Biology subjects

Speare, L.

Publications and source records attributed to Speare, L..

3 recordsLinked to original sources

bioRxiv2023

Nutrient enrichment alters gene expression in 'Ca.' Aquarickettsia rohweri, promoting parasite expansion and horizontal transmission

Ocean warming, disease, and pollution contributed to global declines in coral abundances and diversity. In the Caribbean, corals previously dominated reefs, providing an architectural framework for diverse ecological habitats, but have significantly declined due to infectious microbial disease. Key species like coral Acropora cervicornis, are now considered critically endangered, prompting researchers to focus on scientific endeavors to identify factors that influence coral disease resistance and resilience. We previously showed that disease susceptibility, growth rates, and bleaching risk were all associated with the abundance of a single bacterial parasite, Ca. Aquarickettsia rohweri which proliferates in vivo under nutrient enrichment. Yet how nutrients influence parasite physiology and life history strategies within its host are unknown. We performed microscopy and transcriptomic analyses of Ca. A. rohweri populations during a 6-week nutrient exposure experiment. Microscopy showed that this parasite was abundant in coral tissue and densely packed in mucocytes prior to nutrient enrichment. Ca. A. rohweri energy scavenging genes and those potentially involved in this habitat transition are significantly upregulated during enrichment. Specifically, transcripts involved in signaling, virulence, two-component systems, and nutrient import genes are elevated under higher nutrients. These data support the predicted role of Ca. A. rohweri as a highly active nutrient-responsive A. cervicornis parasite, and provide a glimpse at the mechanism of induced disease susceptibility while implicating nutrient exposure in its horizontal transmission. SignificanceThe coral disease crisis has contributed to global declines in coral abundance and diversity and is exacerbated by environmental stressors like eutrophication. Thus, identifying factors that influence coral disease resistance and resilience is a top priority. The Rickettsiales-like bacterium, Candidatus Aquarickettsia rohweri is ubiquitous coral symbiont that is strongly linked to coral disease susceptibility in staghorn coral, and is undergoing positive selection across the Caribbean. Although Ca. A. rohweri is a putative parasite, little is known about the activity of this bacterium in coral tissue. This work supports the role of Ca. A. rohweri as a highly active, nutrient-responsive parasite and proposes a mechanism for how Ca. A. rohweri contributes to coral disease susceptibility, parasite expansion, and horizontal transmission.

microbiology↗

bioRxiv2022

Cultivation and Fluorescent in situ hybridization suggest that some shipworm species acquire endosymbiotic bacteria through indirect horizontal transmission

Beneficial microbial symbionts provide essential functions for their host from nutrients to defense against disease. Whether hosts acquire their symbionts directly from parents (vertical transmission) or by sampling from the environment (horizontal transmission) can have dramatic impacts on host adaptability and, in the case of ecosystem engineers, ecosystem health. Wood-boring bivalve mollusks (Teredinidae shipworms) act as ecosystem engineers in marine environments, creating habitat out of submerged wood for fish and invertebrates. Essential to shipworm success is their community of endosymbiotic gill bacteria that produce the enzymes necessary for wood digestion. How shipworms acquire their symbionts, however, remains largely unexplored. Using culturing, fluorescence in-situ hybridization, confocal microscopy, and tank experiments, we provide evidence suggesting the mode of symbiont transmission the shipworms for either the shipworm, Lyrodus pedicellatus or Teredo bartschi or both. Symbiotic bacteria were not detected by cultivation or microscopy in brooding larvae within gravid adults or as veliger larvae collected from the water column, but were observed in adult specimens and juveniles that had begun burrowing into wood. These data suggest that the specimens examined have both aposymbiotic and symbiotic life phases and acquire their symbionts through indirect horizontal transmission. Our findings reveal how the long-term brooders L. pedicellatus and/or T. bartschi acquire their gill endosymbionts. IMPORTANCEHow eukaryotic hosts acquire their microbial symbionts can have significant consequences for their ability to adapt to varied environments. Although wood-boring bivalve shipworms have diverse reproductive strategies and are found in unique environments across the globe, little is known about how they transmit their essential gill endosymbionts. We used the closely related shipworms, Lyrodus pedicellatus and/or Teredo bartschi to study how these long-term brooding shipworms acquire their gill endosymbionts. Our work, unlike previous claims for the broadcast spawning species Bankia setacae which reportedly transmits its symbionts directly from parent to offspring, suggests that juvenile L. pedicellatus and/or T. bartschi acquire their symbionts through horizontal transmission rather than directly from their parents. This work reveals the mechanism by which some brooding shipworm species acquire their symbionts, adding to our limited understanding of intracellular symbiont transmission of Teredinidae.

microbiology↗

bioRxiv2021

A large lipoprotein mediates target specificity for T6SS-dependent killing

Interbacterial competition is prevalent in host-associated microbiota, where it can shape community structure and function, impacting host health in both positive and negative ways. However, the factors that permit bacteria to discriminate among their various neighbors for targeted elimination of competitors remain elusive. We identified a specificity factor in Vibrio species that is used to target specific competitors for elimination. Here, we describe this specificity factor, which is associated with the broadly-distributed type VI secretion system (T6SS), by studying symbiotic Vibrio fischeri, which use the T6SS to compete for colonization sites in their squid host. We demonstrate that a large lipoprotein (TasL) allows V. fischeri cells to restrict T6SS-dependent killing to certain genotypes by selectively integrating competitor cells into aggregates while excluding other cell types. TasL is also required for T6SS-dependent competition within juvenile squid, indicating the adhesion factor is active in the host. Because TasL homologs are found in other host-associated bacterial species, this newly-described specificity factor has the potential to impact microbiome structure within diverse hosts.

microbiology↗