Desmazierella acicola

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1. Classification

The classification of D. acicola can be visualized through its phylogenetic tree. While previously in the Sarcosomataceae family, a study by Pfister (2008) created a new family, named Chorioactidaceae, and reclassified genera Desmazierella, Chorioactis, Wolfina, and Neournula into this new family using molecular and morphological approaches (Pfister et al. 2008).

a. Higher order taxa

Fungi; Ascomycota; Pezizomycetes; Pezizales; Chorioactidaceae; Desmazierella acicola (Pfister et al. 2008).

2. Description and significance

Desmazierella acicola is a part of the Chorioactidaceae family which is in the Pezizales order (Pfister et al. 2008). This classification is relatively new, only being placed in the Chorioactidaceae family in 2007. D. acicola was originally characterized as part of the Sarcosomataceae family in Pezizales, a sister family of Chorioactidaeceae (Pfister et al. 2008). It is one of the most common fungi found on dead leaves and plant materials, otherwise known as litter, on forest floors. This fungi is particularly key for the decomposition of leaf litter as it is found in all litter layers (Xiaoxu and Fuqiang 2011). It also helps in the litter transition between these two layers of decay (Kendrick and Burges 1962). A lack of D. acicola can make this transition much less efficient and interfere with the breakdown of dead plant tissue (Kendrick and Burges 1962). While many studies have speculated on the widespread nature of D. acicola (Xiaoxu and Fuqiang 2011), eight geographically distinct lineages have been clearly identified based on rDNA ITS sequences (Martinovic et al. 2015).

3. Genome structure

By using rDNA sequences from species in the Pezizales order, D. acicola was originally placed in either the Sarcoscyphaceae, Sarcosomataceae, or Otideaceae lineages (Landvik et al. 1997). 18s rRNA from species in Pezizales were aligned in an attempt to create a phylogenetic tree through unweighted parsimony (Harrington et al. 1999). However, one gene was not sufficient enough to organize the taxa from this order (Harrington et al. 1999). Based on 18s nrDNA from fungal representatives, D. acicola was determined to be a part of the Pezizalean lineage, similar to Chorioactis geaster (Peterson et al. 2004). The later sequencing the ribosomal primers and genes (LSU, SSU, and RPB2 RNA) resulted in a phylogenetic tree with the new family, Chorioactidaceae (Pfister et al. 2008). There is currently no sequenced genome of D. acicola. However, it has been targeted to be sequenced by the DOE Joint Genome Institute as part of the 1000 Fungal Genomes project (JGI GOLD 2016).

4. Cell structure

D. acicola has a small, cup-shaped apothecium, or reproductive portion, up to 5 mm in diameter; it either does not have a stalk, or has a very small one (Pfister et al. 2008). The apothecium has setose, or bristles, on its surface and sits on a brown subiculum, a supporting structure (Pfister et al. 2008). The hymenium, which holds the spores, is covered in flattened dark brown hairs, of which there are two type, superficial and rooting hairs (Pfister et al. 2008). The light brown superficial hairs are regularly separated by septa, dividing walls, and have blunt ends (Pfister et al. 2008). Rooting hairs are covered in long pointed warts and are dark brown or black in color (Pfister et al. 2008). The asci, cells holding the spores in the hymenium, contain 4 to 8 spores and are cylindrical in shape, with an operculum, or capping, end (Pfister et al. 2008). The asci are bifurcated or lobed at the base, with the base itself being rounded (Pfister et al. 2008). The ascospores, spores produced by and held within an ascus, are transparent ellipsoids with a smooth surface, containing 6 to 8 nuclei (Pfister et al. 2008). They have a cyanophilic covering and sometimes end in a point or have ridges running lengthwise (Pfister et al. 2008). The paraphyses (reproductive organs) are branched and transparent, forming a crisscross network along their length, with each of these cells containing 2 to 6 nuclei (Pfister et al. 2008). D. acicola has an anamorph, or asexual reproduction stage, known as Verticicladium trifidum (Mycobank 2016). A morphological comparison revealed similarity in spores for the previously defined Sarcosomataceae family and the newly defined Chorioactidaceae (Pfister et al. 2008). Both families have multinucleate spores (Pfister et al. 2008). Sarcosomataceae have dark ascomata, or fruiting body, uninucleate paraphyses, and a gelatinous material within the tissue of the apothecium (Pfister et al. 2008). In contrast, the species moved to Chorioactidaceae (including D. acicola) have a lighter hymenia, or surface, multinucleate paraphyses, and lack the same gelatinous material (Pfister et al. 2008).

5. Metabolic processes

D. acicola is particularly effective in the breakdown of cellulose, hemicellulose, and chitin through the production of hydrolytic enzymes (Martinovic et al., 2015). The fungi inserts itself into the pine litter during degradation, and turns black in pigment when it reaches its final growth size (Millar, 1974). However, the specific mechanisms behind the metabolism of D. acicola have not been researched.

6. Ecology

D. acicola is one of the most common species growing in pine leaf litter, and can be found all over the world where there are trees that produce pine needle litter (Martinovic et al. 2015). It has been reported growing in 28 C, 32 C, and 35 C, with optimal growth appearing to be around 28 C (Martinovic et al. 2015). Additionally, it can be found across Europe, North America, the Mediterranean, Serbia, Japan, Kyrgystan, and the Canary Islands (Martinovic et al. 2015). D. acicola is a decomposer of pine needle litter on mixed and coniferous forest floors (Przybył et al. 2008). The fungi lives inside individual pine needles (Kendrick and Burges 1962).  D. acicola appears to be important in the transition from the litter layer (characterized as the un-decomposed leaf layer) to the first fermentation layer (characterized by the soft, low tensile strength pine needles and high moisture content) (Kendrick and Burges, 1962). D. acicola has very high abundance in the litter layer just below the surface, and its prevalence drastically drops in the first fermentation layer due to competition from other microorganisms (Kendrick and Burges, 1962). This drastic change in abundance suggests that D. acicola is a key step in the transition between the two layers of decomposition (Kendrick and Burges, 1962). It is not known whether D. acicola replaces previous competitors in fungal succession, or if it uses uncolonized litter (Millar 1974). Regardless, it goes through cycles of dominance depending on the temperature, and time after degradation begins (Millar 1974).

7. Pathology

There is no known pathology for D. acicola.

8. Current Research

Current research on D. acicola primarily focuses on the phylogenetic organization of the species. One study published in Mycologia in 2015 did this with over 100 samples on pine and spruce needles collected from around the world (Martinovic et al. 2015). In total 33 strains were identified across seven pine needle species using DNA sequencing (Martinovic, 2015). This yielded eight different clades in D. acicola based on similarity grouping with a distinct clade from each of Continental-Atlantic Europe, Serbia, Japan, Kyrgystan, the Mediterranean, Canary Islands, and a combined clade from North America and Poland (Martinovic et al. 2015). Although there were some differences in host specificity, temperatures resistance, and morphology to be better adapted to their unique environment, there was little difference between the separate clades and strains within the clades (Martinovic et al. 2015). None of the differences found warrant the differentiation of the strains into distinct species, only strains within the D. acicola species (Martinovic et al. 2015).    As previously stated, the sequencing of this species is being targeted through the 1000 Fungal Genomes project at the DOE Joint Genome Institute (JGI GOLD 2016). The end date of this project is not known (JGI GOLD 2016). No other known research is currently being conducted concerning D. acicola.

9. References

1. Harrington, F.A., Pfister, D.H., Potter, D., and Donoghue, M.J. 1999. Phylogenetic Studies within the Pezizales. I. 18S rRNA Sequence Data and Classification. Mycological Society of America, 91 (1): 41-50.
2. International Mycological Association. 2016. Mycobank Database. Desmazierella acicola [Data file]. Retrieved from http://www.mycobank.org/BioloMICS.aspx?TableKey=14682616000000067&Rec=8144&Fields=All [Database] (Accessed November 29th, 2016)
3. Joint Genome Institute. n.d. Genome Online Database [JGI GOLD]. Desmazierella acicola CBS 302.81 Standard Draft [Data file]. Retrieved from https://gold.jgi.doe.gov/project?id=113653 [Database]. (Accessed November 29th, 2016).
4. Kendrick, W. B., and Burges A. 1962. Biological Aspects of the Decay of Pinus sylvestris leaf litter. Nova Hedwigia, 4 (3): 313-359.
5. Landvik, S., Egger, K. N. and Schumacher, T. 1997. Towards a subordinal classification of the Pezizales (Ascomycota): phylogenetic analyses of SSU rDNA sequences. Nordic Journal of Botany, 17 (4): 403–418.
6. Martinovic, T., Ondrej, K., and Hirose D. 2015. Distinct Phylogeographic Structure Recognized with Desmazierella acicola. Mycolgia, 108 (1): 20-30.
7. Millar, C. S. 1974. Decomposition of coniferous leaf litter. Biology of Plant Litter Decomposition, 1: 105-128.
8. Peterson, K.R., Bell, C.D., Kurogi, S., and Pfister, D.H. 2004. Phylogeny and Biogeography of Chorioactis geaster (Pezizales, Ascomycota) Inferred from Nuclear Ribosomal DNA Sequences. Harvard Papers in Botany 8 (2): 141-52.
9. Pfister, D., Slater, C., and Hansen, K. 2008. Chorioactidaceae: a new family in the Pezizales (Ascomycota) with four genera. Mycological Research 112 (5): 513-527
10. Przybył, K., Karolewski, P., Oleksyn, J., Labedzki, J., and Reich, P.B. 2008. Fungal Diversity of Norway Spruce Litter: Effects of Site Conditions and Premature Leaf Fall Caused By Bark Beetle Outbreak. Microbial Ecology, 56: 332.
11. Xiaoxu, F., and Fuqiang, S. 2011. Dynamics of fungal diversity in different phases of Pinus litter degradation revealed through denaturing gradient gel electrophoresis (DGGE) coupled with morphological examination. African Journal of Microbiology Research 5 (31): 5674-5681.