Morphological and Phylogenetic Characterization of Endophytic Fungi Isolated from Brown Algae (Phaeophyceae) in Korea

Abstract

Seaweed-associated endophytic fungi have recently attracted considerable attention due to their ecological significance and potential application as biological resources. Accordingly, research efforts to isolate and characterize fungal endophytes from marine macroalgae have accelerated. This study aimed to isolate and identify endophytic fungi from two brown algae, Sargassum thunbergii and S. muticum, collected from intertidal zones in Tongyeong and Pohang, Korea. Identification was performed based on morphological characteristics and multilocus phylogenetic analyses using ITS, LSU, TEF1, TUB2, and RPB2 gene sequences. As a result, three previously unrecorded fungal species in Korea were identified: Neopyrenochaeta telephoni, Trichoderma cyanodichotomum, and Microascus intricatus. This study provides detailed descriptions of their morphological features and phylogenetic relationships. These findings contribute to a better understanding of fungal diversity associated with brown algae in Korea and highlight the potential significance of endophytic fungi in marine ecosystems.

Keywords: Brown algae; Phylogenetic analysis; endophytic fungi; sargassum; seaweed-associated fungi.

Figure 1.

Maximum likelihood tree of Neopyrenochaeta telephoni KNUE24S146 based on concatenated sequences of internal transcribed spacer (ITS), large subunit ribosomal RNA (LSU), and RNA polymerase II second largest subunit (RPB2). Pyrenochaetopsis leptospora was used as an outgroup. Bootstrap values greater than 50% (1,000 replicates) are shown at the nodes. T indicates an ex-type culture.

Figure 2.

Maximum likelihood tree of Trichoderma cyanodichotomum strain KNUE 24S153, based on concatenated sequences of the internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF1), and the second largest subunit of RNA polymerase II (RPB2). Nectria berolinensis was used as the outgroup. Bootstrap values greater than 50% (1,000 replicates) are shown at the nodes. T indicates an ex-type culture.

Figure 3.

Maximum likelihood tree of Microascus intricatus strain KNUE 24S192, based on concatenated sequences of the internal transcribed spacer (ITS), large subunit ribosomal RNA (LSU), translation elongation factor 1-alpha (TEF1), and beta-tubulin (TUB2). Scopulariopsis carbonaria was used as the outgroup. Bootstrap values greater than 50% (1,000 replicates) are shown at the nodes. T indicates an ex-type culture.

Figure 4.

Morphology of Neopyrenochaeta telephoni KNUE 24S146. A–B Colonies after 7 days of growth at 25 °C. The left side shows the front view and the right side shows the reverse view, on malt extract agar (A), and potato dextrose agar (B). Pycnidia observed on the colony surface on PDA (C) and on a slide glass (F). Conidiogenous cell (D) and conidia (E). Scale bars: C, F = 500 μm, D, E: 10 μm.

Figure 5.

Morphology of Trichoderma cyanodichotomum KNUE 24S153. A-B Colonies after 7 days of growth at 25 °C. The left side shows the front view and the right side shows the reverse view, on malt extract agar (A), and potato dextrose agar (B). Conidiophore bearing cluster of phialides and conidia (C, F), microconidia (marked with arrows) and macroconidia (D, E). Scale bars: C = 20 μm, F = 10 μm, D-E = 5 μm.

Figure 6.

Morphology of Microascus intricatus KNUE 24S192. A–B Colonies after 7 days of growth at 25 °C. The left side shows a front view and the right side shows the reverse side, on malt extract agar (A), and potato dextrose agar (B). Conidiomata formed on the colony surface (C), Conidiophore with a slightly elongated annellide (D), Conidiophore bearing a group of 3 annellides (E), Conidia arranged in short chains (F). Scale bar: C = 100 μm, D = 10 μm, E, F = 5 μm.