Enterobacter sp. I-3, a bio-herbicide inhibits gibberellins biosynthetic pathway and regulates abscisic acid and amino acids synthesis to control plant growth

Very few bacterial species were identified as bio-herbicides for weed control. The present research was focused to elucidate the plant growth retardant properties of Enterobacter sp. I-3 during their interaction by determining the changes in endogenous photosynthetic pigments, plant hormones and amino acids. The two bacterial isolates I-4-5 and I-3 were used to select the superior bacterium for controlling weed seeds (Echinochloa crus-galli L. and Portulaca oleracea L.) germination. The post-inoculation of I-3 (Enterobacter sp. I-3) significantly inhibited the weeds seed germination than their controls. The mechanism of bacterium induced plant growth reduction was identified in lettuce treated with I-3 bacterium and compared their effects with known chemical herbicide, trinexapac-ethyl (TE). The treatment of I-3 and TE showed a significant inhibitory effect on shoot length, leaf number, leaf length, leaf width, shoot weight, root weight and chlorophyll content in lettuce seedlings. The endogenous gibberellins (GAs) and abscisic acid (ABA) analysis showed that Enterobacter sp. I-3 treated plants had lower levels of GAs (GA₁₂, GA₁₉, GA₂₀ and GA₈) and GAs/ABA ratio and then, the higher level of ABA when compared to their controls. Indeed, the individual amino acids ie., aspartic acid, glutamic acid, glycine, threonine, alanine, serine, leucine, isoleucine and tyrosine were declined in TE and I-3 exposed plants. Our results suggest that the utilization of Enterobacter sp. I-3 inhibits the GAs pathway and amino acids synthesis in weeds to control their growth can be an alternative to chemical herbicides.