Molecular identification of photosynthetic bacteria associated with hardcoral Acropora spp. from different depths in Gosong Cemara Karimunjawa Waters using 16S rRNA gene sequencing

Acropora spp. corals dominate the waters of Gosong Cemara, Karimunjawa. These corals can live at various depths through the association of photosynthetic bacteria. This research aims to determine the abundance and types of photosynthetic bacteria associated with Acropora spp. corals at different depths. The method used in this research is the explorative descriptive method. This research was conducted from November 2023 to March 2024.The results of this research showed that the highest bacterial abundance in medium R2A (1/5 strength) was found in Acropora coral at a depth of 1 meter, with 7.4 × 10¹ CFU/ml. At a depth of 5 meters, the abundance was 6.6 × 10¹ CFU/ml, while at 15 meters, the bacterial count was classified as too few to count (TFTC). Three isolates from R2A medium (1/5 strength) were selected for molecular analysis based on colony color, which indicated potential photosynthetic activity. Molecular identification using the 16S rRNA gene revealed that two of the isolates were photosynthetic bacteria, as indicated by the presence of carotenoid pigments involved in the photosynthesis process. Isolate KJA1-1-2 was identified as Kocuria rhizophila with 99.72% similarity, and isolate KJA2-1-3 as Sphingopyxis terrae with 98.39% similarity.