Effect of Stenotrophomonas maltophilia Bacteria and Environmental Factors on the Thallus of Red Seaweed Kappaphycus alvarezii

Interaction between environmental factors, particularly temperature and salinity with bacteria is considered one of the main triggers of disease infection in various hosts including seaweed. Therefore, this study aimed to evaluate the effects of interactions between temperature and salinity with pathogenic bacteria on the manifestation of ice-ice disease in red seaweed Kappaphycus alvarezii. Red seaweed was weighed to 50-51 g for each treatment replicate, incubated at 25°C and 28°C, then infected with Stenotrophomonas maltophilia bacteria at a concentration of 100-106 cfu/mL in a culture medium (30 g/L salinity). Salinity treatment was conducted in variations of 28, 30 and 35 g/L with the same bacteria concentration (106 cfu/mL) and temperature (28°C). The results showed that seaweed infected by S. maltophilia and incubated at 28°C had a higher reduction in weight and greater thallus bleaching compared to the 25°C treatment. A significant difference was observed in the percentage of bleaching on the secondary thallus in both temperature treatments. The onset of disease transmission affected K. alvarezii morphological structure, which showed severe condition on day 4. In conclusion, both temperature and salinity affected ice-ice disease infection in red seaweed. However, this study could not fully elucidate the interactions between biotic and abiotic factors and the effect on ice-ice disease. Further investigations are needed to examine the effect of the interaction.