Seaweed production represents one of the rising activities in the aquaculture industry. This study explores the impact of bacteria associated with the growth of Ulva clathrata, a promising alga in the field of food and bioremediation. Fifty-six bacteria isolated from four seaweed (Caulerpa sp., Gracilaria sp., Ulva lactuca and U. clathrata) were tested to evaluate their effect on U. clathrata growth. Eight of them showed a significant growth-promoting effect (p < .05). Isolates Ul-11 and Ul-12 from U. lactuca induced an increase of 73 and 81% of growth respectively. They were classified as Reugeria sp. and Alteromonas sp. based on 16S DNA sequencing (>95.0% sequence identity). Multiple combinations of the growth-promoting bacteria were also tested on U. clathrata, and the best result was achieved by combining Ca-3/Uc-18/Ul-12 isolates with a significant increase in seaweed growth of up to 76%; however, no synergistic effect was observed compared to Ul-12 alone. Scanning electron microscopy revealed no alteration in the cell wall of U. clathrata when inoculated with selected bacteria, showing an average increase of bacterial density on U. clathrata.