Genomic insights into Neopusillimonas aestuarii sp. nov., a novel estuarine bacterium with adaptations for ectoine biosynthesis and stress tolerance.

A novel Gram-stain-negative, aerobic rod-shaped bacterial strain, which was catalase- and oxidase-positive, designated as DMV24BSW_D, was isolated from the estuarine waters of the Bhavnagar (India) coast of the Arabian Sea. Its 16S rRNA gene exhibited 99.52% similarity with Neopusillimonas maritima 17-4A, followed by 97.95% similarity with the Pusillimonas caeni strain EBR-8-1 and 97.4% similarity with the P. noertemannii strain BN9. Phylogenomic analysis using BPGA (14,332 aa) and UBCG (90,261 bp) tools revealed a unique phylogenetic position within the genus Neopusillimonas. The genome exhibited a G + C content of 53.25%. In comparison with N. maritima 17-4A, the strain demonstrated an average nucleotide identity (ANIb) of 94.47% and a digital DNA-DNA hybridization (dDDH) value of 60.1%, indicating distinct genomic divergence. The genome of DMV24BSW_D contains several unique metabolic genes that facilitate efficient electron transfer during aerobic respiration. Additionally, it harbours one intact prophage and four defective prophages, indicating ongoing viral interactions. The genome encodes a complete pathway for ectoine biosynthesis and transportation. Strain DMV24BSW_D tested positive for gelatin hydrolysis and demonstrated the ability to utilize a wide range of carbohydrates, including α-D-glucose, D-melibiose, D-fructose, L-rhamnose, and various organic acids, such as methyl pyruvate and propionic acid, along with tolerance to fluctuating pH (5 to 10) and salinity (0-4% NaCl). The major polar lipids included phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylethanolamine, while fatty acid analysis revealed C, C, C cyclo, and summed feature 2 (C aldehyde/unknown) as major components. The respiratory quinones identified were MK-7 and MK-8. These comprehensive phenotypic, chemotaxonomic, and genomic characteristics support the unique taxonomic position of DMV24BSW_D within the genus Neopusillimonas and the proposal of a novel species of the genus Neopusillimonas, for which the name Neopusillimonas aestuarii sp. nov. (Type strain DMV24BSW_D = MCC 2506 = KCTC 72453 = JCM 34508) is proposed.