Complete genome sequence of a heavy metal resistant bacterium Maribacter cobaltidurans B1T, isolated from the deep-sea sediment of the South Atlantic Ocean

Elucidating the impacts of cobalt (II) ions on extracellular electron transfer and pollutant degradation by anodic biofilms in bioelectrochemical systems during industrial wastewater treatment

Electrogenic biofilms in bioelectrochemical systems (BES) are critical in wastewater treatment. Industrial effluents often contain cobalt (Co2+); however, its impact on biofilms is unknown. This study investigated how increasing Co2+ concentrations (0-30 mg/L) affect BES biofilm community dynamics, extracellular polymeric substances, microbial metabolism, electron transfer gene expression, and electrochemical performance. The research revealed that as Co2+ concentrations increased, power generation progressively declined, from 345.43 ± 4.07 mW/m2 at 0 mg/L to 160.51 ± 0.86 mW/m2 at 30 mg/L Co2+. However, 5 mg/L Co2+ had less effect. The Co2+ removal efficiency in the reactors fed with 5 and 10 mg/L concentrations exceeded 99% and 94%, respectively. However, at 20 and 30 mg/L, the removal efficiency decreased substantially, likely because of reduced biofilm viability. FTIR indicated the participation of biofilm functional groups in Co2+ uptake. XPS revealed Co2+ presence in biofilms as CoO and Co(OH)2, indicating precipitation also aided removal. Cyclic voltammetry and electrochemical impedance spectroscopy tests revealed that 5 mg/L Co2+ had little impact on the electrocatalytic activity, while higher concentrations impaired it. Furthermore, at a concentration of 5 mg/L Co2+, there was an increase in the proportion of the genus Anaeromusa-Anaeroarcus, while the genus Geobacter declined at all tested Co2+ concentrations. Additionally, higher concentrations of Co2+ suppressed the expression of extracellular electron transfer genes but increased the expression of Co2+-resistance genes. Overall, this study establishes how Co2+ impacts electrogenic biofilm composition, function, and treatment efficacy, laying the groundwork for the optimized application of BES in remediating Co2+-contaminated wastewater.

Unveiling a Virulence-Regulating Mechanism in Aeromonas hydrophila: a Quantitative Exoproteomic Analysis of an AraC-Like Protein

Bacterial AraC is a transcription factor family that initiates transcription by recruiting RNA polymerase to the promoter and directly regulating various bacterial phenotypes. It also directly regulates various bacterial phenotypes. However, how this transcription factor regulates bacterial virulence and affects host immunity is still largely unknown. In this study, deleting the orf02889 (AraC-like transcription factor) gene in virulent Aeromonas hydrophila LP-2 affected several important phenotypes, such as increasing biofilm formation and siderophore production abilities. Moreover, Δorf02889 also significantly decreased the virulence of A. hydrophila and has promising attenuated vaccine potential. To better understand the effects of orf02889 on biological functions, a data independent acquisition (DIA)-based quantitative proteomics method was performed to compare the differentially expressed proteins between Δorf02889 and the wild-type strain in extracellular fractions. The following bioinformatics analysis suggested that ORF02889 may regulate various metabolic pathways, such as quorum sensing and ATP binding cassette (ABC) transporter metabolism. Moreover, 10 selected genes from the top 10 decreasing abundances in proteomics data were deleted, and their virulence to zebrafish was evaluated, respectively. The results showed that ΔcorC, Δorf00906, and Δorf04042 significantly reduced bacterial virulence. Finally, the following chromatin immunoprecipitation and polymerase chain reaction (ChIP-PCR) assay validated that the promoter of corC was directly regulated by ORF02889. Overall, these results provide insight into the biological function of ORF02889 and demonstrate its inherent regulatory mechanism for the virulence of A. hydrophila.

Complete genome sequence of a multiple-stress-tolerant bacterium Halomonas piezotolerans NBT06E8T isolated from a deep-sea sediment sample of the New Britain Trench

Halomonas piezotolerans NBT06E8T is a Gram-stain-negative, moderately halophilic, piezotolerant, H2O2 and heavy metal-resistant bacterium, isolated from a deep-sea sediment sample collected from the New Britain Trench at depth of 8900 m. Growth of the strain was observed at 4-45 °C (optimum 30 °C), at pH 5-11 (optimum 8-9) and in 0.5-21% (w/v) NaCl (optimum 3-7%). The optimum pressure for growth was 0.1-30 MPa (megapascal) with tolerance up to 60 MPa. Under optimum growth conditions, the strain could tolerant 15 mM H2O2. Here, we report the complete genome of H. piezotolerans NBT06E8T, which consists of 3,945,801 bp (G + C content of 57.93%) with a single chromosome, 3509 protein-coding genes, 60 tRNAs and 6 rRNA operons. Genomic analysis revealed the capability of utilizing various carbon and nitrogen sources, the presence of multiple toxin-antitoxin systems and strain-specific type VI secretion system benefitting its adaptation to the oligotrophic hadal environments. Multiple respiratory chain components, especially the strain-specific anaerobic enzymes, could allow its survival in both surficial and buried sediments with variable oxygen concentrations. Gene function and metabolic pathway analysis showed that strain NBT06E8T encodes a series of genes related to high hydrostatic pressure tolerance, antioxidative stress and heavy metal resistance, which could also contribute to its deep-sea adaptation strategies. The complete genome sequence of H. piezotolerans NBT06E8T provides further insights into the stress adaptation strategies of deep-sea bacteria and potential biotechnological application of Halomonas species.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03283-3.

Nisaea sediminum sp. nov., a heavy metal resistant bacterium isolated from marine sediment in the East China Sea

A Gram-negative, rod-shaped, motile and strictly aerobic bacterium, designated NBU1469^T, was isolated from marine sediment sampled on Meishan Island located in the East China Sea. Strain NBU1469^T grew optimally at temperature of 40 °C, NaCl concentration of 2.0% (w/v) and pH 7.5. Catalase and oxidase activities, H₂S production, nitrate reduction and hydrolysis of Tween 20 were positive. Indole, methyl red reaction, urease, hydrolysis of gelatin, starch, casein, Tweens 40, 60 and 80 were negative. The major cellular fatty acids were C_16:0, C_19:0 cyclo ω8c and summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c). The only respiratory quinone was ubiquinone-10 (Q-10). The major polar lipids were phosphatidylglycerol, two unidentified amino-phospholipids and two unidentified phospholipids. Comparative analysis of the 16S rRNA gene sequence showed highest similarities to the species with validated name Nisaea nitritireducens DR41_18^T (98.1%) and Nisaea denitrificans DR41_21^T (97.6%). Phylogenetic analyses indicated that strain NBU1469^T formed a distinct lineage with strains Nisaea nitritireducens DR41_18^T and Nisaea denitrificans DR41_21^T within the genus Nisaea. The average nucleotide identity and digital DNA-DNA hybridization values between strain NBU1469^T and related species of genus Nisaea were well below the threshold limit for prokaryotic species delineation. The DNA G + C content was 63.6%. Based on its phenotypic, chemotaxonomic and genotypic data, strain NBU1469^T is considered to be a representative of a novel species in the genus Nisaea, for which the name Nisaea sediminum sp. nov. is proposed. The type strain is NBU1469^T (=KCTC 82224 ^T =MCCC 1K04763^T).