Photosystems, the machines of photosynthesis, are highly complex and energetically disordered pigment-protein structures. Yet, they perform their function, be it highly efficient energy transfer and charge separation or the ability to switch between light-harvesting and photoprotective states, extremely well. In this opinioned review we describe the interplay of disorder and exciton delocalization in photosynthetic light harvesting. By discussing recent research advances on grounds of well-established concepts, we demonstrate that not only is the excitation delocalization a robust phenomenon, but that it in fact enables the light-harvesting function in the disordered environment.
The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure-function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments-with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Qx band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.
- MeSH
- bakteriochlorofyly metabolismus MeSH
- časové faktory MeSH
- Fourierova analýza MeSH
- karotenoidy metabolismus MeSH
- lasery MeSH
- přenos energie * MeSH
- Proteobacteria metabolismus MeSH
- spektrofotometrie ultrafialová MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
Microbes can modulate ecosystem function since they harbor a vast genetic potential for biogeochemical cycling. The spatial and temporal dynamics of this genetic diversity should be acknowledged to establish a link between ecosystem function and community structure. In this study, we analyzed the genetic diversity of bacterial phosphorus utilization genes in two microbial assemblages, microbialites and bacterioplankton of Lake Alchichica, a semiclosed (i.e., endorheic) system with marked seasonality that varies in nutrient conditions, temperature, dissolved oxygen, and water column stability. We focused on dissolved organic phosphorus (DOP) utilization gene dynamics during contrasting mixing and stratification periods. Bacterial alkaline phosphatases (phoX and phoD) and alkaline beta-propeller phytases (bpp) were surveyed. DOP utilization genes showed different dynamics evidenced by a marked change within an intra-annual period and a differential circadian pattern of expression. Although Lake Alchichica is a semiclosed system, this dynamic turnover of phylotypes (from lake circulation to stratification) points to a different potential of DOP utilization by the microbial communities within periods. DOP utilization gene dynamics was different among genetic markers and among assemblages (microbialite vs. bacterioplankton). As estimated by the system's P mass balance, P inputs and outputs were similar in magnitude (difference was <10 %). A theoretical estimation of water column P monoesters was used to calculate the potential P fraction that can be remineralized on an annual basis. Overall, bacterial groups including Proteobacteria (Alpha and Gamma) and Bacteroidetes seem to be key participants in DOP utilization responses.
- MeSH
- alkalická fosfatasa genetika MeSH
- Bacteria enzymologie genetika metabolismus MeSH
- Bacteroidetes genetika metabolismus MeSH
- bakteriální geny genetika MeSH
- bakteriální RNA analýza MeSH
- DNA bakterií analýza MeSH
- ekosystém MeSH
- fosfor chemie metabolismus MeSH
- fylogeneze * MeSH
- genetická variace * MeSH
- genetické markery genetika MeSH
- jezera mikrobiologie MeSH
- kyslík chemie MeSH
- polymerázová řetězová reakce metody MeSH
- Proteobacteria genetika metabolismus MeSH
- regulace genové exprese u bakterií MeSH
- roční období MeSH
- sekvence nukleotidů MeSH
- sekvenční analýza MeSH
- sloučeniny fosforu chemie metabolismus MeSH
- voda chemie MeSH
- vodní organismy genetika metabolismus MeSH
- životní prostředí MeSH
- Publikační typ
- časopisecké články MeSH
- Geografické názvy
- Mexiko MeSH
Quantum dots (QDs) absorb ultraviolet and long-wavelength visible light energy much more efficiently than natural bacterial light-harvesting proteins and can transfer the excitation energy to photosynthetic reaction centers (RCs). Inclusion of RCs combined with QDs as antennae into liposomes opens new opportunities for using such hybrid systems as a basis for artificial energy-transforming devices that potentially can operate with greater efficiency and stability than devices based only on biological components or inorganic components alone. RCs from Rhodobacter sphaeroides and QDs (CdSe/ZnS with hydrophilic covering) were embedded in lecithin liposomes by extrusion of a solution of multilayer lipid vesicles through a polycarbonate membrane or by dialysis of lipids and proteins dispersed with excess detergent. The efficiency of RC and QD interaction within the liposomes was estimated using fluorescence excitation spectra of the photoactive bacteriochlorophyll of the RCs and by measuring the fluorescence decay kinetics of the QDs. The functional activity of the RCs in hybrid complexes was fully maintained, and their stability was even increased. The efficiency of energy transfer between QDs and RCs and conditions of long-term stability of function of such hybrid complexes in film preparations were investigated as well. It was found that dry films containing RCs and QDs, maintained at atmospheric humidity, are capable of maintaining their functional activity for at least some months as judged by measurements of their spectral characteristics, efficiency of energy transfer from QDs to RCs and RC electron transport activity. Addition of trehalose to the films increases the stability further, especially for films maintained at low humidity. These stable hybrid film structures are promising for further studies towards developing new phototransformation devices for biotechnological applications.
Microbial mats are abundant in many alpine and polar aquatic ecosystems. With warmer temperatures, new hydrologic pathways are developing in these regions and increasing dissolved nutrient fluxes. In the McMurdo Dry Valleys, thermokarsting may release both nutrients and sediment, and has the potential to influence mats in glacial meltwater streams. To test the role of nutrient inputs on community structure, we created nutrient diffusing substrata (NDS) with agar enriched in N, P and N + P, with controls, and deployed them into two Dry Valley streams. We found N amendments (N and N + P) to have greater chlorophyll-a concentrations, total algal biovolume, more fine filamentous cyanobacteria and a higher proportion of live diatoms than other treatments. Furthermore, N treatments were substantially elevated in Bacteroidetes and the small diatom, Fistulifera pelliculosa. On the other hand, species richness was almost double in P and N + P treatments over others, and coccoid green algae and Proteobacteria were more abundant in both streams. Collectively, these data suggest that nutrients have the potential to stimulate growth and alter community structure in glacial meltwater stream microbial mats, and the recent erosion of permafrost and accelerated glacial melt will likely impact resident biota in polar lotic systems here and elsewhere.
- MeSH
- chlorofyl analýza MeSH
- Chlorophyta metabolismus MeSH
- dusík analýza MeSH
- ekosystém MeSH
- fosfor analýza MeSH
- ledový příkrov mikrobiologie MeSH
- Proteobacteria izolace a purifikace metabolismus MeSH
- řeky mikrobiologie MeSH
- rozsivky izolace a purifikace metabolismus MeSH
- sinice izolace a purifikace metabolismus MeSH
- společenstvo MeSH
- teplota MeSH
- Publikační typ
- časopisecké články MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Geografické názvy
- Antarktida MeSH
Magnesium-protoporphyrin IX monomethylester cyclase is one of the key enzymes of the bacteriochlorophyll biosynthesis pathway. There exist two fundamentally different forms of this enzyme. The oxygen-dependent form, encoded by the gene acsF, catalyzes the formation of the bacteriochlorophyll fifth ring using oxygen, whereas the oxygen-independent form encoded by the gene bchE utilizes an oxygen atom extracted from water. The presence of acsF and bchE genes was surveyed in various phototrophic Proteobacteria using the available genomic data and newly designed degenerated primers. It was found that while the majority of purple nonsulfur bacteria contained both forms of the cyclase, the purple sulfur bacteria contained only the oxygen-independent form. All tested species of aerobic anoxygenic phototrophs contained acsF genes, but some of them also retained the bchE gene. In contrast to bchE phylogeny, the acsF phylogeny was in good agreement with 16S inferred phylogeny. Moreover, the survey of the genome data documented that the acsF gene occupies a conserved position inside the photosynthesis gene cluster, whereas the bchE location in the genome varied largely between the species. This suggests that the oxygen-dependent cyclase was recruited by purple phototrophic bacteria very early during their evolution. The primary sequence and immunochemical similarity with its cyanobacterial counterparts suggests that acsF may have been acquired by Proteobacteria via horizontal gene transfer from cyanobacteria. The acquisition of the gene allowed purple nonsulfur phototrophic bacteria to proliferate in the mildly oxygenated conditions of the Proterozoic era.
- MeSH
- bakteriální proteiny analýza chemie genetika MeSH
- fotosyntéza genetika MeSH
- fylogeneze MeSH
- genom bakteriální MeSH
- kyslík metabolismus MeSH
- oxygenasy analýza chemie genetika MeSH
- protein - isoformy analýza chemie genetika MeSH
- Proteobacteria enzymologie genetika metabolismus MeSH
- sinice enzymologie genetika MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Carotenoids are known to offer protection against the potentially damaging combination of light and oxygen encountered by purple phototrophic bacteria, but the efficiency of such protection depends on the type of carotenoid. Rhodobacter sphaeroides synthesizes spheroidene as the main carotenoid under anaerobic conditions whereas, in the presence of oxygen, the enzyme spheroidene monooxygenase catalyses the incorporation of a keto group forming spheroidenone. We performed ultrafast transient absorption spectroscopy on membranes containing reaction center-light-harvesting 1-PufX (RC-LH1-PufX) complexes and showed that when oxygen is present the incorporation of the keto group into spheroidene, forming spheroidenone, reconfigures the energy transfer pathway in the LH1, but not the LH2, antenna. The spheroidene/spheroidenone transition acts as a molecular switch that is suggested to twist spheroidenone into an s-trans configuration increasing its conjugation length and lowering the energy of the lowest triplet state so it can act as an effective quencher of singlet oxygen. The other consequence of converting carotenoids in RC-LH1-PufX complexes is that S(2)/S(1)/triplet pathways for spheroidene is replaced with a new pathway for spheroidenone involving an activated intramolecular charge-transfer (ICT) state. This strategy for RC-LH1-PufX-spheroidenone complexes maintains the light-harvesting cross-section of the antenna by opening an active, ultrafast S(1)/ICT channel for energy transfer to LH1 Bchls while optimizing the triplet energy for singlet oxygen quenching. We propose that spheroidene/spheroidenone switching represents a simple and effective photoprotective mechanism of likely importance for phototrophic bacteria that encounter light and oxygen.
- MeSH
- bakteriální proteiny chemie metabolismus MeSH
- bakteriochlorofyly chemie metabolismus MeSH
- buněčná membrána metabolismus MeSH
- karotenoidy chemie metabolismus MeSH
- kyslík metabolismus MeSH
- molekulární struktura MeSH
- přenos energie účinky záření MeSH
- Proteobacteria chemie metabolismus MeSH
- Rhodobacter sphaeroides chemie metabolismus MeSH
- spektrofotometrie MeSH
- světlo MeSH
- světlosběrné proteinové komplexy chemie metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
As part of the EU project MULTIBARRIERS, six new endogenous aerobic bacterial isolates able to grow in the presence of BTmX (benzene, toluene, m-xylene) were characterized with respect to their growth specificities. Preliminary analysis included restriction fragment length polymorphism profiles and 16S rDNA sequencing. The diversity of these strains was confirmed by denaturing gradient gel electrophoresis. Additional aerobic bacterial strains were isolated from the rhizospheres of plants grown in polychlorinated biphenyl (PCB)-contaminated soils. Pot experiments were designed to show the beneficial effect of plants on the bacterial degradation of PCBs. The effect of PCB removal from soil was evaluated and bacteria isolated from three different plant species were examined for the presence of the bph operon.
- MeSH
- Actinobacteria genetika klasifikace metabolismus MeSH
- aromatické uhlovodíky metabolismus MeSH
- biodegradace MeSH
- chemické látky znečišťující vodu metabolismus MeSH
- dekontaminace metody MeSH
- ekosystém MeSH
- financování organizované MeSH
- kořeny rostlin mikrobiologie MeSH
- látky znečišťující půdu metabolismus MeSH
- Proteobacteria genetika klasifikace metabolismus MeSH
- půdní mikrobiologie MeSH
- rostliny mikrobiologie MeSH
