Mucor soli C.A. de Souza, E.V. de Medeiros & R.J.V de Oliveira, sp. nov.

Index Fungorum number: IF 902417; Mycobank number: MB 902417; Facesoffungi number: FoF 09923; Fig. 1

Etymology – Referring to the substrate, soil, from which the fungus was first isolated.

Holotype – URM 95261

Saprobic on submerged decaying wood. Sexual morph: Not observed. Asexual morph: Colonies fast growing (9 cm diam.×0.5 cm in height after four days at 25 ℃ on PDA), initially white then becoming yellowish to cream (MP 19D1), reverse brownish (MP 12K13) with irregular margins. Odour acid. Sporangiophores growing directly from the substrate, cylindrical, up to 22.5 μm diam., simple and sympodially branched (up to four times), with short or long branches, hyaline, presenting a texture that varies between smooth-walled and slightly rough (striated). Occasionally exhibiting one to three septate below sporangia (either in sporangiophores or in sporangiophore branches), some showing a swelling close to the columellae, especially on short branches sporangiophores. Sporangia globose (15.5‒) 20–80 (–80.5) µm diam. very rarely reach 95 μm diam., and subglobose to slightly dorsiventrally flattened 12.5–55 × 18.5–60 µm, wall evanescent, light brown, slightly echinulate. Columellae variable in shape, smooth-walled, hyaline, frequently globose to subglobose, (13.5‒) 15.5–72.5 (‒76.5) µm diam., cylindrical, 50–75 ×40–65 µm diam., obovoid to slightly ellipsoidal, 12.5–40×10–50 µm, ovoid 20–65×15.5–50 µm, conical or oblong, 15–30×10.5–25 µm, pyriform 20.5–50×10.5–40 and rarely applanate, 12–25× 15–25 µm. Collar evident. Sporangiospores globose and subglobose, (2.5–) 3–6 (–7.5) µm diam. Chlamydospores infrequent, barrel shaped.

Culture characteristics – colonies PDA. At 10 °C—very limited growth (3.2 cm in diam. in 168 h); total lack of reproductive structures; At 15 °C—low colonies (<1 mm in height) with slow growth (6 cm in diam. in 168 h); good sporulation. At 20 °C—colonies up to 3 mm diam. with good growth (9 cm in 120 h) and good sporulation. At 25 °C—better growth (9 cm in 96 h) and excellent sporulation. At 30 °C—good growth (8 cm in 96 h) and excellent sporulation. At 35ºC—lack of growth and sporulation. Mucor soli exhibited a better growth rate and sporulation on PDA than on MEA at all tested temperatures. At 15 °C, on PDA, the production of reproductive structures was good, and the sporangiophores were simple or slightly sympodially branched, whereas on MEA the production of reproductive structures was very poor and the sporangiophores were simply branched. The columellae were mostly globose (up to 24 μm diam.) at 15 °C on PDA and MEA. At 36 °C after 1 week in the dark, colonies on PDA and MEA growing fast and attaining a diameter of 90 mm and morphologically similar as described at 25 °C.

Material examined – BRAZIL, Pernambuco State, Quipapá Municipally, Serra do Quipapá, 8° 48′ 21.15″ S, 36° 20′ 80″ W, from soils of a semi-arid region, 15 April 2022, C.A. de Souza, LEMA 77962 (URM 95261, holotype); ex-type, URM 8698; living culture ibid. URM 8699.

GenBank accession numbers – URM 8698, ex-type: ITS = OQ939972 and LSU: OQ939973; URM 8699: ITS=OQ944938 and LSU: OQ944939.

Notes – Phylogenetic analysis of two sequence datasets (ITS and LSU rDNA) revealed that Mucor soli sp. nov. formed a distinct lineage among other species of Mucor. The new species is phylogenetically positioned in a well supported clade (ML=100% and BY =1) among species of the Mucor flavus group. Morphologically, M. soli sp. nov. exhibits a strong resemblance to most species of the M. flavus group (Schipper 1975). Mucor soli sp. nov. predominantly produces globose sporangia, with diameters ranging from 20 to 80 µm, occasionally reaching up to 95 µm diam. In contrast, M. merdophylus exhibits globose to slightly dorsally flattened sporangia, with 35.5 to 95 µm diam., and occasionally reaching up to (–110) μm diam. (Lima et al. 2020). Mucor minutus, on the other hand, is characterized by globose sporangia reaching up to 160 µm in length (Alves et al. 2021). Mucor flavus has larger sporangia than those observed in the present study, with a maximum of 175 µm diam., whereas M. aligarensis and M. saturninus have sporangia with a maximum diameter of 100 µm. These differences in sporangia are distinctive morphological characteristics that differentiate M. soli sp. nov. from the other species in the group. Mucor soli also exhibit variable columella shapes and sizes, measuring 15.5 to 72.5 µm diam. Despite the close morphological and phylogenetic affinity of M. soli with species of the M. flavus group, differences in the formation of columellae and their sizes are distinctive morphological characteristics. Mucor aligarensis, M. flavus, M. minutus, and M. saturninus have been described as producers of columellae up to 130 μm diam. (Schipper 1975), larger than those observed for M. soli sp. nov. Mucor soli sp. nov. also differ from other related species by the production of globose and subglobose sporangiospores ranging from 3 to 6 µm diam. having thin and smooth-walled. Mucor merdophylus has larger sporangiospores (5 to 26 µm diam.) with granular content and smooth-walled (Lima et al. 2020), while M. saturninus has sporangiospores with up to 8 µm diam. and thick-walled and predominantly ellipsoidal (Schipper 1975). The sporangiospores of M. aligarensis and M. flavus are also larger (up to 12×6.5 μm) and M. minutus has subglobose to ellipsoidal sporangiospores of up to 7 μm diam. (Schipper 1975; Alves et al. 2021). These differences in sporangiospore sizes and shapes provide additional criteria for distinguishing Mucor soli sp. nov. from the other species in the group.

Figure 1 – Mucor soli (URM 95261, holotype). a Colonies (verse and reverse) on MEA and PDA at 25 °C after 1 week. b Observed columellae types. c‒d Simple sporangiophore with sporangia. e Simple branched sporangiophore with sporangia. f Sympodially branched sporangiophore. g Sporangiospores.
Scale bars: b and g=20 µm, c‒f=50 µm