Putting life on ice: bacteria that bind to frozen water.

Ice-binding proteins (IBPs) are typically small, soluble proteins produced by cold-adapted organisms to help them avoid ice damage by either resisting or tolerating freezing. By contrast, the IBP of the Antarctic bacterium Marinomonas primoryensis is an extremely long, 1.5 MDa protein consisting of five different regions. The fourth region, a 34 kDa domain, is the only part that confers ice binding. Bioinformatic studies suggest that this IBP serves as an adhesin that attaches the bacteria to ice to keep it near the top of the water column, where oxygen and nutrients are available. Using temperature-controlled cells and a microfluidic apparatus, we show that M. primoryensis adheres to ice and is only released when melting occurs. Binding is dependent on the mobility of the bacterium and the functionality of the IBP domain. A polyclonal antibody raised against the IBP region blocks bacterial ice adhesion. This concept may be the basis for blocking biofilm formation in other bacteria, including pathogens. Currently, this IBP is the only known example of an adhesin that has evolved to bind ice.

Marinomonas profundimaris sp. nov., isolated from deep-sea sediment sample of the Arctic Ocean.

A taxonomic study was carried out on strain D104(T), which was isolated from deep-sea subsurface sediment sample from the Arctic Ocean. The bacterium was found to be Gram-negative, oxidase negative and catalase weakly positive, rod shaped, motile by means of polar flagellum. The organism grows between 4 and 37 °C (optimum 25-28 °C) and 0.5-6 % NaCl (optimum 3 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain D104(T) belongs to the genus Marinomonas, with highest sequence similarities of 97.7 % to Marinomonas ushuaiensis DSM 15871(T), followed by M. dokdonensis DSW10-10(T) (96.9 %), M. arenicola KMM 3893(T) (96.7 %), M. arctica 328(T) (96.6 %) and other 18 species of the genus Marinomonas (94.4-96.5 %). The average nucleotide identity and estimated DNA-DNA hybridization values between strain D104(T) and M. ushuaiensis DSM 15871(T) were 84.24 % and 20.80 ± 2.33 % respectively. The principal fatty acids were C16:0, sum in feature 3 (C16:1 ω7c/C16:1 ω6c), sum in feature 8 (C18:1 ω7c/C18:1 ω6c) and C12:1 3OH. The G + C content of the chromosomal DNA was determined to be 44.8 mol%. The respiratory quinone was found to be Q8 (100 %). Polar lipids include phosphatidylglycerol and phosphatidylethanolamine as major phospholipids and aminolipid and phospholipid as minor components. The results of the genotypic and phenotypic analyses indicate that strain D104(T) represents a novel species of the genus Marinomonas, for which the name Marinomonas profundimaris sp. nov. is proposed, with the type strain D104(T) (=MCCC 1A07573(T) = LMG 27696(T)).

Marinomonas basaltis sp. nov., a marine bacterium isolated from black sand.

A Gram-negative, aerobic, slightly halophilic, rod-shaped bacterium was isolated from black sand in Soesoggak, Jeju island, Korea. The strain, designated J63(T), was oxidase- and catalase-positive and arginine dihydrolase-negative. The isolate required Na(+) for growth and differed from phenotypically related species by being able to utilize sucrose and d-galactose as a carbon source. Phylogenetic analysis based on the sequence of the 16S rRNA gene revealed that strain J63(T) belongs to the genus Marinomonas. It exhibited 16S rRNA gene sequence similarities of 97.6-98.7 % to the closely related species Marinomonas communis, Marinomonas ostreistagni, Marinomonas aquimarina and Marinomonas vaga. The phylogenetic analysis revealed that strain J63(T) comprised a relatively long subline of descent, shared a branch point with the outlying species Marinomonas communis and occupied a phylogenetically distant position on the main Marinomonas branch. Based on DNA-DNA hybridization, the levels of relatedness between strain J63(T) and M. communis NBRC 102224(T), M. aquimarina CIP 108405(T) and M. vaga JCM 20774(T) were 56.2, 45.1 and 51.3 %, respectively. On the basis of the phenotypic, genetic and phylogenetic data, strain J63(T) should be placed in the genus Marinomonas as representing a novel species, for which the name Marinomonas basaltis sp. nov. is proposed. The type strain is J63(T) (=KCTC 22118(T)=JCM 14948(T)).

Hydrogen peroxide linked to lysine oxidase activity facilitates biofilm differentiation and dispersal in several gram-negative bacteria.

The marine bacterium Pseudoalteromonas tunicata produces an antibacterial and autolytic protein, AlpP, which causes death of a subpopulation of cells during biofilm formation and mediates differentiation, dispersal, and phenotypic variation among dispersal cells. The AlpP homologue (LodA) in the marine bacterium Marinomonas mediterranea was recently identified as a lysine oxidase which mediates cell death through the production of hydrogen peroxide. Here we show that AlpP in P. tunicata also acts as a lysine oxidase and that the hydrogen peroxide generated is responsible for cell death within microcolonies during biofilm development in both M. mediterranea and P. tunicata. LodA-mediated biofilm cell death is shown to be linked to the generation of phenotypic variation in growth and biofilm formation among M. mediterranea biofilm dispersal cells. Moreover, AlpP homologues also occur in several other gram-negative bacteria from diverse environments. Our results show that subpopulations of cells in microcolonies also die during biofilm formation in two of these organisms, Chromobacterium violaceum and Caulobacter crescentus. In all organisms, hydrogen peroxide was implicated in biofilm cell death, because it could be detected at the same time as the killing occurred, and the addition of catalase significantly reduced biofilm killing. In C. violaceum the AlpP-homologue was clearly linked to biofilm cell death events since an isogenic mutant (CVMUR1) does not undergo biofilm cell death. We propose that biofilm killing through hydrogen peroxide can be linked to AlpP homologue activity and plays an important role in dispersal and colonization across a range of gram-negative bacteria.