Mangrovimonas cancribranchiae sp. nov., a novel bacterial species associated with the gills of the fiddler crab Cranuca inversa (Brachyura, Ocypodidae) from Red Sea mangroves

Abstract

Two bacteria, UG2_1^T and UG2_2, were isolated from the gill tissues of the mangrove fiddler crab Cranuca inversa collected on the east coast of the Red Sea (Thuwal, Saudi Arabia). The cells are Gram-negative, rod-shaped, orange-pigmented, motile by gliding with no flagella, strictly aerobic, and grow at 20-37 °C (optimum, 28-35 °C), at pH 5.0-9.0 (optimum, pH 6.0-7.0), and with 1-11 % (w/v) NaCl (optimum, 2-4 %). They were positive for oxidase and catalase activity. Phylogenetic analysis based on 16S rRNA gene sequences indicated that isolates UG2_1^T and UG2_2 belong to the genus Mangrovimonas, showing the highest similarity to Mangrovimonas spongiae HN-E26^T (99.4 %). Phylogenomic analysis based on the whole genomes, independently using 49 and 120 concatenated genes, showed that strains UG2_1^T and UG2_2 formed a monophyletic lineage in a different cluster from other type strain species within the genus Mangrovimonas. The genome sizes were 3.08 and 3.07 Mbp for UG2_1^T and UG2_2, respectively, with a G+C content of 33.8 mol% for both strains. Values of average nucleotide identity and digital DNA-DNA hybridization between the strains and closely related species were 91.0 and 43.5 %, respectively. Chemotaxonomic analysis indicated that both strains had iso-C_{15 : 0} and iso-C_{15 : 1} G as dominant fatty acids, and the primary respiratory quinone was identified as MK-6. The major polar lipids comprised phosphatidylethanolamine, one unidentified glycolipid, one unidentified phospholipid, two unidentified aminolipids, and four unidentified lipids. Based on phylogenetic, phylogenomic, genome relatedness, phenotypic, and chemotaxonomical data, the two isolates represent a novel species within the genus Mangrovimonas, with the proposed name Mangrovimonas cancribranchiae sp. nov., and the type strain UG2_1^T (=KCTC 102158^T=DSM 117025^T).

Keywords: Bacteroidota; Cranuca inversa; Mangrovimonas; brachyuran crabs; gills; mangrove; symbionts.

Fig. 1.. Cranuca inversa’s gill microenvironment and morphological features of the novel strains. (a) A male individual of Cranuca inversa before the dissection; the box shows the right gills exposed after the carapace removal. (b) A single dissected gill of C. inversa under the stereomicroscope. (c) Microscope images of C. inversa gill lamellae and (d) the associated microbiome taken under a teneo scanning electron microscope (FEI); the gill tissue specimen was fixed, prepared and imaged as described by Garuglieri and colleagues [11]. (e) UG2_1^T colony observed under the stereomicroscope, and (f and g) its cells under the optical microscope and scanning electron microscope, respectively.

Fig. 2.. Maximum-likelihood phylogenetic tree based on 16S rRNA gene sequences and reconstructed using megaX version 11.0.10 [26], showing the relationships among UG2_1^T, UG2_2 and close relative species in the family Flavobacteriaceae. UG2_1^T and UG2_2 are shown in bold. Cryomorpha ignava 1-22^T (AF170738) was used as the outgroup. The NCBI accession numbers are given after the species name. Numbers at the nodes are percentages of bootstrap values based on 1000 resampled datasets. Bar represents 0.01 substitutions per nucleotide position.

Fig. 3.. Phylogenetic tree with proposed strains UG2_1^T, UG2_2 and related species based on 120 concatenated single-copy genes using the maximum-likelihood method made using the software GTDB-Tk [38]. The NCBI accession numbers are given after the species name. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Numbers at nodes indicate bootstrap percentages using 1000 replicates. UG2_1^T and UG2_2 are shown in bold. Confluentibacter citreus XJNY^T (GCF_002807055.1) was used as the outgroup. Bar, 0.1 substitutions per site.