J. Basic Microbiol. 40 (2000) 5 – 6, 333 – 342 ( 1 Natural and Microbial Products Dept., National Research Centre, Tahrir Street, Dokki, Cairo, Egypt and 2 Bioprocess Development Dept. Genetic Engineering and Biotechnology Research Institute, Mubarak City for Scientific Research, Burg-Al-Arab, Alexandria, Egypt) Influence of inoculum type and cultivation conditions on natamycin production by Streptomyces natalensis HESHAM A. EL-ENSHASY 1,2 , MOHAMED A. FARID 1 and EL-SAYED A. EL-SAYED 1 (Received 29 June 2000/Accepted 22 August 2000) This study demonstrates the effect of cultivation conditions on the production of natamycin. Of these conditions, the effect of oxygen limitation and type of inoculum were extensively investigated. In- creasing the shaking speed and decreasing the medium volume improved both the volumetric and specific natamycin production. Also, decreasing the dissolved oxygen level in the cultivation medium through the addition of soluble biopolymer (alginate) resulted in a significant decrease in the natamy- cin yield without effect on the cell growth. On the other hand, spore inoculum yielded higher concen- tration of natamycin compared to the vegetative cells by about 40%. The maximal cell productivity based on biomass [Y p/x ] of about 0.4 [g/g] was obtained by using shake flask of 50 ml working volume agitated at 200 rpm and the inoculum was in the form of spore 2 K 10 8 spores/ml. These results showed that the production process of natamycin is highly dependent on oxygen level in the cultiva- tion medium and type of inoculum as well. Actinomycetes belongs to genus Streptomyces are characterized by their high ability to produce a variety of secondary metabolites most of them with antibiotic activity. Of these antibiotics natamycin, a polyene compound produced in submerged culture of Streptomyces natalensis, is very attractive antifungal substance. The importance of this antibiotic lies in its wide spectrum activity against both molds and yeasts with low toxicity against mam- malian cells. Beside its medical applications, natamycin is used in food preservation and approved as a GRAS (Generally Regarded As a Safe) product by FDA (Food and Drug Administration) for use in food manufacturing. Therefore, natamycin is widely used in many food industries to increase the shelf time without any effect on flavor or appearance (DAVIDSON and DOAN 1993). In the antibiotic production research, mainly two levels of control regulate the polyene antibiotics biosynthetic capacity in actinomycetes. The first is the nature and concentrations of different medium components such as carbon, nitrogen and phosphate sources (MARTIN and MCDANIEL 1977, MARTIN and DEMAIN 1980, GIL et al. 1984). Also other medium constituents like beef, meat and yeast extracts are necessary for the biosynthesis of natamy- cin (STRUYK and WAISVISZ 1975, EISENSCHINK et al. 1993, EISENSCHINK et al. 1997, FARID et al. 2000). The second level of control is the cultivation conditions such as pH, temperature, oxygen supply, type and concentration of inoculum. Microbial growth and antibiotic production by spore forming strains like actinomycetes are not only highly dependent on medium composition but also cultivation conditions as well. Of those different cultivation conditions, aeration plays an important role in the growth and production of antibiotics by actinomycetes. Oxygen limitation is able to induce or repress the production of antibiotic like other nutrients as observed in case of carbon and nitrogen limitation (OKABE et al. 1992, CLARK et al. 1995, KOJIMA et al. 1995, HEYDARIAN et al. 1996). In shake flask cultures, the most important operating parameters affecting the gas-liquid mass transfer in the cultivation media are mainly the shape and volume of culti-