Comparative Genome Analysis of Psychrobacillus Strain PB01, Isolated from an Iceberg

Genome and pan-genome analysis of a new exopolysaccharide-producing bacterium Pyschrobacillus sp. isolated from iron ores deposit and insights into iron uptake

Bacterial exopolysaccharides (EPS) have emerged as one of the key players in the field of heavy metal-contaminated environmental bioremediation. This study aimed to characterize and evaluate the metal biosorption potential of EPS produced by a novel Psychrobacillus strain, NEAU-3TGS, isolated from an iron ore deposit at Tamra iron mine, northern Tunisia. Genomic and pan-genomic analysis of NEAU-3TGS bacterium with nine validated published Psychrobacillus species was also performed. The results showed that the NEAU-3TGS genome (4.48 Mb) had a mean GC content of 36%, 4,243 coding sequences and 14 RNA genes. Phylogenomic analysis and calculation of nucleotide identity (ANI) values (less than 95% for new species with all strains) confirmed that NEAU-3TGS represents a potential new species. Pangenomic analysis revealed that Psychrobacillus genomic diversity represents an "open" pangenome model with 33,091 homologous genes, including 65 core, 3,738 shell, and 29,288 cloud genes. Structural EPS characterization by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy showed uronic acid and α-1,4-glycosidic bonds as dominant components of the EPS. X-ray diffraction (XRD) analysis revealed the presence of chitin, chitosan, and calcite CaCO3 and confirmed the amorphous nature of the EPS. Heavy metal bioabsorption assessment showed that iron and lead were more adsorbed than copper and cadmium. Notably, the optimum activity was observed at 37°C, pH=7 and after 3 h contact of EPS with each metal. Genomic insights on iron acquisition and metabolism in Psychrobacillus sp. NEAU-3TGS suggested that no genes involved in siderophore biosynthesis were found, and only the gene cluster FeuABCD and trilactone hydrolase genes involved in the uptake of siderophores, iron transporter and exporter are present. Molecular modelling and docking of FeuA (protein peptidoglycan siderophore-binding protein) and siderophores ferrienterobactine [Fe+3 (ENT)]-3 and ferribacillibactine [Fe+3 (BB)]-3 ligand revealed that [Fe+3 (ENT)]-3 binds to Phe122, Lys127, Ile100, Gln314, Arg215, Arg217, and Gln252. Almost the same for [Fe+3 (ENT)]-3 in addition to Cys222 and Tyr229, but not Ile100.To the best of our knowledge, this is the first report on the characterization of EPS and the adsorption of heavy metals by Psychrobacillus species. The heavy metal removal capabilities may be advantageous for using these organisms in metal remediation.

Isolation of novel cold-tolerance genes from rhizosphere microorganisms of Antarctic plants by functional metagenomics

The microorganisms that thrive in Antarctica, one of the coldest environments on the planet, have developed diverse adaptation mechanisms to survive in these extreme conditions. Through functional metagenomics, in this work, 29 new genes related to cold tolerance have been isolated and characterized from metagenomic libraries of microorganisms from the rhizosphere of two Antarctic plants. Both libraries were hosted in two cold-sensitive strains of Escherichia coli: DH10B ΔcsdA and DH10B ΔcsdA Δrnr. The csdA gene encodes a DEAD-box RNA helicase and rnr gene encodes an exoribonuclease, both essential for cold-adaptation. Cold-tolerance tests have been carried out in solid and liquid media at 15°C. Among the cold-tolerance genes identified, 12 encode hypothetical and unknown proteins, and 17 encode a wide variety of different proteins previously related to other well-characterized ones involved in metabolism reactions, transport and membrane processes, or genetic information processes. Most of them have been connected to cold-tolerance mechanisms. Interestingly, 13 genes had no homologs in E. coli, thus potentially providing entirely new adaptation strategies for this bacterium. Moreover, ten genes also conferred resistance to UV-B radiation, another extreme condition in Antarctica.

A genomic approach to analyze the cold adaptation of yeasts isolated from Italian Alps

Microorganisms including yeasts are responsible for mineralization of organic matter in cold regions, and their characterization is critical to elucidate the ecology of such environments on Earth. Strategies developed by yeasts to survive in cold environments have been increasingly studied in the last years and applied to different biotechnological applications, but their knowledge is still limited. Microbial adaptations to cold include the synthesis of cryoprotective compounds, as well as the presence of a high number of genes encoding the synthesis of proteins/enzymes characterized by a reduced proline content and highly flexible and large catalytic active sites. This study is a comparative genomic study on the adaptations of yeasts isolated from the Italian Alps, considering their growth kinetics. The optimal temperature for growth (OTG), growth rate (Gr), and draft genome sizes considerably varied (OTG, 10°C–20°C; Gr, 0.071–0.0726; genomes, 20.7–21.5 Mpb; %GC, 50.9–61.5). A direct relationship was observed between calculated protein flexibilities and OTG, but not for Gr. Putative genes encoding for cold stress response were found, as well as high numbers of genes encoding for general, oxidative, and osmotic stresses. The cold response genes found in the studied yeasts play roles in cell membrane adaptation, compatible solute accumulation, RNA structure changes, and protein folding, i.e., dihydrolipoamide dehydrogenase, glycogen synthase, omega-6 fatty acid, stearoyl-CoA desaturase, ATP-dependent RNA helicase, and elongation of very-long-chain fatty acids. A redundancy for several putative genes was found, higher for P-loop containing nucleoside triphosphate hydrolase, alpha/beta hydrolase, armadillo repeat-containing proteins, and the major facilitator superfamily protein. Hundreds of thousands of small open reading frames (SmORFs) were found in all studied yeasts, especially in Phenoliferia glacialis. Gene clusters encoding for the synthesis of secondary metabolites such as terpene, non-ribosomal peptide, and type III polyketide were predicted in four, three, and two studied yeasts, respectively.

Comparative Genomic Analysis of Agarolytic Flavobacterium faecale WV33T

Flavobacteria are widely dispersed in a variety of environments and produce various polysaccharide-degrading enzymes. Here, we report the complete genome of Flavobacterium faecale WV33^T, an agar-degrading bacterium isolated from the stools of Antarctic penguins. The sequenced genome of F. faecale WV33^T represents a single circular chromosome (4,621,116 bp, 35.2% G + C content), containing 3984 coding DNA sequences and 85 RNA-coding genes. The genome of F. faecale WV33^T contains 154 genes that encode carbohydrate-active enzymes (CAZymes). Among the CAZymes, seven putative genes encoding agarases have been identified in the genome. Transcriptional analysis revealed that the expression of these putative agarases was significantly enhanced by the presence of agar in the culture medium, suggesting that these proteins are involved in agar hydrolysis. Pangenome analysis revealed that the genomes of the 27 Flavobacterium type strains, including F. faecale WV33^T, tend to be very plastic, and Flavobacterium strains are unique species with a tiny core genome and a large non-core region. The average nucleotide identity and phylogenomic analysis of the 27 Flavobacterium-type strains showed that F. faecale WV33^T was positioned in a unique clade in the evolutionary tree.

Melanin biopolymer synthesis using a new melanogenic strain of Flavobacterium kingsejongi and a recombinant strain of Escherichia coli expressing 4-hydroxyphenylpyruvate dioxygenase from F. kingsejongi

BACKGROUND

Melanins are a heterologous group of biopolymeric pigments synthesized by diverse prokaryotes and eukaryotes and are widely utilized as bioactive materials and functional polymers in the biotechnology industry. Here, we report the high-level melanin production using a new melanogenic Flavobacterium kingsejongi strain and a recombinant Escherichia coli overexpressing F. kingsejongi 4-hydroxyphenylpyruvate dioxygenase (HPPD).

RESULTS

Melanin synthesis of F. kingsejongi strain was confirmed via melanin synthesis inhibition test, melanin solubility test, genome analysis, and structural analysis of purified melanin from both wild-type F. kingsejongi and recombinant E. coli expressing F. kingsejongi HPPD. The activity of F. kingsejongi HPPD was demonstrated via in vitro assays with 6 × His-tagged and native forms of HPPD. The specific activity of F. kingsejongi HPPD was 1.2 ± 0.03 μmol homogentisate/min/mg-protein. Bioreactor fermentation of F. kingsejongi produced a large amount of melanin with a titer of 6.07 ± 0.32 g/L, a conversion yield of 60% (0.6 ± 0.03 g melanin per gram tyrosine), and a productivity of 0.03 g/L·h, indicating its potential for industrial melanin production. Additionally, bioreactor fermentation of recombinant E. coli expressing F. kingsejongi HPPD produced melanin at a titer of 3.76 ± 0.30 g/L, a conversion yield of 38% (0.38 ± 0.03 g melanin per gram tyrosine), and a productivity of 0.04 g/L·h.

CONCLUSIONS

Both strains showed sufficiently high fermentation capability to indicate their potential as platform strains for large-scale bacterial melanin production. Furthermore, F. kingsejongi strain could serve as a model to elucidate the regulation of melanin biosynthesis pathway and its networks with other cellular pathways, and to understand the cellular responses of melanin-producing bacteria to environmental changes, including nutrient starvation and other stresses.