehensive Two-dimensional Gas Chromatography - Time-of-Flight Mass Spectrometry

Dunaliella tertiolecta is a marine microalgae that has been studied extensively as a potential carbon-neutral biofuel source [1]. Microalgae oil contains high quantities of energy-rich fatty acids and lipids, but is not yet commercially viable as an alternative fuel. Carefully optimised growth conditions, and more recently, algal-bacterial co-cultures have been explored as a way of improving the yield of Dunaliella tertiolecta microalgae oils. The relationship between the host microalgae and bacterial co-cultures is currently poorly understood. Here, a complete workflow is proposed to analyse the global metabolomic profile of co-cultured Dunaliella tertiolectra and Phaeobacter italicus R11, which will enable researchers to explore the chemical nature of this relationship in more detail. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=88 SRC="FIGDIR/small/461748v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@18c3cb0org.highwire.dtl.DTLVardef@1e48735org.highwire.dtl.DTLVardef@68a98borg.highwire.dtl.DTLVardef@15306bc_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIA method for direct microalgae sample introduction is proposed. C_LIO_LIAdvanced chemometric tools can extract, useful and discriminating metabolomic features even from very noisy complex datasets. C_LI

plant biology↗