H2 production by photofermentation in an innovative plate-type photobioreactor with meandering channels.

Hydrogen production by Rhodobacter capsulatus is an anaerobic, photobiological process requiring specific mixing conditions. In this study, an innovative design of a photobioreactor is proposed. The design is based on a plate-type photobioreactor with an interconnected meandering channel to allow culture mixing and H2 degassing. The culture flow was characterized as a quasi-plug-flow with radial mixing caused by a turbulent-like regime achieved at a low Reynolds number. The dissipated volumetric power was decreased 10-fold while maintaining PBR performances (production and yields) when compared with a magnetically stirred tank reactor. To increase hydrogen production flow rate, several bacterial concentrations were tested by increasing the glutamate concentration using fed-batch cultures. The maximum hydrogen production flow rate (157.7 ± 9.3 ml H2 /L/h) achieved is one of the highest values so far reported for H2 production by R. capsulatus. These first results are encouraging for future scale-up of the plate-type reactor.

Transcriptome analysis of Rhodobacter capsulatus grown on different nitrogen sources.

This study investigated the effect of different nitrogen sources, namely, ammonium chloride and glutamate, on photoheterotrophic metabolism of Rhodobacter capsulatus grown on acetate as the carbon source. Genes that were significantly differentially expressed according to Affymetrix microarray data were categorized into Clusters of Orthologous Groups functional categories and those in acetate assimilation, hydrogen production, and photosynthetic electron transport pathways were analyzed in detail. Genes related to hydrogen production metabolism were significantly downregulated in cultures grown on ammonium chloride when compared to those grown on glutamate. In contrast, photosynthetic electron transport and acetate assimilation pathway genes were upregulated. In detail, aceA encoding isocitrate lyase, a unique enzyme of the glyoxylate cycle and ccrA encoding the rate limiting crotonyl-CoA carboxylase/reductase enzyme of ethylmalonyl-coA pathway were significantly upregulated. Our findings indicate for the first time that R. capsulatus can operate both glyoxylate and ethylmalonyl-coA cycles for acetate assimilation.

Functional flexibility of electron flow between quinol oxidation Qo site of cytochrome bc1 and cytochrome c revealed by combinatory effects of mutations in cytochrome b, iron-sulfur protein and cytochrome c1.

Transfer of electron from quinol to cytochrome c is an integral part of catalytic cycle of cytochrome bc1. It is a multi-step reaction involving: i) electron transfer from quinol bound at the catalytic Qo site to the Rieske iron-sulfur ([2Fe-2S]) cluster, ii) large-scale movement of a domain containing [2Fe-2S] cluster (ISP-HD) towards cytochrome c1, iii) reduction of cytochrome c1 by reduced [2Fe-2S] cluster, iv) reduction of cytochrome c by cytochrome c1. In this work, to examine this multi-step reaction we introduced various types of barriers for electron transfer within the chain of [2Fe-2S] cluster, cytochrome c1 and cytochrome c. The barriers included: impediment in the motion of ISP-HD, uphill electron transfer from [2Fe-2S] cluster to heme c1 of cytochrome c1, and impediment in the catalytic quinol oxidation. The barriers were introduced separately or in various combinations and their effects on enzymatic activity of cytochrome bc1 were compared. This analysis revealed significant degree of functional flexibility allowing the cofactor chains to accommodate certain structural and/or redox potential changes without losing overall electron and proton transfers capabilities. In some cases inhibitory effects compensated one another to improve/restore the function. The results support an equilibrium model in which a random oscillation of ISP-HD between the Qo site and cytochrome c1 helps maintaining redox equilibrium between all cofactors of the chain. We propose a new concept in which independence of the dynamics of the Qo site substrate and the motion of ISP-HD is one of the elements supporting this equilibrium and also is a potential factor limiting the overall catalytic rate.

Inhibition of bacteriochlorophyll biosynthesis in the purple phototrophic bacteria Rhodospirillumrubrum and Rhodobacter capsulatus grown in the presence of a toxic concentration of selenite.

Background In many works, the chemical composition of bacterially-produced elemental selenium nanoparticles (Se0-nanoparticles) was investigated using electron dispersive X-ray analysis. The results suggest that these particles should be associated with organic compounds. However, a complete analysis of their chemical composition is still missing. Aiming at identifying organic compounds associated with the Se0-nanoparticles produced by the purple phototrophic bacteria Rhodospirillum rubrum and Rhodobacter capsulatus (α group of the proteobacteria), we used MALDI-TOF spectrometry.Results This technic revealed that numerous signals obtained from particles produced by both species of bacteria were from metabolites of the photosynthetic system. Furthermore, not only bacteriochlorophyll a, bacteriopheophytin a, and bacteriopheophorbide a, which are known to accumulate in stationary phase cultures of these bacteria grown phototrophically in the absence of selenite, were identified. The particles were also associated with intermediary metabolites of the bacteriochlorophyll a biosynthesis pathway such as protoporphyrin IX, protoporphyrin IX monomethyl ester, bacteriochlorophyllide a and, most likely, Mg-protoporphyrin IX-monomethyl ester, as well as with oxidation products of the substrates of protochlorophyllide reductase and chlorin reductase.Conclusion Accumulation of intermediary metabolites of the bacteriochlorophyll biosynthesis pathway in these purple phototrophic bacteria was attributed to inhibition of oxygen-sensitive enzymes involved in this pathway. Consistent with this interpretation it has been reported that these bacteria reduce selenite intracellularly, that they contain high levels of glutathione and that the reduction of selenite with glutathione is a very fast reaction accompanied by the production of reactive oxygen species. As many enzymes involved in the biosynthesis of bacteriochlorophyll contain [Fe-S] clusters in their active site, which are known to be degraded in the presence of reactive oxygen species as well as in the presence of molecular oxygen, we concluded that the substrates of these enzymes accumulate in cells during selenite reduction.Association of metabolites of bacteriochlorophyll biosynthesis and degradation with the Se0-nanoparticles produced by Rhodospirillum rubrum and Rhodobacter capsulatus is proposed to result from coating of the nanoparticles with the intracytoplasmic membrane of these bacteria, where the photochemical apparatus is concentrated.

Implementation and analysis of temperature control strategies for outdoor photobiological hydrogen production.

For outdoor photobiological hydrogen production, the effective control of temperature in photobioreactors is a challenge. In this work, an internal cooling system for outdoor tubular photobioreactors was designed, built, and tested. The temperatures in the reactors with bacteria were consistently higher than those without bacteria, and were also strongly influenced by solar irradiation and ambient air temperature. The cooling protocol applied successfully kept the reactor temperatures below the threshold limit (38 °C) required for the bioprocess and provided a uniform distribution of temperature along the reactor tube length. The biomass growth and hydrogen production were similar in the reactors cooled co-currently and counter-currently. The biomass growth rate was 0.1 l/h, the maximum hydrogen production rate was 1.28 mol/m3/h, and the overall hydrogen yield obtained was 20 %. The change in the biomass was fitted using the logistic model while cumulative hydrogen production was fitted using the modified Gompertz equation.

Hybrid fusions show that inter-monomer electron transfer robustly supports cytochrome bc1 function in vivo.

Electronic connection between Qo and Qi quinone catalytic sites of dimeric cytochrome bc1 is a central feature of the energy-conserving Q cycle. While both the intra- and inter-monomer electron transfers were shown to connect the sites in the enzyme, mechanistic and physiological significance of the latter remains unclear. Here, using a series of mutated hybrid cytochrome bc1-like complexes, we show that inter-monomer electron transfer robustly sustains the function of the enzyme in vivo, even when the two subunits in a dimer come from different species. This indicates that minimal requirement for bioenergetic efficiency is to provide a chain of cofactors for uncompromised electron flux between the catalytic sites, while the details of protein scaffold are secondary.

Identification of a predicted partner-switching system that affects production of the gene transfer agent RcGTA and stationary phase viability in Rhodobacter capsulatus.

BACKGROUND: Production of the gene transfer agent RcGTA in the α-proteobacterium Rhodobacter capsulatus is dependent upon the response regulator protein CtrA. Loss of this regulator has widespread effects on transcription in R. capsulatus, including the dysregulation of numerous genes encoding other predicted regulators. This includes a set of putative components of a partner-switching signaling pathway with sequence homology to the σ-regulating proteins RsbV, RsbW, and RsbY that have been extensively characterized for their role in stress responses in gram-positive bacteria. These R. capsulatus homologues, RbaV, RbaW, and RbaY, have been investigated for their possible role in controlling RcGTA gene expression. RESULTS: A mutant strain lacking rbaW showed a significant increase in RcGTA gene expression and production. Mutation of rbaV or rbaY led to a decrease in RcGTA gene expression and production, and these mutants also showed decreased viability in the stationary phase and produced unusual colony morphologies. In vitro and in vivo protein interaction assays demonstrated that RbaW and RbaV interact. A combination of gene disruptions and protein-protein interaction assays were unsuccessful in attempts to identify a cognate σ factor, and the genetic data support a model where the RbaV protein that is the determinant regulator of RcGTA gene expression in this system. CONCLUSIONS: These findings provide new information about RcGTA regulation by a putative partner-switching system and further illustrate the integration of RcGTA production into R. capsulatus physiology.

Zinc biosorption by the purple non-sulfur bacterium Rhodobacter capsulatus.

This paper presents the first report providing information on the zinc (Zn) biosorption potentialities of the purple non-sulfur bacterium Rhodobacter capsulatus. The effects of various biological, physical, and chemical parameters on Zn biosorption were studied in both the wild-type strain B10 and a strain, RC220, lacking the endogenous plasmid. At an initial Zn concentration of 10 mg·L(-1), the Zn biosorption capacity at pH 7 for bacterial biomass grown in synthetic medium containing lactate as carbon source was 17 and 16 mg Zn·(g dry mass)(-1) for strains B10 and RC220, respectively. Equilibrium was achieved in a contact time of 30-120 min, depending on the initial Zn concentration. Zn sorption by live biomass was modelled, at equilibrium, according to the Redlich-Peterson and Langmuir isotherms, in the range of 1-600 mg Zn·L(-1). The wild-type strain showed a maximal Zn uptake capacity (Qm) of 164 ± 8 mg·(g dry mass)(-1) and an equilibrium constant (Kads) of 0.017 ± 0.00085 L·(mg Zn)(-1), compared with values of 73.9 mg·(g dry mass)(-1) and 0.361 L·mg(-1) for the strain lacking the endogenous plasmid. The Qm value observed for R. capsulatus B10 is one of the highest reported in the literature, suggesting that this strain may be useful for Zn bioremediation. The lower Qm value and higher equilibrium constant observed for strain RC220 suggest that the endogenous plasmid confers an enhanced biosorption capacity in this bacterium, although no genetic determinants for Zn resistance appear to be located on the plasmid, and possible explanations for this are discussed.

Variation in composition and relative content of accumulated photopigments in a newly isolated Rhodobacter capsulatus strain XJ-1 in response to arsenic.

This study aimed to isolate and characterize a new arsenic (As)-tolerant bacterial strain (XJ-1) from the Halosol soil, to evaluate its As tolerance, and to examine the variation in composition and relative content of accumulated photosynthetic pigments in response to As. The experiments were performed with high-performance liquid chromatography (HPLC), inductively-coupled plasma mass spectrometry (ICP-MS), liquid chromatography/mass spectrometry (LC/MS), thin-layer chromatography (TLC) and grayscale intensity image analysis using Gel-Pro analyzer software. Strain XJ-1 was identified as Rhodobacter (R.) capsulatus based on 16S rRNA gene sequencing and physiological characteristics. Strain XJ-1 was able to grow when exposed to arsenite [As(III)] and arsenate [As(V)] under anaerobic-light conditions. The median effective concentrations (EC50) of As(III) and As(V) were 0.61 mM and 2.03 mM, respectively. Strain XJ-1 could reduce As(V) to As(III), but As(III) could not be transformed back to As(V) or other organic As compounds. Accumulation of bacteriochlorophylls and carotenoids in strain XJ-1 varied in the presence of 0.2-1.2 mM As(III) and 0-2.5 mM As(V). As exposure resulted in pronounced variation in compositions and contents of photosynthetic pigments, especially hydroxyspheroidene, bacteriophaeophytin, the ratio of tetrahydrogeranylgeranyl to phytylated BChl a, and the ratio of spheroidene to spheroidenone. This research highlights the adaptative response of R. capsulatus strain XJ-1 photosystems to environmental As, and demonstrates the potential of utilizing the sensitivity of its photosynthetic pigments to As(III) and As(V) for the biodetection of As in the environment.

Missense mutations in cytochrome c maturation genes provide new insights into Rhodobacter capsulatus cbb3-type cytochrome c oxidase biogenesis.

The Rhodobacter capsulatus cbb(3)-type cytochrome c oxidase (cbb(3)-Cox) belongs to the heme-copper oxidase superfamily, and its subunits are encoded by the ccoNOQP operon. Biosynthesis of this enzyme is complex and needs dedicated biogenesis genes (ccoGHIS). It also relies on the c-type cytochrome maturation (Ccm) process, which requires the ccmABCDEFGHI genes, because two of the cbb(3)-Cox subunits (CcoO and CcoP) are c-type cytochromes. Recently, we reported that mutants lacking CcoA, a major facilitator superfamily type transporter, produce very small amounts of cbb(3)-Cox unless the growth medium is supplemented with copper. In this work, we isolated "Cu-unresponsive" derivatives of a ccoA deletion strain that exhibited no cbb(3)-Cox activity even upon Cu supplementation. Molecular characterization of these mutants revealed missense mutations in the ccmA or ccmF gene, required for the Ccm process. As expected, Cu-unresponsive mutants lacked the CcoO and CcoP subunits due to Ccm defects, but remarkably, they contained the CcoN subunit of cbb(3)-Cox. Subsequent construction and examination of single ccm knockout mutants demonstrated that membrane insertion and stability of CcoN occurred in the absence of the Ccm process. Moreover, while the ccm knockout mutants were completely incompetent for photosynthesis, the Cu-unresponsive mutants grew photosynthetically at lower rates and produced smaller amounts of cytochromes c(1) and c(2) than did a wild-type strain due to their restricted Ccm capabilities. These findings demonstrate that different levels of Ccm efficiency are required for the production of various c-type cytochromes and reveal for the first time that maturation of the heme-Cu-containing subunit CcoN of R. capsulatus cbb(3)-Cox proceeds independently of that of the c-type cytochromes during the biogenesis of this enzyme.

Tyrosine triad at the interface between the Rieske iron-sulfur protein, cytochrome c1 and cytochrome c2 in the bc1 complex of Rhodobacter capsulatus.

A triad of tyrosine residues (Y152-154) in the cytochrome c(1) subunit (C1) of the Rhodobacter capsulatus cytochrome bc(1) complex (BC1) is ideally positioned to interact with cytochrome c(2) (C2). Mutational analysis of these three tyrosines showed that, of the three, Y154 is the most important, since its mutation to alanine resulted in significantly reduced levels, destabilization, and inactivation of BC1. A second-site revertant of this mutant that regained photosynthetic capacity was found to have acquired two further mutations-A181T and A200V. The Y152Q mutation did not change the spectral or electrochemical properties of C1, and showed wild-type enzymatic C2 reduction rates, indicating that this mutation did not introduce major structural changes in C1 nor affect overall activity. Mutations Y153Q and Y153A, on the other hand, clearly affect the redox properties of C1 (e.g. by lowering the midpoint potential as much as 117 mV in Y153Q) and the activity by 90% and 50%, respectively. A more conservative Y153F mutant on the other hand, behaves similarly to wild-type. This underscores the importance of an aromatic residue at position Y153, presumably to maintain close packing with P184, which modeling indicates is likely to stabilize the sixth heme ligand conformation.

[Investigation of the anaerobic metabolism of Rhodobacter capsulatus with a flux model].

A flux model of the anaerobic metabolism of Rhodobacter capsulatus related to hydrogen production has been constructed. The performance of this model has been assessed by comparing the computed metabolic fluxes with experimental values obtained by several research groups who worked on various strains of R. capsulatus and utilized different growth setups. We have investigated the photoheterotrophic metabolism of R. capsulatus on acetate and have shown that in this mode the bacterium can produce hydrogen or biopolymers. Analysis of the flux model reveled several mutants that can evolve hydrogen with a higher rate than the wild type.

Functional prokaryotic RubisCO from an oceanic metagenomic library.

Culture-independent studies have indicated that there is significant diversity in the ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) enzymes used by marine, freshwater, and terrestrial autotrophic bacteria. Surprisingly, little is known about the catalytic properties of many environmentally significant RubisCO enzymes. Because one of the goals of RubisCO research is to somehow modify or select for RubisCO molecules with improved kinetic properties, a facile means to isolate functional and novel RubisCO molecules directly from the environment was developed. In this report, we describe the first example of functional RubisCO proteins obtained from genes cloned and characterized from metagenomic libraries derived from DNA isolated from environmental samples. Two form IA marine RubisCO genes were cloned, and each gene supported both photoheterotrophic and photoautotrophic growth of a RubisCO deletion strain of Rhodobacter capsulatus, strain SBI/II(-), indicating that catalytically active recombinant RubisCO was synthesized. The catalytic properties of the metagenomic RubisCO molecules were further characterized. These experiments demonstrated the feasibility of studying the functional diversity and enzymatic properties of RubisCO enzymes without first cultivating the host organisms. Further, this "proof of concept" experiment opens the way for development of a simple functional screen to examine the properties of diverse RubisCO genes isolated from any environment, and subsequent further bioselection may be possible if the growth conditions of complemented R. capsulatus strain SBI/II(-) are varied.

Overproduction or absence of the periplasmic protease DegP severely compromises bacterial growth in the absence of the dithiol: disulfide oxidoreductase DsbA.

Facultative phototrophic bacterium Rhodobacter capsulatus DsbA-null mutants are proficient in photosynthesis but are defective in respiration especially in enriched growth medium at 35 degrees C. They also exhibit severe pleiotropic phenotypes extending from motility defects to osmofragility and oxidative stresses. In this work, using a combined proteomics and molecular genetics approach, we demonstrated that the respiratory defect of R. capsulatus DsbA-null mutants originates from the overproduction of the periplasmic protease DegP, which renders them temperature-sensitive for growth. The DsbA-null mutants reverted frequently to overcome this growth defect by decreasing, but not completely eliminating, their DegP activity. In agreement with these findings, we showed that overproduction of DegP abolishes the newly restored respiratory growth ability of the revertants in all growth media. Structural localizations of the reversion mutations in DegP revealed the regions and amino acids that are important for its protease-chaperone activity. Remarkably although R. capsulatus DsbA-null or DegP-null mutants were viable, DegP-null DsbA-null double mutants were lethal at all growth temperatures. This is unlike Escherichia coli, and it indicates that in the absence of DsbA some DegP activity is required for survival of R. capsulatus. Absence of a DegQ protease homologue in some bacteria together with major structural variations among the DegP homologues, including a critical disulfide bond-bearing region, correlates well with the differences seen between various species like R. capsulatus and E. coli. Our findings illustrate the occurrence of two related but distinct periplasmic protease families in bacterial species.

A Rubisco mutant that confers growth under a normally "inhibitory" oxygen concentration.

Ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) is a globally significant biocatalyst that facilitates the removal and sequestration of CO2 from the biosphere. Rubisco-catalyzed CO2 reduction thus provides virtually all of the organic carbon utilized by living organisms. Despite catalyzing the rate-limiting step of photosynthetic and chemoautotrophic CO2 assimilation, Rubisco is markedly inefficient as the competition between O2 and CO2 for the same substrate limits the ability of aerobic organisms to obtain maximum amounts of organic carbon for CO2-dependent growth. Random and site-directed mutagenesis procedures were coupled with genetic selection to identify an "oxygen-insensitive" mutant cyanobacterial (Synechococcus sp. strain PCC 6301) Rubisco that allowed for CO2-dependent growth of a host bacterium at an oxygen concentration that inhibited growth of the host containing wild-type Synechococcus Rubisco. The mutant substitution, A375V, was identified as an intragenic suppressor of D103V, a negative mutant enzyme incapable of supporting autotrophic growth. Ala-375 (Ala-378 of spinach Rubisco) is a conserved residue in all form I (plant-like) Rubiscos. Structure-function analyses indicate that the A375V substitution decreased the enzyme's oxygen sensitivity (and not CO2/O2 specificity), possibly by rearranging a network of interactions in a fairly conserved hydrophobic pocket near the active site. These studies point to the potential of engineering plants and other significant aerobic organisms to fix CO2 unfettered by the presence of O2.

Selection of Cyanobacterial (Synechococcus sp. Strain PCC 6301) RubisCO Variants with Improved Functional Properties That Confer Enhanced CO2-Dependent Growth of Rhodobacter capsulatus, a Photosynthetic Bacterium.

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) is a ubiquitous enzyme that catalyzes the conversion of atmospheric CO2 into organic carbon in primary producers. All naturally occurring RubisCOs have low catalytic turnover rates and are inhibited by oxygen. Evolutionary adaptations of the enzyme and its host organisms to changing atmospheric oxygen concentrations provide an impetus to artificially evolve RubisCO variants under unnatural selective conditions. A RubisCO deletion strain of the nonsulfur purple photosynthetic bacterium Rhodobacter capsulatus was previously used as a heterologous host for directed evolution and suppressor selection studies that led to the identification of a conserved hydrophobic region near the active site where amino acid substitutions selectively impacted the enzyme's sensitivity to O2 In this study, structural alignments, mutagenesis, suppressor selection, and growth complementation with R. capsulatus under anoxic or oxygenic conditions were used to analyze the importance of semiconserved residues in this region of Synechococcus RubisCO. RubisCO mutant substitutions were identified that provided superior CO2-dependent growth capabilities relative to the wild-type enzyme. Kinetic analyses of the mutant enzymes indicated that enhanced growth performance was traceable to differential interactions of the enzymes with CO2 and O2 Effective residue substitutions also appeared to be localized to two other conserved hydrophobic regions of the holoenzyme. Structural comparisons and similarities indicated that regions identified in this study may be targeted for improvement in RubisCOs from other sources, including crop plants.IMPORTANCE RubisCO catalysis has a significant impact on mitigating greenhouse gas accumulation and CO2 conversion to food, fuel, and other organic compounds required to sustain life. Because RubisCO-dependent CO2 fixation is severely compromised by oxygen inhibition and other physiological constraints, improving RubisCO's kinetic properties to enhance growth in the presence of atmospheric O2 levels has been a longstanding goal. In this study, RubisCO variants with superior structure-functional properties were selected which resulted in enhanced growth of an autotrophic host organism (R. capsulatus), indicating that RubisCO function was indeed growth limiting. It is evident from these results that genetically engineered RubisCO with kinetically enhanced properties can positively impact growth rates in primary producers.

Utilization of distillery wastewater for hydrogen production in one-stage and two-stage processes involving photofermentation.

In this study, distillery wastewater was treated by dark fermentation or photofermentation alone, and by sequential dark and photofermentation processes using anaerobic saccharolytic consortium and purple nonsulfur bacteria. Combination of dark and photofermentation resulted in the maximal H2 yield of 17.6L/L of distillery waste with chemical oxygen demand 40g/L. It is equivalent to 205kJ/L distillery wastewater and corresponds to recovery of approximately 4-8% of energy consumed during ethanol production. Optimal performance of photofermentation was observed at 20% concentration of pre-fermented distillery waste. In photofermentation, the range of the suitable distillery waste concentrations was extended and the H2 yield was improved by choosing the tolerant strain of purple bacteria Rhodobacter sphaeroides B-3059. After two stages, organic acids and sugars were completely consumed that means wastewater treatment concomitant to H2 production.

Differing isoforms of the cobalamin binding photoreceptor AerR oppositely regulate photosystem expression.

Phototrophic microorganisms adjust photosystem synthesis in response to changes in light intensity and wavelength. A variety of different photoreceptors regulate this process. Purple photosynthetic bacteria synthesize a novel photoreceptor AerR that uses cobalamin (B12) as a blue-light absorbing chromophore to control photosystem synthesis. AerR directly interacts with the redox responding transcription factor CrtJ, affecting CrtJ's interaction with photosystem promoters. In this study, we show that AerR is translated as two isoforms that differ by 41 amino acids at the amino terminus. The ratio of these isoforms was affected by light and cell growth phase with the long variant predominating during photosynthetic exponential growth and the short variant predominating in dark conditions and/or stationary phase. Pigmentation and transcriptomic analyses show that the short AerR variant represses, while long variant activates, photosynthesis genes. The long form of AerR also activates many genes involved in cellular metabolism and motility.

Effect of dietary Rhodobacter capsulatus on egg-yolk cholesterol and laying hen performance.

The present study was conducted to investigate the effects of dietary Rhodobacter capsulatus on the laying hen. A total of forty 23-wk-old Hy-Line Brown laying hens were randomly assigned into 4 treatment groups (10 laying hens/group) and fed diets supplemented with 0 (control), 0.01, 0.02, and 0.04% R. capsulatus during the 60-d feeding period. Dietary supplementation of R. capsulatus (0.04%) reduced (P < 0.05) cholesterol and triglycerides concentration in serum (15 and 11%), as well as in egg-yolk (13 and 16%) over a 60-d feeding period. Cholesterol and triglycerides concentrations in serum as well as egg-yolk were changed linearly in accordance with increasing levels of dietary R. capsulatus. Supplementation of R. capsulatus in diets increased high-density lipoprotein cholesterol level and decreased (P < 0.05) atherogenic index in serum. Yolk color was improved (P < 0.05) in the group fed the 0.04% R. capsulatus supplemented diet compared with the control group. Hepatic cholesterol and triglycerides were reduced (P < 0.05) by 0.04% R. capsulatus. Moreover, the supplementation of R. capsulatus in layer diets did not appear to cause any adverse effects on egg production, shell weight, shell thickness, Haugh unit, yolk index, and feed conversion efficiency compared with the same parameters for the control laying hens. It is postulated that known and unknown factors are present in R. capsulatus presumably responsible for the hypocholesterolemic effect on laying hens. Therefore, the dietary supplementation of R. capsulatus may lead to the development of low-cholesterol chicken eggs as demanded by health-conscious consumers.

[Synthesis of bacteriochlorophyll a by the purple nonsulfur bacterium Rhodobacter capsulatus].

The ability of purple nonsulfur bacteria Rhodobacter capsulatus B10 to synthesize bacteriochlorophyll under phototrophic and dark conditions was studied. The modes for cultivation in the dark with oxygen limitation in a continuous culture at D = 0.1 h(-1) were selected. The yield of biomass reached 20 g/l; the bacteriochlorophyll a output of the process amounted to 16.6 mg/l h(-1).