Influence of temperature changes on symbiotic Symbiodiniaceae and bacterial communities’ structure: an experimental study on soft coral Sarcophyton trocheliophorum (Anthozoa: Alcyoniidae)

It is well concluded that microbial composition and diversity of coral species can be affected under temperature alterations. However, the interaction of environmental accumulation of corals and temperature stress on symbiotic Symbiodiniaceae and bacterial communities are rarely studied. In this study, two groups of soft coral Sarcophyton trocheliophorum were cultured under constant (26 °C) and inconstant (22 °C to 26 °C) temperature conditions for 30 days as control treatments. After that, water was cooled rapidly to decrease to 20 °C in 24 h. The results of diversity analysis showed that symbiotic Symbiodiniaceae and bacterial communities had a significant difference between the two accumulated groups. The principal coordinate analyses confirmed that symbiotic Symbiodiniaceae and bacterial communities of both control treatments were clustered into two groups. Our results evidenced that rapid cooling stress could not change symbiotic Symbiodiniaceae and bacterial communities’ composition. On the other hand, cooling stress could alter only bacterial communities in constant group. In conclusion, our study represents a clear relationship between environmental accumulation and the impact of short-term cooling stress in which microbial composition structure can be affected by early adaptation conditions.

New Naturally Occurring Compounds from Sarcophyton trocheliophorum

Corals are rich sources of secondary metabolites used as chemical defense compounds against predators. The production of diverse metabolites has characterized soft corals belonging to the genus Sarcophyton. However, phenolic compounds are slightly rare in soft corals. Through a further bioassay-guided fractionation for the chloroform-soluble extract of soft coral Sarcophyton trocheliophorum, collected from the Red Sea, three closely related phenolic compounds: 2,4-di-tert-butyl-6-nitro-phenol (1), 2,4-di-tert-butyl-phenol (2), and 2,4-bis(1-methyl-1-phenylethyl)-phenol (3), along with the wax tricosyldocosanoiate (4) were isolated herein for the first time from nature in addition to cholesterol. Structures of the isolated compounds 1-4 were identified by NMR spectroscopy (1H, 13C, 1H,1H COSY, HMQC and HMBC) and mass spectrometry (EI, HRESI-MS) for the first time so far. The antimicrobial activities of the soft coral extract, along with the isolated compounds, were evaluated against Staphylococcus aureus, Bacillus subtilis ATCC6051, Streptomyces viridochromogenes Tü 57, Escherichia coli, Mucor miehei Tü 284, Candida albicans, and the green alga Chlorella vulgaris. The crude extract exhibited a moderate activity against Streptomyces viridochromogenes Tü 57 (12 mm) at a concentration of 400 µg/disc, while the reported compounds 1-4 showed no activity against the reported test microorganisms at a concentration of 40 µg/disc.