Radioresistance and radiosensitivity: a biophysical approach on bacterial cells robustness

The study of radiosensitivity and radioresistance of organisms exposed to ionizing radiation has acquired additional relevance since a new bio-concept, coined as The primacy of Proteome over Genome, was proposed and demonstrated elsewhere a few years ago. According to that finding, genome integrity would require an actively functioning Proteome. However, when exposure to radiation takes place, Reactive Oxygen Species (ROS) from water radiolysis induce protein carbonylation (PC), an irreversible oxidative Proteome damage. The bio-models used in that study were the radiosensitive Escherichia coli and the extraordinarily robust Deinococcus radiodurans. The production of ROS induces protective reactions rendering them non-reactive forms. Protective entities present in the cytosol, moieties smaller than 3 kDa, shield the Proteome against ROS, yielding protection against carbonylation. Shown in the present study is the fact that the fate of proteins functionality is determined by the magnitude of the Protein Carbonylation Yield (Y_PC), a quantity here analytically defined using published Y_PC numerical results. Analytical Y_PC expressions for E. coli and D. radiodurans were the input for a phenomenological approach, where the radiobiological magnitudes P_P and P_N, the probabilities for production of protein damage and ROS neutralization, respectively, were also analytically deduced. These highly relevant magnitudes, associated with key radiosensitivity and radioresistance issues, are addressed and discussed in this study. Among the plethora of information and conclusions derived from the present study, those endowed with higher conceptual degree, vis-à-vis the "Primacy of Proteome over Genome" concept, are as follows: (1) the ROS neutralization process in D. radiodurans reaches a maximum at a dose interval corresponding to the repairing shoulder. Therefore, it is a signature of the higher efficiency of the PC neutralization process. (2) ROS neutralization in D. radiodurans is nearly one order of magnitude higher than in E. coli, thus accounting for its extraordinary radioresistance. (3) Both physical (ROS-induced carbonyl radicals) and biological (protein modifications) processes are imbedded in the Protein Carbonylation Yield. The amalgamation of these two processes was accomplished by means of a statistical formalism.

Microcystin-LR bioaccumulation and depuration kinetics in lettuce and arugula: Human health risk assessment

Microcystin-LR (MC-LR) is one of the most toxic and common microcystins (MCs) variant found in aquatic ecosystems. Little is known about the possibility of recovering microcystins contaminated agricultural crops. The objectives of this study were to determine the bioaccumulation and depuration kinetics of MC-LR in leaf tissues of lettuce and arugula, and estimate the total daily intake (ToDI) of MC-LR via contaminated vegetables by humans. Arugula and lettuce were irrigated with contaminated water having 5 and 10μgL(-1) of MC-LR for 7days (bioaccumulation), and subsequently, with uncontaminated water for 7days (depuration). Quantification of MC-LR was performed by LC-MS/MS. The one-compartment biokinetic model was employed for MC-LR bioaccumulation and depuration data analysis. MC-LR was only accumulated in lettuce. After 7days of irrigation with uncontaminated water, over 25% of accumulated MC-LR was still retained in leaf tissues of plants treated with 10μgL(-1) MC-LR. Total daily toxin intake by adult consumers (60kg-bw) exceeded the 0.04μgMC-LRkg(-1) limit recommended by WHO. Bioaccumulation was found to be linearly proportional to the exposure concentration of the toxin, increasing over time; and estimated to become saturated after 30days of uninterrupted exposure. On the other hand, MC-LR depuration was less efficient at higher exposure concentrations. This is because biokinetic half-life calculations gave 2.9 and 3.7days for 5 and 10μgL(-1) MC-LR treatments, which means 29-37days are required to eliminate the toxin. For the first time, our results demonstrated the possibility of MC-LR decontamination of lettuce plants.

Lettuce irrigated with contaminated water: Photosynthetic effects, antioxidative response and bioaccumulation of microcystin congeners

The use of microcystins (MCs) contaminated water to irrigate crop plants represents a human health risk due to their bioaccumulation potential. In addition, MCs cause oxidative stress and negatively influence photosynthetic activities in plants. The present study was aimed at investigating the effect of MCs on photosynthetic parameters and antioxidative response of lettuce. Furthermore, the bioaccumulation factor (BAF) of total MCs, MC-LR and MC-RR in the vegetable after irrigation with contaminated water was determined. Lettuce crops were irrigated for 15 days with water containing cyanobacterial crude extracts (Microcystis aeruginosa) with MC-LR (0.0, 0.5, 2.0, 5.0 and 10.0 µg L(-1)), MC-RR (0.0, 0.15, 0.5, 1.5 and 3.0 µg L(-1)) and total MCs (0.0, 0.65, 2.5, 6.5 and 13.0 µg L(-1)). Increased net photosynthetic rate, stomatal conductance, leaf tissue transpiration and intercellular CO2 concentration were recorded in lettuce exposed to different MCs concentrations. Antioxidant response showed that glutathione S-transferase activity was down-regulated in the presence of MCs. On the other hand, superoxide dismutase, catalase and peroxidase activities were upregulated with increasing MCs concentrations. The bioaccumulation factor (BAF) of total MCs and MC-LR was highest at 6.50 and 5.00 µg L(-1), respectively, while for MC-RR, the highest BAF was recorded at 1.50 µg L(-1) concentration. The amount of total MCs, MC-LR and MC-RR bioacumulated in lettuce was highest at the highest exposure concentrations. However, at the lowest exposure concentration, there were no detectable levels of MC-LR, MC-RR and total MCs in lettuce. Thus, the bioaccumulation of MCs in lettuce varies according to the exposure concentration. In addition, the extent of physiological response of lettuce to the toxins relies on exposure concentrations.