Mucor caatinguensis A.L. Santiago, C.A. de Souza & D.X. Lima, sp. nov.
Index Fungorum number: IF 551680, Facesoffungi number: FoF 01328, Fig. 1
Etymology – caatinguensis. Referring to the biome where the species was first isolated.
Holotype – URM 7322
Fast growing colonies, 9 cm diam. after 72 h in MEA at 25 °C, firstly white then turning cream with grey spots (MP 18A1), touching the plate lid in the central region. Reverse yellow (MP 10H2). Sterile mycelium abundant. Sporangiophores coenocytic, simple or slightly sympodially branched with long branches, (5–)7.5 – 15(–17) μm diam. with or without yellowish contents, slightly roughed-wall. Some sporangiophores show a globular swelling distant from the columellae. Sporangia first yellow then becoming light brown, globose, subglobose, 25 – 65μm diam., subglobose to slightly flattened, 30 – 60 × 32 – 55μm with a slightly echinulate wall. Columellae light gray, smooth-walled, globose, subglobose, (20–)2 – 45 (–60) μm in diam., ellipsoid, obovoid with a truncated base (mostly) and piriform (–25)30 – 60(–75) × (20–)27 – 45(–55) μm. Collar evident. Columellae cylindrical with or without a constriction in the central part, 24.5 – 35 × 30 – 55 μm where rarely observed. Sporangiospores hyaline, smooth-walled, regular in size and containing granules at each end, mostly ellipsoid, 5 – 6(–7) × 3 – 5 μm and cylindrical ellipsoid, 5 – 6 × 3 – 4 μm., some subglobose and globose, 3 – 5 μm diam. Chlamydospores abundant, globose, subglobose and doliform, sometimes produced in the sporangiophores. Zygosporangia not observed.
Material examined – BRAZIL, Buíque: Parque Nacional do Catimbau (8°31′55.8″S, 37°15′34.2″W), in soil samples. Soil, 11.III.2014, leg. C. Lira (URM 7322) and deposited in the Jena Microbial Resource Collection (University of Jena and Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany) (JMRC:SF:012174).
Media and temperature tests – On MEA. At 10 °C – very limited growth (2 cm in diam. in 120 h); total lack of reproductive structures. At 15 °C – low colonies (< 1 mm in height) with slow growth (4 cm in diam. after 120 h); poor sporulation. At 20 °C – low colonies (<1 mm diam.) with slow growth (5 cm in 120 h); good sporulation. At 25 °C – better growth (9 cm in 72 h); excellent sporulation. At 30 °C – good growth (8 cm in 72 h); excellent sporulation. At 35 °C – better growth than at 15 and 20 °C (9 cm in 120 h); rare sporangiophores production and poor sporulation. At 40 °C – lack of growth and sporulation. The growth of M. caatinguensis on PDA was slightly slower than on MEA at all tested temperatures. However, at 35 °C, on PDA, the production of reproductive structures was good, and the sporangiophores were more sympodially branched (up to seven times) than in at other temperatures. The columellae were mostly applanate and bizarrely shaped sporangiophores were also observed.
Notes – Mucor caatinguensis is distinguished from the other species of the genus as it simultaneously produces numerous chlamydospores in mycelia (sometimes in sporangiophores), unbranched or weakly branched sporangiophores, columella and sporangiospores that are variable in shape and size. At first, Mucor caatinguensis could be confused with M. silvaticus Hagem because of the unbranched or weakly sympodially branched sporangiophores, the small size of the sporangia (up to 70 μm diam.) and by the production of cylindrical ellipsoid sporangiospores. However, colonies of M. silvaticus are pale olive gray, and it produces blackish brown sporangia (Schipper 1973), in contrast to the cream colonies of the new species, which show light brown sporangia. The former only produces sphaerical columella, which are rarely ellipsoidal, never obovoid with a truncated base or piriform, as observed in M. caatinguensis. Additionally, the sporangiospores of M. silvaticus are 3.5 – 5.2 × 2.6 – 3.7 μm, smaller than the M. caatinguensis sporangiospores, and no chlamydospores where reported in M. silvaticus
The abundant production of chlamydospores, sometimes observed in sporangiophores, is also very common in M. racemosus f. racemosus Fresen. (Schipper 1976), although we did not observe these structures inside the columellae of M. caatinguensis. Nevertheless, the sporangiophores of M. caatinguensis are not as branched as those of M. racemosus f. racemosus which may be sympodially and monopodially branched. Additionally, the sporangiospores of M. racemosus f. racemosus are broadly ellipsoidal to subglobose, and the colonies of M. racemosus f. racemosus are pale smoke gray, whereas the colonies of the new species are cream with grey spots.
Our molecular analysis (ITS and LSUrDNA, Figs. 2, and 3, respectively) showed that M. caatinguensis is genetically different from the other species of the genus, and placed the new species within the M. amphibiorum group, close to M. indicus Lendn. (Walther et al. 2013). In fact, the colour of both colonies of M. indicus and M. caatinguensis may be similar, but the sporangiophores of M. indicus are repeatedly sympodially branched (with long branches) and the columellae are mostly applanate and subglobose. We found repeatedly sympodial branches in M. caatinguensis at 35 °C on PDA. According to Schipper (1978), chlamydospores of M. indicus are also abundant in cultures grown in darkness at 20 °C, but only in substrate hyphae, and the sporangiospores are ellipsoidal to globose.
Fig. 1 Mucor caatinguensis (holotype) a Colony surface b, b1 Simple sporangiophore with chlamydospores c Simple sporangiophore with sporangia d Sporangiophore branch e–g Simple sporangiophores with columellae with different shapes h Chlamydospores i Sporangiospores.
Fig. 2 a Phylogenetic tree of M. amphibiorum group constructed using the ITS rDNA sequences. Mortierella parvispora was used as outgroup. b Phylogenetic tree of M. hiemalis group constructed using the ITS rDNA sequences. Mucor gigasporus was used as outgroup. Sequences are labeled with their database accession numbers. Support values are from Bayesian inference and maximum likelihood analyses (values above and below of the branches, respectively). Sequences with only ITS1 and 5.8 s rDNA are marked with *. New taxa are in blue and ex-type strains in bold.
Fig. 3 Phylogenetic tree of Mucor constructed using the large subunit (LSU) rDNA sequence data. Circinella species were used as outgroup. Sequences are labeled with their database accession numbers. Support values are from Bayesian inference and maximum likelihood analyses (values above and below the branches, respectively). The sequences obtained in this study are annotated in blue.