THIRTY-FOUR actinobacteria strains were recovered from diorite rocks of South Sinai, Egypt, using direct isolation. The predominant types were Streptomyces and Nocardioides (8 strains, each), followed by Kitasatosporia and Nocardiopsis (4 strains, each). Twenty-five strains were active against Escherichia coli NCMB 11943, two clinical cultures (Staphylococcus aureus, Candida albicans) and/or three solid tumor cell lines (colon C38, colon H-116, lung H-125 M).
One strain showed potent activity towards S. aureus, C. albicans and inhibited colon HCT116 and liver HepG2 carcinoma cell lines at IC50 3.2 and 1.3μg/ml, respectively. Phylogenetic analysis indicated its identity as Micromonospora citrea, at 99.6% similarity. MALDI/TOF-MS analysis of its metabolic extract revealed 18 compound masses, molecular weight range of 585.52 to 669.64Da. Statistical general full factorial design indicated varying effects of four-carbon and three-nitrogen sources on its bioactivity. Starch and potassium nitrate at 1% w/v, as C- and N-sources, respectively, were significantly effective for enhancing the antitumor activity up to 1.3-fold (P = 0.007).
M. citrea extract revealed non-significant cytotoxic effects in rats, at 10mg/kg injection dose, every two days for two weeks. The kidney and liver functions were not significantly impaired, as indicated from results of serum enzymatic activities, urea, total protein and albumin levels. The strain was deposited at the Egyptian Microbial Culture Collection as M. citrea SP1 EMCC 1923 and was patent registered (Egyptian Patent Office, No. 655). These results indicate the importance of actinobacteria inhabiting arid rocks of Sinai for production of promising antibiotic leads.