Cancer is one of the most deadly diseases in the world, being related to the disordered growth of defective cells which produces harmful substances to the body. In this context, one of the great challenges of science is finding an effective bioactive compound for treating of this disease and microorganisms from restrictive environments, such as caves, are indicated as a promising source of these compounds. The objective of this work was to evaluate the extracts cytotoxic effects obtained from cultures of two bacterial strains isolated from Pedra da Cachoeira cave, Altamira-PA, located in a preserved forest fragment in the Eastern Amazon. Bacteria were identified by DNA sequencing analysis encoding ribosomal RNA. The choice of the ideal period of microbial development, aiming at the biocompounds production, was based in a kinetic study realized from a growth curve. Organic extracts were produced after 30 hours (stationary phase) and 40 hours (decline phase) of cultivation, obtaining four extracts by liquid -liquid partition of culture medium and four extracts from the bacterial cells. In vitro cytotoxicity tests were performed with B16F10 tumor cells using the MTT method. From the phylogenetic analyzes of the DNA sequences of both strains, a cluster with the species Bacillus subtilis was verified. The extracts obtained were subjected to cytotoxic assays and their cell viability was evaluated based on the minimum inhibitory concentration (IC50) and selectivity index (IS), with the CV26AI30H extract having an IC50 value of 83.99 and IS greater than 4.70.

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