Pedobiologia 51 (2008) 335—342 Selective consumption and digestion of litter microbes by Porcellio scaber (Isopoda: Oniscidea) Karen Ihnen, Martin Zimmer à Zoologisches Institut, Christian-Albrechts-Universita¨t zu Kiel, Am Botanischen Garten 9, D-24118 Kiel, Germany Received 16 March 2007; received in revised form 13 June 2007; accepted 20 June 2007 Dedicated to Werner Topp, Ko¨ln, to mark his retirement and to express gratitude for having had the opportunity to conduct research under his supervision. KEYWORDS Actinomycetes; Feeding preference; Isopoda; Leaf litter-colonising microbes; Nutritive value Summary In feeding preference tests with artificial diets consisting of food sources inoculated with different types of litter microbes, Porcellio scaber was capable of discriminat- ing between different microbe species. Generally, microbial colonisation increased the attractiveness of a given food source, in particular, when the food source was of low quality (cellulose) and when food sources were inoculated with single species of actinomycetes (Streptomyces celluloflavus or Pseudonocardia autotrophica). In most cases, actinomycetes (Gram-positive bacteria) were preferred over both Gram- negative bacteria and fungi, whether or not these microbes exhibited cellulolytic activity. Enzymatic in vitro digestion of both the Gram-positive S. celluloflavus and P. autotrophica was significantly greater than that of Gram-negative bacteria (Pseudomonas fluorescens and Myxococcus xanthus) or fungi (Chaetomium globosum and Fusarium ventricosum). S. celluloflavus biomass was more effectively incorporated into isopod biomass than that of fungi and Gram-negative bacteria; P. autotrophica was more effectively incorporated into isopod biomass than that of Gram-negative bacteria. Based on these results, we hypothesise that P. scaber preferentially feeds on those microbes that it can readily digest. Whether this holds true for other Gram-positive bacteria or for other detritivores awaits investigation. & 2007 Elsevier GmbH. All rights reserved. Introduction Both free-living and symbiotic microbes play a crucial role in the nutrition of soil inverteb- rates that feed upon nitrogen-poor food sources. Terrestrial isopods, for instance, that feed on ARTICLE IN PRESS www.elsevier.de/pedobi 0031-4056/$ - see front matter & 2007 Elsevier GmbH. All rights reserved. doi:10.1016/j.pedobi.2007.06.001 à Corresponding author. Tel.: +49431 8804153; fax: +49 431 880 4747. E-mail address: mzimmer@zoologie.uni-kiel.de (M. Zimmer).