Massive algal proliferations known as Harmful Algal Blooms (HABs) represent one of the most important threats to coastal areas. Among them, the so-called Florida Red Tides (FRTs, caused by blooms of the dinoflagellate Karenia brevis and associated brevetoxins) are particularly detrimental in the southeastern U.S., causing high mortality rates and annual losses in excess of $40 million. The ability of marine organisms to cope with environmental stressors (including those produced during HABs) is influenced by genetic and epigenetic mechanisms, the latter resulting in phenotypic changes caused by heritable modifications in gene expression, without involving changes in the genetic (DNA) sequence. Yet, studies examining cause-effect relationships between environmental stressors, specific epigenetic mechanisms and subsequent responses are still lacking. The present work contributes to increase this knowledge by investigating the effects of Florida Red Tides on two types of mechanisms participating in the epigenetic memory of Eastern oysters: histone variants and DNA methylation. For that purpose, a HAB simulation was conducted in laboratory conditions, exposing oysters to increasing concentrations of K. brevis. The obtained results revealed, for the first time, the existence of H2A.X, H2A.Z and macroH2A genes in this organism, encoding histone variants potentially involved in the maintenance of genome integrity during responses to the genotoxic effect of brevetoxins. Additionally, an increase in H2A.X phosphorylation (γH2A.X, a marker of DNA damage) and a decrease in global DNA methylation were observed as the HAB simulation progressed. Overall, the present work provides a basis to better understand how epigenetic mechanisms participate in responses to environmental stress in marine invertebrates, opening new avenues to incorporate environmental epigenetics approaches into management and conservation programs.
Abstract(1) Background: Native microbiota represent a potential resource for biocontrol of arthropod vectors. Ixodes scapularis are mostly inhabited by the endosymbiotic Rickettsia buchneri, but the bacterial communty composition varies with life stage, fed status, and/or geographic location. We investigated sex-specific bacterial community diversity from I. scapularis collected from central Pennsylvania between populations within a small geographic range. (2) Methods: We sequenced the bacterial 16S rRNA genes from individuals and pooled samples and investigated the abundance or infection frequency of key taxa using taxon-specific PCR and/or qPCR. (3) Results: Bacterial communities were more diverse in pools of males than females. When R. buchneri was not the dominant taxon, Coxiellaceae was dominant. We determined that the infection frequency of Borrelia burgdorferi ranged between 20 to 75%. Titers of Anaplasma phagocytophilum were significantly different between sexes. High Rickettsiella titer in pools were likely due to a few heavily infected males. (4) Conclusion: Bacterial 16S sequencing is useful for establishing the baseline community diversity and focusing hypotheses for targeted experiments. However, care should be taken not to overinterpret data concerning microbial dominance between geographic locations based on a few individuals as this may not accurately represent the bacterial community within tick populations.
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