Research Article |
Corresponding author: Artur Alves ( artur.alves@ua.pt ) Academic editor: Andrew Miller
© 2019 Micael F. M. Gonçalves, Tânia F. L. Vicente, Ana C. Esteves, Artur Alves.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Gonçalves MFM, Vicente TFL, Esteves AC, Alves A (2019) Neptunomyces aureus gen. et sp. nov. (Didymosphaeriaceae, Pleosporales) isolated from algae in Ria de Aveiro, Portugal. MycoKeys 60: 31-44. https://doi.org/10.3897/mycokeys.60.37931
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A collection of fungi was isolated from macroalgae of the genera Gracilaria, Enteromorpha and Ulva in the estuary Ria de Aveiro in Portugal. These isolates were characterized through a multilocus phylogeny based on ITS region of the ribosomal DNA, beta-tubulin (tub2) and translation elongation factor 1 alpha (tef1-α) sequences, in conjunction with morphological and physiological data. These analyses showed that the isolates represented an unknown fungus for which a new genus, Neptunomyces gen. nov. and a new species, Neptunomyces aureus sp. nov. are proposed. Phylogenetic analyses supported the affiliation of this new taxon to the family Didymosphaeriaceae.
Didymosphaeriaceae, marine fungi, phylogeny, taxonomy
The family Didymosphaeriaceae is an important family in the order Pleosporales introduced by
Accurate species’ identification in genera of the family Didymosphaeriaceae was discussed in detail by
During an extensive survey of the fungal diversity from macroalgae species in the salt marsh of Ria de Aveiro in Portugal, we gathered a collection of fungal isolates. Here we report the morphological, cultural and phylogenetic characterization of these fungal isolates and introduce a novel genus and species to accommodate them.
Macroalgae (Gracilaria gracilis, Enteromorpha intestinalis, and other macroalgae species identified at genus-level only) were collected from various sites in the estuary Ria de Aveiro in Portugal (Table
Locality name | GPS coordinates | Sampling date | Algae species collected |
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Ria de Aveiro | 40°37'45"N, 8°43'27"W | 26/09/18 | Ulva sp. |
40°39'33"N, 8°43'27"W | Enteromorpha sp. | ||
40°40'38"N, 8°42'20"W | Gracilaria gracilis, Ulva sp. | ||
40°43'00"N, 8°42'04"W | Enteromorpha intestinalis, Ulva sp. |
Genomic DNA was extracted from fresh mycelium of cultures growing on PDA according to
Observations of morphological characters were made with a SMZ1500 stereoscopic microscope (Nikon, Japan) and a Nikon Eclipse 80i microscope (Nikon, Japan) equipped with differential interference contrast. Fungal structures were mounted in 100% lactic acid. Photographs and measurements were taken with a Nikon DSRi1 camera (Nikon, Japan) and the NIS-Elements D program (Nikon, Japan). Colony characters and pigment production were registered after 2 weeks of growth on PDA, Malt Extract Agar (MEA) and Oatmeal Agar (OA) incubated at 25 °C. Colony colors (obverse and reverse) were assessed according to the color charts of
Temperature growth studies were performed for the new species described. A 5-mm diameter plug was taken from the margin of an actively growing colony (14-day-old) and placed in the center of PDA, MEA and OA plates. Three replicate plates per isolate were incubated at 10, 15, 20, 25, 30 and 35 °C in the dark. Colony diameter was measured after 1 and 2 weeks.
To evaluate the growth requirements for sea salts, the new species was cultured in PDA with 3% (w/m) sea salts. Three replicate plates per isolate were incubated at 25 °C for 2 weeks in the dark. After incubation the diameter of the colonies was measured and compared.
Regarding conidial morphology, the fungal isolates studied were characterized by being aseptate and subcylindrical with rounded apices golden yellow conidia. For all media tested, the minimum, maximum and optimal growth temperatures were 10, 30 and 25 °C, respectively. No differences were observed in terms of colony diameter when grown in PDA with and without the addition of 3% sea salts, indicating that this fungus does not require salt for growth.
BLASTn searches against the NCBI nucleotide database using the ITS, tub2 and tef1-α sequences of the isolates retrieved various hits, of which those with the highest sequence similarity belonged to members of the family Didymosphaeriaceae. Based on a megablast search using the ITS sequence, the closest matches for MUM 19.38 = CMG 10A in GenBank were Dothideomycetes sp. (GenBank accession: HQ631008; Identities 549/564 (97%), no gaps) and Letendraea sp. (GenBank accession: LT796897; Identities 548/564 (97%), no gaps). The closest hits using the tub2 sequence were Letendraea sp. (GenBank accession: LT796988; Identities 457/516 (89%), 5 gaps). Closest hits using tef1-α sequence also had highest similarity to Letendraea sp. (GenBank accession: LT797101; Identities 935/957 (98%), no gaps).
To confirm the phylogenetic placement of the fungal isolates within the family Didymosphaeriaceae, sequences of ITS, ITS + tub2 and ITS + tef1-α were aligned against those of several genera/species belonging to Didymosphaeriaceae (Suppl. material
Phylogenetic relationships of Didymosphaeriaceae species based on ITS sequence data and inferred using the Maximum Likelihood method under the Kimura 2-parameter model. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site and rooted to Cucurbitaria berberidis (CBS 130007) and Coniothyrium palmarum (CBS 400.71). Bootstrap values (> 70%) are shown at the nodes. Ex-type strains are in bold and the isolates from the current study are in blue.
Phylogenetic relationships of Didymosphaeriaceae species based on ITS and tub2 sequence data and inferred using the Maximum Likelihood method under the Kimura 2-parameter model. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site and rooted to Cucurbitaria berberidis (CBS 130007) and Coniothyrium palmarum (CBS 400.71). Bootstrap values (> 70%) are shown at the nodes. Ex-type strains are in bold and the isolates from the current study are in blue.
Phylogenetic relationships of Didymosphaeriaceae species based on ITS and tef1-α sequence data and inferred using the Maximum Likelihood method under the Kimura 2-parameter model. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site and rooted to Cucurbitaria berberidis (CBS 130007) and Coniothyrium palmarum (CBS 400.71). Bootstrap values (> 70%) are shown at the nodes. Ex-type strains are in bold and the isolates from the current study are in blue.
Asexual morph: mycelium consisting of septate, smooth hyphae, thick-walled, hyaline and rarely with nucleus. Conidia aseptate, golden yellow, smooth, subcylindrical with rounded apices. Chlamydospores not observed. Sexual morph unknown.
Referring to Neptune (Latin: Neptūnus) the god of the seas in Roman mythology.
Neptunomyces aureus M. Gonçalves, T. Vicente & A. Alves. Portugal
Portugal, Ria de Aveiro (40°40'38"N, 8°42'21"W), isolated from Gracilaria gracilis, 26th September 2018, M. Gonçalves, (holotype: a dried culture sporulating on pine needles AVE-F-1; ex-type living culture, MUM 19.38 = CMG 10A).
Referring to the golden yellow conidia.
Phylogenetic analysis based on the ITS, ITS and tub2 and ITS and tef1-α dataset considered in the present study clustered the retrieved strains in a monophyletic lineage in the family Didymosphaeriaceae. Therefore, a new genus Neptunomyces gen. nov., and a new species Neptunomyces aureus sp. nov. are here proposed.
Mycelium smooth, white, 2–3 μm wide hyphae. Hyphae thick-walled, smooth, hyaline and rarely with nucleus. Conidiomata aggregated or solitary, globose to subglobose, dark brown, immersed or rarely superficial. Conidiomata wall pseudoparenchymatous. Conidiophores reduced to ampulliform to subcylindrical, hyaline, smooth conidiogenous cells (mean ± S.D. = 5.2 ± 0.3 × 2.0 ± 0.6 μm, n = 20). Conidia solitary, subcylindrical with rounded apices, aseptate, initially hyaline, smooth, becoming golden yellow (mean ± S.D. = 7.0 ± 0.6 × 2.7 ± 0.2 μm, n = 100). Sexual morph unknown.
Neptunomyces aureus (MUM 19.38). A, B Colony after 2 weeks at 25 °C on PDA (obverse and reverse) C, D colony after 2 weeks at 25 °C on MEA (obverse and reverse) E, F colony after 2 weeks at 25 °C on OA (obverse and reverse) G, H conidiomata after 1 month at 25 °C on pine needles and PDA. I, J conidiogenous cells K conidia. Scale bars: 2.5 μm.
On 2 weeks old PDA and OA plates, at 25 °C, colonies growing to 50 mm in diameter, regular and above and a little immersed into agar. PDA obverse white near the center getting flesh orange towards the borders; reverse buff orange in the center and lighter in periphery. OA obverse skimmed milk white; reverse snow white. On 2 weeks old MEA plates, at 25 °C, colonies growing to 44 mm in diameter, regular and above and a little immersed into agar. Obverse orange-colored white; reverse reddish orange in the center and ochre yellow in periphery. At 35 °C, there was no growth in any media tested.
Estuary Ria de Aveiro, Portugal
Portugal, Ria de Aveiro (Table
Neptunomyces aureus clustered in a distinct lineage in the family Didymosphaeriaceae with high p-distances (= 0.07) of nucleotide sites among the two-loci sequences (ITS and tef1-α) with closest genus Xenocamarosporium. Although the morphology of conidiomata, conidiomata wall and conidiogenous cells can be very similar in the genera of this family, conidial morphology distinguishes Neptunomyces from Xenocamarosporium (Table
Species | Neptunomyces aureus | Xenocamarosporium acaciae | |
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Strain | MUM 19.38 | CBS 139895 | |
Nucleotide differences | ITS | 65 | |
tef1-α | 58 | ||
(p-distance) | ITS + tef1-α | 0.07 | |
Conidia | Size (μm) | 7.0 ± 0.6 × 2.7 ± 0.2 | (11–)12–14(–15) × (3.5–)4(–5) |
Morphology | Subcylindrical | Ellipsoidal to subcylindrical | |
Apex and base | Rounded | Obtuse and rounded to truncate base | |
Color | Hyaline becoming golden yellow | Hyaline becoming golden brown | |
Septation | Aseptate | (1–)3-septate | |
Conidiogenous cells | Size (μm) | 5.2 ± 0.3 × 2.0 ± 0.6 | 7–12 × 5–7 |
Morphology | Ampulliform | Ampulliform | |
Color | Hyaline | Hyaline | |
References | Present study |
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This study adds to the family Didymosphaeriaceae a new genus/species, namely Neptunomyces aureus isolated from macroalgae in the estuary of Ria de Aveiro in Portugal. The family Didymosphaeriaceae contains now 26 genera described.
The majority of the genera in the Didymosphaeriaceae remain under studied, which makes the family still poorly understood and not well resolved (
Comparison of the ITS and tef1-α sequences from N. aureus and the closest genus/species X. acaciae revealed 65 and 58 base pair differences, respectively, with high p-distances (= 0.07) supporting the establishment of Neptunomyces as a distinct genus. Although the morphology of conidiomata, conidiomata wall and conidiogenous cells are similar, the conidiogenous cells of N. aureus are smaller than those of X. acaciae. Also, both can be easily discriminated by their conidia morphology, color and size. The conidia of N. aureus are aseptate, subcylindrical with rounded apices and initially hyaline and soon become golden yellow, while conidia of X. acaciae are mostly tri-septate, ellipsoidal to subcylindrical, sometimes with truncate base and golden brown. Moreover, conidia of N. aureus are considerably smaller than those of X. acaciae.
Neptunomyces aureus was isolated from healthy tissues of the macroalgae analyzed, where it may occur as endophyte or epiphyte. Further investigations are essential for clarifying its biology, ecology, physiological characteristics and host-specificity. Moreover, we did not obtain any sexual morph for this new species and there is no molecular support to link possible sexual taxa.
So far, species of Didymosphaeriaceae seem to be cosmopolitan in distribution: they have been recorded from both temperate and tropical regions. Also, Didymosphaeriaceae have been found on various hosts and substrates, including plants, humans and soil, being regarded as saprobes, endophytes or pathogens of a wide variety of plant substrates worldwide (
Physiological tests allowed us to characterize the retrieved isolates as a slight halophile as they grow equally well in the presence and absence of 3% sea salts. Information regarding NaCl tolerance is still poorly described in Didymosphaeriaceous species, but future studies related to tolerance to salinity in these organisms (especially in this new species) may provide physiological unique characteristics which may have some biotechnological potential.
The authors acknowledge financial support from the Portuguese Foundation for Science and Technology (FCT) to CESAM (UID/AMB/50017/2019) and the PhD grant of M. Gonçalves (SFRH/BD/129020/2017).
Table S1. List of isolates used in this study
Data type: species data