Isolation, cytotoxic activity and phylogenetic analysis of Bacillus sp. bacteria associated with the red sea sponge Amphimedon ochracea

Most of marine sponges harbor dense and diverse microbial communities of bioactivity importance. Four Gram positive bacterial cultures (HA-21, HA-68, HA- MS-105 and HA-MS-119) were isolated from the sponge Amphimedon ochracea, collected from the Red Sea coast of Egypt. Bacterial species were identified based on the phylogenetic analysis of the nucleotide sequences of their 16S rDNA genes. The Sequences similarity values of 98% - 100% to other strains in the NCBI database showed strong similarities with the 16S rDNA genes of firmicutes (Bacillus sp.). The four bacterial species were submitted to the GenBank database and had accession numbers of: HA-21 [JQ-768238]; HA-68 [JQ751264]; HA-MS-105 [JQ768239]; HAMS-119 [JQ768240]. The cytotoxic activities of the bacterial isolates were tested against three established human cancer cell lines; HepG2 (hepatocellular carcinoma), HCT (colon carcinoma) and MCF-7 (breast carcinoma). The inhibitory effect on these cell lines, measured by MTT cell assay protocol, revealed promising cytotoxic activity of the four isolates (IC50 values (μg/mL) were: HA-21: 13.2, 9.3 and 12.2; HA-68: 10.42, 4.3 and 5.5; HA-MS-105: 46.9, 28.6 and 21.3; HAMS-119: 10.42, 6.3 and 22.1; respectively). The recovery of bacterial strains with cytotoxic activity suggests that marine invertebrates remain a rich source for the isolation of culturable isolates capable of producing novel bioactive secondary metabolites.