Saccharomonospora actinobacterium alleviates phytotoxic hazards of tungsten nanoparticles on legumes? growth and osmotic status

Like its bulk counterpart, tungsten (W) nanoparticles (WNPs) could induce environmental hazard to plant growth and yield, however no study investigated their phytotoxicity. On the other hand, plant growth-promoting bacteria (PGPB) can be effectively applied to reduce WNPS toxicity. Therefore, we aimed at investigating the phytotoxic effect of WPNs upon some leguminous plants and how could PGPB ameliorate this phytotoxic impact. Soil contaminated with WPNS induced the accumulation of W in all tested species, leading to marked retardation in both growth and photosynthesis as well as a noticeable oxidative damage. Five isolates of actinobacteria were isolated from Jazan, Saudi Arabia. Morphological and biochemical characterizations indicated that isolate (3) was the most bioactive one. Furthermore, PCR was performed to amplify 16S rDNA of the isolate 3 and the amplified sequence exhibited a high similarity with 16S rRNA gene from Saccharomonospora sp. Although, Saccharomonospora sp. did not affect growth of control plants, it markedly quenched the negative impact of WNPs. This was accompanied by a significant reduction in W levels in Saccharomonospora-treated plants. To cope with heavy metal stress, all tested legumes activated their osmolytes metabolism through the production of soluble sugars, proline, and polyamines, particularly in pea plants. Concomitantly, the biosynthetic key enzymes involved in sucrose, proline and spermidine polyamine biosynthesis experienced a remarkable elevation. These increases were further induced by co-application of Saccharomonospora sp. and WNPs. Overall, application of Saccharomonospora sp. under WNPs treatment induced similar metabolic responses in the three legume species, particularly pea plants, which triggered stress recovery.