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Spatial Differentiation in the Vegetative Mycelium of Aspergillus niger ^,

Ana M. Levin,^1, Ronald P. de Vries,^1, Ana Conesa,^2, Charissa de Bekker,¹ Manuel Talon,² Hildegard H. Menke,³ Noel N. M. E. van Peij,³ and Han A. B. Wösten^1*

Microbiology, Institute of Biomembranes, Utrecht University, Padulaan 8, 3584 CH Utrecht, The Netherlands,¹ Centro de Genomica, Instituto Valenciano de Investigaciones Agrarias, Moncada, Valencia, Spain,² DSM Food Specialties, P.O. Box 1, 2600 MA Delft, The Netherlands³

Received 5 July 2007/ Accepted 10 October 2007

Fungal mycelia are exposed to heterogenic substrates. The substrate in the central part of the colony has been (partly) degraded, whereas it is still unexplored at the periphery of the mycelium. We here assessed whether substrate heterogeneity is a main determinant of spatial gene expression in colonies of Aspergillus niger. This question was addressed by analyzing whole-genome gene expression in five concentric zones of 7-day-old maltose- and xylose-grown colonies. Expression profiles at the periphery and the center were clearly different. More than 25% of the active genes showed twofold differences in expression between the inner and outermost zones of the colony. Moreover, 9% of the genes were expressed in only one of the five concentric zones, showing that a considerable part of the genome is active in a restricted part of the colony only. Statistical analysis of expression profiles of colonies that had either been or not been transferred to fresh xylose-containing medium showed that differential expression in a colony is due to the heterogeneity of the medium (e.g., genes involved in secretion, genes encoding proteases, and genes involved in xylose metabolism) as well as to medium-independent mechanisms (e.g., genes involved in nitrate metabolism and genes involved in cell wall synthesis and modification). Thus, we conclude that the mycelia of 7-day-old colonies of A. niger are highly differentiated. This conclusion is also indicated by the fact that distinct zones of the colony grow and secrete proteins, even after transfer to fresh medium.

Published ahead of print on 19 October 2007.

Supplemental material for this article may be found at http://ec.asm.org/.

These authors contributed equally to the manuscript.

Present address: Bioinformatics Department, CIPF, 46013 Valencia, Spain.