Mueller, R. S. | Search bioRxiv

bioRxiv2022

A marine probiotic treatment against the bacterial pathogen Vibrio coralliilyticus to improve the performance of Pacific (Crassostrea gigas) and Kumamoto (C. sikamea) oyster larvae

Oyster larvae reared in hatcheries on the U.S. West coast often experience severe Vibrio coralliilyticus-related mortalities early in their development. Current treatment options for these molluscs are either not available or feasible; however, for decades, probiotics have been successfully used in finfish and crustacean shellfish culture. Consequently, the objectives of this work were to 1) isolate marine bacteria from oysters and evaluate their protective activity against Vibrio coralliilyticus infection of Pacific oyster (Crassostrea gigas) larvae, and 2) to determine the long-term effects of probiotic additions on growth and metamorphosis of larval Pacific and Kumamoto oysters (C. sikamea). A combination of three probiotic strains applied once 24 hours post-fertilization was more effective in improving survival of larval C. gigas exposed to lethal concentrations of V. coralliilyticus strain RE22, compared with separate additions of individual probiotics. In addition, a single application of the probiotic combination to one-day-old larvae increased the larval metamorphosis success of C. sikamea and both the Midori and Myiagi stocks of C. gigas. These results suggest that probiotics are effective at preventing bacterial infections and can significantly improve performance of oyster larvae, using a single application early in their development. Highlights* A combination of marine bacteria improved survival of Pacific oyster larvae exposed to virulent V. coralliilyticus. * Metamorphosis was increased after adding a single dose of probiotics to one-day-old larvae. * Repetitive dosing after each water change was not superior to a single dose one day post egg-fertilization. * A single dose of the probiotic combination resulted in larger size on day 12.

microbiology↗

bioRxiv2020

Recovery and Community Succession of the Zostera marina Rhizobiome After Transplantation

Seagrasses can form mutualisms with their microbiomes that facilitate the exchange of energy sources, nutrients, and hormones, and ultimately impact plant stress resistance. Little is known about community succession within the belowground seagrass microbiome after disturbance and its potential role in the plants recovery after transplantation. We transplanted Zostera marina shoots with and without an intact rhizosphere and cultivated plants for four weeks while characterizing microbiome recovery and effects on plant traits. Rhizosphere and root microbiomes were compositionally distinct, likely representing discrete microbial niches. Furthermore, microbiomes of washed transplants were initially different from those of sod transplants, and recovered to resemble an undisturbed state within fourteen days. Conspicuously, changes in microbial communities of washed transplants corresponded with changes in rhizosphere sediment mass and root biomass, highlighting the strength and responsive nature of the relationship between plants, their microbiome, and the environment. Potential mutualistic microbes that were enriched over time include those that function in the cycling and turnover of sulfur, nitrogen, and plant-derived carbon in the rhizosphere environment. These findings highlight the importance and resiliency of the seagrass microbiome after disturbance. Consideration of the microbiome will have meaningful implications on habitat restoration practices. ImportanceSeagrasses are important coastal species that are declining globally, and transplantation can be used to combat these declines. However, the bacterial communities associated with seagrass rhizospheres and roots (the microbiome) are often disturbed or removed completely prior to transplantation. The seagrass microbiome benefits seagrasses through metabolite, nutrient, and phytohormone exchange, and contributes to the ecosystem services of seagrass meadows by cycling sulfur, nitrogen, and carbon. This experiment aimed to characterize the importance and resilience of the seagrass belowground microbiome by transplanting Zostera marina with and without intact rhizospheres and tracking microbiome and plant morphological recovery over four weeks. We found the seagrass microbiome to be resilient to transplantation disturbance, recovering after fourteen days. Additionally, microbiome recovery was linked with seagrass morphology, coinciding with increases in rhizosphere sediment mass and root biomass. Results of this study can be used to include microbiome responses in informing future restoration work.

microbiology↗