Structural and molecular basis for urea recognition by Prochlorococcus.

Nitrogen (N) is an essential element for microbial growth and metabolism. The growth and reproduction of microorganisms in more than 75% of areas of the ocean are limited by N. Prochlorococcus is numerically the most abundant photosynthetic organism on the planet. Urea is an important and efficient N source for Prochlorococcus. However, how Prochlorococcus recognizes and absorbs urea still remains unclear. Prochlorococcus marinus MIT 9313, a typical Cyanobacteria, contains an ABC-type transporter, UrtABCDE, which may account for the transport of urea. Here, we heterologously expressed and purified UrtA, the substrate-binding protein of UrtABCDE, detected its binding affinity toward urea, and further determined the crystal structure of the UrtA/urea complex. Molecular dynamics simulations indicated that UrtA can alternate between "open" and "closed" states for urea binding. Based on structural and biochemical analyses, the molecular mechanism for urea recognition and binding was proposed. When a urea molecule is bound, UrtA undergoes a state change from open to closed surrounding the urea molecule, and the urea molecule is further stabilized by the hydrogen bonds supported by the conserved residues around it. Moreover, bioinformatics analysis showed that ABC-type urea transporters are widespread in bacteria and probably share similar urea recognition and binding mechanisms as UrtA from P. marinus MIT 9313. Our study provides a better understanding of urea absorption and utilization in marine bacteria.

Complete genome sequence of Bacillus cereus 2-6A, a marine exopolysaccharide-producing bacterium isolated from deep-sea hydrothermal sediment of the Pacific Ocean.

Bacillus cereus 2-6A, was isolated from the sediments in the hydrothermal area of the Pacific Ocean with a water depth of 2628 m. In this study, we report the whole genome sequence of strain 2-6A and analyze that to understand its metabolic capacities and biosynthesis potential of natural products. The genome of strain 2-6A consists of a circular chromosome of 5,191,018 bp with a GC content of 35.3 mol% and two plasmids of 234,719 bp and 411,441 bp, respectively. Genomic data mining reveals that strain 2-6A has several gene clusters involved in exopolysaccharides (EPSs) and polyhydroxyalkanoates (PHAs) production and complex polysaccharides degradation. It also possesses a variety of genes for allowing strain 2-6A to cope with osmotic stress, oxidative stress, heat shock, cold shock and heavy metal stress, which could play a vital role in the adaptability of the strain to hydrothermal environments. Gene clusters for secondary metabolite production, such as lasso peptide and siderophore, are also predicted. Therefore, genome sequencing and data mining provide insights into the molecular mechanisms of Bacillus in adapting to hydrothermal deep ocean environments and can facilitate further experimental exploration.

Genomic analysis of Thalassospira sp. SW-3-3 reveals its genetic potential for phthalate pollution remediation.

Thalassospira sp. SW-3-3 is a bacterial strain isolated from deep seawater of the Pacific Ocean at a water depth of 3112 m. It is a Gram-negative, aerobic, and curved rod-shaped bacterium belonging to the family Thalassospiraceae. In this study, we report the complete genome sequence of strain SW-3-3. It has a circular chromosome with a size of 4,764,478 bp and a G + C content of 54.7%. The genome contains 4296 protein-coding genes, 63 tRNA genes, and 12 rRNA genes. Genomic analysis shows that strain SW-3-3 contains genes and catalytic pathways relevant to phthalate metabolism. Phthalates are well-known emerging contaminants that are harmful to environments and human health. They are chemically stable compounds that are widely used in plastic products and are pervasive in our life. With the discharge of plastic pollutants, a huge number of phthalate compounds enter the ocean. The genetic information of strain SW-3-3 suggests that it has the potential to metabolize phthalates. There are 9 key enzymes in the metabolization pathway, and phthalates are finally catalyzed to produce succinyl-CoA which is further degraded through the tricarboxylic acid (TCA) cycle pathway. This genomic analysis will be helpful for further understanding of the applications of strain SW-3-3 in the remediation of phthalate pollution.