Macroalgal virosphere assists with host-microbiome equilibrium regulation and affects prokaryotes in surrounding marine environments.

The microbiomes in macroalgal holobionts play vital roles in regulating macroalgal growth and ocean carbon cycling. However, the virospheres in macroalgal holobionts remain largely underexplored, representing a critical knowledge gap. Here we unveil that the holobiont of kelp (Saccharina japonica) harbors highly specific and unique epiphytic/endophytic viral species, with novelty (99.7% unknown) surpassing even extreme marine habitats (e.g. deep-sea and hadal zones), indicating that macroalgal virospheres, despite being closest to us, are among the least understood. These viruses potentially maintain microbiome equilibrium critical for kelp health via lytic-lysogenic infections and the expression of folate biosynthesis genes. In-situ kelp mesocosm cultivation and metagenomic mining revealed that kelp holobiont profoundly reshaped surrounding seawater and sediment virus-prokaryote pairings through changing surrounding environmental conditions and virus-host migrations. Some kelp epiphytic viruses could even infect sediment autochthonous bacteria after deposition. Moreover, the presence of ample viral auxiliary metabolic genes for kelp polysaccharide (e.g. laminarin) degradation underscores the underappreciated viral metabolic influence on macroalgal carbon cycling. This study provides key insights into understanding the previously overlooked ecological significance of viruses within macroalgal holobionts and the macroalgae-prokaryotes-virus tripartite relationship.

Adverse Environmental Perturbations May Threaten Kelp Farming Sustainability by Exacerbating Enterobacterales Diseases.

Globally kelp farming is gaining attention to mitigate land-use pressures and achieve carbon neutrality. However, the influence of environmental perturbations on kelp farming remains largely unknown. Recently, a severe disease outbreak caused extensive kelp mortality in Sanggou Bay, China, one of the world's largest high-density kelp farming areas. Here, through in situ investigations and simulation experiments, we find indications that an anomalously dramatic increase in elevated coastal seawater light penetration may have contributed to dysbiosis in the kelp Saccharina japonica's microbiome. This dysbiosis promoted the proliferation of opportunistic pathogenic Enterobacterales, mainly including the genera Colwellia and Pseudoalteromonas. Using transcriptomic analyses, we revealed that high-light conditions likely induced oxidative stress in kelp, potentially facilitating opportunistic bacterial Enterobacterales attack that activates a terrestrial plant-like pattern recognition receptor system in kelp. Furthermore, we uncover crucial genotypic determinants of Enterobacterales dominance and pathogenicity within kelp tissue, including pathogen-associated molecular patterns, potential membrane-damaging toxins, and alginate and mannitol lysis capability. Finally, through analysis of kelp-associated microbiome data sets under the influence of ocean warming and acidification, we conclude that such Enterobacterales favoring microbiome shifts are likely to become more prevalent in future environmental conditions. Our study highlights the need for understanding complex environmental influences on kelp health and associated microbiomes for the sustainable development of seaweed farming.

Plastoquinone synthesis inhibition by tetrabromo biphenyldiol as a widespread algicidal mechanism of marine bacteria.

Algae and bacteria have complex and intimate interactions in the ocean. Besides mutualism, bacteria have evolved a variety of molecular-based anti-algal strategies. However, limited by the unknown mechanism of synthesis and action of these molecules, these strategies and their global prevalence remain unknown. Here we identify a novel strategy through which a marine representative of the Gammaproteobacteria produced 3,3',5,5'-tetrabromo-2,2'-biphenyldiol (4-BP), that kills or inhibits diverse phytoplankton by inhibiting plastoquinone synthesis and its effect cascades to many other key metabolic processes of the algae. Through comparative genomic analysis between the 4-BP-producing bacterium and its algicidally inactive mutant, combined with gene function verification, we identified the gene cluster responsible for 4-BP synthesis, which contains genes encoding chorismate lyase, flavin-dependent halogenase and cytochrome P450. We demonstrated that in near in situ simulated algal blooming seawater, even low concentrations of 4-BP can cause changes in overall phytoplankton community structure with a decline in dinoflagellates and diatoms. Further analyses of the gene sequences from the Tara Oceans expeditions and 2750 whole genome sequences confirmed the ubiquitous presence of 4-BP synthetic genes in diverse bacterial members in the global ocean, suggesting that it is a bacterial tool potentially widely used in global oceans to mediate bacteria-algae antagonistic relationships.

Phage Infection Benefits Marine Diatom Phaeodactylum tricornutum by Regulating the Associated Bacterial Community.

The interaction between marine phyto- and bacterioplankton is regulated by multiple environmental and biological factors. Among them, phages as the major regulators of bacterial mortality are considered to have important impacts on algae-associated bacteria and algae-bacteria relationship. However, little is currently known about the actual impact of phages from this perspective. Here, we revealed that phage infection improved the maximum quantum efficiency of photosystem II of Phaeodactylum tricornutum by regulating the associated bacterial community. Specifically, phage infection weakened bacterial abundance and eliminated their negative effects on the diatom. Unexpectedly, the structure of the bacterial community co-cultured with the diatom was not significantly affected, likely because the shaping effect of the diatom on the bacterial community structure can far outcompete or mask the impact of phage infection. Our results established a link between algae, bacteria, and phages, suggesting that phage infection benefits the diatom by regulating the associated bacterial community.

Inherent tendency of Synechococcus and heterotrophic bacteria for mutualism on long-term coexistence despite environmental interference.

Mutualism between Synechococcus and heterotrophic bacteria has been found to support their prolonged survival in nutrient-depleted conditions. However, environmental interference on the fate of their mutualism is not understood. Here, we show that exogenous nutrients disrupt their established mutualism. Once the exogenous nutrients were exhausted, Synechococcus and heterotrophic bacteria gradually reestablished their metabolic mutualism during 450 days of culture, which revived unhealthy Synechococcus cells. Using metagenomics, metatranscriptomics, and the 15N tracer method, we reveal that the associated bacterial nitrogen fixation triggered the reestablishment of the mutualism and revival of Synechococcus health. During this process, bacterial community structure and functions underwent tremendous adjustments to achieve the driving effect, and a cogeneration of nitrogen, phosphorus, iron, and vitamin by the heterotrophic bacteria sustained Synechococcus's prolonged healthy growth. Our findings suggest that Synechococcus and heterotrophic bacteria may have an inherent tendency toward mutualism despite environmental interference. This may exhibit their coevolutionary adaptations in nutrient-deficient environments.

Carbon Sequestration in the Form of Recalcitrant Dissolved Organic Carbon in a Seaweed (Kelp) Farming Environment.

Under climate change scenarios, the contribution of macroalgae to carbon sequestration has attracted wide attention. As primary producers, macroalgae can release substantial amounts of dissolved organic carbon (DOC) in seawater. However, little is known about the molecular composition and chemical properties of DOC derived from macroalgae and which of them are recalcitrant DOC (RDOC) that can be sequestered for a long time in the ocean. In the most intensive seaweed (kelp) farming area (Sanggou Bay) in China, we found that kelp mariculture not only significantly increased DOC concentration, but also introduced a variety of new DOC molecular species, many of which were sulfur-containing molecules. A long-term DOC degradation experiment revealed that those DOC with strong resistance to microbial degradation, i.e., RDOC, account for approximately 58% of the DOC extracted from kelp mariculture area. About 85% (3587 out of 4224 with different chemical features) of the RDOC molecular species were steadily present throughout the long-term degradation process. 15% (637 out of 4224 with different chemical features) of the RDOC molecular species were likely newly generated by microorganisms after metabolizing macroalgae-derived labile DOC. All these stable RDOC should be included in the blue carbon budgets of seaweed.

A Novel Phage Indirectly Regulates Diatom Growth by Infecting a Diatom-Associated Biofilm-Forming Bacterium.

Algae and heterotrophic bacteria have close and intricate interactions, which are regulated by multiple factors in the natural environment. Phages are the major factor determining bacterial mortality rates. However, their impacts on the alga-associated bacteria and thus on the alga-bacterium interactions are poorly understood. Here, we obtained a diatom-associated bacterium, Stappia indica SNL01, that could form a biofilm and had an inhibitory effect on the growth of the diatom Thalassiosira pseudonana. Meanwhile, phage SI01, with a double-stranded circular DNA genome (44,247 bp), infecting S. indica SNL01 was isolated. Phylogenetic analysis revealed that phage SI01 represents a novel member of the Podoviridae family. The phage contained multiple lysis genes encoding cell wall-lysing muramidase and spore cortex-lysing SleB, as well as depolymerase-like tail spike protein. By lysing the host bacterium and inhibiting the formation of biofilm, this phage could indirectly promote the growth of the diatom. Our results provide new insights into how phages indirectly regulate algal growth by infecting bacteria that are closely associated with algae or in the phycosphere. IMPORTANCE The impact of phage infection on the alga-bacterium relationship in the ocean is poorly understood. Here, a novel phage infecting the diatom-associated bacterium Stappia indica SNL01 was isolated. This bacterium could form a biofilm and had a negative effect on diatom growth. We revealed that this phage contained multiple lysis genes and could inhibit the formation of the bacterial biofilm, thus indirectly promoting diatom growth. This study suggests that phages not only are important regulators of bacteria but also have substantial indirect effects on algae and the alga-bacterium relationship.

A dark-tolerant diatom (Chaetoceros) cultured from the deep sea.

Although the extreme conditions of the deep sea are typically not suitable for the growth of photosynthetic algae, accumulating evidence indicates that there are diverse healthy phytoplankton living in this environment. However, living phytoplankton from the deep sea have rarely been isolated and cultivated, and so our understanding of where they come from and how they adapt to (or tolerate) the extreme deep-sea environment is limited. Here, under long-term dark stress and subsequent light treatment, we successfully isolated a diatom from a depth of 1,000 m in the Western Pacific Ocean. Morphological observations and molecular phylogenetic analysis revealed that it is affiliated to the genus Chaetoceros, and thus, we tentatively named it Chaetoceros sp. DS1. We observed that the chloroplast genome of this species, is most closely related to that of Chaetoceros simplex. It was shown to have a strong tolerance to darkness in that it maintained its morphological integrity and vitality for up to 3 months in complete darkness at room temperature. We also demonstrated that Chaetoceros sp. DS1 presented a facultative heterotrophic function. Its growth was promoted by many organic carbon sources (e.g., glycerine, ethanol, and sodium acetate) under low light conditions. However, under dark and high light conditions, the growth promotion effect of organic carbon was not obvious. Indeed, Chaetoceros sp. DS1 grew best under low light conditions, indicating that it likely came from the deeper layer of the euphotic zone. The facultative heterotrophic function of this diatom and tolerance to darkness may help it survive in these conditions or enter a dormant period in the deep sea.

Long-Term Survival of Synechococcus and Heterotrophic Bacteria without External Nutrient Supply after Changes in Their Relationship from Antagonism to Mutualism.

Marine phytoplankton and heterotrophic bacteria share a very close but usually changeable relationship. However, the ultimate fate of their unstable relationship on a long-term scale is unclear. Here, the relationship between Synechococcus and heterotrophic bacterial communities underwent a dramatic shift from antagonism to commensalism and eventually to mutualism during long-term cocultivation. The relationship change is attributed to the different (even opposite) effects of diverse bacterial members on Synechococcus and the ratio of beneficial to harmful bacteria. Different bacterial members also interact with each other (e.g., quorum-sensing communication, hostility, or mutual promotion) and drive a dynamic succession in the entire community structure that corresponds exactly to the shift in its relationship with Synechococcus. In the final mutualism stage, a self-sufficient nitrogen cycle, including nitrogen fixation, denitrification, and organic nitrogen degradation, contributed to the healthy survival of Synechococcus for 2 years without an exogenous nutrient supply. This natural selective trait of Synechococcus and heterotrophic bacteria toward mutualism under long-term coexistence provides a novel clue for understanding the ubiquity and competitive advantage of Synechococcus in global oceans. IMPORTANCE Phytoplankton and heterotrophic bacteria have a close but usually changeable relationship. Uncovering the dynamic changes and driving factors of their interrelationships is of great significance for an in-depth understanding of the ecological processes and functions of marine microorganisms. Here, we observed that Synechococcus and heterotrophic bacterial communities underwent a dramatic change in their relationship from antagonism to mutualism during a long-term cocultivation process. We revealed that the interactions between different members of the bacterial community and the combined effects of different bacterial individuals on Synechococcus promoted the dynamic changes of the Synechococcus-bacterium relationship. In the end, a self-sufficient nutrient cycle (especially nitrogen) established by Synechococcus and bacterial communities supported their long-term survival without any external nutrition supply. This study provides novel insight into the interaction between Synechococcus and heterotrophic bacteria in the ocean and provides a novel clue for understanding the ubiquity and competitive advantage of Synechococcus in global oceans.

DOC dynamics and bacterial community succession during long-term degradation of Ulva prolifera and their implications for the legacy effect of green tides on refractory DOC pool in seawater.

Under climate warming and coastal eutrophication, outbreaks of green tides have increased in recent decades; e.g., the world's largest green tide caused by Ulva prolifera has occurred in the Yellow Sea for 13 consecutive years. The massive assemblage of macroalgae absorbs large amounts of atmospheric CO2 and converts it into biomass. After the green tide, millions of tons of the macroalgal biomass sink to the seabed to be degraded eventually; this inevitably has a significant impact on the coastal organic carbon pool and microbial community. However, this impact is poorly understood. Here, the degradation of Ulva prolifera over 520 days revealed that relatively sufficient degradation of the macroalgae occurred at ca. 7 months. The rapid release of dissolved organic carbon (DOC) mainly occurred in the first week, which not only increased the size and diversity of the DOC pool in a short time but also promoted the rapid growth of bacteria and led to hypoxia and acidification of the seawater. After that, the labile portion of DOC was gradually used up by bacteria within one month, while the degradation of semi-labile or semi-refractory DOC occurred in half a year. The remaining DOC existed in the form of refractory DOC (RDOC), resisting bacterial consumption and remaining stable for 10 months. During the long-term degradation process, bacterial community structure and metabolic function showed obvious successional characteristics, driving the gradual transformation of DOC from labile to refractory through the microbial carbon pump mechanism. After the long-term degradation, the remaining RDOC accounted for approximately 1.6% of the macroalgal carbon biomass. As RDOC can maintain long-term stability, we propose that the frequent outbreaks of green tides not only affect microbial processes but also may have an important cumulative effect on the coastal RDOC pool.

Flavicella sediminum sp. nov., isolated from marine sediment.

A novel, Gram-stain-negative, motile, flagellated, aerobic, rod-shaped (0.5-0.7 µm wide and 1.0-1.2 µm long) and faint-yellow strain, designated ALS 84T, was isolated from marine sediment sampled at Ailian bay, Rongcheng, PR China. Growth occurred in the presence of 1-3 % (w/v) NaCl (optimum, 2 % NaCl), at pH 4.0-8.0 (pH 6.0-7.0) and at 8-30 °C (28 °C). The genome size was 4.37 Mbp. The G+C content of the genomic DNA was 33.6 mol%. The results of phylogenetic analysis based on 16S rRNA gene sequences suggested that strain ALS 84T belongs to the genus Flavicella within the family Flavobacteriaceae, and is most closely related to Flavicella marina (95.6 % similarity). The major fatty acids (>10 %) were iso-C15 : 0 3-OH (22.9 %), iso-C15 : 0 (14.0 %) and C16 : 0 (10.9 %). The major polar lipids were phosphatidylethanolamine and three unidentified lipids. Menaquinone-6 (MK-6) was identified as the respiratory quinone. On the basis of the phenotypic, phylogenetic and chemotaxonomic data obtained in the study, strain ALS 84T is considered to represent a novel species of the genus Flavicella, for which the name Flavicella sediminum sp. nov. is proposed. The type strain of the novel species is strain ALS 84T (=KCTC 62398T=MCCC 1K03480T).

Ulvibacterium marinum gen. nov., sp. nov., a novel marine bacterium of the family Flavobacteriaceae, isolated from a culture of the green alga Ulva prolifera.

A Gram-stain negative, aerobic, rod-shaped, and non-motile bacterium, designated strain CCMM003T, was isolated from a culture of the green alga Ulva prolifera. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain CCMM003T belongs to the family Flavobacteriaceae and exhibits a close relationship to Pseudozobellia thermophila DSM 19858T (92.5%). Optimal growth occurred in the presence of 4% (w/v) NaCl, at pH 7.0 and 30 °C. The polar lipids of strain CCMM003T consisted of phosphatidylethanolamine and six unidentified lipids. The predominant isoprenoid quinone was MK-6. The major fatty acids were iso-C15:0, iso-C15:1 G, iso-C17:0 3-OH and summed feature 3 (C16:1ω7c and/or iso-C15:0 2-OH). The DNA G + C content of strain CCMM003T calculated on the basis of the genome sequence was 41.2 mol% and the genome size was 5.9 Mbp. On the basis of data from this polyphasic study, strain CCMM003T is considered to represent a novel genus and species of the family Flavobacteriaceae, for which the name Ulvibacterium marinum gen. nov., sp. nov. is proposed. The type strain is CCMM003T (= MCCC 1K03244T =KCTC 52639T).

Algihabitans albus gen. nov., sp. nov., isolated from a culture of the green alga Ulva prolifera.

A bacterial strain, designated HHTR 118T, was isolated from a culture of the green alga Ulvaprolifera obtained from offshore seawater of Qingdao, Shandong Province, China. Cells of strain HHTR 118T were rod-shaped and motile with a single flagellum, and approximately 0.3-0.4 µm wide and 0.8-1.4 µm long. The strain was Gram-stain-negative, strictly aerobic, catalase-negative and oxidase-positive. Optimal growth was observed at 30 °C, at pH 8.0 and with 1 % (w/v) NaCl. Nitrate was not reduced. Sucrose, sodium citrate and l-leucine stimulated growth, but not lactose, fructose, xylose, d-mannose, glucose, raffinose, rhamnose, ornithine or lysine. The DNA G+C content of strain HHTR 118T calculated on the basis of the genome sequence was 64.9 mol% and the genome size is 4.6 Mbp. The major quinone was ubiquinone 10 and the predominant cellular fatty acids (>10 % of total fatty acids) were summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c). The predominant polar lipids were phosphatidylglycerol, one unidentified phospholipid, two unidentified aminolipids and three unidentified polar lipids. Phylogenetic analysis, based on 16S rRNA gene sequences, demonstrated that strain HHTR 118T was affiliated with the family Rhodospirillaceae. On the basis of the 16S rRNA gene sequence data as well as physiological and biochemical characteristics, we concluded that strain HHTR 118T represents a novel species of a novel genus. We propose the name of Algihabitans albus gen. nov., sp. nov. for this novel species. The type strain of the novel species is strain HHTR 118T (=KCTC 62395T=MCCC 1K03486T).

Marinicaulis aureum sp. nov., isolated from a culture of the green alga Ulva prolifera, and emended description of the genus Marinicaulis.

A Gram-stain negative, facultatively anaerobic, rod-shaped motile bacterium with a single polar flagellum, designed strain HHTR114T, was isolated from a culture of the green alga Ulva prolifera obtained from offshore seawater at Qingdao, China. Optimum growth occurred in the presence of 2-3% (w/v) NaCl, at pH 7.0-8.0 and 30 °C. The major fatty acids (> 10% of total fatty acids) were C16:0 (24.7%), C18:1ω7c 11-methyl (24.3%) and summed feature 3 (C16:1ω6c and/or C16:1ω7c, 19.7%). The major polar lipids were phosphatidylethanolamine, glycolipid and four unidentified polar lipids. The DNA G + C content of strain HHTR114T calculated on the basis of the genome sequence was 58.2% and the genome size is 4.1 Mbp. The predominant isoprenoid quinone was Q-10. The estimated DNA-DNA hybridization values were 21.4% [18.6-24.4%] between strain HHTR114T and Marinicaulis flavus SY-3-19T. On the basis of polyphasic analysis, strain HHTR114T is considered to represent a novel species, for which the name Marinicaulis aureum sp. nov. is proposed. The type strain of the type species is HHTR114T (= KCTC 62394T = MCCC 1K03481T).

Roseicyclus marinus sp. nov., isolated from a Synechococcus culture, and emended description of the genus Roseicyclus.

A novel Gram-stain-negative, aerobic, non-flagellated, pink-pigmented and rod-shaped strain with gliding motility, designated strain CCMM001T, was isolated from a mixed culture of Synechococcus species PCC7002 and a natural bacterial community from a sample of offshore seawater from Qingdao, China, during September 2014. The strain contained bacteriochlorophyll a with a small peak at 802 nm and a large in vivo absorption band at 870 nm. Strain CCMM001T grew optimally at pH 7.0 and 30 °C in the presence of 3 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CCMM001T is most closely related to the genus Roseicyclus and its type and only species Roseicyclus mahoneyensis ML6T with 96.9 % sequence similarity. The polar lipids of strain CCMM001T consisted of phosphatidylethanolamine, phosphatidylcholine, one unidentified aminolipid, and five unidentified lipids. The predominant isoprenoid quinone was Q-10. The major fatty acids included C18 : 1ω7c and C19 : 0cyclo ω8c. The DNA G+C content of strain CCMM001T was 63.5 mol%. These phylogenetic, physiological and chemotaxonomic data indicated that strain CCMM001T represents a novel species of the genus Roseicyclus, for which the name Roseicyclus marinus sp. nov. is proposed. The type strain is CCMM001T (=MCCC 1K03242T=KCTC 52641T).

Optimization of robustness of interdependent network controllability by redundant design.

Controllability of complex networks has been a hot topic in recent years. Real networks regarded as interdependent networks are always coupled together by multiple networks. The cascading process of interdependent networks including interdependent failure and overload failure will destroy the robustness of controllability for the whole network. Therefore, the optimization of the robustness of interdependent network controllability is of great importance in the research area of complex networks. In this paper, based on the model of interdependent networks constructed first, we determine the cascading process under different proportions of node attacks. Then, the structural controllability of interdependent networks is measured by the minimum driver nodes. Furthermore, we propose a parameter which can be obtained by the structure and minimum driver set of interdependent networks under different proportions of node attacks and analyze the robustness for interdependent network controllability. Finally, we optimize the robustness of interdependent network controllability by redundant design including node backup and redundancy edge backup and improve the redundant design by proposing different strategies according to their cost. Comparative strategies of redundant design are conducted to find the best strategy. Results shows that node backup and redundancy edge backup can indeed decrease those nodes suffering from failure and improve the robustness of controllability. Considering the cost of redundant design, we should choose BBS (betweenness-based strategy) or DBS (degree based strategy) for node backup and HDF(high degree first) for redundancy edge backup. Above all, our proposed strategies are feasible and effective at improving the robustness of interdependent network controllability.

Salinisphaera aquimarina sp. nov., isolated from seawater.

A Gram-stain-negative, aerobic, rod-shaped, motile bacterium with a subpolar flagellum, designated strain CCMM005T, was isolated from offshore seawater at Qingdao, China. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain CCMM005T belonged to the genus Salinisphaera and exhibited highest 16S rRNA gene sequence similarity to Salinisphaera dokdonensis CL-ES53T (96.9 %). It showed lower sequence similarities (94.9-96.4 %) with all other representatives of the genus Salinisphaera. Optimal growth occurred in the presence of 4 % (w/v) NaCl, at 30 °C and at pH 7.0. The polar lipids of strain CCMM005T consisted of phosphatidylethanolamine, phosphatidylcholine, phosphatidylglycerol, one unidentified phosphoglycolipid and one unidentified phospholipid. The predominant isoprenoid quinone was Q-8. The major fatty acids were C19 : 0cyclo ω8c, C18 : 0 and C18 : 1ω7c. The DNA G+C content of strain CCMM005T was 65.3 mol%. On the basis of data from this polyphasic study, strain CCMM005T is considered to represent a novel species of the genus Salinisphaera, for which the name Salinisphaera aquimarina sp. nov. is proposed. The type strain is CCMM005T (=MCCC 1K03246T=KCTC 52640T).

Polaribacter pacificus sp. nov., isolated from a deep-sea polymetallic nodule from the Eastern Pacific Ocean.

A Gram-staining-negative, yellow-colony-forming, rod-shaped, non-flagellated and facultatively aerobic strain, designed HRA130-1T, was isolated from a deep-sea polymetallic nodule from the Pacific Clarion-Clipperton Fracture Zone (CCFZ). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain HRA130-1T belonged to the genus Polaribacter (96.3-93.2 % 16S rRNA gene sequence similarity), and exhibited 94 % 16S rRNA gene sequence similarity to Polaribacter filamentus KCTC 23135T (type species) and the highest sequence similarity to Polaribacter huanghezhanensis KCTC 32516T (96.3 %). Optimal growth occurred in the presence of 4 % (w/v) NaCl, at pH 7.0 and 16 °C. The DNA G+C content of strain HRA130-1T was 35.9 mol%. The major fatty acid was iso-C15 : 0. The predominant respiratory quinone was menaquinone-6 (MK-6). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, one unidentified phospholipid and an unidentified aminolipid. On the basis of data from the present taxonomic study using a polyphasic approach, strain HRA130-1T represents a novel species of the genus Polaribacter, for which the name Polaribacter pacificus sp. nov. is proposed. The type strain is HRA130-1T (=KCTC 52370T=MCCC 1K03199T=JCM 31460T=CGMCC 1.15763T).

Redundant Design in Interdependent Networks.

Modern infrastructure networks are often coupled together and thus could be modeled as interdependent networks. Overload and interdependent effect make interdependent networks more fragile when suffering from attacks. Existing research has primarily concentrated on the cascading failure process of interdependent networks without load, or the robustness of isolated network with load. Only limited research has been done on the cascading failure process caused by overload in interdependent networks. Redundant design is a primary approach to enhance the reliability and robustness of the system. In this paper, we propose two redundant methods, node back-up and dependency redundancy, and the experiment results indicate that two measures are effective and costless. Two detailed models about redundant design are introduced based on the non-linear load-capacity model. Based on the attributes and historical failure distribution of nodes, we introduce three static selecting strategies-Random-based, Degree-based, Initial load-based and a dynamic strategy-HFD (historical failure distribution) to identify which nodes could have a back-up with priority. In addition, we consider the cost and efficiency of different redundant proportions to determine the best proportion with maximal enhancement and minimal cost. Experiments on interdependent networks demonstrate that the combination of HFD and dependency redundancy is an effective and preferred measure to implement redundant design on interdependent networks. The results suggest that the redundant design proposed in this paper can permit construction of highly robust interactive networked systems.