Phytoextraction efficiency of Pteris vittata grown on a naturally As-rich soil and characterization of As-resistant rhizosphere bacteria.

This study evaluated the phytoextraction capacity of the fern Pteris vittata grown on a natural arsenic-rich soil of volcanic-origin from the Viterbo area in central Italy. This calcareous soil is characterized by an average arsenic concentration of 750 mg kg-1, of which 28% is bioavailable. By means of micro-energy dispersive X-ray fluorescence spectrometry (µ-XRF) we detected As in P. vittata fronds after just 10 days of growth, while a high As concentrations in fronds (5,000 mg kg-1), determined by Inductively coupled plasma-optical emission spectrometry (ICP-OES), was reached after 5.5 months. Sixteen arsenate-tolerant bacterial strains were isolated from the P. vittata rhizosphere, a majority of which belong to the Bacillus genus, and of this majority only two have been previously associated with As. Six bacterial isolates were highly As-resistant (> 100 mM) two of which, homologous to Paenarthrobacter ureafaciens and Beijerinckia fluminensis, produced a high amount of IAA and siderophores and have never been isolated from P. vittata roots. Furthermore, five isolates contained the arsenate reductase gene (arsC). We conclude that P. vittata can efficiently phytoextract As when grown on this natural As-rich soil and a consortium of bacteria, largely different from that usually found in As-polluted soils, has been found in P. vittata rhizosphere.

Intraband dynamics and exciton trapping in the LH2 complex of Rhodopseudomonas acidophila.

Over the last several decades, the light-harvesting protein complexes of purple bacteria have been among the most popular model systems for energy transport in excitonic systems in the weak and intermediate intermolecular coupling regime. Despite this extensive body of scientific work, significant questions regarding the excitonic states and the photo-induced dynamics remain. Here, we address the low-temperature electronic structure and excitation dynamics in the light-harvesting complex 2 of Rhodopseudomonas acidophila by two-dimensional electronic spectroscopy. We find that, although at cryogenic temperature energy relaxation is very rapid, exciton mobility is limited over a significant range of excitation energies. This points to the presence of a sub-200 fs, spatially local energy-relaxation mechanism and suggests that local trapping might contribute substantially more in cryogenic experiments than under physiological conditions where the thermal energy is comparable to or larger than the static disorder.

Benchmark and performance of long-range corrected time-dependent density functional tight binding (LC-TD-DFTB) on rhodopsins and light-harvesting complexes.

The chromophores of rhodopsins (Rh) and light-harvesting (LH) complexes still represent a major challenge for a quantum chemical description due to their size and complex electronic structure. Since gradient corrected and hybrid density functional approaches have been shown to fail for these systems, only range-separated functionals seem to be a promising alternative to the more time consuming post-Hartree-Fock approaches. For extended sampling of optical properties, however, even more approximate approaches are required. Recently, a long-range corrected (LC) functional has been implemented into the efficient density functional tight binding (DFTB) method, allowing to sample the excited states properties of chromophores embedded into proteins using quantum mechanical/molecular mechanical (QM/MM) with the time-dependent (TD) DFTB approach. In the present study, we assess the accuracy of LC-TD-DFT and LC-TD-DFTB for rhodopsins (bacteriorhodopsin (bR) and pharaonis phoborhodopsin (ppR)) and LH complexes (light-harvesting complex II (LH2) and Fenna-Matthews-Olson (FMO) complex). This benchmark study shows the improved description of the color tuning parameters compared to standard DFT functionals. In general, LC-TD-DFTB can exhibit a similar performance as the corresponding LC functionals, allowing a reliable description of excited states properties at significantly reduced cost. The two chromophores investigated here pose complementary challenges: while huge sensitivity to external field perturbation (color tuning) and charge transfer excitations are characteristic for the retinal chromophore, the multi-chromophoric character of the LH complexes emphasizes a correct description of inter-chromophore couplings, giving less importance to color tuning. None of the investigated functionals masters both systems simultaneously with satisfactory accuracy. LC-TD-DFTB, at the current stage, although showing a systematic improvement compared to TD-DFTB cannot be recommended for studying color tuning in retinal proteins, similar to some of the LC-DFT functionals, because the response to external fields is still too weak. For sampling of LH-spectra, however, LC-TD-DFTB is a viable tool, allowing to efficiently sample absorption energies, as shown for three different LH complexes. As the calculations indicate, geometry optimization may overestimate the importance of local minima, which may be averaged over when using trajectories. Fast quantum chemical approaches therefore may allow for a direct sampling of spectra in the near future.

Assessing density functional theory in real-time and real-space as a tool for studying bacteriochlorophylls and the light-harvesting complex 2.

We use real-time density functional theory on a real-space grid to calculate electronic excitations of bacteriochlorophyll chromophores of the light-harvesting complex 2 (LH2). Comparison with Gaussian basis set calculations allows us to assess the numerical trust range for computing electron dynamics in coupled chromophores with both types of techniques. Tuned range-separated hybrid calculations for one bacteriochlorophyll as well as two coupled ones are used as a reference against which we compare results from the adiabatic time-dependent local density approximation (TDLDA). The tuned range-separated hybrid calculations lead to a qualitatively correct description of the electronic excitations and couplings. They allow us to identify spurious charge-transfer excitations that are obtained with the TDLDA. When we take into account the environment that the LH2 protein complex forms for the bacteriochlorophylls, we find that it substantially shifts the energy of the spurious charge-transfer excitations, restoring a qualitatively correct electronic coupling of the dominant excitations also for TDLDA.

Characterization of 3-Acetyl Chlorophyll a and 3-Acetyl Protochlorophyll a Accommodated in the B800 Binding Sites of Photosynthetic Light-Harvesting Complex 2 in the Purple Photosynthetic Bacterium Rhodoblastus acidophilus.

We present the detailed characterization on the reconstitution of two cyclic tetrapyrrole pigments that have the same substituents but differ in the degree of hydrogenation in the macrocycles from bacteriochlorophyll (BChl) a (7,8,17,18-tetrahydroporphyrin) into the binding sites of B800 BChl a in light-harvesting complex 2 (LH2) of purple photosynthetic bacteria. Both 3-acetyl chlorophyll (Chl) a (17,18-dihydroporphyrin) and 3-acetyl protochlorophyll (PChl) a (porphyrin) were inserted into the B800-binding pockets in LH2, indicating that these pockets allow alteration of the degree of hydrogenation in the cyclic tetrapyrroles. Redshifts of the Qy peak positions of 3-acetyl (P)Chl a by insertion into the B800-binding sites were smaller than that of BChl a. The relative Qy absorbance of 3-acetyl (P)Chl a to B850 BChl a in the reconstituted proteins was significantly smaller than that of B800 BChl a in native LH2 in spite of their high occupancy in the B800-binding sites. These are ascribable to the smaller dipole strengths of 3-acetyl (P)Chl a. We also performed the coreconstitution of both 3-acetyl Chl a and BChl a into the nine B800-binding sites in LH2, indicating that the affinity of 3-acetyl Chl a to the B800-cavity was slightly higher than that of BChl a.

Stable-Isotope Probing Identifies Uncultured Planctomycetes as Primary Degraders of a Complex Heteropolysaccharide in Soil.

The exopolysaccharides (EPSs) produced by some bacteria are potential growth substrates for other bacteria in soil. We used stable-isotope probing (SIP) to identify aerobic soil bacteria that assimilated the cellulose produced by Gluconacetobacter xylinus or the EPS produced by Beijerinckia indica. The latter is a heteropolysaccharide comprised primarily of l-guluronic acid, d-glucose, and d-glycero-d-mannoheptose. (13)C-labeled EPS and (13)C-labeled cellulose were purified from bacterial cultures grown on [(13)C]glucose. Two soils were incubated with these substrates, and bacteria actively assimilating them were identified via pyrosequencing of 16S rRNA genes recovered from (13)C-labeled DNA. Cellulose C was assimilated primarily by soil bacteria closely related (93 to 100% 16S rRNA gene sequence identities) to known cellulose-degrading bacteria. However, B. indica EPS was assimilated primarily by bacteria with low identities (80 to 95%) to known species, particularly by different members of the phylum Planctomycetes. In one incubation, members of the Planctomycetes made up >60% of all reads in the labeled DNA and were only distantly related (<85% identity) to any described species. Although it is impossible with SIP to completely distinguish primary polysaccharide hydrolyzers from bacteria growing on produced oligo- or monosaccharides, the predominance of Planctomycetes suggested that they were primary degraders of EPS. Other bacteria assimilating B. indica EPS included members of the Verrucomicrobia, candidate division OD1, and the Armatimonadetes. The results indicate that some uncultured bacteria in soils may be adapted to using complex heteropolysaccharides for growth and suggest that the use of these substrates may provide a means for culturing new species.

Comparison of one- and two-dimensional liquid chromatography approaches in the label-free quantitative analysis of Methylocella silvestris.

The proteome of the bacterium Methylocella silvestris has been characterized using reversed phase ultra high pressure liquid chromatography (UPLC) and two-dimensional reversed phase (high pH)-reversed phase (low pH) UPLC prior to mass spectrometric analysis. Variations in protein expression levels were identified with the aid of label-free quantification in a study of soluble protein extracts from the organism grown using methane, succinate, or propane as a substrate. The number of first dimensional fractionation steps has been varied for 2D analyses, and the impact on data throughput and quality has been demonstrated. Comparisons have been made regarding required experimental considerations including total loading of biological samples required, instrument time, and resulting data file sizes. The data obtained have been evaluated with respect to number of protein identifications, confidence of assignments, sequence coverage, relative levels of proteins, and dynamic range. Good qualitative and quantitative agreement was observed between the different approaches, and the potential benefits and limitations of the reversed phase-reversed phase UPLC technique in label-free analysis are discussed. A preliminary screen of the protein regulation data has also been performed, providing evidence for a possible propane assimilation route.

Camelimonas abortus sp. nov., isolated from placental tissue of cattle.

A gram-negative, rod-shaped, non-spore-forming bacterium, isolated from placental tissue of a cow, was investigated for its taxonomic position. On the basis of 16S rRNA gene sequence similarities, strain UK34/07-5(T) was shown to belong to the class Alphaproteobacteria, closely related to the type strain of Camelimonas lactis (96.0 % sequence similarity). The polyamine pattern showed the major compound spermidine and moderate amounts of putrescine. The major quinone was ubiquinone Q-10. The polar lipid profile was composed of the major compounds phosphatidylethanolamine, phosphatidylcholine, phosphatidylglycerol and phosphatidylmonomethylethanolamine and moderate amounts of diphosphatidylglycerol, three unidentified aminolipids and an unidentified phospholipid. The profile of major fatty acids, consisting of C(19 : 0) cyclo ω8c and C(18 : 1)ω7c, with C(18 : 0) 3-OH as the hydroxylated fatty acid, was very similar to that of C. lactis M 2040(T). The results of DNA-DNA hybridization and physiological and biochemical tests allowed both genotypic and phenotypic differentiation of the isolate from C. lactis. The relatively low 16S rRNA gene sequence similarity of 96.0 % to C. lactis M 2040(T) and marked differences in the polar lipid profiles as well as the results of physiological tests and the DNA-DNA hybridization data support the creation of a novel species, for which the name Camelimonas abortus sp. nov. is proposed, with the type strain UK34/07-5(T) ( = CIP 110303(T)  = CCUG 61094(T)  = DSM 24741(T)  = CCM 7941(T)).

Camelimonas lactis gen. nov., sp. nov., isolated from the milk of camels.

Three strains of Gram-negative, rod-shaped, non-spore-forming bacteria (M 2040(T), M 1973 and M 1878-SK2), isolated from milk of camels at a camel-milk production farm in the United Arab Emirates, were investigated for their taxonomic allocation. On the basis of 16S rRNA gene sequence similarities, all three strains were shown to belong to the Alphaproteobacteria and were most closely related to Chelatococcus asaccharovorans and Chelatococcus daeguensis (95.1 and 95.2 % sequence similarity to the respective type strains). meso-Diaminopimelic acid was detected as the characteristic peptidoglycan diamino acid. The predominant compound in the polyamine pattern was spermidine, and sym-homospermidine was not detectable. The quinone system was ubiquinone Q-10. The polar lipid profile included the major compounds phosphatidylcholine and diphosphatidylglycerol and moderate amounts of phosphatidylethanolamine, phosphatidylglycerol, an unidentified glycolipid and two unidentified aminolipids. Minor lipids were also detected. The major fatty acid profile, consisting of C19 :0 cyclo ω8c and C18:1 ω7c, with C18 :03-OH as the major hydroxylated fatty acid, was similar to those of the genus Chelatococcus. The results of DNA-DNA hybridization experiments and physiological and biochemical tests allowed both genotypic and phenotypic differentiation of the isolates from described Chelatococcus species. Isolates M 2040(T), M 1973 and M 1878-SK2 were closely related on the basis of DNA-DNA reassociation and therefore represent a single novel species. In summary, low 16S rRNA gene sequence similarities of 95 % with Chelatococcus asaccharovorans and marked differences in polar lipid profiles as well as in polyamine patterns support the description of a novel genus and species to accommodate these strains, for which the name Camelimonas lactis gen. nov., sp. nov. is proposed. The type strain of Camelimonas lactis is M 2040(T) (=CCUG 58638(T) =CCM 7696(T)).