Phylogenetic analyses
The isolates (K-2T and S1) were related to T. assiutensis CBS 147.48, T. assiutensis CMV007A4, T. assiutensis CBS 118440 and T. trachyspermus CBS 373.48 identified via BLAST against the NCBI nucleotide collection (nr/nt) database by using the ITS gene sequence as the search query. The isolates (K-2T and S1) differed from them by exhibiting 7%-7.88% sequence divergence (30–36 nt substitutions and 4–9 gaps). The phylogenetic analysis showed that the isolates (K-2T and S1) belonged to the genus Talaromyces, and were genetically distinct from all of these species (Fig. 1). The phylogenetic trees based on benA, cam, and rpb2 also were constructed to confirming phylogenetic position of K-2T and S1 (Figs. S1-S3). The closest relatives of the isolates (K-2T and S1) also were T. assiutensis, and T. trachyspermus (Figs. S1-S3). Although K-2T and S1 were found to cluster most frequently with the T. trachyspermus species, they were hardly ever on the same branch in any case. These results indicated that isolates (K-2T and S1) formed a distinct clade and were distantly separated from all species previously described in Talaromyces (Figs. S1-S3). To further confirm the phylogenetic position of K-2T and S1, we constructed a phylogenetic tree based on the concatenated sequences of the four genes (ITS, benA, cam, and rpb2 genes). The phylogenetic relationships showed that although K-2T and S1clearly clustered with the other types of strains belonging to the genus Talaromyces, they formed a distinct branch with other valid species of the genus Talaromyces (Fig. 2). The above results suggested that the K-2T and S1 belonged to the genus Talaromyces but was phylogenetically distinguished from other Talaromyces species.
Physicochemical characteristics
Physicochemical characteristics of the isolates K-2T and S1 were tested and compared with other species under the genus Talaromyces as shown in Table 2. Firstly, K-2T and S1 could grow over a wide temperature range (4–50°C) with an optimal growth temperature of 28°C, which significantly differed from other species like T. assiutensis (Yaguchi et al., 1994), T. aculeatus (Katar et al., 2017; Suleman et al., 2022), T. trachyspermus (Fang and Shi, 2016), T. alveolaris (Guevara et al., 2017). Secondly, K-2T and S1 were able to grow at pH 1.5–12 with an optimal growth pH of 7.0. Contrastingly, the pH range of other species under the genus Talaromyces was only 4–8 (Table 2), except for T. aculeatus which could survived at pH of 1–7 (Katar et al., 2017; Suleman et al., 2022). Thirdly, the results revealed that K-2T and S1 were halotolerant and flourished at a NaCl range of 0–14% (w/v) which also was clearly different from other species of genus Talaromyces. Finally, the assimilation of carbon sources, nitrogen sources, and inorganic salts were also different between K-2T and S1 and their closely related species under the genus Talaromyces. For example, the K-2T and S1 did not grow on sucrose, tryptone, and KH2PO4, while almost all other species could grow on these substrates.
Table 2
Physicochemical characteristics of K-2T and S1 and its closely related species
Characteristic | K-2T | S1 | T. assiutensis | T. aculeatus | T. trachyspermus | T. alveolaris |
Temperature range (℃) | 4–50 | 4–50 | 25–37 | 25–40 | 28 | 25–37 |
Growth pH | 1.5–12 | 1.5–12 | 5.6-7 | 1–7 | 4–8 | 5.5–7.5 |
Tolerance to NaCl (w/v, %) | 0–14 | 0–14 | n | 0.2 | n | n |
Assimilation of carbon sources | | | | | | |
Glucose | + | + | + | + | + | + |
Maltose | + | + | + | + | + | + |
Sucrose | - | - | + | + | + | + |
Lactose | + | + | n | n | n | n |
Xylose | + | + | n | n | n | n |
Soluble starch | + | + | n | n | n | n |
Glycerol | + | + | n | n | n | n |
Assimilation of nitrogen sources | | | | | | |
Peptone | + | + | + | + | + | + |
Tryptone | - | - | n | n | n | n |
Soybean peptone | + | + | n | n | n | n |
Yeast extract | + | + | + | + | + | + |
Ammonium sulfate | + | + | n | n | n | n |
Inorganic salt | | | | | | |
K2HPO4 | + | + | + | + | + | + |
KH2PO4 | - | - | + | + | + | + |
KCl | + | + | + | + | + | + |
MgSO4 | + | + | + | + | + | + |
Reference | This study | This study | (Yaguchi et al., 1994) | (Katar et al., 2017; Suleman et al., 2022) | (Fang and Shi, 2016) | (Guevara et al., 2017) |
+: growth; −: no growth; n: not available |
Morphology characteristics
Colonies of isolates K-2T and S1 grew on SM plates with a diameter of 45 ± 0.1 mm after 7 days at 28℃ as shown in Fig. 3 and table S2. The colonies were nearly circular, plain, with an entire margin, and the mycelia were white. The colony's texture was floccose. Colonies of isolates K-2T and S1 grew on SDAY plates with a diameter of 45 ± 0.05 mm after 7 days at 28℃. The front- and back-side of the mycelium were white, with a regular margin. The texture of the colonies was velutinous. Contrastingly, the diameters of colonies of isolates K-2T and S1 were about 32 ± 0.3 mm after 7 days at 28℃ on YPD plates, with their colonies being plain with a regular margin, and white mycelia. The texture of the colonies was floccose. The isolates K-2T and S1 formed colonies with a diameter of 35 ± 0.18 mm on MES plates after 7 days at 28℃. Their texture was velutinous. The front and back sides of the mycelium were white, the center was protuberant, and the colonies were plain, with an irregular margin. Furthermore, they, grew on PDA plates with a diameter of 34 ± 0.05 mm after 7 days at 28℃, had a velutinous texture (Fig. 3 and Table S2). The front- and back-side of the mycelium were white, and the colonies were nearly circular, plain, with a regular margin.
Conidiophores came from the basal mycelium were biverticillate. The stipes were smooth-walled, around 10–25 × 2.5–3.0 µm. 3–4 Metulae per stipe were observed, around 10–20 × 2–2.5 µm. Phialides (3–5 per metulae) were acerose, around 12–25 × 1.5-–2.5 µm (Figs. 3 and S4). Conidia were ellipsoidal to broad fusiform, smooth-wall, about 2.5–3.5 × 1.5–2.5 µm. These morphology characteristics were different from other Talaromyces species (Table 3).
Table 3
Morphological characteristics of K-2T and S1 and other Talaromyces species
Species | MEA (mm) | Conidia Shape | Conidia Wall | Conidia Size (µm) | Reference |
K-2T | 46–48 | ellipsoidal | smooth | 1.8–4.5 × 1.8–3.6 | This study |
S1 | 46–48 | ellipsoidal | smooth | 1.8–4.5 × 1.8–3.6 | This study |
T. assiutensis | 21–25 | biverticillate ellipsoidal | smooth | 3.5–4.5 × 2.2–2.5 | (Yaguchi et al., 1994) |
T. aculeatus | 30–35 | globose | rough | 3–3.5 × 3–3.5 | (Yilmaz et al., 2014) |
T. trachyspermus | 20–25 | biverticillate ellipsoidal or fusiform | smooth | 3-3.5 × 2-2.5 | (Yaguchi et al., 1994) |
T. alveolaris | 21–23 | subglobose to somewhat ellipsoidal | smooth | 2.5-3×2-2.5 | (Guevara et al., 2017) |
T. chongqingensis | 17–18 | ellipsoidal to broad fusiform | smooth | 2.5–3.5 × 2–2.5 | (Zhang et al., 2021) |
T. minioluteus | 21–22 | ellipsoidal | smooth | 2.5–4 × 1.5–2.5 | (Yilmaz et al., 2014) |
T. minnesotensis | 13–15 | ellipsoidal | smooth | 2.5–3.5 × 2–3 | (Guevara et al., 2017) |
T. udagawae | 10–11 | subglobose to ellipsoidal | smooth | 3–4 × 2–3 | (Yilmaz et al., 2014) |
T. cnidii | 38–43 | ellipsoidal | smooth to finely rough | 3–4 × 2–2.5 | (Sang et al., 2013) |
T. siamensis | 32–33 | ellipsoidal to fusiform | smooth to finely rough | 3–4 × 2–3 | (Yilmaz et al., 2014) |
Taxonomic Conclusion
Taken together, the overall phylogenetic, physicochemical, and morphological properties distinguished the isolates K-2T and S1 from their closely related species, suggesting that they represent a novel species within the genus Talaromyces. We propose the name Talaromyces sedimenticola sp. nov. for the isolates K-2T and S1.
Description of Talaromyces sedimenticola sp. nov.
Talaromyces sedimenticola (se.di.men.ti′co.la. L. neut. n. sedimentum, sediment, L. masc./fem. suffix –cola dweller, inhabitant, N.L. masc. n. sedimenticola, a dweller of sediments).
Growth is observed at 4–50°C (optimum 28°C), at pH 1.5–12.0 (optimum pH 7.0) and at 0–14% concentration of NaCl. After 7 days of incubation at 28°C, colonies are basically circular and plain with entire margin, white mycelia and floccose texture on SM, SDAY, YPD, MES and PDA plates. The diameter of colonies was about 45 mm on the first two plates (SM and SDAY), was between 32 and 35 mm on the last three plates (YPD, MES and PDA). The Conidiophores are biverticillate and stipes smooth-walled with 10–25 × 2.5–3.0 µm. The phialides (12–25 × 1.5–2.5 µm) are acerose with 3–5 per metula which has 3–4 stipe with 10–20 × 2–2.5 µm. Conidia are ellipsoidal to broad fusiform and smooth-wall with about 2.5–3.5 × 1.5–2.5 µm. Cells can assimilate glucose, maltose, lactose, xylose, soluble starch, glycerol, peptone, soybean peptone, yeast extract, ammonium sulfate, K2HPO4, KCl, and MgSO4, but not assimilate sucrose, tryptone, and KH2PO4.
The type strain, K-2T (= GDMCC 3.746 = JCM 39451), along with strain S1, were isolated from the sediments of the Challenger Deep in the Mariana Trench of the western Pacific Ocean. The MycoBank number was MB842071.