Aspergillus nidulans grows by apical extension of multinucleate cells called hyphae that are subdivided by the insertion of crosswalls called septa. Apical cells vary in length and number of nuclei, whereas subapical cells are typically 40 μm long with three to four nuclei. Apical cells have active mitotic cycles, whereas subapical cells are arrested for growth and mitosis until branch formation reinitiates tip growth and nuclear divisions. This multicellular growth pattern requires coordination between localized growth, nuclear division, and septation. We searched a temperature-sensitive mutant collection for strains with conditional defects in growth patterning and identified six mutants (designated hyp for hypercellular). The identified hyp mutations are nonlethal, recessive defects in five unlinked genes (hypA-hypE). Phenotypic analyses showed that these hyp mutants have aberrant patterns of septation and show defects in polarity establishment and tip growth, but they have normal nuclear division cycles and can complete the asexual growth cycle at restrictive temperature. Temperature shift analysis revealed that hypD and hypE play general roles in hyphal morphogenesis, since inactivation of these genes resulted in a general widening of apical and subapical cells. Interestingly, loss of hypA or hypB function lead to a cessation of apical cell growth but activated isotropic growth and mitosis in subapical cells. The inferred functions of hypA and hypB suggest a mechanism for coordinating apical growth, subapical cell arrest, and mitosis in A. nidulans.

Fungi impact humans and the environment in many ways, for good and ill. Some fungi support the growth of terrestrial plants or are used in biotechnol

High spatial resolution methods to assess the physiology of growing cells should permit analysis of fungal biochemical composition. Whole colony methods cannot capture the details of physiology and organism–environment interaction, in part because the structure, function and composition of fungal hyphae vary within individual cells depending on their distance from the growing apex. Surface Enhanced Raman Scattering (SERS) can provide chemical information on materials that are in close contact with appropriate metal substrates, such as nanopatterned gold surfaces and gold nanoparticles (AuNPs). Since nanoparticles can be generated by living cells, we have created conditions for AuNP formation within and on the surface of Aspergillus nidulans hyphae in order to explore their potential for SERS analysis. AuNP distribution and composition have been assessed by UV-Vis spectroscopy, fluorescence light microscopy, transmission electron microscopy, and scanning transmission X-ray microscopy. AuNPs were often associated with hyphal walls, both in the peripheral cytoplasm and on the outer wall surface. Interpretation of SERS spectra is challenging, and will require validation for the diversity of organic molecules present. Here, we show proof-of-principle that it is possible to generate SERS spectra from nanoparticles grown in situ by living hyphae.