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Amorphus coralli gen. nov., sp. nov., a marine bacterium isolated from coral mucus, belonging to the order Rhizobiales

Zeevi Ben Yosef, Dafna, Ben-Dov, Eitan, Kushmaro, Ariel

International Journal of Systematic and Evolutionary Microbiology 2008; 58(12):2704 · https://doi.org/10.1099/ijs.0.65462-0

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Summary auto-generated

Researchers isolated a novel bacterial strain, designated RS.Sph.026T, from mucus of the coral Fungia granulosa collected from the Red Sea. The bacterium was characterized as Gram-negative, non-motile, halotolerant, and heterotrophic, belonging to the order Rhizobiales. Phylogenetic analysis based on 16S rRNA gene sequences showed 92% similarity to Rhodobium orientis. The strain grew optimally at 3-4% salinity, pH 7.5-8, and 25-30°C. Key biochemical features include the ability to metabolize various sugars found in coral mucus (glucose, mannose, maltose, sorbitol) and possession of a distinctive fatty acid profile dominated by cis-7-octadecenoic acid (57.2%). Unlike its closest relatives, the bacterium lacks photosynthetic pigments and bacteriochlorophyll, despite possessing lamellar intracytoplasmic membranes. The DNA G+C content was 67.1 mol%. Based on significant phenotypic and phylogenetic differences from known genera, the authors propose this organism as a new genus and species: Amorphus coralli gen. nov., sp. nov., with the type strain RS.Sph.026T. This discovery represents one of the few marine members of Rhizobiales isolated from coral reef ecosystems and highlights the unexplored microbial diversity associated with coral mucus.

Key findings

  • Amorphus coralli is a novel heterotrophic bacterium isolated from coral mucus belonging to the order Rhizobiales, with only 92% 16S rRNA gene similarity to its closest relative Rhodobium orientis
  • The bacterium exhibits amorphous cell morphology (0.5-3 μm), is non-motile, and lacks photosynthetic pigments and bacteriochlorophyll despite possessing lamellar intracytoplasmic membranes, suggesting loss of photosynthetic capability in the nutrient-rich coral mucus environment
  • A. coralli preferentially utilizes sugars abundant in coral mucus (glucose, mannose, maltose, sorbitol) and has optimal growth at 3-4% salinity, pH 7.5-8, and 25-30°C, representing adaptation to its coral-associated ecological niche
  • The strain's unique fatty acid composition, particularly high levels of C18:1ω7c and C19:0 cyclo ω8c, combined with a DNA G+C content of 67.1 mol%, distinguishes it as a new genus within Rhizobiales

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Abstract

A bacterial strain, designated RS.Sph.026T, was isolated from mucus of the coral Fungia granulosa collected from the northern Red Sea (Gulf of Eilat, Israel). The bacterium was found to be Gram-negative, non-motile, halotolerant and heterotrophic. Comparative 16S rRNA gene sequence analyses showed that strain RS.Sph.026T belonged to the order Rhizobiales, with the highest levels of 16S RNA gene sequence similarity with Rhodobium orientis (92 %). Strain RS.Sph.026T grew optimally at a salinity of 3–4 %, pH 7.5–8 and 25–30 °C. The major cellular fatty acids were cis-7-octadecenoic acid (C18 : 1ω7; 57.2 %) and C19 : 0 cyclo ω8 (15.5 %). The DNA G+C content of strain RS.Sph.026T was 67.1 mol%. On the basis of its phenotypic properties and phylogenetic distinctiveness, strain RS.Sph.026T represents a novel genus and species in the order Rhizobiales, for which the name Amorphus coralli gen. nov., sp. nov. is proposed. The type strain is RS.Sph.026T (=LMG 24307T=DSM 19760T).