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External control of chemical reactions in biological settings with spatial and temporal precision is a grand challenge for noninvasive diagnostic and therapeutic applications. While light is a conventional stimulus for remote chemical activation, its penetration is severely attenuated in tissues, which limits biological applicability. On the other hand, ultrasound is a biocompatible remote energy source that is highly penetrant and offers a wide range of functional tunability. Coupling ultrasound to the activation of specific chemical reactions under physiological conditions, however, remains a challenge. Here, we describe a synergistic platform that couples the selective mechanochemical activation of mechanophore-functionalized polymers with biocompatible focused ultrasound (FUS) by leveraging pressure-sensitive gas vesicles (GVs) as acousto-mechanical transducers. The power of this approach is illustrated through the mechanically triggered release of covalently bound fluorogenic and therapeutic cargo molecules from polymers containing a masked 2-furylcarbinol mechanophore. Molecular release occurs selectively in the presence of GVs upon exposure to FUS under physiological conditions. These results showcase the viability of this system for enabling remote control of specific mechanochemical reactions with spatiotemporal precision in biologically relevant settings and demonstrate the translational potential of polymer mechanochemistry. [ABSTRACT FROM AUTHOR]

Lakes are important water resources for human beings, but Microcystis blooms pose a serious threat to drinking water security and aquatic ecosystems. Gas vesicles (GVs) are an important trigger for the occurrence of Microcystis blooms. To understand the effects of light and nutrients on GV content, the phytoplankton in Lake Erhai were investigated. The results showed that the average GV content in the surface water was higher than that in the deep water. The total nitrogen in water affected the GV content by limiting the protein content, and the content of GVs increased by 9.2 μm3/cell for each 1.0 pg/cell increase in the intracellular nitrogen content. Moreover, light and total phosphorus affected the GV content in deep water by limiting the energy supply, and the content of GVs increased by 52.4 μm3/cell for each 1.0 pg/cell increase in the intracellular phosphorus content. These results indicate that for lakes with low transparency, decreasing the total phosphorus concentration can reduce the GV content. Reducing the total nitrogen concentration can reduce the GV content and decrease the dominance of Microcystis in all lakes. This study provides useful information for the control of Microcystis. [ABSTRACT FROM AUTHOR]

Background: Various bacteria and archaea, including halophilic archaeon Halobacterium sp. NRC-1 produce gas vesicle nanoparticles (GVNPs), a unique class of stable, air-filled intracellular proteinaceous nanostructures. GVNPs are an attractive tool for biotechnological applications due to their readily production, purification, and unique physical properties. GVNPs are spindle- or cylinder-shaped, typically with a length of 100 nm to 1.5 μm and a width of 30–250 nm. Multiple monomeric subunits of GvpA and GvpC proteins form the GVNP shell, and several additional proteins are required as minor structural or assembly proteins. The haloarchaeal genetic system has been successfully used to produce and bioengineer GVNPs by fusing several foreign proteins with GvpC and has shown various applications, such as biocatalysis, diagnostics, bioimaging, drug delivery, and vaccine development. Results: We demonstrated that native GvpC can be removed in a low salt buffer during the GVNP purification, leaving the GvpA-based GVNP's shell intact and stable under physiological conditions. Here, we report a genetic engineering and chemical modification approach for functionalizing the major GVNP protein, GvpA. This novel approach is based on combinatorial cysteine mutagenesis within GvpA and genetic expansion of the N-terminal and C-terminal regions. Consequently, we generated GvpA single, double, and triple cysteine variant libraries and investigated the impact of mutations on the structure and physical shape of the GVNPs formed. We used a thiol–maleimide chemistry strategy to introduce the biotechnological relevant activity by maleimide-activated streptavidin–biotin and maleimide-activated SpyTag003-SpyCatcher003 mediated functionalization of GVNPs. Conclusion: The merger of these genetic and chemical functionalization approaches significantly extends these novel protein nanomaterials' bioengineering and functionalization potential to assemble catalytically active proteins, biomaterials, and vaccines onto one nanoparticle in a modular fashion. [ABSTRACT FROM AUTHOR]

Gas vesicle nanoparticles (GVNPs) are hollow, buoyant prokaryotic organelles used for cell flotation. GVNPs are encoded by a large gas vesicle protein (gvp) gene cluster in the haloarchaeon, Halobacterium sp. NRC-1, including one gene, gvpC, specifying a protein bound to the surface of the nanoparticles. Genetically engineered GVNPs in the Halobacterium sp. have been produced by fusion of foreign sequences to gvpC. To improve the versatility of the GVNP platform, we developed a method for displaying exogenously produced GvpC fusion proteins on the haloarchaeal nanoparticles. The streptococcal IgG-binding protein domain was fused at or near the C-terminus of GvpC, expressed and purified from E. coli, and shown to bind to wild-type GVNPs. The two fusion proteins, GvpC3GB and GvpC4GB, without or with a highly acidic GvpC C-terminal region, were found to be able to bind nanoparticles equally well. The GVNP-bound GvpC-IgG-binding fusion protein was also capable of binding to an enzyme-linked IgG-HRP complex which retained enzyme activity, demonstrating the hybrid system capability for display and delivery of protein complexes. This is the first report demonstrating functional binding of exogenously produced GvpC fusion proteins to wild-type haloarchaeal GVNPs which significantly expands the capability of the platform to produce bioengineered nanoparticles for biomedical applications. Key points: • Haloarchaeal gas vesicle nanoparticles (GVNPs) constitute a versatile display system. • GvpC-streptococcal IgG-binding fusion proteins expressed in E. coli bind to GVNPs. • IgG-binding proteins displayed on floating GVNPs bind and display IgG-HRP complex. [ABSTRACT FROM AUTHOR]

Background: Bacterial gas vesicles, composed of two major gas vesicle proteins and filled with gas, are a unique class of intracellular bubble-like nanostructures. They provide buoyancy for cells, and thus play an essential role in the growth and survival of aquatic and soil microbes. Moreover, the gas vesicle could be applied to multimodal and noninvasive biological imaging as a potential nanoscale contrast agent. To date, cylinder-shaped gas vesicles have been found in several strains of cyanobacteria. However, whether the functional gas vesicles could be produced in the model filamentous cyanobacteria Anabaena sp. PCC 7120 remains controversial. Results: In this study, we found that an intact gvp gene cluster indeed exists in the model filamentous cyanobacteria Anabaena sp. PCC 7120. Real-time PCR assays showed that the gvpA gene is constitutively transcribed in vivo, and its expression level is upregulated at low light intensity and/or high growth temperature. Functional expression of this intact gvp gene cluster enables the recombinant Escherichia coli to gain the capability of floatation in the liquid medium, thanks to the assembly of irregular gas vesicles. Furthermore, crystal structure of GvpF in combination with enzymatic activity assays of GvpN suggested that these two auxiliary proteins of gas vesicle are structurally and enzymatically conserved, respectively. Conclusions: Our findings show that the laboratory strain of model filamentous cyanobacteria Anabaena sp. PCC 7120 possesses an intact but partially degenerated gas vesicle gene cluster, indicating that the natural isolate might be able to produce gas vesicles under some given environmental stimuli for better floatation. [ABSTRACT FROM AUTHOR]

In order to effectively remove theMicrocystisfrom drinking-water sources, pre-pressure treatment was first used to make theMicrocystislose buoyancy, and then it is easily removed by coagulation and sedimentation processes. TheMicrocystis-containing water from Taihu Lake was taken for the pre-pressure coagulation and sedimentation treatments in this study. Both intermittent laboratory experiment and continuous-flow field experiment were conducted. Experimental results showed that the optimum pre-pressure condition was pressuring at 0.6–0.8 MPa for at least 10 s, and 60 s was the best. Comparing with the pre-oxidation, pre-pressure could obviously increase the removal efficiency ofMicrocystisby following coagulation and sedimentation, and would not increase the dissolved microcystins. The mechanism of pre-pressure treatment was that the pre-pressure destroys the gas vesicles inMicrocystiscells and the gas diffuses out of the cells, which leads theMicrocystisto lose buoyancy and make them to sink. The recovery time of gas vesicles was longer than the sludge discharge period of sedimentation tank; therefore, the sinkingMicrocystiswould not re-float in the sedimentation tank. In the practical application of drinking water treatment plant, the continuous-flow pressure device could be chosen, with the energy consumption of about 22.9 kw·h per 10,000 m3. [ABSTRACT FROM PUBLISHER]

Summary: Sooty moulds on crape myrtle leaves were investigated using light and electron microscopy. The adaxial leaf surface was distinctly covered with soot‐like masses of dark brown hyphae and conidia. The main characteristics of the sooty moulds included stauroconidia, conidial clusters, hyphal degeneration and extracellular melanin depositions. Some conidia were round, measured ~10 μm in diameter, and mostly one‐septate; others were branched and multiseptate (stauroconidia). Based on their morphology, the sooty moulds were determined to consist of several component fungal species belonging to genera such as Antennaria, Metacapnodium and Tripospermum. Enclosed in electron‐dense melanin layers, hyphae and conidial clusters had concentric bodies exhibiting electron‐transparent cores and electron‐dense shells with fibrillar sheaths. Concentric bodies are hypothesized to function as multilayer lipid‐encapsulated nanobubbles or eukaryotic gas vesicles for cytoplasmic volume control. Intrahyphal hyphae possessed electron‐dense cytoplasm and lipid globules. These results suggest that sooty moulds are equipped with melanized cell walls, multicelled resting structures, hyphal regeneration, intrahyphal growth and gas vesicles to adapt to their xeric phylloplane environment. Condensed and elongated starch granules in the chloroplasts of mesophyll tissues may indicate the acclimation of the sooty leaf regions to light reduction and temperature increase. [ABSTRACT FROM AUTHOR]

Gas vesicles are hollow, air-filled polyprotein structures that provide the buoyancy to cells. They are found in a variety of prokaryotes. In this study, we isolated a partial gas vesicle protein gene cluster containing gvpA and gvpC20Ψ from Planktothrix rubescens, and inserted it into an expression vector and expressed it in E. coli. The gas vesicle was developed in bacterial cells, which made bacterial cells to float on medium surface. We also amplified gvpA and gvpC20Ψ separately and synthesized an artificial operon by fusing these two genes with the standardized gene expression controlling elements of E. coli. The artificial operon was expressed in E. coli, forming gas vesicles and floating bacteria cells. Our findings verified that the whole set of genes and the overall structure of gas vesicle gene cluster are not necessary for developing gas vesicles in bacteria cells. Two genes, gvpA and gvpC20Ψ, of the gas vesicle gene cluster are sufficient for synthesizing an artificial operon that can develop gas vesicles in bacteria cells. Our findings provided a wide range of applications including easing the harvest of cultured microalgae and bacteria, as well as enriching and remediating aquatic pollutants by constructing gas vesicles in their cells. [ABSTRACT FROM AUTHOR]

Cyanobacteria (blue-green algae) are the most primitive prokaryotic photosynthetic organisms, that have survived and flourished on the planet for more than 3 billion years and produced the oxygen that enabled aerobic metabolism. Anabaena is a genus of filamentous cyanobacteria, known for its nitrogen fixing abilities and is one of cyanobacterial genera that produce toxins. Because of plasmid DNA, the nontoxic strain ofAnabaena flos-aquae, transformed into a toxic strain that producing neuro-toxins. The major toxins those were produced by this species are anatoxin-a, homoanatoxin-a, and anatoxin-a(s). Presence of these toxins in the source of fresh water makes water toxic and every year so many reports on death of animals were documented. Several studies have been done over this toxic cyanobacterium and showed that under controlled environment this species is very useful for human being. However, presence of this alga in the water sources makes environment toxic. Several analytical methods were reported for the detection of these toxins. This review is be focused on the detailed literature survey on fresh water cyanobacterium,Anabaena flos-aquae, with respect to its importance and cure. [ABSTRACT FROM AUTHOR]

Water bloom (named cyanobacterial bloom) is becoming a serious pollution problem all over the world. In this paper, a method of cyanobacteria treatment using underwater streamer-like discharge is reported. Repetitive underwater discharges are generated by all solid-state pulsed power system. Output voltage of the pulsed power system is 30 kV with 4 \mus pulse width. We can generate repetitive underwater streamer-like discharge by the pulsed power system. And we have the system mounted in the water-bloom treatment apparatus. The size of streamer-like discharge is about 30-mm diameter. We conducted the experiment at a dam in Kyushu district in Japan. We have measured chlorophyll concentration, turbidity, potential of hydrogen, dissolved oxygen, conductivity, and temperature of water during treatment of cyanobacteria bloom. The treatment time is 60 min. All of them could be reduced. In particular, the chlorophyll concentration and the turbidity are remarkably decreased. Initial chlorophyll concentration is 600 \mug/L, and initial turbidity is 1000 nephelometric turbidity unit (NTU). We obtained that treatment results of chlorophyll concentration and turbidity were 85 \mug/L and 80 NTU, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In cyanobacteria the protein on the outside of the gas vesicle, GvpC, is characterised by the presence of a 33 amino acid residue repeat (33RR), which in some genera is highly conserved. The number of 33RRs correlates with the diameter of the gas vesicle and inversely with its strength. Gas vesicles isolated from Microcystis aeruginosa strain PCC 7806 were found to be wider and have a lower critical collapse pressure than those from Microcystis sp. strain BC 8401. The entire gas-vesicle gene cluster of the latter strain was sequenced and compared with the published sequence of the former: the sequences of nine of the ten gvp genes differed by only 1–5% between the two strains; the only substantial difference was in gvpC which in strain BC 8401 lacked a 99-nucleotide section encoding a 33RR. This observation further narrows the correlation of gas vesicle width to the number of 33RRs and suggests how Microcystis strains might be used in experimental manipulation of gas vesicle width and strength. [Copyright &y& Elsevier]

s.-g. kim, a. choi, c.-y. ahn, c.-s. park, y.-h. park and h.-m. oh. 2005.To investigate an effective harvesting method forSpirulina platensis.Eighty per cent ofS. platensiscells in the logarithmic growth phase were harvested by flotation when the cells were set in a static condition for 2 h. The optimum harvesting time was about day 6 of cultivation. The flotation activity ofS. platensiscells was enhanced by the addition of NaCl.The harvesting ofS. platensisby flotation is a cost-effective and straightforward method that can retain the algal quality. The optimum harvesting time ofS. platensiscan be predicted by the cellular protein to carbon ratio.Flotation harvesting is also applicable to other cyanobacteria with gas vesicles. [ABSTRACT FROM AUTHOR]

Wild-type strains of the cyanobacterium Planktothrix rubescens have a cluster of gas vesicle (gvp) genes with repeats of alternating gvpA and gvpC. The gvpC occurs in three length variants, all with the same 3′-sequence, ΩC. Spontaneous non-buoyant mutants had lost some of the alternating gvpAC copies and their gvpC genes had a novel 3′-end sequence, ΨC; additional gvpC genes terminating in this sequence were also found in the wild-type and representatives of other GV genotypes. Alleles of gvpC terminating in ΨC occurred only at the downstream ends of the gvpAC clusters investigated; all other gvpCs terminated in ΩC. Mutants of strains with the GV3 genotype produced only 30–50% of the gas vesicles present in the wild-type; their gas vesicles had lower mean critical pressures (0.70–0.78 MPa) than those in the wild-type (1.05–1.10 MPa). [Copyright &y& Elsevier]

Transformation experiments with Haloferax volcanii show that the amino acid sequence of the gas vesicle protein GvpA influences the morphology and strength of gas vesicles produced by halophilic archaea. A modified expression vector containing p-gvpA was used to complement a Vac− strain of Hfx. volcanii that harboured the entire p-vac region (from Halobacterium salinarum PHH1) except for p-gvpA. Replacement of p-gvpA with mc-gvpA (from Haloferax mediterranei) led to the synthesis of gas vesicles that were narrower and stronger. Other gene replacements (using c-gvpA from Hbt. salinarum or mutated p-gvpA sequences) led to a significant but smaller increase in gas vesicle strength, and less marked effects on gas vesicle morphology. [Copyright &y& Elsevier]

In our efforts to elucidate the mechanism of high-frequency mutation of Halobacterium halobium to a gas vesicle deficient state, we discovered insertions, deletions, inversions, and complex DNA rearrangements associated with a large endogenous plasmid, pNRC100. The rearrangements are mostly IS element-mediated, and when they occur in a region of pNCRC100 containing a cluster of thirteen genes, gas vesicle mutants result. We have characterized the structure and expression of this gas vesicle protein ( gvp) gene cluster and demonstrated its requirement for gas vesicle synthesis and cell flotation by genetic transformation. [ABSTRACT FROM AUTHOR]

In this study, we confirmed the effects of light and K+ concentration on the buoyancy of the cyanobacterium Microcystis aeruginosa (Kutzing) Lemmermann (NIES-843), and the relationship between the gas vesicle and buoyancy of M. aeruginosa was revealed through the culture experiment. The results showed that under laboratory conditions, light illumination and K+ concentration strongly affected the flotation and settlement of M. aeruginosa, and that the floating and settling cycle of M. aeruginosa could be reproduced in a test tube by controlling light illuminance. The ability of M. aeruginosa buoyancy weakened with the increase in the K+ concentration, and M. aeruginosa could not exhibit buoyancy at the K+ concentration of 0.03 mol/L. The phase-contrast microscope observation revealed that M. aeruginosa that floated on the water surface had gas vesicles, while none of the gas vesicles was detected for M. aeruginosa at the bottom of a test tube. [ABSTRACT FROM AUTHOR]