Idiomarina andamanensis sp. nov., an alkalitolerant bacterium isolated from Andaman Sea water

The Hypersaline Soils of the Odiel Saltmarshes Natural Area as a Source for Uncovering a New Taxon: Pseudidiomarina terrestris sp. nov

The hypersaline soils of the Odiel Saltmarshes Natural Area are an extreme environment with high levels of some heavy metals; however, it is a relevant source of prokaryotic diversity that we aim to explore. In this study, six strains related to the halophilic genus Pseudidiomarina were isolated from this habitat. The phylogenetic study based on the 16S rRNA gene sequence and the fingerprinting analysis suggested that they constituted a single new species within the genus Pseudidiomarina. Comparative genomic analysis based on the OGRIs indices and the phylogeny inferred from the core genome were performed considering all the members of the family Idiomarinaceae. Additionally, a completed phenotypic characterization, as well as the fatty acid profile, were also carried out. Due to the characteristics of the habitat, genomic functions related to salinity and high heavy metal concentrations were studied, along with the global metabolism of the six isolates. Last, the ecological distribution of the isolates was studied in different hypersaline environments by genome recruitment. To sum up, the six strains constitute a new species within the genus Pseudidiomarina, for which the name Pseudidiomarina terrestris sp. nov. is proposed. The low abundance in all the studied hypersaline habitats indicates that it belongs to the rare biosphere in these habitats. In silico genome functional analysis suggests the presence of heavy metal transporters and pathways for nitrate reduction and nitrogen assimilation in low availability, among other metabolic traits.

Comparative genomics of seven genomes of genus Idiomarina reveals important halo adaptations and genes for stress response

The genus Idiomarina consists of halophilic and/or haloalkaliphilic organisms. We compared the complete genomes of seven strains of the genus Idiomarina to investigate its adaptation to saline environment. A total of 1,313 core genes related to salinity tolerance, stress response, antibiotic resistance genes, virulence factors, and drug targets were found. Comparative genomics revealed various genes involved in halo adaptations of these organisms, including transporters and influx or efflux systems for elements such as Fe, Cu, Zn, Pb, and Cd. In agreement with their isolation sources (such as hydrothermal vents and marine sediments) and environments abundant in heavy metals, various resistance proteins and transporters associated with metal tolerance were also identified. These included copper resistance proteins, zinc uptake transcriptional repressor Zur, MerC domain-containing protein, Cd(II)/Pb(II)-responsive transcriptional regulator, Co/Zn/Cd efflux system protein, and mercuric transporter. Interestingly, we observed that the carbohydrate metabolism pathways were incomplete in all the strains and transporters used for absorption of small sugars were also not found in them. Also, the presence of higher proportion of genes involved in protein metabolism than carbohydrate metabolism indicates that proteinaceous substrates act as the major food substrates for these bacterial strains than carbohydrates. Genomic islands were detected in some species, highlighting the role of horizontal gene transfer for acquisition in novel genes. Genomic rearrangements in terms of partially palindromic regions were detected in all strains. To our knowledge, this is the first comprehensive comparative genomics study among the genus Idiomarina revealing unique genomic features within bacterial species inhabiting different ecological niches.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03887-3.

Draft Genome Sequence of Idiomarina sp. Strain W-5T, Isolated from the Andaman Sea

Here, we report the draft genome sequence of Idiomarina sp. strain W-5T, which was isolated from the Andaman Sea. The genome encodes 2,207 proteins. The Idiomarina sp. strain W-5T whole-genome sequence will help us to understand the metabolic diversity in marine bacteria.

Here, we report the draft genome sequence of Idiomarina sp. strain W-5T, which was isolated from the Andaman Sea. The genome encodes 2,207 proteins. The Idiomarina sp. strain W-5T whole-genome sequence will help us to understand the metabolic diversity in marine bacteria.

Trophic Specialization Results in Genomic Reduction in Free-Living Marine Idiomarina Bacteria

The streamlining hypothesis is usually used to explain the genomic reduction events in free-living bacteria like SAR11. However, we find that the genomic reduction phenomenon in the bacterial genus Idiomarina is different from that in SAR11. Therefore, we propose a new hypothesis to explain genomic reduction in this genus based on trophic specialization that could result in genomic reduction, which would be not uncommon in nature. Not only can the trophic specialization hypothesis explain the genomic reduction in the genus Idiomarina, but it also sheds new light on our understanding of the genomic reduction processes in other free-living bacterial lineages.

The streamlining hypothesis is generally used to explain the genomic reduction events related to the small genome size of free-living bacteria like marine bacteria SAR11. However, our current understanding of the correlation between bacterial genome size and environmental adaptation relies on too few species. It is still unclear whether there are other paths leading to genomic reduction in free-living bacteria. The genome size of marine free-living bacteria of the genus Idiomarina belonging to the order Alteromonadales (Gammaproteobacteria) is much smaller than the size of related genomes from bacteria in the same order. Comparative genomic and physiological analyses showed that the genomic reduction pattern in this genus is different from that of the classical SAR11 lineage. Genomic reduction reconstruction and substrate utilization profile showed that Idiomarina spp. lost a large number of genes related to carbohydrate utilization, and instead they specialized on using proteinaceous resources. Here we propose a new hypothesis to explain genomic reduction in this genus; we propose that trophic specialization increasing the metabolic efficiency for using one kind of substrate but reducing the substrate utilization spectrum could result in bacterial genomic reduction, which would be not uncommon in nature. This hypothesis was further tested in another free-living genus, Kangiella, which also shows dramatic genomic reduction. These findings highlight that trophic specialization is potentially an important path leading to genomic reduction in some marine free-living bacteria, which is distinct from the classical lineages like SAR11.