ISSN 1607-6729, Doklady Biochemistry and Biophysics, 2007, Vol. 413, pp. 47–49. © Pleiades Publishing, Ltd., 2007. Original Russian Text © K.B. Aslanidi, M.A. Tsyganov, A.E. Ivanova, T.A. Belozerskaya, G.R. Ivanitskii, 2007, published in Doklady Akademii Nauk, 2007, Vol. 413, No. 2, pp. 261–263. 47 Microscopic fungi are potent destructors and utiliz- ers of organic and some inorganic substances. For example, microscopic fungi were shown to actively cover and destruct engineering and technological con- structions in the exclusion zone of the Chernobyl Atomic Power Plant [1]. The main sources of radioac- tive contamination in this zone are the so-called “hot” particles of 1–100 μm in size, which have various radi- onuclide composition and possess a high specific activ- ity (10–1000 Bq/particle) [2]. Upon interaction with water, all types of sources radiation generate active rad- icals, primarily hydrogen peroxide as the most stable compound [3]. These isolated radiation sources create local gradients of hydrogen peroxide on moist sub- strates, affecting the growth rate of microscopic fungus hyphae. In this work, we used mathematic modeling to study the dynamics of growth of colonies of microscopic fungi in a hydrogen peroxide gradient. A study of nine strains of four species of filamen- tous fungi [4, 5] revealed two principally different types of growth responses of filamentous fungi to hydrogen peroxide (Fig. 1). Hypha elongation rate of type A fungi gradually decreased as the hydrogen peroxide concen- tration increase and completely stopped at high hydro- gen peroxide concentrations (10 –2 –10 –1 M). Type B was characterized by an initial increase in the hypha elonga- tion rate upon an increase in the hydrogen peroxide concentration from 10 –6 to 10 –5 M, which was then changed by a decrease and complete stop of growth at high hydrogen peroxide concentrations (10 –2 –10 –1 M). In the fungus strains isolated from background hab- itats, both types (A and B) of responses to hydrogen peroxide have been observed, whereas the strains iso- lated from the radioactively contaminated habitats had only the first (A) type of response. Extremal types of dependences of the hypha growth on the hydrogen per- oxide concentration were found in strains A. alternata 60 and A. alternata 224, isolated from radioactively uncontaminated habitats. The hypha growth of strain A. alternata 60 was activated by low concentrations of hydrogen peroxide (type B), whereas strain A. alternata 224 was characterized by a continuous decrease in the Simulation of Growth of Colonies of Filamentous Fungi in a Hydrogen Peroxide Gradient K. B. Aslanidi a , M. A. Tsyganov a , A. E. Ivanova b , T. A. Belozerskaya c , and Corresponding Member of the RAS G. R. Ivanitskii a Received October 9, 2006 DOI: 10.1134/S1607672907020020 a Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow oblast, 142290 Russia b Faculty of Soil Science, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia c Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 119071 Russia BIOCHEMISTRY, BIOPHYSICS, AND MOLECULAR BIOLOGY 140 120 100 80 60 40 20 0 –9 –8 –7 –6 –5 –4 –3 –2 –1 log C[å] V m (C), % 1 2 3 4 5 6 7 8 9 Type Ä Type B Fig. 1. Dependences of relative rates of hypha elongation (V m (C), %) for different species and strains of filamentous fungi on the hydrogen peroxide concentration ( [M]) in an agar nutrient medium. The rates were normalized to the corresponding values of elongation rates, obtained in the hydrogen peroxide-free medium (10 –9 M) [6]. Designa- tions: (1) M. hiemalis; (2) A. alternata 60; (3) A. alternate 224; (4) C. cladosporioides 396; (5) P. lilacinus 10; (6) A. alternate 56; (7) C. cladosporioides 5; (8) C. cla- dosporioides 4; (9) P. lilacinus 1941. C log