Affinity of singleS. cerevisiaecells to 2-NBDglucose under changing substrate concentrations

BACKGROUND

Saccharomyces cerevisiae is a widely employed microorganism in biotechnological processes. Since proliferation and product formation depend on the capacity of the cell to access and metabolize a carbon source, a technique was developed to enable for analyzing the S. cerevisiae H155 cells' affinity to extracellular glucose concentrations.

METHODS

The fluorescent glucose analogue 2-NBDglucose was employed as a functional parameter to analyze the cells' affinity to glucose. Structural parameters (proliferation, neutral lipid content, granularity, and cell size) were also investigated. Cells were grown both in batches and in chemostat regimes.

RESULTS

The 2-NBDglucose uptake in individual cells proceeds in a time- and concentration-dependent manner and is affected by respiratory and respirofermentative modes of growth. The process is inhibited by D-glucose, D-fructose, D-mannose, and sucrose, but not L-glucose, D-galactose or lactose; maltose is a weak inhibitor. The affinity of the individual cells to 2-NBDglucose was found to be high at low extracellular glucose concentrations, and weak at high concentrations. An additional, underlying pattern in the cells' affinity to glucose was detected, illustrated by the recurrent appearance of two subpopulations showing distinctly differing quantities of this substrate.

CONCLUSIONS

A multiparameter flow cytometry approach is presented that enables, for the first time, for analysis of the affinity of individual S. cerevisiae cells to glucose. Besides the adjustment of the yeast cell metabolism to extracellular glucose concentrations by altering their affinity to glucose, at least one further mechanism is clearly involved. Two subpopulations of cells were resolved, with different affinities not correlated with other cellular parameters measured.

Non-conventional yeasts as producers of polyhydroxyalkanoates?genetic engineering of Arxula adeninivorans

The non-conventional yeast Arxula adeninivorans was equipped with the genes phbA, phbB and phbC of the polyhydroxyalkanoate (PHA) biosynthetic pathway of Ralstonia eutropha, which encode beta-ketothiolase, NADPH-linked acetoacetyl-CoA reductase and PHA synthase, respectively. Arxula strains transformed solely with the PHA synthase gene (phbC) were able to produce PHA. However, the maximum content of the polymer detected in these strains was just 0.003% poly-3-hydroxybutyrate (PHB) and 0.112% poly-3-hydroxyvalerate (PHV). The expression of all three genes (phbA, phbB, phbC) resulted in small increases in the PHA content of the transgenic Arxula cells. However, under controlled cultivation conditions with minimal medium and ethanol as the carbon source, the recombinant yeast was able to accumulate up to 2.2% PHV and 0.019% PHB. Possible reasons for these differences are discussed.

Analysis of bacterial DNA patterns—an approach for controlling biotechnological processes

Optimisation of biotechnological processes catalysed by microbial cells requires detailed information about operational limits of the single cells. Their performance is correlated with distinct physiological states. We related these states to cell cycle events, which were found to proceed extremely diversely in different bacterial strains. Characteristic DNA patterns were found flow cytometrically, depending on the type of strain, substrates and growth conditions involved; this information can be used for the development of control strategies of bioprocesses, although some skill is required. Four bacterial strains (the Gram-negative strains Acinetobacter calcoaceticus 69-V, Ralstonia eutropha JMP 134, Ochrobactrum anthropi K2-14 and the Gram-positive strain Rhodococcus erythropolis K2-3) were grown in mono- and mixed cultures on different substrates, and analysed regarding their proliferation behaviour. The resulting DNA distribution patterns provided three types of valuable information. First, correlation of proliferation activity with the appearance of a major part of cells within the C(2) stage of the cell cycle is a strain-specific feature. Second, bacteria usually maintain more than one chromosome under limiting growth conditions: DNA replication is completed in such cases, but cell division fails. Third, high growth rates are associated with uncoupled DNA synthesis. Its general initiation might be genetically determined in the first place, but it is promoted by optimal growth conditions and the presence of substrates that can be metabolised at high rates, thereby allowing substantial amounts of carbon, other nutrients and energy to be used exclusively for DNA synthesis.

Energization of Comamonas testosteroni ATCC 17454 for indicating toxic effects of chlorophenoxy herbicides

The toxicity of chlorophenoxy herbicides to a bacterium, strongly related to the well-known species Delftia (formerly Comamonas) acidovorans that are able to detoxify these xenobiotics, was investigated. The oxidation of n-hexanol via alcohol dehydrogenases, coupled with the generation of ATP by electron transport phosphorylation (ETP), was used as an indicator for energy-toxic effects on the growth of Comamonas testosteroni ATCC 17454. Uncoupling--reductions in ATP synthesis accompanied by increased respiration--was found to be induced by 1 mM of the classic uncoupler 2,4-dinitrophenol (2,4-DNP) at pH 7.0 and 8.0. At pH 5.4 and 6.0, the ATP synthesis and respiration were strongly inhibited by both 2,4-DNP and the chlorophenoxy herbicides tested. In contrast, 5 mM of 2,4-dichlorophenoxyacetic acid (2,4-D) and of 2-(2,4-dichlorophenoxy)-propanoic acid (2,4-DCPP) were required for detectable uncoupling effects--reduction of the P/O ratios by about 30%--at pH 7.0. These chemicals may have less uncoupling power because the concentration of their protonated (undissociated) forms (pKa values 2.7 and 3.0) is an order of magnitude lower than that of 2,4-DNP (pKa = 4.0) at this pH value. Strong uncoupling accompanied by increased respiration, like that induced by 1 mM 2,4-DNP, was also caused by 5 mM 4-(2,4-dichlorophenoxy)-butyric acid (2,4-DCPB), which correlates with its high pKa value of 4.6. The order of toxicity of the chlorophenoxy herbicides (2,4-D < 2,4-DCPP < 2,4-DCPB) to the ETP, which correlates well with the lipophilicity of their undissociated forms (log P 2.7 < 3.4 < 3.5, respectively), was confirmed by measuring their capacity to inhibit the growth of Comamonas testosteroni ATCC 17454. The results show that energization via alcohol dehydrogenases can be used as an indicator for investigating energy-toxic effects of organics on the ETP and growth of chlorophenoxy herbicide-detoxifying bacteria.

Diversity of ribulose-1,5-bisphosphate carboxylase/oxygenase large-subunit genes from groundwater and aquifer microorganisms

To test our hypothesis that microbial autotrophic CO2 fixation plays an important role in subsurface systems of two large groundwater remediation projects, several anaerobic/microaerobic aquifer and groundwater samples were taken and used to investigate the distribution and phylogenetic diversity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) large-subunit genes. Two primer sets were designed for amplifying partial-subunit genes of RubisCO forms I and II from the DNA, directly extracted from the samples. PCR products were used to construct five clone libraries with putative RubisCO form I sequences, and two libraries of DNA amplified by form II primers. Selected clones were screened for variation by restriction fragment length polymorphism analysis, and a total of 28 clone inserts were sequenced and further analyzed. The phylogenies constructed from amino acid sequences derived from the partial RubisCO large-subunit sequences showed a distinct pattern. Diverse sequences affiliated to the cluster of green-like type IA RubisCO sequences were found, representing various obligate and facultative chemolithoautotrophic Proteobacteria, whereas type II RubisCO sequences detected were most closely related to those of thiobacilli species. An isolate obtained from aquifer enrichment culture, which has been provisionally named Halothiobacillus sp. RA13 on the basis of its 16S rDNA sequence, was found to contain both types of RubisCO genes, i.e., forms I and II. Physiological and ecological considerations are discussed in the context of additional microbial data and physicochemical properties.

Physiological and genetic characteristics of two bacterial strains utilizing phenoxypropionate and phenoxyacetate herbicides

Two strains, Rhodoferax sp. P230 and Delftia (Comamonas) acidovorans MCI, have previously been shown to carry activities for the degradation of the two enantiomers of (RS)-2-(2,4-dichlorophenoxy-)propionate (dichlorprop) and (RS)-2-(4-chloro-2-methylphenoxy-)propionate (mecoprop) and, in addition, are capable of degrading phenoxyacetate derivatives 2.4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA). Metabolism of the herbicides is initiated by alpha-ketoglutarate-dependent dioxygenases for both enantiomers of the phenoxypropionate herbicides and for 2,4-D. These activities were constitutively expressed for both enantiomers of dichlorprop in strain MC1 and for the Renantiomer in strain P230. Enzyme activities for the complete degradation of phenoxyacetate and phenoxypropionate herbicides were induced during incubation on either of these herbicides. Strain MC1 has about threefold higher activities for the degradation of dichlorprop and for growth on this substrate (mumax = 0.15 h(-1)) than strain P230; the maximum growth rate on 2,4-D amounts to 0.045 h(-1) with strain MC1. Dichlorprop is utilized faster than mecoprop and the R-enantiomers are cleaved with higher rates than the S-enantiomers. The degradation of the chlorophenolic intermediates seems to proceed via the modified ortho cleavage pathway as indicated by activities of the respective enzymes. The enzymatic results were supported by genetic investigations by which the presence of the genes tfdB (encoding a dichlorophenol hydroxylase), tfdC (encoding a chlorocatechol 1,2-dioxygenase) and tfdD (encoding a chloromuconate cycloisomerase) could be demonstrated in both strains by PCR after application of respective primers. The presence of the tfdA gene (encoding a 2,4-D/alpha-ketoglutarate dioxygenase) was only shown for strain P230 but was lacking in strain MC1. Sequence analysis of the tfd gene fragments revealed high homology to the degradative genes of other proteobacterial strains degrading chloroaromatic compounds. Strain MC1 carries a plasmid of about 120 kb which apparently harbors herbicide degradative genes as concluded from deletion mutants which have lost 2,4-D[phenoxalkanoate]/alpha-ketoglutarate dioxygenase activities for cleavage of the R- and S-enantiomer, and of 2,4-D. For strain P230, no plasmid could be demonstrated; the activity was stably conserved in this strain during growth under nonselective conditions.

Expression of the 2,4-D degradative pathway of pJP4 in an alkaliphilic, moderately halophilic soda lake isolate, Halomonas sp. EF43

The broad host range plasmid pJP4, which carries genes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid, and 3-chlorobenzoic acid, was used in conjugation experiments with mixed cultures enriched from water and sediment samples from an alkaline pond in the area of Szegedi Fehértó, a soda lake in south Hungary. pJP4-encoded mercury resistance was used as a selection marker. One of the transconjugants, the alkaliphilic, moderately halophilic strain EF43, stably maintained the plasmid and was able to degrade 2,4-D and 3-chlorobenzoate under alkaline conditions in the presence of an additional carbon source such as pyruvate, benzoate, or alpha-ketoglutarate, indicating that the degradative genes of pJP4 were expressed in this strain. However, it was unable to grow on these chloroaromatic substrates when the substrate was the sole source of carbon and energy. Chemostat cultivation experiments revealed that the 2,4-D degradation rate during growth on benzoate or pyruvate was limited by the low activity of chlorocatechol-degrading enzymes, particularly chloromuconate cycloisomerase. Strain EF43 was identified as Halomonas sp. on the basis of 16S rRNA sequencing and additional taxonomic studies. 16S rRNA sequence analysis revealed that strain EF43 is closely related to typical soda lake isolates belonging to the genus Halomonas.

Suitability of the trans/cis ratio of unsaturated fatty acids in Pseudomonas putida NCTC 10936 as an indicator of the acute toxicity of chemicals

This study explored the suitability of using the trans/cis ratio of unsaturated fatty acids as an indicator of the acute toxicity of membrane active hazardous chemicals. The conversion of cis into trans fatty acids in Pseudomonas putida NCTC 10936 in response to 4-chlorophenol and temperature changes was compared with the results from another kind of toxicity test using the same organism, based on the sensitivity of its xylose oxidation-driven ATP synthesis to uncoupling. The response of both indicators is believed to be largely due to changes in the fluidity of the cytoplasmic membrane. However, the electron transport phosphorylation reacted faster and more sensitively to the fluidizing effect of 4-chlorophenol than the isomerization of unsaturated fatty acids. Therefore, measuring the trans/cis ratio does not provide as good early warning signals of acute toxicity as monitoring the response of the electron transport phosphorylation. If used as an indicator of chemostress, with Pseudomonas species as test organisms, the ratio should only be used in conjunction with other parameters reflecting the energetic state of the cells.

Calorimetrically obtained information about the efficiency of ectoine synthesis from glucose in Halomonas elongata

Compatible solutes are becoming more and more attractive commercially. Thus, knowledge of the efficiency of synthesis of compatible solutes from different carbon substrates is very important. As the growth rate and rates of formation of compatible solutes correspond to the heat flux, calorimetric measurements are particularly suitable for providing this information. By growing microorganisms continuously in a calorimeter, and generating a feeding stream with gradually increasing salinity without changing any other growth conditions, we were able to determine the efficiency of growth-associated synthesis of compatible solutes. This was shown for Halomonas elongata DMSZ 2581(T) growing on glucose, which synthesizes (at 25 degrees C) 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine) as its main osmotic counterweight. The requirement of biologically usable energy for its growth-associated synthesis was found to be very low: a 100% efficiency of the conversion of the substrate-carbon into ectoine is both theoretically possible and was reached approximately in practice. The growth rate and yield coefficient were essentially independent of the ectoine formation rate, and the rate of substrate-carbon assimilation was far greater than the rate of dissimilation. The specific maximum growth rate was limited by the rate of formation of ectoine.

Protein synthesis patterns in Acinetobacter calcoaceticus induced by phenol and catechol show specificities of responses to chemostress

The proteins induced in Acinetobacter calcoaceticus by the potentially toxic growth substrates phenol and catechol were analyzed by 2D-electrophoresis of cell extracts and compared with those induced by heat shock and oxidative stress. Although both aromatic compounds are quite similar, the only difference being that catechol has an additional hydroxyl group, the responses obtained differed considerably. Phenol has greater lipophilicity and mainly induced heat shock proteins, whereas catechol, which causes the production of reactive oxygen species, predominantly induced oxidative stress proteins. Furthermore, some special proteins were induced by phenol or catechol, which might be useful as biomarkers for chemostress, and could be involved in the catalytic degradation of potentially toxic compounds.

Physiology, regulation, and limits of the synthesis of poly(3HB)

The properties of poly(3-hydroxybutyrate) combined with the fact that it can be produced easily by numerous prokaryotes from renewable resources and even from potentially toxic waste products using well-known fermentation processes have generated keen interest in this biopolyester as a substitute for chemo-synthetic petroleum-derived polymers in many applications. However, the high price of poly(3HB) compared with the conventional synthetic materials currently in use has restricted its availability in a wide range of applications. If the economic viability of poly(3HB) production and its competitiveness are to be improved, more must be found out about the phenotypic optimization and the upper limits of bacterial systems as the factory of poly(3HB). In this chapter, two aspects of poly(3HB) are reviewed--poly(3HB) formation as a physiological response to external limitations and overcoming internal bottlenecks, and poly(3HB) as a commercially attractive polyester. From a physiological viewpoint, the ability to synthesize and degrade poly(3HB) is considered an investment in the future and provides organisms with a selective advantage. Poly(3HB) is presented as a strategic survival polymer, and it is shown that growth-associated synthesis is not as rare as reported. The influence of the efficiency and velocity of cell multiplication and product formation, of poly(3HB) content and of productivity on the overall yield, and finally on the economics of the whole process are discussed and evaluated from the technological or consumer's point of view. The specific production rate and poly(3HB) content appear to be more important than the yield coefficients.

A calorimetrically based method to convert toxic compounds into poly-3-hydroxybutyrate and to determine the efficiency and velocity of conversion

A fed-batch method for converting toxic substrates into poly-3-hydroxybutyrate is presented. The method involves a series of batch-growth processes, regulated by adding small amounts of carbon substrate, during the course of which the concentration of the nitrogen source decreases and controls the distribution of the substrate-carbon assimilated. The addition of carbon substrate is controlled, and the small changes that occur in the growth pattern are interpreted using high-resolution reaction calorimetry. The method was tested with Ralstonia eutropha DSM 4058 growing on phenol, and Variovorax paradoxus DSM 4065 growing on sodium benzoate. The maximum carbon conversion efficiencies (CCEs) obtained, 23% and 27% respectively, were compared with the theoretically possible values.

Influence of special surfactants on the microbial degradation of mineral oils

Various surfactants belonging to the group of fatty acid-acylated amino acids were tested for their ability to accelerate the microbial degradation of mineral oil. Of the lauric acid-acylated amino acids, aliphatic acids and histidine were found to be the most suitable. By the aid of these compounds additional 20-60% of a residual oil fraction could be degraded. The longer the chain of the fatty acid moiety, the more effective the surfactants are. Natural L-amino acids were more effective than their D-configuration. Since the special surfactants are easily biologically degradable, multiple replenishment is required in long-term experiments. The faster, more complete degradation of mineral oil is caused solely by interfacial activity; the growth of biomass due to the function of surfactants as substrate had no effect.

Etherolytic cleavage of 4-(2,4-dichlorophenoxy)butyric acid and 4-(4-chloro-2-methylphenoxy)butyric acid by species of Rhodococcus and Aureobacterium isolated from an alkaline environment

Bacterial strains were isolated from the concrete rubble of a demolished herbicide production plant. The predominant feature of these strains was the etherolytic cleavage of 4-(2,4-dichlorophenoxy)butyric acid (DCPB)1) and 4-(4-chloro-2-methylphenoxy)butyric acid (MCPB) while liberating 2,4-dichlorophenol (DCP) and 4-chloro-2-methylphenol (MCP) respectively. Some of the isolates were identified by 16S rDNA sequence analysis and shown to belong to the genera Aureobacterium sp. (strain K2-17) and Rhodococcus (Rh. erythropolis K2-12). The other strains isolated clustered into these two groups according to fatty acid analysis. Etherolytic cleavage proceeded under neutral to alkaline conditions with an optimum at around pH 8.5. With Aureobacterium sp. No. K2-17, the degradation rate was zero at a pH of 6 but as much as 60% of the maximum activity was observed at pH 10.5. With Rh. erythropolis K2-12, by contrast, pronounced activity was detected at pH 6.5 while degradation was no longer observed at pH 10.5. The maximum rates of cleavage were about 1 mmol DCPB/h.g dry mass with Aureobacterium sp. No. K2-17 and about 0.6 mmol DCPB/h.g dry mass with Rh. erythropolis K2-12. DCPB and MCPB were utilized to the same extent. Substrate cleavage and product formation (DCP) proceeded at almost equal rates with Aureobacterium sp. No. K2-17 and Rh. erythropolis K2-12, which indicates that this compound was not further metabolized. Only phenoxybutyric acid compounds served as substrates; phenoxyacetic acid and phenoxypropionic acid derivatives were not utilized by these strains.

Degradation of various chlorophenols under alkaline conditions by gram-negative bacteria closely related to Ochrobactrum anthropi

From concrete debris of a demolished herbicide production plant several Gram-negative bacterial strains were isolated, which exhibit metabolic capabilities for the degradation of 2,4-dichlorophenol (DCP)l), 4-chloro-2-methylphenol (MCP) and 4-chlorophenol (4-CP), while 2-chlorophenol (2-CP) was degraded at a slower rate. Degradative activity was inducible and was impeded by adding of 100 mg/l of chloramphenicol to growing cultures. The strains displayed alkaliphilic properties with optimum DCP/MCP degradation at pH values around 8.5-9.5; activity was observed up to pH values of 11. Degradation was most likely complete according to chlorine balances; formation of intermediary products was observed with MCP some time. Specific activity of up to 380 mumol/h.g dry mass was found within the concentration range of 10-20 mg/l DCP; higher concentrations retarded the activity with complete inhibition at 200-400 mg/l. Some of the strains carry plasmids whose presence was not unambiguously correlated to the degradative properties. Ribotyping revealed a high degree of relationship between the strains. Preliminary taxonomic investigations showed close relationship to Ochrobactrum anthropi.

Flow cytometric techniques to characterise physiological states of Acinetobacter calcoaceticus

Monitoring biotechnological processes involves acquiring information about key metabolic events and, ideally, single cell states should be determined to obtain comprehensive data on the physiological status of the surveyed population. In this paper, growth stages of the strain Acinetobacter calcoaceticus 69-V were characterised at the single cell level using flow cytometry. Four methods for analysing bacterial cellular characteristics by fluorescence were compared with respect to their sensitivity to changes in the physiological states induced by changing micro-environmental conditions. DNA analysis was confirmed to be highly informative with regard to the multiplication activity of the population. Measuring the membrane potential related fluorescence intensity (MPRFI) and the rRNA content were found to be useful for describing high-active cell states. A method for the measurement of the fluidity related fluorescence intensity (FRFI) was developed, since it allowed changes in the fluidity of the bacterial membrane to be detected, and thereby provided a valuable means of tracking adaptation of the population to micro-environmental deviations from optimal growth conditions.

Calorimetrically recognized maximum yield of poly-3-hydroxybutyrate (PHB) continuously synthesized from toxic substrates

The broader usage of poly-beta-hydroxybutyrate (PHB), for instance as bulk plastics, calls for cheap raw materials and greater overall process efficiency. The bacterial synthesis is generally induced and promoted by the limitation of growth via nitrogen, oxygen or phosphate depletion with the simultaneous excess and higher concentration of the carbon substrate. Consequently, toxic substrates have been considered unsuitable for PHB synthesis. Nevertheless, a single-stage continuous process for producing PHB from toxic substrates using microorganisms was developed and is reported here. The maximum heat flux during continuous growth and the maximum yield of PHB versus the substrate consumption rate were found to coincide. This suggests the possibility of controlling the conversion of a growth-inhibiting substrate into PHB and maximizing the process efficiency. The observed correlation occurred irrespective of the substrates investigated (phenol or sodium benzoate), the PHB-producing strain (Ralstonia eutropha JMP 134 or Variovorax paradoxus JMP 116), or the type of limitation imposed. The maximum PHB yields obtained comprised up to 50% of cell dry mass.

A theoretical study on the metabolic requirements resulting from alpha-ketoglutarate-dependent cleavage of phenoxyalkanoates

The etherolytic cleavage of phenoxyalkanoic acids in various bacteria is catalyzed by an alpha-ketoglutarate-dependent dioxygenase. In this reaction, the electron acceptor is oxidatively decarboxylated to succinate, whereas the proper substrate is cleaved by forming the oxidized alkanoic acid and the phenolic intermediate. The necessity of regenerating alpha-ketoglutarate and the consequences for the overall metabolism were investigated in a theoretical study. It was found that the dioxygenase mechanism is accompanied by a significant loss of carbon amounting to up to 62.5% in the assimilatory branch, thus defining the upper limit of carbon conversion efficiency. This loss in carbon is almost compensated for in comparison to a monooxygenase-catalyzed initial step when the dissimilatory efforts of the entire metabolism are included: the yield coefficients become similar. The alpha-ketoglutarate-dependent dioxygenase mechanism has more drastic consequences for microorganisms which are restricted in their metabolism to the first step of phenoxyalkanoate degradation by excreting the phenolic intermediate as a dead-end product. In the case of phenoxyacetate derivatives, the cleavage reaction would quickly cease due to the exhaustion of alpha-ketoglutarate and no growth would be possible. With the cleavage products of phenoxypropionate and phenoxybutyrate herbicides, i.e., pyruvate and succinate(semialdehyde), respectively, as the possible products, the regeneration of alpha-ketoglutarate will be guaranteed for stoichiometric reasons. However, the maintenance of the cleavage reaction ought to be restricted due to physiological factors owing to the involvement of other metabolic reactions in the pool of metabolites. These effects are discussed in terms of a putative recalcitrance of these compounds.