Miracula polaris - A New Species of Miracula from the East Fjords of Iceland.

There is increasing evidence that holocarpic oomycetes, i.e., those converting their entire vegetative thallus into zoospores upon maturation, are a phylogenetically diverse group in both freshwater and marine ecosystems. Most of the known holocarpic oomycete species diverge before the main split of Peronosporomycetes and Saprolegniomycetes and are, thus, termed as early-diverging oomycetes. In environmental sequencing studies, it was revealed that of the early-diverging genera especially Sirolpidium, Miracula, and Diatomophthora are widespread. As in these studies especially the Arctic Ocean seemed to harbor many undiscovered species, sampling was conducted at the Blávík research station on Fáskrúðsfjörður in the East Fjords of Iceland, where there is both an influence from the Arctic Ocean and the North Atlantic. During the screening for infected diatoms, a parasitoid was found in the marine diatom genus Melosira, which is one of the most abundant genera in arctic ecosystems. Molecular phylogenetics and morphological characterization revealed that the parasitoid belonged to the genus Miracula and corresponded to one of the lineages previously found in single-cell sequencing. Thus, the current study both contributes to the knowledge of the genus Miracula and the increasing diversity of the genus suggests that the many linages found in environmental sequencing which can still not be associated with known species might represent actual species to be discovered in future studies.

Pontisma blauvikense sp. nov. the first member of the early-diverging oomycete genus Pontisma parasitizing brown algae.

Holocarpic oomycetes have been neglected over several decades, until interest in these organisms has recently resurged. One of the most widespread genera of holocarpic oomycetes is Pontisma, parasitic to red seaweeds throughout all oceans. Recently, the genus Sirolpidium (parasitic to green algae) was found to be congeneric with Pontisma. This hinted at a high pathogenic versatility and prompted the screening of other macroalgae on the coastline of Iceland. During this survey a parasite of the brown algae Pylaiella littoralis was found, which formed anisolpidium-like thalli, but produced biflagellate zoospores. Phylogenetic investigations revealed that the parasite was placed in the genus Pontisma. In reconstructions based on partial nrSSU sequences, it grouped with some sequences of parasitoids of the diatom genus Licmophora, but the more variable mitochondrial cox2 sequences were divergent. Based on phylogenetic evidence and the unique parasitism of brown algae, the parasitoid is described as Pontisma blauvikense in this study. Pontisma blauvikense is the fourth oomycete species parasitic to Pylaiella, which is also parasitised by Euychasma dicksonii and two Anisolpidium species. For a better understanding of the ecology and evolution of holocarpic oomycetes, further research is necessary to investigate the host spectrum of Pontisma in general and Pontisma blauvikense in particular.

Miracula einbuarlaekurica sp. nov., a new holocarpic endoparasitoid species from pennate freshwater diatoms in Iceland.

Holocarpic oomycetes infecting freshwater diatoms are obligate endobiotic parasites reported from a wide range of habitats. So far, the taxonomy of and phylogeny of most species remains unresolved, since most have not been reported throughout the past decades and sequence data are available for only the four species, Aphanomycopsis bacillariacearum, Diatomophthora gillii, Ectrogella bacillariacearum, and the recently-discovered species Miracula moenusica. In the current study, a new freshwater diatom parasite resembling Ectrogella bacillariacearum in the sense of Scherffel was discovered from pennate diatoms (Ulnaria acus, Ulnaria ulna) collected from the small stream Einbúalækur on Víkurskarð, North Iceland and investigated for its life cycle and phylogenetic placement. In contrast to the original description, Scherffel reports an achlya-like spore discharge for Ectrogella bacillariacearum. The phylogenetic reconstruction and morphological characterisation in this study revealed that Scherffel's E. bacillariacearum is largely unrelated to the epitype of the species and is a member of the early-diverging genus Miracula. Consequently, the new species is described as M. einbuarlaekurica in the present study. This adds a second freshwater member to the genus, demonstrating the high ecological adaptability of the genus, which thrives in both freshwater and marine ecosystems.

A New Marine Species of Miracula (Oomycota) Parasitic to Minidiscus sp. in Iceland†.

Obligate endoparasitic oomycetes are known to ubiquitously occur in marine and freshwater diatoms, but their diversity is still largely unexplored. Many of these parasitoids are members of the early-diverging oomycete lineages (Miracula, Diatomophthora), others are within the Leptomitales of the Saprolegniomycetes (Ectrogella, Lagenisma) and some have been described in the Peronosporomycetes (Aphanomycopsis, Lagenidium). Even though some species have been recently described and two new genera were introduced (Miracula and Diatomophthora), the phylogeny and taxonomy of most of these organisms remain unresolved. This is contrasted by the high number of sequences from unclassified species, as recently revealed from environmental sequencing, suggesting the presence of several undiscovered species. In this study, a new species of Miracula is reported from a marine centric diatom (Minidiscus sp.) isolated from Skagaströnd harbor in Northwest Iceland. The morphology and life cycle traits of this novel oomycete parasite are described herein, and its taxonomic placement within the genus Miracula is confirmed by molecular phylogeny. As it cannot be assigned to any previously described species, it is introduced as Miracula islandica in this study. The genus Miracula thus contains three described holocarpic species (M. helgolandica, M. islandica, M. moenusica) to which likely additional species will need to be added in the future, considering the presence of several lineages known only from environmental sequencing that clustered within the Miracula clade.

Author Correction: The oomycete Lagenisma coscinodisci hijacks host alkaloid synthesis during infection of a marine diatom.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Promoter Activation in Δhfq Mutants as an Efficient Tool for Specialized Metabolite Production Enabling Direct Bioactivity Testing.

Natural products (NPs) from microorganisms have been important sources for discovering new therapeutic and chemical entities. While their corresponding biosynthetic gene clusters (BGCs) can be easily identified by gene-sequence-similarity-based bioinformatics strategies, the actual access to these NPs for structure elucidation and bioactivity testing remains difficult. Deletion of the gene encoding the RNA chaperone, Hfq, results in strains losing the production of most NPs. By exchanging the native promoter of a desired BGC against an inducible promoter in Δhfq mutants, almost exclusive production of the corresponding NP from the targeted BGC in Photorhabdus, Xenorhabdus and Pseudomonas was observed including the production of several new NPs derived from previously uncharacterized non-ribosomal peptide synthetases (NRPS). This easyPACId approach (easy Promoter Activated Compound Identification) facilitates NP identification due to low interference from other NPs. Moreover, it allows direct bioactivity testing of supernatants containing secreted NPs, without laborious purification.

The oomycete Lagenisma coscinodisci hijacks host alkaloid synthesis during infection of a marine diatom.

Flagellated oomycetes frequently infect unicellular algae, thus limiting their proliferation. Here we show that the marine oomycete Lagenisma coscinodisci rewires the metabolome of the bloom-forming diatom Coscinodiscus granii, thereby promoting infection success. The algal alkaloids ß-carboline and 4-carboxy-2,3,4,9-tetrahydro-1H-ß-carboline are induced during infection. Single-cell profiling with AP-MALDI-MS and confocal laser scanning microscopy reveals that algal carbolines accumulate in the reproductive form of the parasite. The compounds arrest the algal cell division, increase the infection rate and induce plasmolysis in the host. Our results indicate that the oomycete manipulates the host metabolome to support its own multiplication.

A glimpse into the biogeography, seasonality, and ecological functions of arctic marine Oomycota.

High-latitude environments are warming, leading to changes in biological diversity patterns of taxa. Oomycota are a group of fungal-like organisms that comprise a major clade of eukaryotic life and are parasites of fish, agricultural crops, and algae. The diversity, functionality, and distribution of these organisms are essentially unknown in the Arctic marine environment. Thus, it was our aim to conduct a first screening, using a functional gene assay and high-throughput sequencing of two gene regions within the 18S rRNA locus to examine the diversity, richness, and phylogeny of marine Oomycota within Arctic sediment, seawater, and sea ice. We detected Oomycota at every site sampled and identified regionally localized taxa, as well as taxa that existed in both Alaska and Svalbard. While the recently described diatom parasite Miracula helgolandica made up about 50% of the oomycete reads found, many lineages were observed that could not be assigned to known species, including several that clustered with another recently described diatom parasite, Olpidiopsis drebesii. Across the Arctic, Oomycota comprised a maximum of 6% of the entire eukaryotic microbial community in Barrow, Alaska May sediment and 10% in sea ice near the Svalbard archipelago. We found Arctic marine Oomycota encode numerous genes involved in parasitism and carbon cycling processes. Ultimately, these data suggest that Arctic marine Oomycota are a reservoir of uncharacterized biodiversity, the majority of which are probably parasites of diatoms, while others might cryptically cycle carbon or interface other unknown ecological processes. As the Arctic continues to warm, lower-latitude Oomycota might migrate into the Arctic Ocean and parasitize non-coevolved hosts, leading to incalculable shifts in the primary producer community.