The genome of the filamentous fungus Aspergillus niger contains two genes for
aegerolysin proteins, nigerolysin A1 (NigA1) and nigerolysin A2 (NigA2). For
nigerolysins NigA1 and NigA2 suggested that they may be involved in fungal defense
mechanisms. Previously, it was assumed that the nigerolysins were secreted by the
fungus. Due to the lack of a signal peptide, they should be secreted by unconventional
secretion. To determine the localization of the aegerolysins NigA1 and NigA2 at the
cellular and/or extracellular level, we used several publicly available online tools to
predict the presence of signal peptides, transmembrane domains, glycosylation sites
and possible cellular and/or extracellular localization. Using confocal microscopy,
imaging of live mycelium of Aspergillus niger strains and fluorescent probes and
dyes, we found that NigA1-mCherry, NigA2-mCherry, and NigA2-eYFP are
uniformly distributed in the cytosol of the cell when young, and fluorescence also
occurs in vacuoles as hyphae age. The presence of NigA2 in the cytoplasm of hyphae
was further confirmed by immunolabeling NigA2 with antibodies. Both aegerolysins
are also present in spores. Cultivation of Aspergillus niger with Bacillus cereus led to
a possible interaction between the organisms and possible secretion of NigA2-eYFP
and NigA2-mCherry from the fungus. Deletion of one or the other nigerolysin gene
could have an effect on reduced germination of fungal spores.
|
