**5. Conclusions**

Fungi, through their ability to acidify their environment, producing strong chelating agents, and the ability to bioaccumulate trace elements in their mycelia, can considerably affect the mobility of elements in soils and locally increase their bioavailability. Our observations affirm that the transformation of ZnO NPs into biogenic mineral phases occurs under the influence of ubiquitous soil fungus *A. niger* and that these processes may happen, under the right circumstances, in the soil environment. The role of soil fungi is seminal in the distribution of ionic and nanoparticulate forms of Zn. Therefore, fungi should be taken into consideration when models of bioavailability and mobility are constructed for soil environments. Furthermore, these fungal abilities can help us develop new methods of bioremediation in the future.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2309-608X/6/4/210/s1, Figure S1: Photographs of Aspergillus niger mycelia after 7-day cultivation in the preliminary test, Table S1: Weight of dry biomass after 7-day static cultivation in the preliminary test.

**Author Contributions:** Conceptualization, M.Š. and M.U.; Data curation, M.Š.; Formal analysis, M.Š.; Funding acquisition, M.U.and P.M.; Investigation, M.Š.; Methodology, M.Š., M.U. and P.M.; Project administration, P.M.; Resources, M.K., I.V., E.D., H.K. and M.B.; Supervision, M.U., M.K. and P.M.; Validation, M.B.; Visualization, M.Š.; Writing—original draft, M.Š.; Writing—review and editing, M.U. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic and the Slovak Academy of Sciences (Vedecká grantová agentúra MŠVVaŠ SR a SAV) under the contracts Nos. VEGA 1/0153/17, VEGA 1/0146/18, and by Cultural and Educational agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic (Kultúrna a edukaˇcná grantová agentúra MŠVVaŠ SR) under the contract No. KEGA 013SPU-4/2019.

**Conflicts of Interest:** The authors declare no conflict of interest.
