| It was one of the international hot topics to study the photopigments and pigmentprotein complexes (PPC) responsive to environmental factor change in anoxygenicphototrophic bacteria (APB), which had been reviewed systematically in this paper.The absorption spectra in living cells were an important marker for the identificationof APB. It was a common view in current reports that the characteristic absorption at~421nm was originated from carotenoid (Car) accumulation in living cells, while ithad been failed to detect the accumulated Car related to the characteristic absorptionat~421nm in our previous study. Focus on exploring the formation cause of thischaracteristic peak, Rhodobacterazotoformans R7was taken as the material, andsome impact factors for forming this characteristic peak as well as the analysis ofphotopigment composition were conducted, suggesting that largely accumulatedmagnesium protoporphyrin IX monomethyl ester (MPE) could be also responsible forforming the characteristic absorption at~421nm. In the literatures, there were littlereports for the photopigments responsive to environmental factor change inOkenone-producing purple sulfur bacteria. Based on the isolation, purification andidentification of Okenone-producing halophilic Marichromatium sp.283-1in ourprevious work, accumulated photopigment components in this strain were analyzedwith absorption spectroscopy, TLC and LC-MS, and the effects of six kinds ofphysicochemical factor on the accumulated photopigment compositions wereinvestigated. Moreover, current preparation methods for Cars were compared, andthen a suitable method for large-scale preparation of Car from Okenone series wasproposed; the applicability of this new method to different strains in purple bacteriawas also investigated. What’s more, it had been reported that Okenone-containingPPCs were unstable in the process of preparation, which made the isolation of thiskind of PPC difficult. So taking it into consideration, the isolation methods of PPCs inOkenone-producing strain283-1were preliminarily explored with the expectation ofobtaining the stable isolation conditions for PPCs, which laid the foundation for PPCregulation in the level of proteins. The main results were listed as following: The characteristic absorption at421nm in living cells of strain R7was observedwhen grown on glutamate as nitrogen source, and the intensity of this characteristicpeak was regulated by glycine. Low concentration of glycine (lower than7mmol/L)enhanced its intensity, while that was inhibited by high concentration of glycine andeven disappeared in the presence of15mmol/L glycine. It was found that largelyaccumulated MPE, rather than Car was responsible for the formation of characteristicpeak at421nm by comparing photopigment compositions of cultures with andwithout characteristic absorption at421nm in living cells of stain R7. It was alsosuggested that not only MPE accumulation was regulated by glycine, but also thecompositions of Car and BChl were obviously influenced by glycine.The results of photopigment component analysis showed that six kinds ofphotopigments were accumulated in stain283-1, and that were BChl aTHGG, BChl aP,OH-R.g-keto I, BPhe, R.g-keto III and Okenone, among which the proportions ofBChl aPand Okenone were biggest in BChl and Car components, respectively. Thebacterial growth could be inhibited by high concentration of DPA and NaNO2, and thedelayed periods of bacterial growth were affected by light intensity, oxygen, salinityand glycine in the range of selected doses, while the final biomass were not largelyaffected. The biosynthetic amounts of Car and BChl were affected significantly,especially for that of BPhe, and the relative contents of Okenone and BChl aP, mainlyaccumulated components, were changed lightly, and that of other components showeda tiny change. It was proposed that at least two Car biosynthesis pathways, Okenoneand R.g-ketoIII, were existed in strain283-1since the accumulations of OH-R.g-ketoI,R.g-ketoIII and Okenone were detected.The results of extractant and extract method selections showed that the biggestextraction amount of Car was archived when using acetone-methanol (7:2, v/v) asextactant for Car extraction after pretreating with2mol/L HCl. The isolated Carcomponents of Okenone series through gel column chromatography were alwaysmixed with BChl or BPhe, but the saponification treatment to extraction couldeliminate the interference of BChl and BPhe. The results of photopigmentcomposition analysis showed that there was a little influence in Car compositionsduring saponification treatment. The results of isolation and purification of PPCs in Okenone-producing strain283-1showed that Tween-80could be considered as a solubilizer to isolate LH2withthe integrated structure and energy transfer function, and the isolated LH2was stableunder low-temperature at dark. It was needed for further studies to explore thesuitable solubilizer for LH1-RC isolation since four selected solubilizers in this paperwere all failed.To sum up, it was proposed that the largely accumulated MPE could also causethe formation of characteristic absorption at421nm, besides of Car, providingreliable evidence and a new thinking for absorption spectrum analysis of living cells.Taken Marichromatium sp.283-1as material, photopigment compositions and theirresponse to different physicochemical factors were investigated, replenishing the lackof photopigment composition analysis in Okenone-producing purple sulfur bacteriaand supplying the material for regulation study. What’s more, a green Car extractmethod only with ethanol and water as extractant was established, laying a foundationfor preparation of large amount of Car. Finally, the preliminary exploration of PPCisolation and purification in strain283-1laid the foundation to the related studies ofPPCs in Okenone-producing strains. |
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