Despite their diversity and ecological importance, many areas of the SAR-Stramenopila, Alveolata, and Rhizaria-clade are poorly understood as the majority (90%) of SAR species lack molecular data and only 5% of species are from well-sampled families. Here, we review and summarize the state of knowledge about the three major clades of SAR, describing the diversity within each clade and identifying synapomorphies when possible. We also assess the "dark area" of SAR: the morphologically described species that are missing molecular data. The majority of molecular data for SAR lineages are characterized from marine samples and vertebrate hosts, highlighting the need for additional research effort in areas such as freshwater and terrestrial habitats and "non-vertebrate" hosts. We also describe the paucity of data on the biogeography of SAR species, and point to opportunities to illuminate diversity in this major eukaryotic clade. See also the video abstract here: https://youtu.be/_VUXqaX19Rw.
Transmission plays a key role in the evolution of symbiosis. Mixed mode transmission combines horizontal and vertical mechanisms for symbiont acquisition. However, features that enable mixed transmission are poorly understood. Here, we determine the mechanistic basis for the recruitment of the beneficial bacterium, Aeromonas veronii by the leech, Hirudo verbana. We demonstrate that host mucosal secretions complement imperfect symbiont vertical transmission. First, we show that the A. veronii population within secretions originates from the host digestive tract and proliferates synchronously with shedding frequency, demonstrating the coupling of partner biology. Furthermore, leeches are attracted to these castings with oral contact proving sufficient for symbiont transmission. Leech attraction to mucus is not affected by the symbiont state of either the host or mucus, suggesting that A. veronii exploits preexisting host behavior and physiological traits. A dual transmission mode, integrating multiple layers of host contributions, may prove evolutionarily advantageous for a wide range of symbioses. Using such a strategy, host infection is ensured, while also providing access to a higher genetic diversity of symbionts. Countless host-associated microbes exhibit mixed mode transmission, supporting the use of the leech symbiosis as a model for enhancing our understanding of the specificity, establishment and persistence of microbiotas.
Sodalis glossinidius is a facultative intracellular bacterium that is a secondary symbiont of the tsetse fly (Diptera: Glossinidae). Since studies with other facultative intracellular bacteria have shown that high-affinity iron acquisition genes are upregulated in vivo, we investigated the regulation of several Sodalis genes that encode putative iron acquisition systems. These genes, SG1538 (hemT) and SG1516 (sitA), are homologous to genes encoding periplasmic heme and iron/manganese transporters, respectively. hemT promoter-and sitA promoter-gfp fusions were constructed, and in both Escherichia coli and Sodalis backgrounds, expression levels of these fusions were higher when the bacteria were grown in iron-limiting media than when the bacteria were grown in iron-replete media. The Sodalis promoters were tested for iron regulation in an E. coli strain that lacks the fur gene, which encodes the iron-responsive transcriptional repressor Fur. Expression of the promoter-gfp fusions in the E. coli fur mutant was constitutively high in both iron-replete and iron-deplete media, and addition of either Shigella flexneri fur or Sodalis fur to a plasmid restored normal regulation. A Sodalis fur mutant was constructed by intron mutagenesis, and semiquantitative reverse transcription-PCR (RT-PCR) showed that iron repression of sitA expression was also abolished in this strain. In vivo expression analysis showed that hemT and sitA are expressed when Sodalis is within tsetse fly hosts, suggesting a biological role for these genes when Sodalis is within the tsetse fly.
Microbial transmission through mucosal-mediated mechanisms is widespread throughout the animal kingdom. One example of this occurs with Hirudo verbana, the medicinal leech, where host attraction to shed conspecific mucus facilitates horizontal transmission of a predominant gut symbiont, the Gammaproteobacterium Aeromonas veronii. However, whether this mucus may harbor other bacteria has not been examined. Here, we characterize the microbiota of shed leech mucus through Illumina deep sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. Additionally, Restriction Fragment Length Polymorphism (RFLP) typing with subsequent Sanger Sequencing of a 16S rRNA gene clone library provided qualitative confirmation of the microbial composition. Phylogenetic analyses of full-length 16S rRNA sequences were performed to examine microbial taxonomic distribution. Analyses using both technologies indicate the dominance of the Bacteroidetes and Proteobacteria phyla within the mucus microbiota. We determined the presence of other previously described leech symbionts, in addition to a number of putative novel leech-associated bacteria. A second predominant gut symbiont, the Rikenella-like bacteria, was also identified within mucus and exhibited similar population dynamics to A. veronii, suggesting persistence in syntrophy beyond the gut. Interestingly, the most abundant bacterial genus belonged to Pedobacter, which includes members capable of producing heparinase, an enzyme that degrades the anticoagulant, heparin. Additionally, bacteria associated with denitrification and sulfate cycling were observed, indicating an abundance of these anions within mucus, likely originating from the leech excretory system. A diverse microbiota harbored within shed mucus has significant potential implications for the evolution of microbiomes, including opportunities for gene transfer and utility in host capture of a diverse group of symbionts.
Seaweeds have been consumed by billions of people around the world and are increasingly popular in United States (US) diets. Some seaweed species have been associated with adverse health effectssuch as heavy metal toxicityand higher priced seaweeds may be more prone to adulteration. Knowing which species of seaweeds are being marketed in the US is important for protecting human health and preventing economic adulteration. Therefore, the United States Food and Drug Administration is developing new DNA-based species identification tools to complement established chemical methods for verifying the accurate labeling of products. Here, seaweed products available in the United States were surveyed using a tiered approach to evaluate a variety of DNA extraction techniques followed by traditional DNA barcoding via Sanger sequencing; if needed, genome skimming of total extracted nuclear DNA via next-generation sequencing was performed. This two-tiered approach of DNA barcoding and genome skimming could identify most seaweed samples (41/46), even those in blends (2/2, 1 out of 3 labeled species in each). Only two commercial samples appeared to be mislabeled or to contain unintended algal species. Five samples, labeled as "hijiki" or "arame", could not be confirmed by these DNA-based identification methods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.