Gamma Radiation Dose-Response of Gram-Positive and Gram-Negative Bacteria

Abstract

Bacterial mutagenesis induced through gamma irradiation is one of the techniques for strain improvement. The DNA changes caused by radiation and reactive oxygen species created from water radiolysis induced bacterial mutagenesis. There is always a constant demand for better quality strains from the bioprocessing industries to speed up production and increase yield. Bacillus strains are Gram-positive bacteria whereas Escherichia coli is a Gram-negative bacteria; they are all model organisms used by the bioprocessing industries. This study investigates the effect of acute gamma irradiation on Gram-positive Bacillus megaterium NMBCC50018, Bacillus subtilis NMBCC50025 and Gram-negative Escherichia coli. Samples were irradiated in Gamma Cell Acute Irradiation Facility at Malaysian Nuclear Agency with irradiation doses from 0.1 kGy to 2.1 kGy. The radiation sources were from two Cesium-137 sealed sources. Dose responses are crucial information for bacterial mutagenesis studies. The survival curves of viable bacterial cell count versus radiation doses were plotted to determine dose-response and lethal dose, 50% (LD50). Viable cells reduce as irradiation doses increase. The LD50 for Bacillus megaterium NMBCC50018, Bacillus subtilis NMBCC50025 and Escherichia coli were 1.2 kGy, 0.2 kGy, and 0.03 kGy, respectively. Bacillus megaterium NMBCC50018 was most resistant to gamma radiation. Dose responses between Gram-positive and Gram-negative bacteria were concluded to be different.

Bacillus megaterium: Evaluation of Chemical Nature of Metabolites and Their Antioxidant and Agronomics Properties

“…These results confirm previous internals results which showed that B. megaterium produces several phenols [29]. A GC-MS analysis of BC Dichlo highlights the presence of cyclic dipeptides (28,34,35,38,39,40,41,46,49,54,57,64) and butanediol (5 ′ , 6 ′ ). Less information is available for BC EtAc and BuOH extracts, with the description of butanediol (5 ′ , 6 ′ ) mostly being available.…”

“…These results are supported in the literature by the description of some exopolysaccharides secretions by B. megaterium [24]. Several studies have also described B. megaterium as a producer of extracellular proteins [19,28]. It could explain that proportion of proteins is still important in BC polar extracts with 10.5 to 19.4%.…”

“…It could explain that proportion of proteins is still important in BC polar extracts with 10.5 to 19.4%. It could also explain that intensity and nature of cyclic dipeptides are changing from CS2 to BC (28,30,34,35,38,39,40,41,46,49,51,54,57,64) and that different peaks on DAD chromatogram suggesting different aromatic compounds from CS2.…”

Unraveling radiation resistance strategies in two bacterial strains from the high background radiation area of Chavara-Neendakara: A comprehensive whole genome analysis

“…The samples were irradiated at 0.77 kGy/hr dose rate and collected at an interval of every one kGy; 1 kGy took ~1 hr 18 min, 2 kGy took ~2 hr 36 min, 3 kGy took ~3hr 54 min, 4 kGy took ~5 hr 12 min and 5 kGy took ~6 hr 30 min. Similar dose rate of 0.7 kGy/hr was used to irradiate Bacillus samples [ 34 ]. Care was taken to maintain accuracy in dosage measurements, so as to avoid chances of experimental error.…”