A chemically defined medium for production of actinomycin D by Streptomyces parvulus

A Chemically Defined Medium for Production of Actinomycin D by Streptomyces parvulus

Maria de Fátima Vieira de Queiroz Sousa1^*, Carlos Edison Lopes¹ and Nei Pereira Júnior2

¹ Departmento de Antibióticos, Centro de Ciências Biológicas da Universidade Federal de Pernambuco, Recife, 50670-901, Pernambuco, ²Departamento de Engenharia Bioquímica, Escola de Química da Universidade Federal do Rio de Janeiro, Rio de Janeiro 21949-900, Brasil

ABSTRACT

A chemically defined medium consisting of D(+)fructose, L(-)threonine, K₂HPO₄, MgSO₄.7H₂O, ZnSO₄.7H₂O, CaCl₂.2H₂O, FeSO₄.7H₂O and deionized water, was developed to maximize the synthesis of actinomycin D by the Streptomyces parvulus DAUFPE 3124 strain. This medium resulted in the maximum antibiotic concentration of 133mg/L while using the original medium the production of actinomycin D was poor not surpassing 43mg/L.

Key words : Actinomycin D, production, Streptomyces. parvulus, synthetic medium

INTRODUCTION

The actinomycins are a family of chromopeptide antibiotics that present antitumoral properties, being employed in the treatment of several human neoplasies (Waksman & Furness, 1960). Structurally, they have a chromophorous group, identical in all actinomycins, and two pentapeptide chains with a variable composition of amino acids (Brockmann, 1960). They are synthesized by Streptomyces as mixtures of different actinomycins, however, the S. parvulus species produces actinomycin D almost exclusively (>95%) (Meienhofer & Atherton, 1973). Over the last ten years, research into actinomycin D has been directed mainly towards clinical applications and no work related to production was found. In a previous study the authors optimized a complex medium for the production of actinomycin D by S. parvulus DAUFPE 3124 strain, increasing the final antibiotic concentration from 245 mg/L to 530 mg/L (Sousa, et al., 1997). Few papers have been found that focus on the nutritional requirements of Streptomyces species for achieving a high actinomycin yield (Katz et al.,1958; Williams & Katz, 1977). Katz et al. (1958) showed that the maximum antibiotic synthesis ocurred in a chemically defined medium containing L(-) galactose (10 g/L), L(-) glutamic acid (2 g/L), phosphate (1 g/L) and mineral salts. Although this composition proved to be satisfactory for production of actinomycin mixtures by S. antibioticus, the synthesis of actinomycin D by S. parvulus was rather poor and extremely variable. Williams & Katz (1977) proposed a chemically defined medium for the synthesis of high yields (500 to 600 mg/L) of actinomycin D by S. parvulus ATCC 12434. Dalili & Chau, (1988) working with the same medium and the same strain immobilized in calcium alginate, using an air lift column operating under discontinuous, fed batch and continuous conditions, obtained 50, 73 and 80 mg/L, respectively. However, since nutritional requirements for growth and product formation vary from strain to strain, the medium suggested by Williams & Katz (1977) resulted in a low antibiotic production by the S. parvulus DAUFPE 3124 strain. This work presents a set of experiments that culminated in the development of a chemically defined medium in which higher concentration of actinomycin D was achieved using the S. parvulus DAUFPE 3124 strain.

MATERIALS AND METHODS

Microorganism: Streptomyces parvulus DAUFPE 3124 strain was used in all assays. This strain was maintained on slants of 4 g/L glucose, 4 g/L yeast extract and 10 g/L malt extract agar medium. Incubation was carried out for 3 to 5 days at 30° C until gray spores developed and the slants were stored at 4°C.

Preparation of Spore Suspension: The spores were scraped from the surface of heavily sporulated slants with 3 ml of 9 g/L NaCl solution containing 1 ml/L of Tween 80, following the Hopwood et al., (1985) technique. The spore concentration was quantified in the suspension and stored in the freezer at -4°C.

Growth and Production Media: The medium used during the biomass growth had the following composition: 5 g/L tryptone and 3 g/L yeast extract. In the antibiotic production several media were used with pH adjusted to 7.0 and in all of them, the following basal mineral salts medium K₂HPO₄ 1.0 g/L; MgSO₄.7H₂O 25 mg/L; ZnSO₄.7H₂O 25 mg/L; CaCl₂.2H₂O 25 mg/L; FeSO₄.7H₂O 25 mg/L was used. A number of amino acids and carbohydrates were tested as carbon and nitrogen sources so that the C/N ratio was held around 41.7, as recommended by Williams & Katz (1977), and several C/N ratios were employed when the best carbon and nitrogen sources were selected. The amino acids, carbohydrates and salts were sterilized separately and added just prior to inoculation.

Experimental Procedure: The growth was performed in two steps. In the first one, the inoculum was prepared in a 250 ml flask containing 25 ml of growth medium inoculated with 50 ml of spore suspension (8.0 x 10⁷ cfu/ml).The flasks were placed on a rotary shaker at 250 rpm at 30ºC for 48 h. In the second step, 20 ml of the mycelial suspension was used to inoculate a 2000 ml flask containing 200 ml of growth medium which was subjected to the same conditions as described above for 24 h. The antibiotic production was conducted in 500 ml shaken flasks, containing 50 ml of the fermentation medium. These flasks were inoculated with 3 ml of mycelial suspensions and subjected to the same conditions as cited above. Samples were taken at 24 hour intervals and analysed in terms of actinomycin D concentration by spectrophotometric method (Katz & Weissbach, 1963). The data reported in all experiments represent the yield of actinomycin D for 144 hours of cultivation except for the last one.

RESULTS AND DISCUSSION

As observed by Williams & Katz (1977), the association of L(-)glutamic acid with another amino acid potentialized the synthesis of actinomycin D by S. parvulus ATCC 12434. This fact was tested using the S. parvulus DAUFPE 3124 and the results are shown in the Table 1. This table shows that a maximum concentration of actinomycin D was obtained when the L(-) glutamic acid was combined with L(-)histidine, L(-)ornithine or L(-)threonine (70.8 mg/L).

Assays were carried out with several L(-) amino acids to determine the one more appropriated for antibiotic synthesis (Table 2). The best result (87.7 mg/L) was achieved when L(-) threonine was the sole nitrogen source. Surprisingly, this result was higher than the one obtained (70.8 mg/L) by the combination of L(-) glutamic acid and L(-) threonine. In the literature there is no explanation for this effect and, furthermore, it results in a cheaper chemically defined medium composition.

L(-) threonine is one of the amino acids constituents of the actinomycin molecules. Katz et al. (1965) employed labeled L(-) threonine - ¹⁴C in experiments of short incubation and verified that S. antibioticus strains metabolizes this amino acid in both protein and actinomycin synthesis. Due to this evidence, these authors came to the conclusion that there is an intracellular pool of threonine commom to the two synthesizer systems although these systems were differents.

A number of carbohydrates were investigated as carbon sources for actinomycin-D production employing the basal mineral salts medium with 1.8 g/L of threonine and the results can be seen in Table 3. This table shows that D(+) fructose was superior to the others carbohydrates tested in the same concentration. This result agrees with the findings of Williams & Katz (1977), who affirmed that D fructose was the most effective carbon source for antibiotic synthesis by S. parvulus. No actinomycin-D production was detected when glucose and galactose were employed as sole carbon sources. Gallo & Katz (1972) demonstrated that glucose supports a rapid growth rate of S. antibioticus, but it exerts severe catabolite repression in antibiotic production, particulary in the synthesis of phenoxazinone synthase, an essential enzyme for the formation of the actinomycin chromophorous group. Williams & Katz (1977) working with S. parvulus ATCC 12434, also showed the repression caused by glucose additions to a chemically defined medium containing fructose (40g/L) as the main substrate. Marshall et al. (1968) verified the inhibitory effect of galactose on phenoxazinone synthetase specific activity in cells of S. antibioticus harvested after six hours of incubation.

To evaluate the quantitative influence of C/N ratios upon antibiotic synthesis by S. parvulus DAUFPE 3124, the concentration of D(+) fructose (20 g/L) was held constant while the amount of L(-) threonine was varied to provide different C/N ratios in the medium. The results of these experiments are shown in Table 4.

Higher production of actinomycin-D (67.9mg/L) was achieved at C/N ratio of 22.5 which corresponded to 20 g/L D(+) fructose and 3.57 g/L L(-) threonine.

Comparative study of the medium reported by Williams & Katz (1977) and the one developed in this work was done employing S. parvulus DAUFPE 3124 strain. The concentration curves of actinomycin D production are shown in Figure 1 where can see that the antibiotic concentration reached the maximum value of 133 mg/L in the proposed medium and in the medium suggested by cited authors the maximum value was 43 mg/L.

The results clearly show the dependence of the antibiotic synthesis on medium constituents. The medium developed in this study to obtain high yield of actinomycin D by S. parvulus DAUFPE 3124 has the following composition: 20 g/L D(+) fructose; 3.57 g/L L(-) threonine; 1.0 g/L K₂HPO₄; 25 mg/L MgSO₄.7H₂O, 25 mg/L ZnSO₄.7H₂O, 25 mg/L CaCl₂.2H₂O and 25 mg/L FeSO₄.7H₂O. This composition allowed an improvement of over 200 % in the concentration of actinomycin D.

ACKNOWLEDGMENTS

This work was supported in part by Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco.

RESUMO

Um meio quimicamente definido composto de D (+) frutose, L (-) treonina, K₂HPO₄, MgSO₄.7H₂O, ZnSO₄.7H₂O, CaCl₂.2H₂O, FeSO₄.7H₂O e água deionizada, foi desenvolvido para maximizar a síntese de actinomicina D pelo Streptomyces parvulus DAUFPE 3124. O meio proposto resultou numa concentração antibiótica máxima de 133 mg/L enquanto que no meio inicial a produção antibiótica foi baixa, não ultrapassando 43 mg/L.

Received: July 05, 2000;

Revised: September 21, 2000;

Accepted: November 30, 2000.

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*

Author for correspondence

Publication Dates

• Publication in this collection
  23 Jan 2002
• Date of issue
  Sept 2001

History

• Accepted
  30 Nov 2000
• Reviewed
  21 July 2000
• Received
  05 July 2000