Efficient low-temperature wastewater treatment by Pseudomonas zhanjiangensis sp. nov.: a novel cold-tolerant bacterium isolated from mangrove sediment

Abstract

A novel heterotrophic, cold-tolerant bacterium, designated Pseudomonas zhanjiangensis 25A3E^T, was isolated from mangrove sediment and demonstrated excellent efficiency in cold wastewater treatment. Phylogenetic analysis based on 16S rRNA gene sequences positioned strain 25A3E^T within the genus Pseudomonas, showing the highest similarity (98.7%) with Pseudomonas kurunegalensis LMG 32023^T. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values were below the species delineation thresholds (70% for dDDH, 95% for ANI), indicating that strain 25A3E^T represents a novel species. This strain demonstrated high efficiency in removing nitrogen (N) and organic pollutants under low-temperature conditions. Specifically, it achieved 72.9% removal of chemical oxygen demand (COD), 70.6% removal of ammoniacal nitrogen (NH₄ ⁺-N), and 69.1% removal of total nitrogen (TN) after 96 h at 10°C. Genomic analysis identified key genes associated with cold adaptation, nitrogen removal and organic matter degradation. These findings indicate that Pseudomonas zhanjiangensis 25A3E^T holds significant potential for application in cold temperature wastewater treatment, offering a promising solution for environmental remediation in regions with low ambient temperatures.

Keywords: Pseudomonas zhanjiangensis; cold tolerant; comparative genomic analysis; nitrogen removal; wastewater treatment.

Figure 1

The morphologies of the strain 25A3E^T. (A) Colony on 2216E plates; (B) microscopic observation of Gram staining; (C) transmission electron micrograph showing the cell morphology of strain 25A3E^T, Bar, 0.5 μm.

Figure 2

Maximum-likelihood phylogenetic tree based on the bac120 gene set showing the phylogenetic relationship of 25A3E^T in the genus Pseudomonas. Bootstrap values based on 1,000 replicates were shown at the branch points nodes. The RefSeq assembly accession number is indicated in the bracket. Bar, 0.01 substitutions per nucleotide position.

Figure 3

COD, NH₄⁺-N, and TN removal characteristics of strain 25A3E^T in the artificial wastewater culture medium at 10°C, respectively. Values are means ± SE (standard error) for three replicates. (A) COD, chemical oxygen demand; (B) NH₄⁺-N, Ammonium nitrogen; (C) TN, total nitrogen.

Figure 4

Metabolic capabilities analysis of the tested strains. (A) An Upset plot shows the intersections among KEGG module sets. The bar chart on the left displays the total number of KEGG modules identified for each strain, while the upper bar chart highlights the intersection size of KEGG modules shared across different strains. Blue connected dots in the bottom panel indicate which substrates are considered in each intersection. (B) Enzyme class distribution across all tested strains. Two specific enzyme classes are predicted among the eight genomes analyzed, with GH representing glycoside hydrolase and PL representing polysaccharide lyase.

Figure 5

Summary diagram illustrates the biogeochemical cycling processes at the genomic level for each strain. (A) Carbon metabolism network; (B) Nitrogen metabolism network; (C) Sulfur metabolism network; (D) Other elements metabolism network. Each arrow corresponds to a specific transformation or step within the cycle. The labels above the arrows denote the step number and the associated reaction, with solid circles of different colors next to each arrow indicating the strains predicted to carry out that particular reaction.