Mucoralean fungi present in soil from arid regions in South Africa

[摘要] English: The aim of the first part of the study was to investigate the ecological niche ofmucoralean fungi in arid soil, with specific reference to the position these fungioccupy in the biogeochemical cycle of nitrogen. Consequently, selected mucoraleantaxa occurring frequently in soil habitats, including strains from culture collections, aswell as isolates obtained from a soil sample from arid Upper Nama Karoo, wereused to evaluate in vitro growth to determine nitrogen sources and aw tolerances.Nine mucoralean fungal genera including 18 species were examined for the ability toutilise a series of nitrogen containing compounds and to grow at an aw of 0.955 onsolid media. The nitrogen concentration in the media was 0.1 g.r1 and the series ofnitrogen containing compounds were ammonium chloride, asparagine, sodiumglutamate, sodium nitrite and potassium nitrate. The genera were ActinomucorSchostak., Backusella Hesselt. & J.J. Ellis, Cunningha'fnella Matr., GongronelIaRibaldi, MortierelIa Coem., Mucor Fresen., Rhizomucor Lucet & Costantin.,Rhizopus Ehrenb. and Thamnostylum Arx & H. P. Upadhyay. Thirty-nine fungalstrains obtained from culture collections (CBS, MUFS and PPRI), as well as 12 soilisolates from the Karoo, were tested. All the species and strains tested in this studywere able to utilise asparagine and glutamate. Strains belonging to CunninghamelIa,Mucor racemosus Fresen., Rhizopus microsporus Tiegh. and Rhizopus stolonifer(Ehrenb.: Fr.) VuilI. were unable to utilise ammonium chloride. Strains ofCunninghamelIa, MortierelIa, Rhizomucor, Rhizopus microsporus and Rhizopusstolonifer were unable to grow on nitrate as sole nitrogen source. Nitrite was foundto be toxic to species belonging to CunninghamelIa, MortierelIa, Rhizomucor,Rhizopus and Thamnostylum. Members of GongronelIa, MortierelIa, Mucorracemosus, Rhizomucor and Thamnostylum were unable to grow at an a, of 0.955.The aim of the second part of the study was firstly to get an indication whether themucoralean diversity of the Karoo, as observed in the first part of the study and inthe records obtainable from literature, differs from data on mucoralean diversity fromother arid regions. The latter included data from literature and what could be found ina soil sample taken from Kimberley Thorn Bushveld. Secondly, the aim was to testthe isolates obtained from the Kimberley Thorn Bushveld soil sample in order tofurther explore the ability of mucoralean fungi to utilise the above mentioned seriesof nitrogen sources and to grow at an a, of 0.955. In addition, selected mucoraleantaxa occurring frequently in soil habitats were tested for the ability to surviveelevated temperatures in soil. It was found that the following species of theMucorales may be encountered in the arid soil of the Karoo; Actinomucor elegans,CunninghamelIa echinulata, MortierelIa isabellina, Mucor circinelloides, Rhizomucorspecies, Rhizopus oryzae Went. Prins. Geerl. and Rhizopus stolonifer. Futuresurveys would reveal if genera like Absidia, GongronelIa and Zygorrhynchus, whichhave been isolated from arid regions, also occur in Karoo soil. Representatives ofmucoralean taxa occurring in arid Karoo soil were able to utilise organic as well asinorganic oxidised nitrogen sources. However, at the concentration tested in thisstudy, nitrite was found to be toxic to representatives of CunninghamelIa,Mortierell8, Rhizomucor and Rhizopus. Nitrate could not be utilised byCunninghamelIa, MortierelIa, Rhizomucor and Rhizopus stolonifer. Whether thisinability to utilise inorganic nitrogen sources would prevail 'during oligotrophic growthin soil, remains a question to be addressed by future research. Representatives ofthe above mucoralean taxa occurring in arid soil were able to survive 55°C for 14 hin soil.

[发布机构] University of the Free State