Vibrio and Heterotrophic Marine Bacteria Composition and Abundance in Nutrient-enriched Kappaphycus striatus

Abstract

Inorganic nutrient application in Kappaphycus seaweed farming has been a practice in the southern Philippines for the past years. To investigate the inorganic nutrient’s influence on the number and assemblage of Vibrio and heterotrophic marine bacteria and on the presence of ice-ice disease-inducing bacteria in Kappaphycus striatus, a field experiment was conducted using ammonium phosphate (16-20-0) fertilizer at high concentration (HC, 8.82 g L–1), low concentration (LC, 0.01 g L–1), and control (C, 0.00 g L–1). Vibrio (VCs) and heterotrophic marine bacterial counts (HMBCs) were found similar among treatments. Based on 16S rRNA gene sequencing, isolates from source K. striatus, nutrient-enriched K. striatus (HC, LC, and C), farm seawater, and fertilizer solutions were identified as Vibrio alginolyticus (three strains), V. parahaemolyticus, V. brasiliensis, V. harveyi, Gilvimarinus chinensis, and species related to Bacillus sp. ST7, Psychrobacter sp. ST8, Enterococcus sp. ST5, Oceanobacillus sp. ST9, and Paracoccus sp. ST10. Bacillus sp. ST7 and Oceanobacillus sp. ST9 were unique and only present in HC and LC. The agarolytic activity of G. chinensis, isolated from all samples, suggests that it is an ice-ice disease-causing bacterium. The microbial community dynamics of farmed K. striatus, when enriched with inorganic nutrients, may pave way in addressing the occurrence of ice-ice disease.