Al-Otaibi, N. | bioRxiv Science

bioRxiv2022

Anticancer and antibacterial activities of secondary bioactive compounds from endosymbiotic bacteria of aphid and their surrounding organisms (predator and protector)

Secondary metabolites of bacterial origin are a valuable source of diverse molecules with antibacterial and anticancer activities. In the current study, 10 endosymbiotic bacteria were isolated from aphids, aphid predators and ants. Bacterial strains were identified based on the 16S rRNA gene. Crude extracts were prepared from each isolated bacteria and tested for their antibacterial activities using the disk diffusion method. The extracts of three bacterial species; Planococcus sp, Klebsiella aerogenes, Enterococcus avium from Aphis punicae, Chrysoperia carnea and Tapinoma magnum, respectively were found to have strong antibacterial activities against one or more of the five pathogenic bacteria tested. The inhibition zones ranged from 10.00{+/-} 0.13 to 20.00{+/-} 1.11mm with minimum inhibitory concentration (MIC) values ranged from 0.156 mg/mL to 1.25 mg/mL. The notable antibacterial activity was for the crude extract of K. aerogenes against Klebsiella pneumonia and Escherichia coli at MIC value of 0.156 mg/mL. The cytotoxic activity of the crude extracts varied according to the tested cell line. The most cytotoxic effect was for the extracts of K. aerogenes and E. avium at a concentration of 0.16 mg/mL against lung carcinoma epithelial cells (A549) with cell reduction of 79.4% and 67.2%, respectively. Crude extracts of K. aerogenes and Pantoea agglomerans at a concentration of 0.16 mg/mL showed 69.4% and 67.8% cell reduction against human colon cancer (Hct116), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of three crude extracts revealed the presence of several bioactive secondary metabolites that have been reported previously to possess antibacterial and anticancer properties. To the best of our knowledge, this is the first study to report the biological activities of endosymbiotic bacteria from aphids, aphid predators and ants. The promising data presented in this study opens a new avenue for alternative drugs to overcome the continuous emergence of multidrug-resistant bacteria and to find alternative drugs for traditional cancer therapies.

biochemistry↗

bioRxiv2019

Dissolved organic matter and heterotrophic prokaryotes diel patterns reveal enhanced growth at the mesopelagic fish layer during daytime

Contrary to epipelagic waters, where biogeochemical processes closely follow the light and dark periods, little is known about diel cycles in the oceans mesopelagic realm. Here, we monitored the dynamics of dissolved organic matter (DOM) and planktonic heterotrophic prokaryotes every 2 h for one day at 0 and 550 m (a depth occupied by vertically migrating fish during light hours) in oligotrophic waters of the central Red Sea. We additionally performed predator-free seawater incubations of samples collected from the same site both at midnight and at noon. Comparable in situ variability in microbial biomass and dissolved organic carbon concentration suggests a diel supply of fresh DOM in both layers. The presence of fish in the mesopelagic zone during daytime promoted a sustained, longer growth of larger prokaryotic cells. The specific growth rates were consistently higher in the noon experiments from both depths (surface: 0.34 vs. 0.18 d-1, mesopelagic: 0.16 vs. 0.09 d-1). Heterotrophic bacteria and archaea in the mesopelagic fish layer were also more efficient at converting DOM into new biomass. These results suggest that the oceans twilight zone receives a consistent diurnal supply of labile DOM from diel vertical migrating fishes, enabling an unexpectedly active community of heterotrophic prokaryotes.

ecology↗