A novel aerobic bacterial strain, designated as Acinetobacter zhairhuonensis sp. nov. A7.4 ^T , was isolated from East China Sea sediments near Zhairuo island. Cells were Gram-stain-negative, non-motile short rods, forming milky, moist colonies. Growth occurred at 10–35 °C, pH 6.0–9.0 and 0–5% NaCl concentrations (w/v). Strain A7.4 ^T was catalase-positive and oxidase-negative. Major fatty acids (>10%) included summed feature 3 (C _16:1 ω7c/C _16 :1 ω6c), C _18:1 ω9c and C _16:0 . The polar lipid profile comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two phospholipids and two aminolipids. Ubiquinone Q-9 and Q-8 predominated. The genome (3.57 Mb, 41.3 mol% GC) included one chromosome and a plasmid. The core-genome phylogeny placed A7.4 ^T within Acinetobacter , forming a distinct clade with Acinetobacter kanungonis PS-1 ^T , Acinetobacter tibetensis Y-23 ^T and Acinetobacter tandoii CIP107469 ^T . Average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA–DNA hybridization (dDDH) values between strain A7.4 ^T and 87 validly published Acinetobacter species were below species thresholds (96% ANI/AAI, 70% dDDH). Phenotypic, genomic and chemotaxonomic data support the proposal of Acinetobacter zhairhuonensis sp. nov., with type strain A7.4 ^T (=MCCC 1K07162 ^T =LMG 32567 ^T ).

Candidatus Hepatincolaceae is a poorly characterized family of obligate Alphaproteobacterial symbionts that are widely detected in ecdysozoans. They were previously assumed to play a nutrient-scavenging role in the gut lumen. In this study, two high-quality metagenome-assembled genomes (MAGs, 1.39 Mb and 1.48 Mb in size) were recovered from the gut of the snapping shrimp Alpheus brevicristatus via metagenomic sequencing. Phylogenetic and whole-genome similarity analyses confirm that these two MAGs represent two novel, undescribed genera within the family Ca. Hepatincolaceae. Metabolic reconstruction reveals that they not only retain the canonical nutrient-scavenging pathways conserved across all Hepatincolaceae members, but also encode previously undocumented functional modules for antioxidant defense, vitamin B₁ and B₂ biosynthesis, and short-chain fatty acid production. They maintain a high oxygen-affinity cytochrome bd terminal oxidase to thrive in the anoxic gut microenvironment. Consistent with their symbiotic lifestyle, their genomes exhibit typical signatures of reductive evolution, such as reduced genome size, low GC content, and gene loss in amino acid and nucleotide de novo biosynthesis pathways. This study presents the first reported high-quality genomes of marine Ca. Hepatincolaceae symbionts, which are predicted to possess multiple metabolic functions extending beyond nutritional mutualism.