Growth‐promoting bacteria for the green seaweed Ulva clathrata

Abstract

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.