<em>De Novo</em> Peroxisome Biogenesis in <em>Penicillium Chrysogenum</em> Is Not Dependent on the Pex11 Family Members or Pex16

<div><p>We have analyzed the role of the three members of the Pex11 protein family in peroxisome formation in the filamentous fungus <em>Penicillium chrysogenum</em>. Two of these, Pex11 and Pex11C, are components of the peroxisomal membrane, while Pex11B is present at the endoplasmic reticulum. We show that Pex11 is a major factor involved in peroxisome proliferation. We also demonstrate that <em>P. chrysogenum</em> cells deleted for known peroxisome fission factors (all Pex11 family proteins and Vps1) still contain peroxisomes. Interestingly, we find that, unlike in mammals, Pex16 is not essential for peroxisome biogenesis in <em>P. chrysogenum</em>, as partially functional peroxisomes are present in a <em>pex16</em> deletion strain. We also show that Pex16 is not involved in <em>de novo</em> biogenesis of peroxisomes, as peroxisomes were still present in quadruple Δ<em>pex11</em> Δ<em>pex11B</em> Δ<em>pex11C</em> Δ<em>pex16</em> mutant cells. By contrast, <em>pex3</em> deletion in <em>P. chrysogenum</em> led to cells devoid of peroxisomes, suggesting that Pex3 may function independently of Pex16. Finally, we demonstrate that the presence of intact peroxisomes is important for the efficiency of ß-lactam antibiotics production by <em>P. chrysogenum</em>. Remarkably, distinct from earlier results with low penicillin producing laboratory strains, upregulation of peroxisome numbers in a high producing <em>P. chrysogenum</em> strain had no significant effect on penicillin production.</p>