MliR, a novel MerR-like regulator of iron homeostasis, impacts metabolism, membrane remodeling, and cell adhesion in the marine Bacteroidetes Bizionia argentinensis

The MerR family is a group of transcriptional activators with conserved N-terminal helix-turn-helix DNA binding domains and variable C-terminal effector binding regions. In most MerR proteins the effector binding domain (EBD) contains a cysteine center suited for metal binding and mediates the response to environmental stimuli, such as oxidative stress, heavy metals or antibiotics. We here present a novel transcriptional regulator classified in the MerR superfamily that lacks an EBD domain and has neither conserved metal binding sites nor cysteine residues. This regulator from the psychrotolerant bacteria Bizionia argentinensis JUB59 is involved in iron homeostasis and was named MliR (MerR-like iron responsive Regulator). In silico analysis revealed that homologs of the MliR protein are widely distributed among different bacterial species. Deletion of the mliR gene led to decreased cell growth, increased cell adhesion and filamentation. Genome-wide transcriptomic analysis showed that genes associated with iron homeostasis were downregulated in mliR-deletion mutant. Through nuclear magnetic resonance-based metabolomics, ICP-MS, fluorescence microscopy and biochemical analysis we evaluated metabolic and phenotypic changes associated with mliR deletion. This work provides the first evidence of a MerR-family regulator involved in iron homeostasis and contributes to expanding our current knowledge on relevant metabolic pathways and cell remodeling mechanisms underlying in the adaptive response to iron availability in bacteria.

Fingerprinting Plastic-Associated Inorganic and Organic Matter on Plastic Aged in the Marine Environment for a Decade

The long-term aging of plastic leads to weathering and biofouling that can influence the behavior and fate of plastic in the marine environment. This is the first study to fingerprint the contaminant profiles and bacterial communities present in plastic-associated inorganic and organic matter (PIOM) isolated from 10 year-aged plastic. Plastic sleeves were sampled from an oyster aquaculture farm and the PIOM was isolated from the intertidal, subtidal, and sediment-buried segments to investigate the levels of metal(loid)s, polyaromatic hydrocarbons (PAHs), per-fluoroalkyl substances (PFAS) and explore the microbial community composition. Results indicated that the PIOM present on long-term aged high-density polyethylene plastic harbored high concentrations of metal(loid)s, PAHs, and PFAS. Metagenomic analysis revealed that the bacterial composition in the PIOM differed by habitat type, which consisted of potentially pathogenic taxa including Vibrio, Shewanella, and Psychrobacter. This study provides new insights into PIOM as a potential sink for hazardous environmental contaminants and its role in enhancing the vector potential of plastic. Therefore, we recommend the inclusion of PIOM analysis in current biomonitoring regimes and that plastics be used with caution in aquaculture settings to safeguard valuable food resources, particularly in areas of point-source contamination.

Flavihalobacter algicola gen. nov. sp. nov., a member of the family Flavobacteriaceae with alginate-degradation activity, isolated from marine alga Saccharina japonica

A Gram-stain-negative, aerobic, yellow, non-motile, rod-shaped and alginate-degrading bacterium, designated Dm15^T, was isolated from marine alga collected in Weihai, PR China. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain Dm15^T represents a distinct line of the family Flavobacteriaceae. Strain Dm15^T had the highest 16S rRNA gene sequence similarity to its closest phylogenetic neighbour Arcticiflavibacter luteus (96.7 %) and 93.7-96.4 % sequence similarity to other phylogenetic neighbours (Bizionia paragorgiae, Winogradskyella thalassocola, Ichthyenterobacterium magnum, Psychroserpens burtonensis and Arcticiflavibacter luteus) in the family Flavobacteriaceae. The novel isolate was able to grow at 10-40 °C (optimum, 30-33 °C), pH 7.0-9.0 (optimum, pH 7.0-7.5) and with 0.5-6.0 % NaCl (optimum 2.0-3.0 %, w/v). It could grow at 40 °C, and degrade alginate and cellulose, which were different from the neighbour genera. The draft genome consisted of 3395 genes with a total length of 3 798 431 bp and 34.1mol% G+C content. Especially, there were some specific genes coding for cellulase and alginate lyase, which provided a basis for the above phenotypic characteristics. The strain's genome sequence showed 71.1-80.2 % average amino acid identity values and 71.8-77.7 % average nucleotide identity values compared to the type strains of related genera within the family Flavobacteriaceae. It shared digital DNA-DNA hybridization identity of 19.8 and 20.9 % with I. magnum and A. luteus, respectively. The sole menaquinone was MK-6. The major fatty acids were iso-C_15 : 0 and iso-C_15 : 1 G. The polar lipids included six unidentified polar lipids, four unidentified aminolipids and phosphatidylethanolamine. Based on the results of phenotypic, chemotaxonomic and phylogenetic analyses, strain Dm15^T represents a novel species of a new genus in the family Flavobacteriaceae, phylum Bacteroidetes, for which the name Flavihalobacter algicola gen. nov., sp. nov. is proposed. The type strain is Dm15^T (KCTC 42256^T=CICC 23815^T).

Aquaticitalea lipolytica gen. nov., sp. nov., isolated from Antarctic seawater

A Gram-stain-negative, rod-shaped bacterium, designated Ar-125^T, was isolated from Antarctic seawater. It produced carotenoid-like pigments and did not produce Bchl a. Ar-125^T was positive for hydrolysis of DNA, aesculin, gelatin, starch, Tween 40 and Tween 60. The sole respiratory quinone was MK-6. The major polar lipids were phosphatidylethanolamine, one unidentified aminolipid, one unidentified glycolipid and two unidentified lipids. The principal fatty acids were branched-chain fatty acids, including iso-C15 : 0, iso-C15 : 1 G, summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c), iso-C16 : 0, iso-C17 : 0 3-OH, iso-C16 : 0 3-OH and iso-C15 : 0 3-OH, as well as C15 : 0. The genomic DNA G+C content was 31.8 mol%. On the basis of 16S rRNA gene sequence analysis, Ar-125^T is closely related to the species of the genera Bizionia(with 16S rRNA gene pairwise sequence similarity of 93.7-96.5 %), Formosa(94.3-95.8 %), Gaetbulibacter(94.2-95.7 %), Geojedonia(95.5 %), Gelidibacter (93.3-95.4 %), Meridianimaribacter(95.3 %) and Psychroserpens (94.8-95.3 %), of the family Flavobacteriaceae. Phylogenetic analysis indicated that it represented an independent lineage and that the closest relatives were members of the genus Gelidibacter. Differential phenotypic properties and chemotaxonomic differences, together with phylogenetic distinctiveness, revealed that Ar-125^T could be differentiated from members of closely related genera. Therefore, it is proposed that Ar-125^T represents a novel species in a new genus, for which the name Aquaticitalea lipolytica gen. nov., sp. nov. (type strain Ar-125^T =CGMCC 1.15295^T =JCM 30876^T) is proposed.

Sedimentitalea todarodis sp. nov., isolated from the intestinal tract of a Japanese flying squid

A novel Gram-stain-negative, motile, aerobic and rod-shaped alphaproteobacterium, designated strain KHS03T, was isolated from the intestinal tract of a Japanese flying squid, Todarodes pacificus, which was collected from the East Sea, Korea. The new isolate shared 97.4 % 16S rRNA gene sequence similarity with Sedimentitalea nanhaiensis NH52FT. The isolate grew optimally at 25 °C and pH 7 in the presence of 1-2 % (w/v) NaCl, and had an absolute requirement of sodium ions for growth. The major cellular fatty acid was C18 : 1ω7c. The primary isoprenoid quinone was ubiquinone-10. Polar lipids comprised diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an unidentified aminolipid and two unidentified lipids. Genotypic analyses indicated that the whole genomic DNA of the isolate had a G+C content of 59.9 mol%. DNA-DNA hybridization showed that the isolate shared 17.1±2.3 % (reciprocal 17.0±1.9 %) genomic relatedness with the closest related type strain, S. nanhaiensis NH52FT. Strain KHS03T is thus suggested to represent a novel species of the genus Sedimentitalea, for which the name Sedimentitalea todarodis sp. nov. is proposed. The type strain is KHS03T (=KCTC 42412T=JCM 31160T).