Summary auto-generated
This study describes the characterization and naming of two marine bacterial strains, DN34T and DN33, isolated from seawater in Taiwan. Both strains are Gram-negative, halophilic, rod-shaped bacteria capable of facultative anaerobic metabolism. Notably, they can perform denitrification—reducing nitrate or nitrite to nitrogen gas—or alternatively ferment carbohydrates like glucose and mannose under anaerobic conditions. The bacteria grew optimally at 30°C, pH 8, and 3% NaCl, and produced mixed acids (formate, lactate, acetate, pyruvate, fumarate) during fermentation. With DNA G+C contents of 51.6-51.7 mol%, these strains differed from known Vibrionaceae family members in their denitrification ability, formation of irregular V- and Y-shaped cells, and resistance to the vibriostatic agent O/129. Phylogenetic analysis of 16S rRNA gene sequences revealed they did not cluster with any recognized bacterial species, sharing only 94.5% similarity with the closest known species. Based on these findings, the authors propose a novel genus Pseudovibrio with Pseudovibrio denitrificans as the type species, representing the first documented halophilic denitrifying bacterium of this type.
Key findings
- Pseudovibrio denitrificans is a novel marine bacterium capable of both denitrification (reducing nitrate to nitrogen gas) and fermentation of specific carbohydrates, representing an unusual metabolic combination in halophilic bacteria
- The two isolated strains have DNA G+C contents of 51.6-51.7 mol% and produce irregular rod-shaped cells including V- and Y-shaped forms, distinguishing them from related Vibrionaceae family members
- 16S rRNA phylogenetic analysis shows these strains form a distinct cluster sharing less than 95% sequence similarity with any known bacterial species, supporting the creation of a new genus Pseudovibrio
- The bacteria are strictly halophilic, requiring 2-6% NaCl for growth with optimal growth at 3% NaCl (comparable to seawater salinity), and show unusual resistance to the vibriostatic agent O/129
- During anaerobic fermentation of glucose, the strains produce a mixed-acid fermentation profile with major products being formate (39-45%), lactate (27-38%), and acetate (21-24%)
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Abstract
Two denitrifying strains of heterotrophic, facultatively anaerobic, marine bacteria, designated DN34T and DN33, were isolated from sea-water samples collected in Nanwan Bay, Kenting National Park, Taiwan. They were Gram-negative. Cells in late exponential to early stationary phase of growth were predominantly straight or curved rods, but Y- or V-shaped forms were also observed. They were motile by means of one to several lateral or subpolar flagella. Both strains required NaCl for growth and exhibited optimal growth at about 30 °C, pH 8 and 3 % NaCl. They were capable of anaerobic growth by carrying out denitrifying metabolism using nitrate, nitrite or nitrous oxide as terminal electron acceptors or, alternatively, by fermenting glucose, mannose, sucrose or trehalose as substrates. Anaerobic fermentative growth on glucose resulted in formation of various organic acids, including formate, lactate, acetate, pyruvate and fumarate. The major cellular fatty acids were 2-OH-14 : 0, 3-OH-14 : 0 and 16 : 0. DN34T and DN33 had DNA G+C contents of 51·7 and 51·6 mol%, respectively. Physiological characterization, together with phylogenetic analysis based on 16S rRNA gene sequence analysis, revealed that the two denitrifying strains could be accommodated in a novel genus, for which the name Pseudovibrio gen. nov. is proposed. Pseudovibrio denitrificans sp. nov. is the type species, with DN34T (=BCRC 17323T=JCM 12308T) as the type strain.