Abstract

Bacteria associated with plants colonizing extreme environments in Chile (Atacama and Antarctic Desert soils) provide a model to study plant growth-promoting mechanisms that can be useful to improve the growth of crops such as Chenopodium quinoa Wild. (Amaranthaceae) growing under severe environmental conditions. This study aimed to determine the tolerance of extremophile rhizobacteria to multiple metal(loid)s and evaluate the effects of formulated consortia in seed germination and growth-promotion of C. quinoa. In our work, five rhizobacteria were isolated and classified into the bacteria genera Streptomyces, Bacillus, and Pseudomonas. The five bacteria showed optimum growth at 26 degrees C, pH 6, and 1% NaCl. In addition, the isolated were resistant to arsenic, manganese, zinc, copper, chromium and showed plant growth-promoting traits, including indole acetic acid production, siderophores production, phosphate solubilization, ACC deaminase activity, and ammonia production. According to compatibility tests, three bacterial consortia were formulated: i) consortium A (Pseudomonas sp. and Bacillus sp. (T1B41)); ii) consortium B (Pseudomonas sp. and Bacillus sp. (B2B24)); and iii) consortium C (Streptomyces sp., Bacillus sp. (B2B24) and Bacillus sp. (T3B45)). In vitro antagonism against phytopathogenic fungi showed that Bacillus sp. (B2B24) and Bacillus sp. (T3B45) have a significant level of antagonism (up to 18.7 and 6.8%, respectively) and consortia were the most effective against B. cinerea (up to 100%). Consortia B and C significantly improved the germination rate (%) of C. quinoa seeds (86 +/- 3.3 and 77 +/- 1.7, respectively) and the number of leaves, wet stem weight, length stem length, wet root weight, and root diameter in the presence of metal(loid)s. Our results showed that rhizobacterial consortia based on extremophile microorganisms can enhance the growth of C. quinoa seedlings under metal(loid) stress, demonstrating beneficial characteristics that may be key in the early stages of development.