Biology subjects

Klinges, J. G.

Publications and source records attributed to Klinges, J. G..

3 recordsLinked to original sources

bioRxiv2026

A dominant coral parasite, Candidatus Aquirickettsia rohweri, resists antibiotic exposure and thermal challenge below the bleaching threshold in disease-susceptible Acropora cervicornis

The critically endangered Caribbean staghorn coral Acropora cervicornis hosts microbiomes frequently dominated by the putatively parasitic intracellular bacterium Candidatus Aquirickettsia rohweri, which is associated with reduced coral growth and heightened disease susceptibility. Whether this dominance can be disrupted through antibiotic treatment and a sequential disturbance of thermal stress, remains unknown. In this study, we exposed disease-susceptible A. cervicornis fragments to broad-spectrum antibiotics, sub-bleaching thermal stress, or the combination of an antibiotic pre-treatment followed by thermal stress, and tracked changes in microbiome composition and diversity across all experimental phases using 16S rRNA amplicon sequencing and quantitative PCR (qPCR). We find that while the minor microbial fraction exhibits sustained compositional shifts in response to treatment, Ca. Aquirickettsia rohweri is resilient to antibiotic and thermal perturbation and may in fact increase in abundance following antibiotic exposure, suggesting that its dominance is actively maintained and not readily displaced by current disease mitigation strategies.These results indicate that antibiotic intervention is unlikely to be a viable strategy for disrupting Ca. A. rohweri dominance in disease-susceptible A. cervicornis, underscoring the urgency of understanding its transmission routes to inform microbiome rescue efforts.

microbiology↗

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↗

bioRxiv2021

The coral symbiont Candidatus Aquarickettsia is variably abundant in threatened Caribbean acroporids and transmitted horizontally.

The aquatic symbiont "Candidatus Aquarickettsia rohweri" infects a diversity of non-bilaterian metazoan phyla. In the threatened coral Acropora cervicornis, Aquarickettsia proliferates in response to increased nutrient exposure, resulting in suppressed growth and increased disease susceptibility and mortality. This study evaluated the extent, as well as the ecology and evolution of Aquarickettsia infecting the Caribbean corals: Ac. cervicornis and Ac. palmata and their hybrid ( Ac. prolifera). The bacterial parasite Aquarickettsia was found in all acroporids, with host and sampling location impacting infection magnitude. Phylogenomic and genome-wide single nucleotide variant analysis found Aquarickettsia clustering by region, not by coral taxon. Fixation analysis suggested within coral colonies, Aquarickettsia are genetically isolated to the extent that reinfection is unlikely. Relative to other Rickettsiales, Aquarickettsia is undergoing positive selection, with Florida populations experiencing greater positive selection relative to the other Caribbean locations. This may be due to Aquarickettsia response to increased nutrient stress in Florida, as indicated by greater in situ replication rates in these corals. Aquarickettsia did not significantly codiversify with either coral animal nor algal symbiont, and qPCR analysis of gametes and juveniles from susceptible coral genotypes indicated absence in early life stages. Thus, despite being an obligate parasite, Aquarickettsia must be horizontally transmitted via coral mucocytes, an unidentified secondary host, or a yet unexplored environmentally mediated mechanism. Importantly, the prevalence of Aquarickettsia in Ac. cervicornis and high abundance in Florida populations suggests that disease mitigation efforts in the US and Caribbean should focus on preventing early infection via horizontal transmission.

microbiology↗