Supramolecular architecture of photosynthetic membrane in red algae in response to nitrogen starvation

The availability of nitrogen is one of the most important determinants that can limit the growth of photosynthetic organisms including plants and algae; however, direct observations on the supramolecular architecture of photosynthetic membranes in response to nitrogen stress are still lacking. Red algae are an important evolutionary group of algae which contain phycobilisomes (PBSs) on their thylakoid membranes, as do cyanobacteria. PBSs function not only as light-harvesting antennae but also as nitrogen storage. In this report, alterations of the supramolecular architecture of thylakoid membranes from red alga Porphyridium cruentum during nitrogen starvation were characterized. The morphology of the intact thylakoid membrane was observed to be round vesicles. Thylakoid membranes were reduced in content and PBSs were degraded during nitrogen starvation. The size and density of PBSs were both found to be reduced. PBS size decreased by less than one-half after 20days of nitrogen starvation, but their hemispherical morphology was retained. The density of PBSs on thylakoid membranes was more seriously affected as time proceeded. Upon re-addition of nitrogen led to increasing of PBSs on thylakoid membranes. This work reports the first direct observation on alterations in the supramolecular architecture of thylakoid membranes from a photosynthetic organism in response to nitrogen stress.

Algimonas arctica sp. nov., isolated from intertidal sand, and emended description of the genus Algimonas

A novel Gram-reaction-negative, aerobic, pale-orange-pigmented bacterium, designated strain SM1216T, was isolated from Arctic intertidal sand. Cells of strain SM1216T were dimorphic rods with a single polar prostheca or flagellum. The strain grew at 4 − 30 °C (optimum at 25 °C) and with 0.5 − 6 % (w/v) NaCl (optimum with 2 − 3 %). It reduced nitrate to nitrite but did not hydrolyse gelatin, DNA or Tween 80. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain SM1216T was affiliated with the genus Algimonas in the family Hyphomonadaceae, sharing 97.5 and 96.3 % similarity with Algimonas ampicilliniresistens 14A-2-7T and Algimonas porphyrae 0C-2-2T, respectively, the two known species in the genus Algimonas. However, the level of DNA–DNA relatedness between strain SM1216T and the type strain of A. ampicilliniresistens, the nearest phylogenetic neighbour, was 57.9 %. The major cellular fatty acids of strain SM1216T were C18 : 1ω7c and C18 : 1 2-OH. The main polar lipids of strain SM1216T were monoglycosyldiglyceride (MGDG), glucuronopyranosyldiglyceride (GUDG), phosphatidylglycerol (PG) and three unidentified phospholipids (PL1–3). The major respiratory quinone was ubiquinone 10 (Q10). The genomic G+C content of strain SM1216T was 60.6 mol%. On the basis of the evidence from this polyphasic study, strain SM1216T represents a novel species in the genus Algimonas, for which the name Algimonas arctica sp. nov. is proposed. The type strain is SM1216T ( = MCCC 1K00233T = KCTC 32513T). An emended description of the genus Algimonas is also given.

Exopolysaccharides Play a Role in the Swarming of the Benthic Bacterium Pseudoalteromonas sp. SM9913

Most marine bacteria secrete exopolysaccharide (EPS), which is important for bacterial survival in the marine environment. However, it is still unclear whether the self-secreted EPS is involved in marine bacterial motility. Here we studied the role of EPS in the lateral flagella-driven swarming motility of benthic bacterium Pseudoalteromonas sp. SM9913 (SM9913) by a comparison of wild SM9913 and ΔepsT, an EPS synthesis defective mutant. Reduction of EPS production in ΔepsT did not affect the growth rate or the swimming motility, but significantly decreased the swarming motility on a swarming plate, suggesting that the EPS may play a role in SM9913 swarming. However, the expression and assembly of lateral flagella in ΔepsT were not affected. Instead, ΔepsT had a different swarming behavior from wild SM9913. The swarming of ΔepsT did not have an obvious rapid swarming period, and its rate became much lower than that of wild SM9913 after 35 h incubation. An addition of surfactin or SM9913 EPS on the surface of the swarming plate could rescue the swarming level. These results indicate that the self-secreted EPS is required for the swarming of SM9913. This study widens our understanding of the function of the EPS of benthic bacteria.

Arcticiflavibacter luteus gen. nov., sp. nov., a member of the family Flavobacteriaceae isolated from intertidal sand

A yellow-pigmented, rod-shaped, non-flagellated, aerobic and Gram-reaction-negative bacterium, designated strain SM1212T, was isolated from intertidal sand of Kongsfjorden, Svalbard. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain SM1212T constituted a distinct lineage within the family Flavobacteriaceae. It shared highest 16S rRNA gene sequence similarities with the type strains of Bizionia echini (96.0 %), Lacinutrix jangbogonensis (95.8 %) and Psychroserpens damuponensis (95.7 %) and < 95.6 % sequence similarity with other recognized species in the family Flavobacteriaceae. The strain grew at 4-35 °C and with 0-6.0 % (w/v) NaCl. It hydrolysed gelatin, DNA, starch and Tween 80 but did not reduce nitrate to nitrite. The major cellular fatty acids were anteiso-C15 : 0, iso-C15 : 0, iso-C15 : 1 G, anteiso-C15 : 1 A, iso-C15 : 0 3-OH, C17 : 0 2-OH and iso-C17 : 0 3-OH and the major respiratory quinone was menaquinone MK-6. Polar lipids included phosphatidylethanolamine, one unidentified phospholipid, one unidentified aminophospholipid, three unidentified aminolipids and nine unidentified lipids. The genomic DNA G+C content of strain SM1212T was 36.6 mol%. On the basis of data from this polyphasic study, strain SM1212T represents a novel species in a new genus in the family Flavobacteriaceae, for which the name Arcticiflavibacter luteus gen. nov., sp. nov. is proposed. The type strain of Arcticiflavibacter luteus is SM1212T ( = MCCC 1K00234T = KCTC 32514T).

Marivirga atlantica sp. nov., isolated from seawater and emended description of the genus Marivirga

A novel Gram-stain-negative, aerobic, orange-pigmented, non-flagellated, gliding, rod-shaped bacterium, designated strain SM1354T was isolated from surface seawater of the Atlantic Ocean. The strain hydrolysed gelatin and DNA but did not reduce nitrate. It grew at 4–40 °C and with 0.5–11 % (w/v) NaCl. Phylogenetic analysis of the 16S rRNA gene sequences revealed that strain SM1354T belonged to the genus Marivirga with 96.0–96.2 % sequence similarities to known species of the genus Marivirga . The major fatty acids of strain SM1354T were iso-C15 : 0, iso-C15 : 1 G, iso-C17 : 03-OH and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 02-OH). Polar lipids of strain SM1354T included phosphatidylethanolamine, three unidentified lipids and one unidentified aminolipid and aminophospholipid. The major respiratory quinone of strain SM1354T was menaquinone 7 (MK-7). The genomic DNA G+C content of strain SM1354T was 33.9±0.4 mol%. On the basis of the results of the polyphasic characterization in this study, it is proposed that strain SM1354T represents a novel species of the genus Marivirga , namely Marivirga atlantica sp. nov. The type strain of Marivirga atlantica is SM1354T ( = CCTCC AB 2014242T = JCM 30305T). An emended description of the genus Marivirga is also proposed.

Mechanistic insights into elastin degradation by pseudolysin, the major virulence factor of the opportunistic pathogen Pseudomonas aeruginosa

Pseudolysin is the most abundant protease secreted by Pseudomonas aeruginosa and is the major extracellular virulence factor of this opportunistic human pathogen. Pseudolysin destroys human tissues by solubilizing elastin. However, the mechanisms by which pseudolysin binds to and degrades elastin remain elusive. In this study, we investigated the mechanism of action of pseudolysin on elastin binding and degradation by biochemical assay, microscopy and site-directed mutagenesis. Pseudolysin bound to bovine elastin fibers and preferred to attack peptide bonds with hydrophobic residues at the P1 and P1’ positions in the hydrophobic domains of elastin. The time-course degradation processes of both bovine elastin fibers and cross-linked human tropoelastin by pseudolysin were further investigated by microscopy. Altogether, the results indicate that elastin degradation by pseudolysin began with the hydrophobic domains on the fiber surface, followed by the progressive disassembly of macroscopic elastin fibers into primary structural elements. Moreover, our site-directed mutational results indicate that five hydrophobic residues in the S1-S1’ sub-sites played key roles in the binding of pseudolysin to elastin. This study sheds lights on the pathogenesis of P. aeruginosa infection.

Mechanistic insight into the elastin degradation process by the metalloprotease myroilysin from the deep-sea bacterium Myroides profundi D25

Elastases have been widely studied because of their important uses as medicine and meat tenderizers. However, there are relatively few studies on marine elastases. Myroilysin, secreted by Myroides profundi D25 from deep-sea sediment, is a novel elastase. In this study, we examined the elastin degradation mechanism of myroilysin. When mixed with insoluble bovine elastin, myroilysin bound hydrophobically, suggesting that this elastase may interact with the hydrophobic domains of elastin. Consistent with this, analysis of the cleavage pattern of myroilysin on bovine elastin and recombinant tropoelastin revealed that myroilysin preferentially cleaves peptide bonds with hydrophobic residues at the P1 and/or P1′ positions. Scanning electron microscopy (SEM) of cross-linked recombinant tropoelastin degraded by myroilysin showed preferential damages of spherules over cross-links, as expected for a hydrophobic preference. The degradation process of myroilysin on bovine elastin fibres was followed by light microscopy and SEM, revealing that degradation begins with the formation of crevices and cavities at the fibre surface, with these openings increasing in number and size until the fibre breaks into small pieces, which are subsequently fragmented. Our results are helpful for developing biotechnological applications for myroilysin.

Filamentous phages prevalent in Pseudoalteromonas spp. confer properties advantageous to host survival in Arctic sea ice

Sea ice is one of the most frigid environments for marine microbes. In contrast to other ocean ecosystems, microbes in permanent sea ice are space confined and subject to many extreme conditions, which change on a seasonal basis. How these microbial communities are regulated to survive the extreme sea ice environment is largely unknown. Here, we show that filamentous phages regulate the host bacterial community to improve survival of the host in permanent Arctic sea ice. We isolated a filamentous phage, f327, from an Arctic sea ice Pseudoalteromonas strain, and we demonstrated that this type of phage is widely distributed in Arctic sea ice. Growth experiments and transcriptome analysis indicated that this phage decreases the host growth rate, cell density and tolerance to NaCl and H2O2, but enhances its motility and chemotaxis. Our results suggest that the presence of the filamentous phage may be beneficial for survival of the host community in sea ice in winter, which is characterized by polar night, nutrient deficiency and high salinity, and that the filamentous phage may help avoid over blooming of the host in sea ice in summer, which is characterized by polar day, rich nutrient availability, intense radiation and high concentration of H2O2. Thus, while they cannot kill the host cells by lysing them, filamentous phages confer properties advantageous to host survival in the Arctic sea ice environment. Our study provides a foremost insight into the ecological role of filamentous phages in the Arctic sea ice ecosystem.

Interdomain hydrophobic interactions modulate the thermostability of microbial esterases from the hormone-sensitive lipase family

Microbial hormone-sensitive lipases (HSLs) contain a CAP domain and a catalytic domain. However, it remains unclear how the CAP domain interacts with the catalytic domain to maintain the stability of microbial HSLs. Here, we isolated an HSL esterase, E40, from a marine sedimental metagenomic library. E40 exhibited the maximal activity at 45 °C and was quite thermolabile, with a half-life of only 2 min at 40 °C, which may be an adaptation of E40 to the permanently cold sediment environment. The structure of E40 was solved to study its thermolability. Structural analysis showed that E40 lacks the interdomain hydrophobic interactions between loop 1 of the CAP domain and α7 of the catalytic domain compared with its thermostable homologs. Mutational analysis showed that the introduction of hydrophobic residues Trp(202) and Phe(203) in α7 significantly improved E40 stability and that a further introduction of hydrophobic residues in loop 1 made E40 more thermostable because of the formation of interdomain hydrophobic interactions. Altogether, the results indicate that the absence of interdomain hydrophobic interactions between loop 1 and α7 leads to the thermolability of E40. In addition, a comparative analysis of the structures of E40 and other thermolabile and thermostable HSLs suggests that the interdomain hydrophobic interactions between loop 1 and α7 are a key element for the thermostability of microbial HSLs. Therefore, this study not only illustrates the structural element leading to the thermolability of E40 but also reveals a structural determinant for HSL thermostability.

Ultrastructural Changes and Putative Phage Particles Observed in Sweet Orange Leaves Infected with 'Candidatus Liberibacter asiaticus'

Huanglongbing (HLB), also known as citrus greening, is currently the most destructive citrus disease. Anatomical analyses of HLB-affected sweet orange were carried out by light and electron microscopy. As compared with healthy citrus, the phloem plasmodesmata were plugged with callose, and in some samples the phloem was collapsed. Chloroplast structures were deformed. Prophage sequences occupy a significant portion of the genome of 'Candidatus Liberibacter asiaticus' and have been used to distinguish strains from Yunnan and Guangdong provinces in China and Florida. Interestingly, a large number of possible putative phage particles were observed attached on the surface of 'Ca. L. asiaticus' cells in plants inoculated with strain FJ3 from Fujian Province, China. Phage particles have been observed previously only in periwinkle plants artificially inoculated in Florida with 'Ca. L. asiaticus' that carried the SC1-type prophage. PCR assays verified the presence of the SC1-type prophage sequences previously described from this bacterium in Florida in the FJ3 isolate. This is the first time that suspected phage particles have been observed in sweet orange trees infected with 'Ca. L. asiaticus.'

Reply to the comment on "The ultrastructure of type I collagen at nanoscale: large or small D-spacing distribution?" by J. Wallace, Nanoscale, 2015, 7, DOI: 10.1039/c4nr03160a

Measuring D-spacing values from collagen fibrils or collagen fascicles with surface curvatures will introduce additional errors. This error might be minimized by studying single collagen fibrils which are parallel to the surface of substrates.

The ultrastructure of type I collagen at nanoscale: large or small D-spacing distribution?

D-Spacing is the most significant topographic feature of type I collagen fibril, and it is important for our understanding of the structure and function in collagens. Traditionally, the D-spacing of type I collagen fibril was shown to have a singular value of 67 nm, but recent works indicated that the D-spacing values have a large distribution of up to 10 nm when measured by atomic force microscopy. We found that this large distribution of D-spacing values mainly resulted from image drift during measurement. Note that the D-spacing was homogeneous in a single type I collagen fibril. Our statistical analysis indicated that the D-spacing values of type I collagen fibrils exhibited only a narrow distribution of 2.5 nm around the value of 67 nm. In addition, the D-spacing values of the collagen fibrils were nearly identical not only within a single fibril bundle, but also in different fibril bundles. The measurement of the D-spacing values of collagen may provide important structural information in many research areas such as collagen related diseases, construction of molecular model of collagen, and collagen fibrogenesis.

Puniceibacterium antarcticum gen. nov., sp. nov., isolated from seawater

A Gram-reaction-negative, aerobic, non-flagellated, rod-shaped bacterium, designated strain SM1211T, was isolated from Antarctic seawater. The isolate grew at 4–35 °C and with 0–10 % (w/v) NaCl. It could produce bacteriochlorophyll a, but did not reduce nitrate to nitrite or hydrolyse DNA. Phylogenetic analysis of 16S rRNA gene sequences revealed that strain SM1211T constituted a distinct phylogenetic line within the family Rhodobacteraceae and was closely related to species in the genera Litorimicrobium , Leisingera , Seohaeicola and Phaeobacter with 95.1–96.0 % similarities. The predominant cellular fatty acid was C18 : 1ω7c. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, an unidentified aminolipid and two unidentified phospholipids. The genomic DNA G+C content of strain SM1211T was 60.7 mol%. Based on the phylogenetic, chemotaxonomic and phenotypic data obtained in this study, strain SM1211T is considered to represent a novel species in a new genus within the family Rhodobacteraceae , for which the name Puniceibacterium antarcticum gen. nov., sp. nov. is proposed. The type strain of Puniceibacterium antarcticum is SM1211T ( = CCTCC AB 2013147T = KACC 16875T).

Optimization of fermentation conditions for the production of the M23 protease Pseudoalterin by deep-sea Pseudoalteromonas sp. CF6-2 with artery powder as an inducer

Proteases in the M23 family have specific activities toward elastin and bacterial peptidoglycan. The peptidoglycan-degrading property makes these proteases have potential as novel antimicrobials. Because M23 proteases cannot be maturely expressed in Escherichia coli, it is significant to improve the production of these enzymes in their wild strains. Pseudoalterin is a new M23 protease secreted by the deep-sea bacterium Pseudoalteromonas sp. CF6-2. In this study, the fermentation conditions of strain CF6-2 for pseudoalterin production were optimized using single factor experiments and response surface methodology to improve the enzyme yield. To reduce the fermentation cost, bovine artery powder instead of elastin was determined as a cheap and efficient inducer. Based on single factor experiments, artery powder content, culture temperature and culture time were determined as the main factors influencing pseudoalterin production and were further optimized by the central composite design. The optimal values of these factors were determined as: artery powder of 1.2%, culture temperature of 20.17 °C and culture time of 28.04 h. Under the optimized conditions, pseudoalterin production reached 100.02±9.0 U/mL, more than twice of that before optimization. These results lay a good foundation for developing the biotechnological potential of pseudoalterin.

Oceanisphaera profunda sp. nov., a marine bacterium isolated from deep-sea sediment, and emended description of the genus Oceanisphaera

A Gram-stain-negative, aerobic, oxidase- and catalase-positive, flagellated, rod-shaped bacterial strain, designated SM1222T, was isolated from the deep-sea sediment of the South China Sea. The strain grew at 4–35 °C and with 0.5–8 % NaCl (w/v). Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SM1222T was affiliated with the genus Oceanisphaera in the class Gammaproteobacteria . It shared the highest sequence similarity with the type strain of Oceanisphaera ostreae (96.8 %) and 95.4–96.6 % sequence similarities with type strains of other species of the genus Oceanisphaera with validly published names. Strain SM1222T contained summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH), C18 : 1ω7c, C16 : 0, C12 : 0 and summed feature 2 (C14 : 0 3-OH and/or iso-C16 : 1 I) as the major fatty acids and ubiquinone Q-8 as the predominant respiratory quinone. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The genomic DNA G+C content of strain SM1222T was 51.5 mol%. On the basis of the evidence presented in this study, strain SM1222T represents a novel species of the genus Oceanisphaera , for which the name Oceanisphaera profunda sp. nov. is proposed. The type strain of Oceanisphaera profunda is SM1222T ( = CCTCC AB 2013241T = KCTC 32510T). An emended description of the genus Oceanisphaera Romanenko et al. 2003 emend. Choi et al. 2011 is also proposed.

Development of a genetic system for the deep-sea psychrophilic bacterium Pseudoalteromonas sp. SM9913

Background

Pseudoalteromonas species are a group of marine gammaproteobacteria frequently found in deep-sea sediments, which may play important roles in deep-sea sediment ecosystem. Although genome sequence analysis of Pseudoalteromonas has revealed some specific features associated with adaptation to the extreme deep-sea environment, it is still difficult to study how Pseudoalteromonas adapt to the deep-sea environment due to the lack of a genetic manipulation system. The aim of this study is to develop a genetic system in the deep-sea sedimentary bacterium Pseudoalteromonas sp. SM9913, making it possible to perform gene mutation by homologous recombination.

Results

The sensitivity of Pseudoalteromonas sp. SM9913 to antibiotic was investigated and the erythromycin resistance gene was chosen as the selective marker. A shuttle vector pOriT-4Em was constructed and transferred into Pseudoalteromonas sp. SM9913 through intergeneric conjugation with an efficiency of 1.8 × 10^-3, which is high enough to perform the gene knockout assay. A suicide vector pMT was constructed using pOriT-4Em as the bone vector and sacB gene as the counterselective marker. The epsT gene encoding the UDP-glucose lipid carrier transferase was selected as the target gene for inactivation by in-frame deletion. The epsT was in-frame deleted using a two-step integration–segregation strategy after transferring the suicide vector pMT into Pseudoalteromonas sp. SM9913. The ΔepsT mutant showed approximately 73% decrease in the yield of exopolysaccharides, indicating that epsT is an important gene involved in the EPS production of SM9913.

Conclusions

A conjugal transfer system was constructed in Pseudoalteromonas sp. SM9913 with a wide temperature range for selection and a high transfer efficiency, which will lay the foundation of genetic manipulation in this strain. The epsT gene of SM9913 was successfully deleted with no selective marker left in the chromosome of the host, which thus make it possible to knock out other genes in the same host. The construction of a gene knockout system for Pseudoalteromonas sp. SM9913 will contribute to the understanding of the molecular mechanism of how Pseudoalteromonas adapt to the deep-sea environment.

Characterization of a novel subtilisin-like protease myroicolsin from deep sea bacterium Myroides profundi D25 and molecular insight into its collagenolytic mechanism

Collagen is an insoluble protein that widely distributes in the extracellular matrix of marine animals. Collagen degradation is an important step in the marine nitrogen cycle. However, the mechanism of marine collagen degradation is still largely unknown. Here, a novel subtilisin-like collagenolytic protease, myroicolsin, which is secreted by the deep sea bacterium Myroides profundi D25, was purified and characterized, and its collagenolytic mechanism was studied. Myroicolsin displays low identity (<30%) to previously characterized subtilisin-like proteases, and it contains a novel domain structure. Protein truncation indicated that the Pro secretion system C-terminal sorting domain in the precursor protein is involved in the cleavage of the N-propeptide, and the linker is required for protein folding during myroicolsin maturation. The C-terminal β-jelly roll domain did not bind insoluble collagen fiber, suggesting that myroicolsin may degrade collagen without the assistance of a collagen-binding domain. Myroicolsin had broad specificity for various collagens, especially fish-insoluble collagen. The favored residue at the P1 site was basic arginine. Scanning electron microscopy and atomic force microscopy, together with biochemical analyses, confirmed that collagen fiber degradation by myroicolsin begins with the hydrolysis of proteoglycans and telopeptides in collagen fibers and fibrils. Myroicolsin showed strikingly different cleavage patterns between native and denatured collagens. A collagen degradation model of myroicolsin was proposed based on our results. Our study provides molecular insight into the collagen degradation mechanism and structural characterization of a subtilisin-like collagenolytic protease secreted by a deep sea bacterium, shedding light on the degradation mechanism of deep sea sedimentary organic nitrogen.

Molecular insights into the terminal energy acceptor in cyanobacterial phycobilisome

The linker protein L(CM) (ApcE) is postulated as the major component of the phycobilisome terminal energy acceptor (TEA) transferring excitation energy from the phycobilisome to photosystem II. L(CM) is the only phycobilin-attached linker protein in the cyanobacterial phycobilisome through auto-chromophorylation. However, the underlying mechanism for the auto-chromophorylation of L(CM) and the detailed molecular architecture of TEA is still unclear. Here, we demonstrate that the N-terminal phycobiliprotein-like domain of L(CM) (Pfam00502, LP502) can specifically recognize phycocyanobilin (PCB) by itself. Biochemical assays indicated that PCB binds into the same pocket in LP502 as that in the allophycocyanin α-subunit and that Ser152 and Asp155 play a vital role in LP502 auto-chromophorylation. By carefully conducting computational simulations, we arrived at a rational model of the PCB-LP502 complex structure that was supported by extensive mutational studies. In the PCB-LP502 complex, PCB binds into a deep pocket of LP502 with a distorted conformation, and Ser152 and Asp155 form several hydrogen bonds to PCB fixing the PCB Ring A and Ring D. Finally, based on our results, the dipoles and dipole-dipole interactions in TEA are analysed and a molecular structure for TEA is proposed, which gives new insights into the energy transformation mechanism of cyanobacterial phycobilisome.

The supramolecular architecture, function, and regulation of thylakoid membranes in red algae: an overview

Red algae are a group of eukaryotic photosynthetic organisms. Phycobilisomes (PBSs), which are composed of various types of phycobiliproteins and linker polypeptides, are the main light-harvesting antennae in red algae, as in cyanobacteria. Two morphological types of PBSs, hemispherical- and hemidiscoidal-shaped, are found in different red algae species. PBSs harvest solar energy and efficiently transfer it to photosystem II (PS II) and finally to photosystem I (PS I). The PS I of red algae uses light-harvesting complex of PS I (LHC I) as a light-harvesting antennae, which is phylogenetically related to the LHC I found in higher plants. PBSs, PS II, and PS I are all distributed throughout the entire thylakoid membrane, a pattern that is different from the one found in higher plants. Photosynthesis processes, especially those of the light reactions, are carried out by the supramolecular complexes located in/on the thylakoid membranes. Here, the supramolecular architecture, function and regulation of thylakoid membranes in red algal are reviewed.

Mechanical manipulation assisted self-assembly to achieve defect repair and guided epitaxial growth of individual peptide nanofilaments

We have succeeded in the production of defect-free and spatially organized individual one-dimensional peptide nanofilaments by real-time control of the self-assembly process on a solid substrate. Using a unique mechanical manipulation method based on atomic force microscopy, we are able to introduce mechanical stimuli to generate active ends at designated positions on an existing peptide nanofilament previously formed. By doing so, defects in the filament were removed, and self-repairing occurred when the active ends extended along the direction of the supporting lattice, resulting in the closure of the broken filament. Furthermore, new active ends of the nanofilaments can be specifically generated to guide the self-assembly of new filaments at designated positions with selected orientations. The mechanism of defect repair and guided epitaxial growth is also discussed.