Cultivation of Sponge-Associated Bacteria from Agelas sventres and Xestospongia muta Collected from Different Depths

Sponge-associated bacteria have been mostly cultured from shallow water (≤30 m) sponges, whereas only few studies targeted specimens from below 30 m. This study assessed the cultivability of bacteria from two marine sponges Xestospongia muta and Agelas sventres collected from shallow (<30 m), upper mesophotic (30–60 m), and lower mesophotic (60–90 m) reefs. Sponge-associated bacteria were cultivated on six different media, and replicate plates were used to pick individual colonies or to recover the entire biomass. Prokaryotic community analysis was conducted using Illumina MiSeq sequencing of 16S rRNA gene amplicons. A total of 144 bacterial isolates were picked following a colony morphology coding scheme and subsequently identified by 16S rRNA gene sequence analysis. Sponge individuals at each depth-range harboured specific cultivable bacteria that were not retrieved from specimens collected at other depths. However, there were substantial differences in the number of colonies obtained for replicate sponges of the same species. In addition, source of inoculum and cultivation medium had more impact on the cultured prokaryotic community than sample collection depth. This suggests that the “plate count anomaly” is larger than differences in sponge-associated prokaryotic community composition related to depth.