Chemoheterotrophic Conditions Research Articles

The genome-scale metabolic model for the purple non-sulfur bacterium Rhodopseudomonas palustris Bis A53 accurately predicts phenotypes under chemoheterotrophic, chemoautotrophic, photoheterotrophic, and photoautotrophic growth conditions.

The purple non-sulfur bacterium Rhodopseudomonas palustris is recognized as a critical microorganism in the nitrogen and carbon cycle and one of the most common members in wastewater treatment communities. This bacterium is metabolically extremely versatile. It is capable of heterotrophic growth under aerobic and anaerobic conditions, but also able to grow photoautotrophically as well as mixotrophically. Therefore R. palustris can adapt to multiple environments and establish commensal relationships with other organisms, expressing various enzymes supporting degradation of amino acids, carbohydrates, nucleotides, and complex polymers. Moreover, R. palustris can degrade a wide range of pollutants under anaerobic conditions, e.g., aromatic compounds such as benzoate and caffeate, enabling it to thrive in chemically contaminated environments. However, many metabolic mechanisms employed by R. palustris to breakdown and assimilate different carbon and nitrogen sources under chemoheterotrophic or photoheterotrophic conditions remain unknown. Systems biology approaches, such as metabolic modeling, have been employed extensively to unravel complex mechanisms of metabolism. Previously, metabolic models have been reconstructed to study selected capabilities of R. palustris under limited experimental conditions. Here, we developed a comprehensive metabolic model (M-model) for R. palustris Bis A53 (iDT1294) consisting of 2,721 reactions, 2,123 metabolites, and comprising 1,294 genes. We validated the model using high-throughput phenotypic, physiological, and kinetic data, testing over 350 growth conditions. iDT1294 achieved a prediction accuracy of 90% for growth with various carbon and nitrogen sources and close to 80% for assimilation of aromatic compounds. Moreover, the M-model accurately predicts dynamic changes of growth and substrate consumption rates over time under nine chemoheterotrophic conditions and demonstrated high precision in predicting metabolic changes between photoheterotrophic and photoautotrophic conditions. This comprehensive M-model will help to elucidate metabolic processes associated with the assimilation of multiple carbon and nitrogen sources, anoxygenic photosynthesis, aromatic compound degradation, as well as production of molecular hydrogen and polyhydroxybutyrate.

Hydrogenophilus thiooxidans sp. nov., a moderately thermophilic chemotrophic bacterium unable to grow on hydrogen gas, isolated from hot spring microbial mats.

A novel thermophilic chemotrophic bacterium, strain SS56T, was isolated from Nakabusa Hot Spring, Japan. The isolate was a rod-shaped (1.5-2.1×0.6-0.8 µm), Gram-stain-negative bacterium. The cells of this strain grew chemoheterotrophically under aerobic and anaerobic conditions. Autotrophic growth was observed with thiosulphate and elemental sulphur under aerobic conditions but not with H2 as the electron donor. Heterotrophic growth in the presence of O2 occurred on yeast extract, tryptone, polypeptone and organic acids. Strain SS56T used nitrite as an alternative electron acceptor under anaerobic chemoheterotrophic conditions. The isolate grew between 35 and 65 °C, with the optimum at 55 °C. The pH range for growth was pH 6.0-9.0; optimal growth occurred at pH 7.0-8.0. The 16S rRNA gene sequence of strain SS56T was 98.9% identical to that of Hydrogenophilus thermoluteolus TH-1T. The draft genome sequence of 2401804 bp for strain SS56T gave values of 53.7% for digital DNA-DNA hybridization, 92.9% for average nucleotide identity and 93.6% for average amino acid identity compared with the genome sequence of 2223143 bp for H. thermoluteolus TH-1T. Based on the information described above, strain SS56T (=DSM 111892T=JCM 34254T) is proposed as the type strain of a novel species, Hydrogenophilus thiooxidans sp. nov.

Slaughterhouse wastewater treatment using purple phototrophic bacteria: A comparison between photoheterotrophic and chemoheterotrophic conditions

This study aimed to evaluate the effectiveness of purple phototrophic bacteria (PPB) biomass, dominated by Rhodopseudomonas, for treating slaughterhouse wastewater (SWW) under photoheterotrophic and chemoheterotrophic conditions in batch bioreactors. Under both the photoheterotrophic and chemoheterotrophic conditions, PPB hydrolyzed SWW quickly, with both carbon (soluble COD: sCOD) and nutrients (soluble total nitrogen: sTN and phosphate: PO43−) reaching maximum concentrations within the first day. Active assimilation caused simultaneous decrease in carbon and nutrient concentrations within the first 8 days under the photoheterotrophic condition, resulting in high removal of sCOD (91.9%), sTN (70.1%), and PO43− (90.9%). Although removal rate constants (k) were almost five-fold lower than those under the photoheterotrophic condition, we observed substantial removal of sCOD (88.4%) and PO43− (78.2%) under the chemoheterotrophic condition, indicating the activation of versatile metabolic pathways (e.g. respiration and phosphorus accumulation). Biomass carbohydrate and protein content on the last day of the photoheterotrophic condition increased by 50% and 76%, respectively, compared with inoculated PPB biomass; the chemoheterotrophic condition saw 13% and 36% increases. Our results confirmed the effectiveness of the photoheterotrophic pathway in SWW treatment. The bacteria were also able to remove carbon and phosphorus from SWW during the prolonged dark period.

Hydrogen-dependent autotrophic growth in phototrophic and chemolithotrophic cultures of thermophilic bacteria, Chloroflexus aggregans and Chloroflexus aurantiacus, isolated from Nakabusa hot springs.

The genus Chloroflexus is a deeply branching group of thermophilic filamentous anoxygenic phototrophic bacteria. The bacteria in this genus have been shown to grow well heterotrophically under anaerobic photosynthetic and aerobic respiratory conditions. We examined autotrophic growth in new isolates of Chloroflexus strains from hot springs in Nakabusa, Japan. The isolates belonging to Chloroflexus aggregans (98.7% identity of 16S rRNA gene sequence to the respective type strain) and Chloroflexus aurantiacus (99.9% identity to the respective type strain) grew photoautotrophically under a 24% H2 atmosphere. We also observed chemolithotrophic growth of these isolates under 80% H2 and 5% O2 conditions in the dark. This is the first report showing that Chloroflexus grew under both photoautotrophic and chemolithotrophic conditions in addition to photoheterotrophic and aerobic chemoheterotrophic conditions.

Progress and challenges in producing polyhydroxyalkanoate biopolymers from cyanobacteria

Growing concerns over conventional plastic materials and their detrimental effects on the environment have paved the way for exploring alternative sources for the production of bioplastics/biodegradable polymers. Polyhydroxyalkanoates (PHAs), being eco-friendly, biodegradable and renewable, with material properties comparable to conventional plastics, have gained significant attention for research and commercial ventures. Bacteria are reported to be the most efficient microbes in accumulating PHAs, where productivity up to 3.2 g L−1 h−1 can be attained. PHA production from a bacterial system, however, is found to be expensive. Cyanobacteria are now considered as prospective photoautotrophic systems with many advantages over higher plants for low-cost production of PHAs. Cyanobacteria have the potential to synthesize polyhydroxybutyrate (PHB) under photoautotrophic and chemoheterotrophic conditions using carbon substrates like glucose, acetate, and maltose, individually or in combination. Several studies have shown improvement in PHA yield in cyanobacteria by limiting nutrients and/or addition of various precursors. Under optimized conditions, PHB and P(3HB-co-3HV) co-polymer accumulation can reach up to 85 and 77% of dry cell weight (dcw) with a productivity of 13.3 and 1.6 mg L−1 h−1, respectively. Despite the strategic increase in the potential of PHA accumulation in cyanobacteria, the productivity does not suffice for economic production. Therefore, economically feasible production of PHA in cyanobacteria might be attained by technological improvements in various aspects like improvement in mass cultivation techniques, alternate low-cost organic substrates, use of various metabolic inhibitors to stimulate intracellular accumulation, and by suppression and overexpression of specific biosynthetic pathways by genetic engineering approaches.

광합성세균 Rhodobater capsulatus PS-2의 대량배양 최적화 및 대사산물 분석

Plant growth promoting (PGP) hormones, which are produced in a small quantity by bacteria, affect in plant growth and development. PGPs play an important role on the crop productivity in agricultural field. In this study, a photosynthetic bacterial strain producing the PGP was isolated from paddy soil. Bacterial isolate was gram negative, rod-shaped and motility positive. From the 16s rRNA gene sequence analysis, the isolate was identified as Rhodobacter capsulatus PS-2. The mass cultivation of R. capsulatus PS-2 was optimized by considering of the carbon, nitrogen and inorganic salt sources. Optimal medium composition was determined as Na-succinate 4.5 g, yeast extract 5 g, <TEX>$K_2HPO_4$</TEX> 1 g, <TEX>$MgSO_4$</TEX> 5 g, per liter. From the result of 500 L fermentation for 2 days using the optimal medium, the viable cells were <TEX>$8.7{\times}10^9cfu/mL$</TEX>. R. capsulatus PS-2 strain produced the carotenoid and indole-3-acetic acid (IAA). The carotenoid extraction and quantitative analysis were performed by HCl-assisting method. Total carotenoid contents from R. capsulatus PS-2 culture broth were measured as <TEX>$7.02{\pm}0.04$</TEX> and <TEX>$6.93{\pm}0.05mg/L$</TEX> under photoheterotrophic and chemoheterotrophic conditions, respectively. To measure the productivity of IAA, colorimetric method was employed using Salkowski reagent at optical density 535 nm. The results showed that the highest content of IAA was <TEX>$197.44{\pm}5.92mg/L$</TEX> in the optimal medium supplemented with 0.3% tryptophan.

Understanding the physiological roles of polyhydroxybutyrate (PHB) in Rhodospirillum rubrum S1 under aerobic chemoheterotrophic conditions.

Polyhydroxybutyrate (PHB) is an important biopolymer accumulated by bacteria and associated with cell survival and stress response. Here, we make two surprising findings in the PHB-accumulating species Rhodospirillum rubrum S1. We first show that the presence of PHB promotes the increased assimilation of acetate preferentially into biomass rather than PHB. When R. rubrum is supplied with (13)C-acetate as a PHB precursor, 83.5% of the carbon in PHB comes from acetate. However, only 15% of the acetate ends up in PHB with the remainder assimilated as bacterial biomass. The PHB-negative mutant of R. rubrum assimilates 2-fold less acetate into biomass compared to the wild-type strain. Acetate assimilation proceeds via the ethylmalonyl-CoA pathway with (R)-3-hydroxybutyrate as a common intermediate with the PHB pathway. Secondly, we show that R. rubrum cells accumulating PHB have reduced ribulose 1,5-bisphosphate carboxylase (RuBisCO) activity. RuBisCO activity reduces 5-fold over a 36-h period after the onset of PHB. In contrast, a PHB-negative mutant maintains the same level of RuBisCO activity over the growth period. Since RuBisCO controls the redox potential in R. rubrum, PHB likely replaces RuBisCO in this role. R. rubrum is the first bacterium found to express RuBisCO under aerobic chemoheterotrophic conditions.

Amino acid substitutions in the transcriptional regulator CbbR lead to constitutively active CbbR proteins that elevate expression of the cbb CO2 fixation operons in Ralstonia eutropha (Cupriavidus necator) and identify regions of CbbR necessary for gene activation.

CbbR is a LysR-type transcriptional regulator that activates expression of the operons containing (cbb) genes that encode the CO2 fixation pathway enzymes in Ralstonia eutropha (Cupriavidus necator) under autotrophic growth conditions. The cbb operons are stringently downregulated during chemoheterotrophic growth on organic acids such as malate. CbbR constitutive proteins (CbbR*s), typically with single amino acid substitutions, were selected and isolated that activate expression of the cbb operons under chemoheterotrophic growth conditions. A large set of CbbR*s from all major domains of the CbbR molecule were identified, except for the DNA-binding domain. The level of gene expression conferred for many of these CbbR*s under autotrophic growth was greater than that conferred by wild-type CbbR. Several of these CbbR*s increase transcription two- to threefold more than wild-type CbbR. One particular CbbR*, a truncated protein, was useful in identifying the regions of CbbR that are necessary for transcriptional activation and, by logical extension, necessary for interaction with RNA polymerase. The reductive assimilation of carbon via CO2 fixation is an important step in the cost-effective production of useful biological compounds. Enhancing CO2 fixation in Ralstonia eutropha through greater transcriptional activation of the cbb operons could prove advantageous, and the use of CbbR*s is one way to enhance product formation.

Transformation and gene replacement in the facultatively chemoheterotrophic, unicellular cyanobacterium Synechocystis sp. PCC6714 by electroporation

The unicellular cyanobacterium Synechocystis sp. PCC6714 can grow not only under photoautotrophic conditions, but also under chemoheterotrophic conditions if glucose is added to the medium. This makes it useful for the study of many aspects of bioenergetic mechanisms. In contrast to its closely related strain Synechocystis sp. PCC6803, which cannot grow chemoheterotrophically, Synechocystis PCC6714 is not naturally transformable. To enable gene transfer in this strain, we established a method for the introduction of self-replicating IncQ plasmids and for gene replacement using electroporation.

Studies on poly-β-hydroxybutyrate synthase activity of Nostoc muscorum

This study compares the PHB synthase activity of Nostoc muscorum, a N(2)-fixing cyanobacterium under control (grown in usual BG-11 medium), nitrogen (N) and phosphorus (P) deprivation and chemoheterotrophic conditions. Specific activity of PHB synthase did not depict significant variations in the latter three types of cultures, except for the control one, where a significantly lower activity was recorded. PHB synthase activity was detected only in the soluble fractions of both the control as well as cells incubated under chemoheterotrophic conditions. A K(m) of 80.2 microM DL-beta-hydroxybutyryl-CoA and V(max) of 197.5 nmol thiobenzoate (TNB) mg protein(-1)min(-1) were observed for the enzyme. PHB synthase remained insensitive to acetyl-CoA, ATP, NADP, NADPH supplementation under in vitro condition. Addition of acetyl phosphate was found to activate the enzyme and the level of activation was dependent on the concentration of acetyl phosphate supplementation. Inhibition of PHB synthase in 2,3-butanedione supplemented cultures and reactivation following acetyl phosphate addition proved the post-translational control of acetyl phosphate over PHB synthase.

The Reaction Center H Subunit Is Not Required for High Levels of Light-Harvesting Complex 1 in Rhodospirillum rubrum Mutants

The gene (puhA) encoding the H subunit of the reaction center (RC) was deleted by site-directed interposon mutagenesis by using a kanamycin resistance cassette lacking transcriptional terminators to eliminate polar effects in both the wild-type strain Rhodospirillum rubrum S1 and the carotenoid-less strain R. rubrum G9. The puhA interposon mutants were incapable of photoheterotrophic growth but grew normally under aerobic chemoheterotrophic conditions. Absorption spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the RCs were absent. In minimal medium and also in modified medium containing succinate and fructose, the light-harvesting 1 complex (LH1) levels of the S1-derived mutants were about 70 to 100% of the wild-type levels in the same media. The correct assembly of LH1 in the membrane and the pigment-pigment interaction were confirmed by near-infrared circular dichroism spectroscopy. LH1 formation was almost absent when the carotenoid-less G9-derived puhA mutants were grown in standard minimal medium, suggesting that carotenoids may stabilize LH1. In the fructose-containing medium, however, the LH1 levels of the G9 mutants were 70 to 100% of the parental strain levels. Electron micrographs of thin sections of R. rubrum revealed photosynthetic membranes in all mutants grown in succinate-fructose medium. These studies indicate that the H subunit of the RC is necessary neither for maximal formation of LH1 nor for photosynthetic membrane formation but is essential for functional RC assembly.

Rhodobacter capsulatus gains a competitive advantage from respiratory nitrate reduction during light-dark transitions.

Rhodobacter capsulatus N22DNAR(+) possesses a periplasmic nitrate reductase and is capable of reducing nitrate to nitrite under anaerobic conditions. In the absence of light this ability cannot support chemoheterotrophic growth in batch cultures. This study investigated the effect of nitrate reduction on the growth of R. capsulatus N22DNAR(+) during multiple light-dark cycles of anaerobic photoheterotrophic/dark chemoheterotrophic growth conditions in carbon-limited continuous cultures. The reduction of nitrate did not affect the photoheterotrophic growth yield of R. capsulatus N22DNAR(+). After a transition from photoheterotrophic to dark chemoheterotrophic growth conditions, the reduction of nitrate slowed the initial washout of a R. capsulatus N22DNAR(+) culture. Towards the end of a period of darkness nitrate-reducing cultures maintained higher viable cell counts than non-nitrate-reducing cultures. During light-dark cycling of a mixed culture, the strain able to reduce nitrate (N22DNAR(+)) outcompeted the strain which was unable to reduce nitrate (N22). The evidence indicates that the periplasmic nitrate reductase activity supports slow growth that retards the washout of a culture during anaerobic chemoheterotrophic conditions, and provides a protonmotive force for cell maintenance during the dark period before reillumination. This translates into a selective advantage during repeated light-dark cycles, such that in mixed culture N22DNAR(+) outcompetes N22. Exposure to light-dark cycles will be a common feature for R. capsulatus in its natural habitats, and this study shows that nitrate respiration may provide a selective advantage under such conditions.

Effects of carbon nutrition on the physiological expression of HCO3- transport and the CO2-concentrating mechanism in the Cyanobacterium chlorogloeopsis sp. ATCC 27193.

We have examined the effect of inorganic and organic carbon nutrition on the physiological expression of HCO3- transport and the CO2-concentrating mechanism (CCM) in the nutritionally versatile cyanobacterium Chlorogloeopsis sp. ATCC 27193. Cells grown under photoautotrophic conditions in the presence of limiting or replete levels of inorganic carbon (Ci), or grown under mixotrophic (light) or chemoheterotrophic (dark) conditions in the presence of sucrose retained both active CO2 and Na(+)-independent HCO3- transport activity. However, two distinct effects on the kinetic properties of HCO3- transport were observed, which segregated on the basis of phototrophic and chemoheterotrophic growth in the dark. In the former, the apparent substrate affinity of the HCO3- transport system (K0.5) varied (12-fold) in response to the growth Ci or mixotrophy while the maximum rate of HCO3- transport was approximately constant. In the latter case, the K0.5 value was unchanged from the starting value (35 microM) of Ci-limited photoautotrophic cells used to initiate the dark-grown cultures, but transport capacity declined 3-fold. Modulation of the K0.5 (HCO3- transport) value required light. Cellular carboxysome content was unaffected by growth under any of the regimes employed and these structures were the predominant location of ribulose-1,5-bisphosphate carboxylase/oxygenase, as indicated by immunogold electron microscopy. Mixotrophic and chemoheterotrophic growth resulted in a diminished ability to concentrate Ci internally and a reduction in Ci accumulation ratios at low external Ci concentrations. The relationship between photosynthetic carbon fixation and the internal Ci pool varied by 2-fold, with high-Ci-grown cells being the most efficient and mixotrophically grown cells the least, indicating that there was limited capacity to modulate this relationship in response to changes in carbon nutrition. Within broad limits this relationship appeared to be a fixed trait of the strain and an important factor in determining growth rate.

GROWTH, PHYSIOLOGY, AND ULTRASTRUCTURE OF A DIAZOTROPHIC CYANOBACTERIUM, CYANOTHECE SP. STRAIN ATCC 51142, IN MIXOTROPHIC AND CHEMOHETEROTROPHIC CULTURES1

ABSTRACTThe growth, physiology, and ultrastructure of the marine, unicellular, diazotrophic cyanobacterium, Cyanothece sp. strain ATCC 51142, was examined under mixotrophic and chemoheterotrophic conditions. Several organic substrates were tested for the capacity to support heterotrophic growth. Glycerol was the only substrate capable of enhancing mixotrophic growth in the light and supporting chemoheterotrophic growth in the dark. Dextrose enhanced mixotrophic growth but could not support chemoheterotrophic growth. Chemoheterotrophic cultures in continuous darkness grew faster and to higher densities than photoautotrophic cultures, thus demonstrating the great respiratory capacity of this cyanobacterial strain. Only small differences in the pigment content and ultrastructure of the heterotrophic strains were observed in comparison to photoautotrophic control strains. The chemoheterotrophic strain grown in continuous darkness and the mixotrophic strain grown in light/dark cycles exhibited daily metabolic oscillations in N2 fixation and glycogen accumulation similar to those manifested in photoautotrophic cultures grown in light/dark cycles or continuous light. This “temporal separation” helps protect O2‐sensitive N2 fixation from photosynthetic O2 evolution. The rationale for cyclic glycogen accumulation in cultures with an ample source of organic carbon substrate is unclear, but the observation of similar daily rhythmicities in cultures grown in light/dark cycles, continuous light, and continuous dark suggests an underlying circadian mechanism.

Functional complementation of an Escherichia coli gap mutant supports an amphibolic role for NAD(P)-dependent glyceraldehyde-3-phosphate dehydrogenase of Synechocystis sp. strain PCC 6803.

The gap-2 gene, encoding the NAD(P)-dependent D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH2) of the cyanobacterium Synechocystis sp. strain PCC 6803, was cloned by functional complementation of an Escherichia coli gap mutant with a genomic DNA library; this is the first time that this cloning strategy has been used for a GAPDH involved in photosynthetic carbon assimilation. The Synechocystis DNA region able to complement the E. coli gap mutant was narrowed down to 3 kb and fully sequenced. A single complete open reading frame of 1,011 bp encoding a protein of 337 amino acids was found and identified as the putative gap-2 gene identified in the complete genome sequence of this organism. Determination of the transcriptional start point, identification of putative promoter and terminator sites, and orientation of the truncated flanking genes suggested the gap-2 transcript should be monocystronic, a possibility further confirmed by Northern blot studies. Both natural and recombinant homotetrameric GAPDH2s were purified and found to exhibit virtually identical physicochemical and kinetic properties. The recombinant GAPDH2 showed the dual pyridine nucleotide specificity characteristic of the native cyanobacterial enzyme, and similar ratios of NAD- to NADP-dependent activities were found in cell extracts from Synechocystis as well as in those from the complemented E. coli clones. The deduced amino acid sequence of Synechocystis GAPDH2 presented a high degree of identity with sequences of the chloroplastic NADP-dependent enzymes. In agreement with this result, immunoblot analysis using monospecific antibodies raised against GAPDH2 showed the presence of the 38-kDa GAPDH subunit not only in crude extracts from the gap-2-expressing E. coli clones and all cyanobacteria that were tested but also in those from eukaryotic microalgae and plants. Western and Northern blot experiments showed that gap-2 is conspicuously expressed, although at different levels, in Synechocystis cells grown in different metabolic regimens, even under chemoheterotrophic conditions. A possible amphibolic role of the cyanobacterial GAPDH2, namely, anabolic for photosynthetic carbon assimilation and catabolic for carbohydrate degradative pathways, is discussed.

Photoheterotrophic and chemoheterotrophic dinitrogen fixation and nitrate utilization by the cyanobacteriumAnabaena torulosa

Anabaena torulosa exhibited fructose-dependent growth, heterocyst differentiation and N2 fixation in nitrate-free (diazotrophic) cultures in photoheterotrophic and chemoheterotrophic conditions. The incorporation of nitrate into such cultures inhibited the formation of heterocysts and N2 fixation. The rate of NO 3 − uptake byA. torulosa in photoautotrophic, photoheterotrophic and chemoheterotrophic conditions was similar but it increased by 100% in phototrophic conditions. The activity of glucose-6-phosphate dehydrogenase was found to be maximum in phototrophic and photoheterotrophic conditions. Ferredoxin-NADP+ reductase, nitrate reductase and glutamate-ammonia ligase activities suggest that nitrate utilization takes place in nonphotosynthetic conditions.

Akinete differentiation in phototrophic, photoheterotrophic and chemoheterotrophic conditions inAnabaena torulosa

Akinete differentiation inAnabaena torulosa occurred under phototrophic, photoheterotrophic and chemoheterotrophic conditions at the expense of fructose in nitrate-free and nitrate media. Maximum frequency of akinetes was recorded in nitrate-free cultures in photoheterotrophic condition followed by chemoheterotrophic condition. The activity of glucose-6-phosphate dehydrogenase (GPDase) and the levels of glycogen exhibited a correlation with the presence and absence of nitrate and maximum activity was detected in photoheterotrophic condition at the maturation phase. The cells in nitrate-free medium exhibited enhanced levels of GPDase, nitrogen fixation and low levels of glycogen in the presence of fructose. A lowering of GPDase activity in nitrate grown cells was found to be associated with the accumulation of glycogen. The results presented here further suggest that a critical balance of the C:N ratio triggers akinete differentiation.

Effect of nutritional regime on accumulation of cobalt, manganese and zinc by green microalgae

Accumulation of cobalt, manganese and zinc by the algae Chlorella emersonii, Chlamydomonas reinhardtii and Scenedesmus obliquus has been characterized under photoautotrophic, photoheterotrophic and chemoheterotrophic nutritional regimes. All three species accumulated smaller amounts of Co2+, Mn2+ and Zn2+ under chemoheterotrophic and photoheterotrophic conditions than under photoautotrophic conditions except in the case of cobalt accumulation by C. reinhardtii where there was little difference in the amount of cobalt accumulated under any of the nutritional regimes. Decreased accumulation of the three metals by C. emersonii and C. reinhardtii largely resulted from a decrease in the initial biosorptive phase of uptake whereas the decrease in Mn2+ and Zn2+ accumulation by C. reinhardtii under chemoheterotrophic and photoheterotrophic conditions was due to a decrease in the slow energy-dependent phase of uptake.

Isolation and characterization of trans-acting mutations involved in oxygen regulation of puc operon transcription in Rhodobacter sphaeroides

Transcriptional expression of the puc operon in Rhodobacter sphaeroides 2.4.1 is dependent on the partial pressure of oxygen. By using transcriptional fusions in trans of a promoterless fragment derived from the aminoglycoside-3'-phosphotransferase gene of Tn903 to puc operon-specific DNA containing a 629-bp 5' cis-acting regulatory region involved in the expression of puc-specific mRNA, we selected Kmr colonies under aerobic conditions. Two broad classes of mutations, trans and cis, which are involved in O2 control of puc operon transcription, fall into several distinct phenotypic classes. The cis-acting regulatory mutations are characterized in detail elsewhere (J.K. Lee and S. Kaplan, J. Bacteriol. 174:1146-1157, 1992). Two trans-acting regulatory mutants, CL1a and T1a, which are B800-850- Car- and apparently B875-, respectively, were shown to derepress puc operon transcription in the presence of oxygen. The mutation giving rise to CL1a has been shown to act at the puc operon-specific cis-acting upstream regulatory region (-629 to -92). On the other hand, the mutation giving rise to T1a, identifying a second trans-acting regulatory factor(s), appears to act at both the upstream (-629 to -92) and the downstream (-92 to -1) regulatory regions of the puc operon as well as at the level(s) of bacteriochlorophyll and carotenoid biosyntheses, as revealed by the presence of the B800-850 complex under chemoheterotrophic growth conditions. Both the B800-850- Car- phenotype and the trans-acting effect on puc operon expression in mutant CL1a were complemented with a 2.2-kb DNA fragment located within the carotenoid gene cluster. Mutant T1a was complemented with a 7.0-kb EcoRI restriction fragment containing the puhA gene and its flanking DNA (6.3 kb) to restore expression of the B875 complex and to suppress the trans-acting effect resulting in the loss of 02 control. Under chemoheterotrophic conditions, mutant T1a was highly unstable, segregating into a PS- mutant designated T4.

Chlorophyll a/b ratio and thylakoid stacking modification in response to glucose in chlorella vulgaris UAM 101

Summary Chlorophyll synthesis is not a light-dependent process in Chlorella vulgaris UAM 101. Glucose exerts a negative effect on chlorophyll synthesis that is more severe under photo- and chemoheterotrophic conditions of growth than under mixotrophic ones and in mixotrophic cultures more marked on chlorophyll b than a. The quantitative and qualitative effect of glucose on the main photosynthetic pigments is accompanied by an increase in the degree of stacking of thylakoid membranes in all cases and an increase of plastoglobuli in photoheterotrophic cells.