Role of bacterial isolates in enhancing the bud induction in the industrially important red alga Gracilaria dura.

Plant growth depends on the integration of environmental cues, nitrogen fixation and phytohormone-signaling pathways. The growth and development of Gracilaria dura was significantly influenced by the association of bacterial isolates. The putative bud-inducing epiphytic Exiguobacterium homiense and endophytic Bacillus pumilus, Bacillus licheniformis were examined for their ability to fix nitrogen and produce indole-3-acetic acid (IAA). These bacterial isolates were identified to the species level by biochemical tests, fatty acid and partial 16S rRNA gene sequence analysis. The B. pumilus, B. licheniformis and E. homiense produced 445.5, 335 and 184.1 μg mL−1 IAA and 12.51, 10.14 and 6.9 mM mL−1 ammonium, respectively, as determined using HPLC and spectroscopy. New bud regeneration observed after the addition of total protein of the bacterial isolates suggests that IAA is conjugated with protein. The epi- and endophytic bacterial isolates were able to induce five and 10 new buds per frond, respectively, in comparison to the control, where one to two buds were observed. The combination of 25 °C and 30‰ showed the optimum condition for bud induction in G. dura when incubated with the total protein of B. pumilus. Our finding revealed for the first time that IAA coupled with nitrogen fixation induce and regenerate new buds in G. dura.