Triterpenoid saponin biosynthesis genes and their expression patterns during the development of sea cucumber Apostichopus japonicus

Sea cucumbers are echinoderm species with a leathery skin and an elongated body.Natural compounds,including saponins,have been previously isolated from sea cucumber.The majority of saponins derived from this organism typically belong to the triterpene glycosides,which exhibit various biological effects(e.g.,antifungal,cytotoxic,hemolytic,and cytostatic immunomodulatory activities).In the present study,30 saponin biosynthesis enzymes,namely 2 AACTs,2 FPSs,2 HMGSs,2 OSCs,1 SS,2 SEs,and 19 UGTs,were found in the genome of sea cucumber Apostichopus japonicus.Compared with upstream saponin biosynthesis enzymes(i.e.,AACTs,FPSs,HMGSs,OSCs,and SSs),the downstream saponin biosynthesis enzymes(SEs and UGTs)shared lower amino acid sequence similarity with the corresponding genes in other echinoderms.It was proposed that the enzyme structures comprised bothα-helices andβ-sheets.Notably,only a low percentage ofβ-sheets were present in FPSs,OSCs,and SS.The saponin biosynthesis enzymes showed dynamic expression patterns during five critical developmental stages of A.japonicus(fertilized oocytes,blastula,gastrula,doliolaria,and penractula).The present study involved elucidation of putative saponin biosynthesis pathways in sea cucumber and provides a valuable platform for further investigation of saponin biosynthesis in echinoderms.

Genes of the adaptive immune system are expressed early in zebrafish larval development following lipopolysaccharide stimulation

Information regarding immunocompetence of the adaptive immune system(AIS) in zebrafish Danio rerio remains limited.Here,we stimulated an immune response in fish embryos,larvae and adults using lipopolysaccharide(LPS) and measured the upregulation of a number of AIS-related genes(Rag2,AID,TCRAC,IgLC-1,mIg,sIg,IgZ and DAB) 3 and 18 h later.We found that all of the genes evaluated were strongly induced following LPS stimulation,with most of them responding at 8 d post fertilization.This confirms that a functional adaptive immune response is present in D.rerio larvae,and provides a window for further functional analyses.

Biocompatibility of marine magnetotactic ovoid strain MO-1 for in vivo application

Magnetotactic bacteria are capable of biosynthesizing magnetic nanoparticles,also called magnetosomes,and swimming along magnetic field lines.The abilities endow the whole cells of magnetotactic bacteria with such applications as targeted therapy and manipulation of microrobots.We have shown that the intact marine magnetotactic bacteria MO-1 kill efficiently antibiotic-resistant pathogen Staphylococcus aureus in vivo,but the biocompatibility of this marine bacterium is unknown.In this study,the strain MO-1 was chosen to analyze its biocompatibility and potential for biomedicine applications.Results showed that MO-1 cells could be guided at 37℃ under an external magnetic field and swim in the blood plasma and urine.They could keep active locomotivity within 40 min in the plasma and urine,although their velocity slowed down.When incubated with human cells,magnetotactic bacteria MO-1 had no obvious effects on cellular viability at low dose,while the cell toxicity increased with the augmentation of the quantity of the MO-1 cells added.In the in-vivo experiments,the median lethal dose of magnetotactic bacteria MO-1 in rats was determined to be 7.9×10^(10) bacteria/kg.These results provided the foundation for the biocompatibility and safety evaluations of magnetotactic bacteria MO-1 and suggested that they could be basically used in clinical targeted therapy.

Morphological and phylogenetic diversity of magnetotactic bacteria and multicellular magnetotactic prokaryotes from a mangrove ecosystem in the Sanya River,South China

Magnetotactic bacteria(MTB)are morphologically and phylogenetically diverse prokaryotes commonly able to produce magnetic nanocrystals within intracellular membrane-bound organelles(i.e.,magnetosomes)and to swim along geomagnetic field lines.We studied the diversity of MTB in the samples collected from a mangrove area in the Sanya River,Hainan,South China,using microscopic and microbial phylogenetic methods.Results of microanalysis and observation in microscopy and energy dispersive X-ray spectroscopy(EDXS)reveal a highly morphological diversity of MTB including unicellular cocci,vibrios,rod-shaped bacteria,and three morphotypes of multicellular magnetotactic prokaryotes(MMPs).In addition,analysis of the 16S rRNA gene showed that these MTB were clustered into 16 operational taxonomic units affi liated to the Alpha-,Delta-,and Gamma-proteobacteria classes within the Proteobacteria phylum.Meanwhile,by using the coupled fluorescence and transmission electron microscopy analysis,rodshaped bacteria,vibrio,and cocci were phylogenetically and structurally identified at the single-cell level.This study demonstrated highly diverse MTB communities in the mangrove ecosystem and provide a new insight into the overall diversity of MTB.

Magnetotactic bacteria and magnetoreception

A broad range of organisms have evolved abilities to exploit the Earth’s magnetic field for orientation and navigation-a behavior known as magnetoreception(Nordmann et al.,2017).Magnetotactic bacteria(MTB),diverse microbes with a patchy distribution across the bacterial tree of life,are the best known and most extensively studied magnetosensitive microorganisms.In order to efficiently achieve magnetotactic behavior,MTB biomineralize intracellular chain-arranged magnetic single-domain crystals of magnetite(Fe_(3)O_(4))and/or greigite(Fe_(3)S_(4))called magnetosomes,which are unique prokaryotic organelles that confer a magnetic moment to the cell and act as an internal compass needle(Bazylinski and Frankel,2004).

MamZ protein plays an essential role in magnetosome maturation process of Magnetospirillum gryphiswaldense MSR-1

Based on analysis of gene structure of mamXY operon in Magnetospirillum gryphiswaldense strain MSR-1,we constructed a mamZ deletion mutant strain(ΔmamZ)and four complemented strains with different mamZ fragment lengths.Various cell phenotypic and physiological parameters were evaluated and compared among the wild-type(WT),mutant,and complemented strains.Cell growth rates were not notably different;however,magnetic response(Cmag)and iron uptake ability were significantly lower inΔmamZ.High-resolution transmission electron microscopy(HR-TEM)showed that magnetosomes inΔmamZ were small and irregular,and rock magnetic measurements suggested that they contained immature particles.In comparison to WT of MSR-1,intracellular iron content ofΔmamZ and the complemented strains cultured with 20mmol/L iron source was similar or slightly higher.The complemented strains were unable to synthesize mature or normal amounts of magnetosomes,apparently because of abnormal expression of the transmembrane domain of MamZ protein.Real-time reverse transcription polymerase chain reaction(RTqPCR)analysis showed that relative transcription levels of mamX and ftsZ-like genes inΔmamZ were higher at 18 h than at 12 h,suggesting that MamXY proteins play cooperative functional roles in the magnetosome maturation process.Transcription level of mms6 was significantly upregulated inΔmamZ(incubated at 12 h)and the complemented strains(incubated at 12 and 18 h),refl ecting possible interaction between MamXY and Mms6 proteins during magnetosome biosynthesis.These findings,taken together,demonstrate the essential role of MamZ in the magnetosome maturation process in MSR-1.

Determination of the heating efficiency of magnetotactic bacteria in alternating magnetic field

Magnetotactic bacteria(MTB)intact cells have been applied in magnetic hyperthermia therapy of tumor,showing great efficiency in heating for tumor cell inhibition.However,the detailed magnetic hyperthermia properties and optimum heat production conditions of MTB cells are still poorly understood due to lack of standard measuring equipment.The specific absorption rate(SAR)of MTB cells is often measured by home-made equipment at a limited frequency and magnetic field amplitude.In this study,we have used a commercial standard system to implement a comprehensive study of the hyperthermic response of Magnetospirillum gryphiswaldense MSR-1 strain under 7 frequencies of 144-764 kHz,and 8 field amplitudes between 10 and 45 kA/m.The measurement results prove that the SAR of MTB cells increases with magnetic field frequency and amplitude within a certain range.In combination with the magnetic measurements,it is determined that the magnetic hyperthermia mechanism of MTB mainly follows the principle of hysteresis loss,and the heat efficiency of MTB cells in alternating magnetic field are mainly aff ected by three parameters of hysteresis loop,saturation magnetisation,saturation remanent magnetisation,and coercivity.Thus when we culture MTB in LA-2 medium containing sodium nitrate as source of nitrogen,the SAR of MTB LA-2 cells with magnetosomes arranged in chains can be as high as 4925.6 W/g(in this work,all SARs are calculated with iron mass)under 764 kHz and 30 kA/m,which is 7.5 times than current commercial magnetic particles within similar size range.

Genomic analysis of a pure culture of magnetotactic bacterium Terasakiella sp.SH-1

Magnetotactic bacteria(MTB)display magnetotaxis ability because of biomineralization of intracellular nanometer-sized,membrane-bound organelles termed magnetosomes.Despite having been discovered more than half a century,only a few representatives of MTB have been isolated and cultured in the laboratory.In this study,we report the genomic characterization of a novel marine magnetotactic spirillum strain SH-1 belonging to the genus Terasakiella that was recently isolated.A gene encoding haloalkane dehalogenase,which is involved in the degradation of chlorocyclohexane,chlorobenzene,chloroalkane,and chloroalkene,was identified.SH-1 genome contained cysCHI and soxBAZYX genes,thus potentially capable of assimilatory sulfate reduction to H_(2)S and using thiosulfate as electron donors and oxidizing it to sulfate.Genome of SH-1 also contained genes encoding periplasmic dissimilatory nitrate reductases(napAB),assimilatory nitrate reductase(nasA)and assimilatory nitrite reductases(nasB),suggesting that it is capable of gaining energy by converting nitrate to ammonia.The pure culture of Terasakiella sp.SH-1 together with its genomic results off ers new opportunities to examine biology,physiology,and biomineralization mechanisms of MTB.

临近空间实验揭示趋磁细菌适应类火星极端环境的机制

地球临近空间指海平面之上20~100 km高度区域,具有高辐射、低温、干燥、低气压等极端条件,是一类典型的类火星环境.研究生命在临近空间的存活机制有助于深化对火星宜居性和生命探测的认识.本研究利用自主研发的临近空间天体生物学载荷和飞行实验平台,将趋磁细菌Magnetospirillum gryphiswaldense MSR-1带入23 km高度区域开展生物暴露实验.结果发现合成磁小体的趋磁细菌经过7小时16分钟的暴露后仍有部分细胞存活,而不合成磁小体的菌株经过暴露后没有检测到存活细胞;临近空间暴露后存活的样品与实验室对照组相比,其磁小体的数量、尺寸和岩石磁学性质等均发生变化.这些结果表明细胞内的磁小体纳米颗粒有助于趋磁细菌抵御临近空间的高辐射等极端环境,为趋磁细菌的起源和早期演化、生命适应类火星极端环境的机制等提供了新认识.鉴于趋磁细菌具有在类火星环境中生存的潜力,这些感磁微生物可以作为天体生物学研究的重要生物类群.

Metagenomic analysis reveals wide distribution of phototrophic bacteria in hydrothermal vents on the ultraslow-spreading Southwest Indian Ridge

Deep-sea hydrothermal vents are known as chemosynthetic ecosystems.However,high temperature vents emit light that hypothetically can drive photosynthesis in this habitat.Metagenomic studies have sporadically reported the occurrence of phototrophic populations such as cyanobacteria in hydrothermal vents.To determine how geographically and taxonomically widespread phototrophs are in deep-sea hydrothermal vents,we collected samples from three niches in a hydrothermal vent on the Southwest Indian Ridge and carried out an integrated metagenomic analysis.We determined the typical community structures of microorganisms found in active venting fields and identified populations of known potential chlorophototrophs and retinalophototrophs.Complete chlorophyll biosynthetic pathways were identified in all samples.By contrast,proteorhodopsins were only found in active beehive smoker diffusers.Taxonomic groups possessing potential phototrophy dependent on semiconductors present in hydrothermal vents were also found in these samples.This systematic comparative metagenomic study reveals the widespread distribution of phototrophic bacteria in hydrothermal vent fields.Our results support the hypothesis that the ocean is a seed bank of diverse microorganisms.Geothermal vent light may provide energy and confer a competitive advantage on phototrophs to proliferate in hydrothermal vent ecosystems.