Endophytic selenobacteria as new inocula for selenium biofortification

• Endophytic selenobacteria were able to produce organic selenium forms.
• Stable selenium nanoparticles in selenobacteria were found.
• Se supplementation does not affect the antioxidant response in selenobacteria.
• Se supplementation is not related with drought stress alleviation.

Selenium (Se) is an important micronutrient for human health especially to fortifying the immune system. Chilean Andisols contain low quantities of Se and we have shown that bacteria can be used to enhance Se content of food plants and to improve the antioxidant system against different abiotic stresses. In this study, we prepared inocula based on previously selected Se tolerant endophytic bacteria (Acinetobacter sp. E6.2 and Bacillus sp. E5), which were supplemented with sodium selenite at 5 mM. We studied the effect of this Se amount on bacterial synthesis of organic compounds and Se toxicity, NanoSe size, together with the role of Se in drought stress mitigation. Our results indicated that Acinetobacter sp. E6.2 produced elevated quantities of seleno-methionine (SeMet) and seleno-methyl-selenocysteine (SeMeSeCys) (10 and 3.77 mg kg−1, respectively). However, highly stable NanoSe (Z potential around −40 mV) was the main Se form found in both inocula. The size of NanoSe in Acinetobacter sp. was greater than in Bacillus sp. over time (i.e. 213 ± 3.4 nm and 169 ± 0.92 nm, respectively at 24 h). Bacteria selenium supplementation did not induce oxidative stress due to similar superoxide dismutase (SOD) and catalase (CAT) activities. Selenium did not affect cell tolerance to water deficit due to similar proline and indole acetic acid (IAA) production under drought stress conditions. The findings of this study suggest that these new endophytic bacteria inocula could be effective for Se biofortification.