Synthesis and antimicrobial activities of chitosan/polypropylene carbonate-based nanoparticles.

Antibiotic resistance is an emerging threat to public health. The development of a new generation of antimicrobial compounds is therefore currently required. Here we report a novel antimicrobial polymer of chitosan/polypropylene carbonate nanoparticles (CS/PPC NPs). These were designed and synthesized from readily available chitosan and a reactive oligomer polypropylene carbonate (PPC)-derived epoxy intermediate. By employing a simple and efficient functionalized strategy, a series of micelle-like chitosan-graft-polypropylene carbonate (CS-g-PPC) polymers and chitosan-polypropylene carbonate (CS-PPC) microgels were prepared by reacting mono-/bis-epoxy capped PPC with chitosan. The chemical structure, particle size, and surface charge of the newly synthesized polymers were characterized by infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. The antimicrobial activities of these nanoparticles were determined in both Gram-positive bacteria (S. aureus) and Gram-negative bacteria (E. coli). Minimum inhibitory concentration (MIC), the nanoparticle concentration needed to completely inhibit the bacterial growth, was found at 128 µg mL-1 to 1024 µg mL-1, strongly depending both on the nature of the epoxy-imine network formed from the functional groups (mono- or bis-capped epoxy groups reacting with amine groups) and the feed ratio of the functional groups (-epoxy/-NH2) between the functionalized PPC and chitosan. No hemolysis was observed at concentrations well in excess of the effective bacteria-inhibiting concentrations. These findings provide a novel strategy to fabricate a new type of nanoantibiotic for antimicrobial applications.

Effects of glycine on cell growth and pigment biosynthesis in Rhodobacter azotoformans.

The effect of exogenous glycine (a precursor for the biosynthesis of bacteriochlorophyll) on the cell growth and photopigment accumulation was investigated in phototrophic growing Rhodobacter azotoformans 134K20. The growth rate and the biomass of strain 134K20 were significantly inhibited by glycine addition when ammonium sulfate or glutamate were used as nitrogen sources and acetate or succinate as carbon sources. A characteristic absorption maximum at approximately 423 nm was present in the absorption spectra of glutamate cultures while it was absent by the addition of high-concentration glycine of 15 mM. The component account for the 423 nm peak was eventually identified as magnesium protoporphyrin IX monomethyl ester, a precursor of bacteriochlorophyll a (BChl a). Comparative analysis of pigment composition revealed that the amount of BChl a precursors was significantly decreased by the addition of 15-mM glycine while the BChl a accumulation was increased. Moreover, glycine changed the carotenoid compositions and stimulated the accumulation of spheroidene. The A850 /A875 in the growth-inhibited cultures was increased, indicating an increased level of the light-harvesting complex 2 compared to the reaction center. The exogenous glycine possibly played an important regulation role in photosynthesis of purple bacteria.

Influences of organic nitrogen on the removal of inorganic nitrogen from complicated marine aquaculture water by Marichromatium gracile YL28.

The sediment-water interface is not only an important location for substrate conversion in a mariculture system, but also a major source of eutrophication. This study aimed to clarify the characteristics of inorganic nitrogen (ammonia, nitrite and nitrate) removal by Marichromatium gracile YL28 in the presence of both organic nitrogen and inorganic nitrogen. The results showed that, in the presence of peptone or urea, seaweed oligosaccharides (SOS) effectively enhanced the ammonia removal capacity of YL28 (6.42 mmol/L) and decreased the residual rate by 54.04% or 8.17%, respectively. With increasing peptone or urea concentrations, the removal of both ammonia and nitrate was gradually inhibited, and the residual rates of ammonia and nitrate reached 22.56-34.36% and 12.03-15.64% in the peptone system and 20.65-24.03% and 12.20-13.21% in the urea system, respectively. However, in the control group the residual rates of ammonia and nitrate reached 11.97% and 5.12%, respectively. In addition, the concentrations of peptone and urea did not affect nitrite removal, and YL28 displayed better cell growth and nitrogen removal activity in the presence of bait and SOS. Overall, the ability of YL28 to remove inorganic nitrogen was enhanced in the presence of organic nitrogen.

Effects of Supplement of Marichromatium gracile YL28 on Water Quality and Microbial Structures in Shrimp Mariculture Ecosystems.

The elevated NH3-N and NO2-N pollution problems in mariculture have raised concerns because they pose threats to animal health and coastal and offshore environments. Supplement of Marichromatium gracile YL28 (YL28) into polluted shrimp rearing water and sediment significantly decreased ammonia and nitrite concentrations, showing that YL28 functioned as a novel safe marine probiotic in the shrimp culture industry. The diversity of aquatic bacteria in the shrimp mariculture ecosystems was studied by sequencing the V4 region of 16S rRNA genes, with respect to additions of YL28 at the low and high concentrations. It was revealed by 16S rRNA sequencing analysis that Proteobacteria, Planctomycete and Bacteroidetes dominated the community (>80% of operational taxonomic units (OTUs)). Up to 41.6% of the predominant bacterial members were placed in the classes Gammaproteobacteria (14%), Deltaproteobacteria (14%), Planctomycetacia (8%) and Alphaproteobacteria (5.6%) while 40% of OTUs belonged to unclassified ones or others, indicating that the considerable bacterial populations were novel in our shrimp mariculture. Bacterial communities were similar between YL28 supplements and control groups (without addition of YL28) revealed by the ß-diversity using PCoA, demonstrating that the additions of YL28 did not disturb the microbiota in shrimp mariculture ecosystems. Instead, the addition of YL28 increased the relative abundance of ammonia-oxidizing and denitrifying bacteria. The quantitative PCR analysis further showed that key genes including nifH and amoA involved in nitrification and nitrate or nitrite reduction significantly increased with YL28 supplementation (p < 0.05). The supplement of YL28 decreased the relative abundance of potential pathogen Vibrio. Together, our studies showed that supplement of YL28 improved the water quality by increasing the relative abundance of ammonia-oxidizing and denitrifying bacteria while the microbial community structure persisted in shrimp mariculture ecosystems.

ArsM-mediated arsenite volatilization is limited by efflux catalyzed by As efflux transporters.

Arsenic (As) methylation is regarded as an efficient strategy for As contamination remediation by As volatilization. However, most microorganisms display low As volatilization efficiency, which is possibly linked to As efflux transporters competing for cytoplasmic As(III) as a substrate. Here, we developed two types of As biosensors in Escherichia coli to compare the As efflux rate of three efflux transporters and to further investigate the correlation between As efflux rates and As volatilization. The engineered As-sensitive E. coli AW3110 expressing arsBRP, acr3RP or arsBEC displayed a higher As resistance compared to the control. The fluorescence intensity was in a linear correlation in the range of 0-2.0 µmol/L of As(III). The intracellular As(III) concentration was negatively related to As efflux activity of As efflux transporter, which was consistent with the As resistance assays. Moreover, arsM derived from R. palustris CGA009 was subsequently introduced to construct an E. coli AW3110 co-expressing arsB/acr3 and arsM, which exhibited higher As(III) resistance, lower fluorescence intensity and intracellular As concentration compared to the engineered E. coli AW3110 expressing only arsB/acr3. The As volatilization efficiency was negatively related to As efflux activity of efflux transporters, the recombinants without arsB/acr3 displayed the highest rate of As volatilization. This study provided new insights into parameters affecting As volatilization with As efflux being the main limiting factor for As methylation and subsequent volatilization in many microorganisms.

Effects of Marichromatium gracile YL28 on the nitrogen management in the aquaculture pond water.

Nitrogen pollution in aquaculture needs the efficient and cost-effective in-situ technology. This study aims to apply Marichromatium gracile YL28 to in-situ bioremediation and test its ability to maintain the nitrogen balance in aquaculture. In laboratory aquaculture system, approximately 99.96% of nitrite (1 mg/L) was removed within 7 d through denitrification coupled with assimilatory nitrate reduction. Ammonium (3.5 mg/L) of 95.6% was directly assimilated by YL28 within 7 d. Moreover, in zero exchange water from shrimp (Penaeus vannamei) aquaculture field trials (20 days), YL28 significantly reduced the ammonium accumulation (0.6 mg/L) and 99.3% of nitrite (1.25 mg/L). Toxicological studies with the Institute of Cancer Research (ICR) mice and Oryzias melastigma indicated that M. gracile YL28 can be safely applied in aquatic ecosystems. All results demonstrate that strain YL28 has high promise for future applications of removing inorganic nitrogen and maintaining the nitrogen balance from in-situ aquaculture.

The Growth-promoting Mechanism of Unusual Spectroscopic Form of LH2 (LH4) from Rhodopseudomonas palustris CGA009 in Low Light.

The experimental evidence for the growth-promoting mechanism and the efficiency of energy transfer (EET) of LH4 under low light are still not available. To elucidate the light adaption mechanism of LH4, we deleted the genes pucBAd involved in the synthesis of the α/ß polypeptides of LH4 in Rhodopseudomonas palustris CGA009. Compared to wild strain, the growth rate of pucBAd mutant significantly decreased under low light, while there were no significant changes in the growth rate, the contents and compositions of photopigments, absorption spectra of cell lysates under high light. Moreover, the fluorescence quantum efficiency (FQE) was used to further compare the EET between LH2 and LH4. The FQE in LH4 increased up to 1.5-fold than did in LH2. Collectively, this study showed that LH4 could provide more and high energetic state photons for promoting bacterial phototrophic growth in response to low-light environment.

Expression and purification of an ArsM-elastin-like polypeptide fusion and its enzymatic properties.

Enzymes could act as a useful tool for environmental bioremediation. Arsenic (As) biomethylation, which can convert highly toxic arsenite [As(III)] into low-toxic volatile trimethylarsine, is considered to be an effective strategy for As removal from contaminated environments. As(III) S-adenosylmethyltransferase (ArsM) is a key enzyme for As methylation; its properties and preparation are crucial for its wide application. Currently, ArsM is usually purified as a His-tag fusion protein restricting widespread use due to high costs. In this study, to greatly reduce the cost and simplify the ArsM preparation process, an Elastin-like polypeptide (ELP) tag was introduced to construct an engineered Escherichia coli (ArsM-ELP). Consequently, a cost-effective and simple non-chromatographic purification approach could be used for ArsM purification. The enzymatic properties of ArsM-ELP were systematically investigated. The results showed that the As methylation rate of purified ArsM-ELP (> 35.49%) was higher than that of E. coli (ArsM-ELP) (> 10.39%) when exposed to 25 µmol/L and 100 µmol/L As(III), respectively. The purified ArsM-ELP was obtained after three round inverse transition cycling treatment in 2.0 mol/L NaCl at 32 °C for 10 min with the yield reaching more than 9.6% of the total protein. The optimal reaction temperature, pH, and time of ArsM-ELP were 30 °C, 7.5 and 30 min, respectively. The enzyme activity was maintained at over 50% at 45 °C for 12 h. The enzyme specific activity was 438.8 ± 2.1 U/µmol. ArsM-ELP had high selectivity for As(III). 2-Mercaptoethanol could promote enzyme activity, whereas SDS, EDTA, Fe2+, and Cu2+ inhibited enzyme activity, and Mg2+, Zn2+, Ca2+, and K+ had no significant effects on it.

Comparative genome analysis of marine purple sulfur bacterium Marichromatium gracile YL28 reveals the diverse nitrogen cycle mechanisms and habitat-specific traits.

Mangrove ecosystems are characteristic of the high salinity, limited nutrients and S-richness. Marichromatium gracile YL28 (YL28) isolated from mangrove tolerates the high concentrations of nitrite and sulfur compounds and efficiently eliminates them. However, the molecular mechanisms of nitrite and sulfur compounds utilization and the habitat adaptation remain unclear in YL28. We sequenced YL28 genome and further performed the comparative genome analysis in 36 purple bacteria including purple sulfur bacteria (PSB) and purple non-sulfur bacteria (PNSB). YL28 has 6 nitrogen cycle pathways (up to 40 genes), and possibly removes nitrite by denitrification, complete assimilation nitrate reduction and fermentative nitrate reduction (DNRA). Comparative genome analysis showed that more nitrogen utilization genes were detected in PNSB than those in PSB. The partial denitrification pathway and complete assimilation nitrate reduction were reported in PSB and DNRA was reported in purple bacteria for the first time. The three sulfur metabolism genes such as oxidation of sulfide, reversed dissimilatory sulfite reduction and sox system allowed to eliminate toxic sulfur compounds in the mangrove ecosystem. Several unique stress response genes facilitate to the tolerance of the high salinity environment. The CRISPR systems and the transposon components in genomic islands (GIs) likely contribute to the genome plasticity in purple bacteria.

Characterization of recombinant E. coli expressing arsR from Rhodopseudomonas palustris CGA009 that displays highly selective arsenic adsorption.

Innovative methods to lower arsenic (As) exposure are sought. The As regulatory protein (ArsR) is reported of having high affinity and specificity to arsenite [As(III)]. Rhodopseudomonas palustris CGA009 is a good model organism for studying As detoxification due to at least three ars operons and four diverse arsRRP1-4 on the genome. In this study, four Escherichia coli harboring arsRRP1-4 derived from CGA009 were engineered and tested regarding their As resistance. The results showed that E. coli (arsRRP2) displayed robust As(III) resistance, and its growth inhibition rate was only 2.9% when exposed to 3.0 mmol/L As(III). At pH 7.0, E. coli (arsRRP2) showed an enhanced As adsorption capacity. As(III) (2.32 mg/g (dry weight, dw)) and 1.47 mg/g arsenate [As(V)] was adsorbed representing a 4.2-fold and 1.3-fold increase respectively compared to the control strain. The adsorption process was well fitted to Langmuir isothermal mode. E. coli (arsRRP2) (1.0~12.0 g/L) could remove 30.3~82.2% of As (III) when exposed to 10 µg/L As(III). No increase in absorption to copper(II), zinc(II), chromium(III), and lead(II) could be detected. Our studies revealed that arsRRP1-4 from CGA009 could confer As(III) resistance; E. coli (arsRRP2) displayed the highest As resistance, selectivity, and adsorption capacity within a wider pH (5.0~9.0) and salinity (0~15.0 g/L NaCl) range, especially important as it could remove As(III) from low concentration As-containing water.

Nitrogen transformation under different dissolved oxygen levels by the anoxygenic phototrophic bacterium Marichromatium gracile.

Marichromatium gracile: YL28 (M. gracile YL28) is an anoxygenic phototrophic bacterial strain that utilizes ammonia, nitrate, or nitrite as its sole nitrogen source during growth. In this study, we investigated the removal and transformation of ammonium, nitrate, and nitrite by M. gracile YL28 grown in a combinatorial culture system of sodium acetate-ammonium, sodium acetate-nitrate and sodium acetate-nitrite in response to different initial dissolved oxygen (DO) levels. In the sodium acetate-ammonium system under aerobic conditions (initial DO = 7.20-7.25 mg/L), we detected a continuous accumulation of nitrate and nitrite. However, under semi-anaerobic conditions (initial DO = 4.08-4.26 mg/L), we observed a temporary accumulation of nitrate and nitrite. Interestingly, under anaerobic conditions (initial DO = 0.36-0.67 mg/L), there was little accumulation of nitrate and nitrite, but an increase in nitrous oxide production. In the sodium acetate-nitrite system, nitrite levels declined slightly under aerobic conditions, and nitrite was completely removed under semi-anaerobic and anaerobic conditions. In addition, M. gracile YL28 was able to grow using nitrite as the sole nitrogen source in situations when nitrogen gas produced by denitrification was eliminated. Taken together, the data indicate that M. gracile YL28 performs simultaneous heterotrophic nitrification and denitrification at low-DO levels and uses nitrite as the sole nitrogen source for growth. Our study is the first to demonstrate that anoxygenic phototrophic bacteria perform heterotrophic ammonia-oxidization and denitrification under anaerobic conditions.

Genome Sequence of Marichromatium gracile YL-28, a Purple Sulfur Bacterium with Bioremediation Potential.

The draft genome sequence of Marichromatium gracile YL-28 contains 3,840,251 bp, with a G+C content of 68.84%. The annotated genome sequence provides the genetic basis for revealing its role as a purple sulfur bacterium in the harvesting of energy and the development of bioremediation applications.

Insights into arsenic multi-operons expression and resistance mechanisms in Rhodopseudomonas palustris CGA009.

Arsenic (As) is widespread in the environment and causes numerous health problems. Rhodopseudomonas palustris has been regarded as a good model organism for studying arsenic detoxification since it was first demonstrated to methylate environmental arsenic by conversion to soluble or gaseous methylated species. However, the detailed arsenic resistance mechanisms remain unknown though there are at least three arsenic-resistance operons (ars1, ars2, and ars3) in R. palustris. In this study, we investigated how arsenic multi-operons contributed to arsenic detoxification in R. palustris. The expression of ars2 or ars3 operons increased with increasing environmental arsenite (As(III)) concentrations (up to 1.0 mM) while transcript of ars1 operon was not detected in the middle log-phase (55 h). ars2 operon was actively expressed even at the low concentration of As(III) (0.01 µM), whereas the ars3 operon was expressed at 1.0 µM of As(III), indicating that there was a differential regulation mechanism for the three arsenic operons. Furthermore, ars2 and ars3 operons were maximally transcribed in the early log-phase where ars2 operon was 5.4-fold higher than that of ars3 operon. A low level of ars1 transcript was only detected at 43 h (early log-phase). Arsenic speciation analysis demonstrated that R. palustris could reduce As(V) to As(III). Collectively, strain CGA009 detoxified arsenic by using arsenic reduction and methylating arsenic mechanism, while the latter might occur with the presence of higher concentrations of arsenic.

[Construction and Characterization of B850-Only LH2 Energy Transfer System in Purple Bacteria].

To seek microscopic molecular mechanism of energy transfer and complex reconstitution in the photosynthesis, the conditions for construction of B850-only peripheral light-harvesting complex (LH2) and their properties were investigated using absorption, fluorescence spectroscopy, molecular sieve chromatography, ultrafiltration and sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) from the purple bacteria. The results indicated that bacteriochlorophylls (BChl) of B800 incubated in 10 mmo · L(-1) Tris-HCl (pH 8.0) buffer are selectively released from their binding sites of LH2 of Rhodobacter azotoformans (A-LH2) by 0.08% (W/V) SDS. B850-only A-LH2 was constructed after removing free BChl mixing with 10% methyl alcohol by ultrafiltration. B850 BChl was released after A-LH2 was incubated for 240 min in dark at room temperature (RT). While BChl of B800 incubated in pH 1.9 buffer were selectively released from their binding sites of LH2 of Rhodopseudomonas palustris (P-LH2). The authors acquired two components using molecular sieve chromatography. Free BChl of one component was not removed and self-assembled to P-LH2. The other removed free BChl and B850-only P-LH2 was constructed. B850 unchanged after P-LH2 was incubated. P-LH2 α and ß subunits have different molecular weights, but those of A-LH2 are in the contrary. It is concluded that B850-only P-LH2 is more stable than A-LH2. The enigmatic split of the B800 absorption band was not observed in these LH2, but we acquired two kinds of B800-released LH2 from Rhodopseudomonas palustris. The authors' results may provide a new light to separate homogeneous Apoprotein LH2.

Selective repression of light harvesting complex 2 formation in Rhodobacter azotoformans by light under semiaerobic conditions.

Photosystem formation in anaerobic anoxygenic phototrophic bacteria (APB) is repressed by oxygen but is de-repressed when oxygen tension decreases. Under semiaerobic conditions, the synthesis of photopigments and pigment protein complexes in Rhodobacter (Rba.) sphaeroides are repressed by light. AppA, a blue-light receptor, mediates this regulation. In the present study, it was showed that the synthesis of bacteriochlorophyll, carotenoid, and pigment protein complexes in Rba. azotoformans 134K20 was significantly repressed by oxygen. Oxygen exposure also led to a conversion of spheroidene to spheroidenone. In semiaerobically growing cells, light irradiation resulted in a decrease in the formation of photosystem, and blue light was found to be the most effective light source. Blue light reduced the contents of bacteriochlorophyll and carotenoid slightly, but had negligible effects on light harvesting complex (LH) 1 content, whereas the content of LH2 was significantly decreased indicating that blue light selectively repressed the synthesis of LH2 in semiaerobically growing 134K20. It was concluded that, similar to Rba. sphaeroides, a blue light receptor presented in strain 134K20 played important roles in its light-dependent repression. A possible mechanism involved in controlling the differential inhibitory of blue light on the synthesis of photosystem was discussed.

Draft genome sequence of an agar-degrading marine bacterium Flammeovirga pacifica WPAGA1.

Flammeovirga pacifica WPAGA1(T), which was isolated from sediment of the west Pacific Ocean in 2009 has the ability to produce agar-oligosaccharides from Gracilaria lemaneiformis directly by enzyme-degradation. The draft genome sequence of this strain was sequenced and annotated. Its draft genome contained 6,507,364 bp with a G+C content of 33.8%. Genome sequence information provided a basis for analyzing the digestion of G. lemaneiformis.

Absorption spectral change of peripheral-light harvesting complexes 2 induced by magnesium protoporphyrin IX monomethyl ester association.

Several spectrally different types of peripheral light harvesting complexes (LH) have been reported in anoxygenic phototrophic bacteria in response to environmental changes. In this study, two spectral forms of LH2 (T-LH2 and U-LH2) were isolated from Rhodobacter azotoformans. The absorption of T-LH2 was extremely similar to the LH2 isolated from Rhodobacter sphaeroides. U-LH2 showed an extra peak at ∼423 nm in the carotenoid region. To explore the spectral origin of this absorption peak, the difference in pigment compositions of two LH2 was analyzed. Spheroidene and bacteriochlorophyll aP were both contained in the two LH2. And magnesium protoporphyrin IX monomethyl ester (MPE) was only contained in U-LH2. It is known that spheroidene and bacteriochlorophyll aP do not produce ∼423 nm absorption peak either in vivo or in vitro. Whether MPE accumulation was mainly responsible for the formation of the ∼423 nm peak? The interactions between MPE and different proteins were further studied. The results showed that the maximum absorption of MPE was red-shifted from ∼415 nm to ∼423 nm when it was mixed with T-LH2 and its apoproteins, nevertheless, the Qy transitions of the bound bacteriochlorophylls in LH2 were almost unaffected, which indicated that the formation of the ∼423 nm peak was related to MPE-LH2 protein interaction. MPE did not bind to sites involved in the spectral tuning of BChls, but the conformation of integral LH2 was affected by MPE association, the alkaline stability of U-LH2 was lower than T-LH2, and the fluorescence intensity at 860 nm was decreased after MPE combination.

A unique low light adaptation mechanism in Rhodobacter azotoformans.

In this paper, we reported for the first time that Rhodobacter azotoformans was capable of synthesizing a spectral variant of peripheral light-harvesting complex (LH3), besides a high light form (LH2), in response to low light intensity. Carotenoid components in these complexes were analyzed by absorption spectra, high-pressure liquid chromatography and mass spectroscopy analysis. Only spheroidene carotenoid was detected in LH2, while LH3 possessed three kinds of carotenoids, spheroidene, spirilloxanthin, and anhydrorhodovibrin. The spirilloxanthin and anhydrorhodovibrin predominated in LH3 and were rarely found in Rhodobacter species. Carotenoid-to-bacteriochlorophyll energy transfer efficiency in LH3 increased by 4% compared to that in LH2. Raman spectroscopic properties of carotenoids in both complexes supported the view that carotenoids altered their planar configuration to a distorted form by interaction with protein matrix in response to low light conditions. In conclusion, the low light adaptation mechanism of Rba. azotoformans involved regulating the synthesis of LH3 and additional carotenoids as well as the configuration change of incorporated carotenoids.

What caused the formation of the absorption maximum at 421 nm in vivo spectra of Rhodopseudomonas palustris.

A spectral peak at ~421 nm appeared in vivo spectrum of Rhodopseudomonas palustris CQV97 cultured in acetate-glutamate medium (M1) but not in acetate-ammonium sulfate medium (M2). However, the spectral origin of 421 nm peak was not clear and frequently attributed to carotenoid component(s). In this study, comparative analysis of the extracted components showed that magnesium protoporphyrin IX monomethylester (MPE) was accumulated as one of the predominate components in M1 culture. The amounts of bacteriochlorophyll a in M1 culture were higher than that in M2, whereas the amounts of carotenoids were nearly identical in both cultures. A simple, rapid and minimum interference with carotenoid and bacteriochlorophyll method to efficiently extract the compounds involving in the formation of 421 nm peak was developed in this study. Assembly of purified MPE with protein components from R. palustris in vitro demonstrated that MPE caused the formation of 421 nm peak. The localization analysis in vivo demonstrated it is MPE associating to protein components and accounting for the peak at ~421 nm. This work clarified the 421 nm peak in vivo mainly originated from MPE accumulation, and will be very helpful to further explore the physiological roles of MPE or its derivatives in photosynthesis.

[Influence of iron on siderophore and photosynthetic pigments biosynthesis by siderophore-producing Rhodopesudomonnas palustris].

OBJECTIVE: To explore the regulation of iron on siderophore production, cell growth and photosynthetic pigments biosynthesis by siderophore-producing anoxygenic phototrophic bacteria. METHODS: Siderophore production was determined using Chrome Azurol S (CAS) assay. The siderophore types were determined by Arnow method, Csaky test and Shenker test. The compositions and contents of photosynthetic pigments were determined by spectrophotometry and HPLC analysis. RESULTS: Rhodopseudomonas palustris (Rps. palustris) CQV97 was capable of producing hydroxamate-type of siderophore. Siderophore production reached the highest yield in the absence of ferric chloride. With increasing ferric chloride concentrations, the lag phase of cell growth was shortened, and the cell growth rate, final biomass and the total amounts of carotenoid and bacteriochlorophyll a were increased significantly. The characteristic absorption maxima of carotenoids from pigment extracts were blueshifted. Iron concentration had little effect on the compositions and relative contents of bacteriochlorophylls a, whereas predominately affected carotenoid compositions, rhodopin was present as major carotenoid component instead of spirillxanthin. Culture tends to accumulate the Cars having shorter conjugated double bonds at the expense of longer conjugated double bonds as the ferric chloride concentration increased. The changes in carotenoid composition were consistent with those of the blue shift of absorption spectra of pigment extracts. CONCLUSION: Rps. palustris CQV97 can produce siderophore and the changes in microbial growth, siderophore production and photosynthetic pigments accumulation of anoxygenic phototrophic bacteria are related to the iron concentration in the medium.