C4 photosynthesis at low temperatures

Abstract. C₄ plants grown in optimum conditions are, by comparison to C₃, capable of higher maximum dry-matter yields and greater efficiencies of water and nitrogen use, yet they are rare outside the subtropics. Both latitudinal and altitudinal limits of C₄ distributions correlate most closely with a mean minimum temperature of 8-10°C during the period of active growth. The possibility that the C₄ process is inherently incapable of functioning at low temperatures is examined. The reversible effects of chilling on the quantum efficiency of C₄ photosynthesis and the functioning of the individual steps in the C₄ cycle are examined. Chilling also produces an irreversible loss of capacity to assimilate CO₂ which is directly proportional to the light received during chilling. It is suggested that the reversible reduction in capacity to assimilate CO₂ and the lack of an alternative pathway for the utilization of lightgenerated reducing power may make C₄ species more prone to chilling-dependent photoinhibition. Laboratory studies and limited field observations suggest that this damage would be most likely to occur during photosynthetic induction at the temperatures and light levels encountered on clear, cool mornings during the spring and early summer in cool climates. Even those C₄ species occurring naturally in cool climates do not appear fully capable of tolerating these conditions; indeed their growth patterns suggest that they may be adapted by avoiding 'rather than enduring' such conditions.     

Phototrophic growth on n-fatty acids by species of the genus Rhodocyclus sensu Imhoff et al.

Abstract Type strains of Rhodocyclus purpureus, R. gelatinosus and R. tenuis along with three local isolates of R. gelatinosus were tested for growth in the light on n -fatty acids ranging in chain length from C₅ (valerate) to C₂₂ (docosanoate).
R. purpureus , the type species of the genus, was anomalous in its limited ability to grow on n -fatty acids; no fatty acids of chain length greater than C₉ (nonanoate) were utilized. R. gelatinosus and R. tenuis , on the other hand, utilized all fatty acids in the range C₅ to C₁₈ inclusive. R. gelatinosus showed some restricted ability to use C₂₀ (eicosanoate) and C₂₂ (docosanoate) fatty acids.     

Effect of non-target cells on the sensitivity of the PCR for Escherichia coli O157 : H7

The fatty acid composition from mycelia of Streptomyces hygroscopicus strains was studied. A significant proportion of C_{18 : 2} was found in cultures. High levels of C_{16 : 0}, iso-C_{16 : 0} and C_{18 : 1} were also detected in all S. hygroscopicus strains. The different representatives of S. hygroscopicus had almost the same proportion of unsaturated fatty acids. Certain shifts in the amount of iso, anteiso and straight-chain fatty acids in some cultures were revealed. This might be explained by the adaptation capability of strains belonging to one species to form a variety of available fatty acids determined by particular cell membrane composition favouring certain antibiotic biosynthesis.     

Volatile compounds produced by meat pseudomonads and related reference strains during growth on beef stored in air at chill temperatures

Volatile compounds produced by 31 strains of pseudomonads and by reference strains of Pseudomonas fragi and Ps. fluorescens biotype 1 during growth on beef stored at 6°C in air were analysed by gas chromatography-mass spectrometry of headspace gases. Compounds of major sensory significance were ethyl and methyl esters of C₂–C₈ fatty acids and sulphur-containing compounds which included methane- and isopropanethiols and their related sulphides and thioesters but not hydrogen sulphide. Ester production was mainly associated with growth of some, but not all, Ps. fragi and related meat strains but sulphur-containing compounds were produced by all but a single meat strain. A minority of other meat strains produced greater amounts of methyl ketones, secondary alcohols and unsaturated hydrocarbons believed to be of lipid origin.     

Cellular fatty acid composition in moderately halophilic Gram-negative rods

The fatty acid compositions for 40 strains of moderately halophilic Gram-negative rods were determined by gas-liquid chromatography. The strains studied were included in the genera: Vibrio, Deleya, Alteromonas, Chromobacterium, Flavobac-terium and Pseudomonas. Although there were quantitative differences all strains showed more or less similar spectra of fatty acids ranging from C₁₂ to C₂₀ chain. The major fatty acid species were C_16:0, C_16:1 and C_18:1. Most striking was the predominance of the C_18:1 component, the major fatty acid in extracts of 29 of the 40 strains.     

Genetics of carbon metabolism in methylotrophic bacteria

Abstract The application of genetic techniques to the methylotrophic bacteria has greatly enhanced studies of these important organisms. Two methylotrophic systems have been studied in some detail, the serine cycle for formaldehyde assimilation and the methanol oxidation system. In both cases, genes have been cloned and mapped in Methylobacterium species (facultative serine cycle methanol-utilizers). In addition, methanol oxidation genes have been studied in an autotrophic methanol-utilizer ( Paracoccus denitrificans ) and three methanotrophs ( Methylosporovibrio methanica, Methylomonas albus and Methylomonas sp. A4). Although much remains to be learned in these systems, it is becoming clear that the order of C₁ genes has been conserved to some extent in methylotrophic bacteria, and that many C₁ genes are loosely clustered on the chromosome. Operons appear to be rare, but some examples have been observed. The extension of genetic approaches to both the obligate and facultative methylotrophs holds much promise for the future in understanding and manipulating the activities of these bacteria.     

Induction of acetoacetate decarboxylase in Clostridium acetobutylicum

Abstract Factors that may initiate the biosynthesis of acetoacetate decarboxylase were investigated in resting cells of Clostridium acetobutylicum . Linear acids from C₁ to C₄ were inducers, whereas branched acids and linear acids from C₅ to C₇ were not inducers of acetoacetate decarboxylase biosynthesis. Induction of acetoacetate decarboxylase was maximal at pH 4.8 in the presence of acid concentrations comparable with those found during fermentation. In growth conditions repression of acetoacetate decarboxylase biosynthesis was found. This fact explains that acetone production by Clostridium acetobutylicum occurs when growth slows down.     

Uptake and utilization of n-octacosane and n-nonacosane by Arthrobacter nicotianae KCC B35

Arthrobacter nicotianae KCC B35 isolated from blue-green mats densely covering oil sediments along the Arabian Gulf coast grew well on C₁₀ to C₄₀ n -alkanes as sole sources of carbon and energy. Growth on C₂₀ to C₄₀ alkanes was even better than on C₁₀ to C₁₈ alkanes. Biomass samples incubated for 6 h with n -octacosane (C₂₈) or n -nonacosane (C₂₉) accumulated these compounds as the predominant constituent alkanes of the cell hydrocarbon fractions. The even chain hexadecane C₁₆ and the odd chain pentadecane C₁₅ were the second dominant constituent alkanes in C₂₈ and C₂₉ incubated cells, respectively. n -Hexadecane-incubated cells accumulated in their lipids higher proportions of C₁₆-fatty acids than control cells not incubated with hydrocarbons. On the other hand, C₂₈ and C₂₉-incubated cells did not contain any fatty acids with the equivalent chain lengths, but the fatty acid patterns of the cell lipids suggest that there should have been mid-chain oxidation of these very long chain alkanes. This activity qualifies A. nicotianae KCC B35 to be used in cocktails for bioremediating environments polluted with heavy oil sediments.     

Seasonal differences in photosynthesis between the C3 and C4 subspecies of Alloteropsis semialata are offset by frost and drought

The regional abundance of C₄ grasses is strongly controlled by temperature, however, the role of precipitation is less clear. Progress in elucidating the direct effects of photosynthetic pathway on these climate relationships is hindered by the significant genetic divergence between major C₃ and C₄ grass lineages. We addressed this problem by examining seasonal climate responses of photosynthesis in Alloteropsis semialata , a unique grass species with both C₃ and C₄ subspecies. Experimental manipulation of rainfall in a common garden in South Africa tested the hypotheses that: (1) photosynthesis is greater in the C₄ than C₃ subspecies under high summer temperatures, but this pattern is reversed at low winter temperatures; and (2) the photosynthetic advantage of C₄ plants is enhanced during drought events. Measurements of leaf gas exchange over 2 years showed a significant photosynthetic advantage for the C₄ subspecies under irrigated conditions from spring through autumn. However, the C₄ leaves were killed by winter frost, while photosynthesis continued in the C₃ plants. Unexpectedly, the C₄ subspecies also lost its photosynthetic advantage during natural drought events, despite greater water-use efficiency under irrigated conditions. This study highlights previously unrecognized roles for climatic extremes in determining the ecological success of C₃ and C₄ grasses.     

Role of growth regulators in the senescence of Arabidopsis thaliana leaves

A homozygous, dominant, C₂H₄-resistant line of Arabidopsis thaliana (L.) Heynh (cv. Columbia; er ) was selected from ethylmethylsulfonate-mutagenized seed, and used to test the role of C₂H₄ and other growth regulators in senescence of mature leaves. Chlorophyll (Chl) loss from disks excised from leaves of er was much slower than that from wild-type (WT) disks, whether they were held in the light or in the dark. C₂H₄ accelerated Che loss from WT disks but had no effect on the yellowing of mutant disks. C₂H₄ biosynthesis was higher in disks from the mutant plants, particularly in the light. In the dark, treatment with the cytokinin, 6-benzyladenine (BA), reduced Chl loss from wild-type disks, but had no effect on mutant disks. In the light, BA treatment stimulated chlorophyll breakdown in both wild type and mutant disks. Treatment with abscisic acid (ABA) stimulated chlorophyll loss in wild-type and mutant disks, whether they were held in the light or the dark. C₂H₄ production was stimulated in ABA-treated disks, but they still yellowed even when C₂H₄ production was inhibited by application of aminooxyacetic acid (AOA). These data indicate that C₂H₄ is only one of the factors involved in leaf senescence, and that the promotion of senescence by ABA is not mediated through its stimulation of C₂H₄ production.     

Arabidopsis CER8 encodes LONG-CHAIN ACYL-COA SYNTHETASE 1 (LACS1) that has overlapping functions with LACS2 in plant wax and cutin synthesis

Plant cuticle is an extracellular lipid-based matrix of cutin and waxes, which covers aerial organs and protects them from many forms of environmental stress. We report here the characterization of CER8 / LACS1 , one of nine Arabidopsis long-chain acyl-CoA synthetases thought to activate acyl chains. Mutations in LACS1 reduced the amount of wax in all chemical classes on the stem and leaf, except in the very long-chain fatty acid (VLCFA) class wherein acids longer than 24 carbons (C₂₄) were elevated more than 155%. The C₁₆ cutin monomers on lacs1 were reduced by 37% and 22%, whereas the C₁₈ monomers were increased by 28% and 20% on stem and leaf, respectively. Amounts of wax and cutin on a lacs1-1 lacs2-3 double mutant were much lower than on either parent, and lacs1-1 lacs2-3 had much higher cuticular permeability than either parent. These additive effects indicate that LACS1 and LACS2 have overlapping functions in both wax and cutin synthesis. We demonstrated that LACS1 has synthetase activity for VLCFAs C₂₀–C₃₀, with highest activity for C₃₀ acids. LACS1 thus appears to function as a very long-chain acyl-CoA synthetase in wax metabolism. Since C₁₆ but not C₁₈ cutin monomers are reduced in lacs1 , and C₁₆ acids are the next most preferred acid (behind C₃₀) by LACS1 in our assays, LACS1 also appears to be important for the incorporation of C₁₆ monomers into cutin polyester. As such, LACS1 defines a functionally novel acyl-CoA synthetase that preferentially modifies both VLCFAs for wax synthesis and long-chain (C₁₆) fatty acids for cutin synthesis.     

Degradation of crude oil by Acinetobacter calcoaceticus and Alcaligenes odorans

Two types of Indian crude oil (Bombay High and Gujarat) were tested for their biodegradability by Acinetobacter calcoaceticus and Alcaligenes odorans. Acinetobacter calcoaceticus S30 and Alc. odorans P20 degraded Bombay High crude oil by 50% and 45%, while only 29% and 37% of Gujarat crude oil (heavy crude oil) was degraded by these isolates, respectively. Acinetobacter calcoaceticus and Alc. odorans in combination deraded 58% and 40% of Bombay High and Gujarat crude oils, respectively, which were significantly higher than that of by individual cultures. Acinetobacter calcoaceticus S30 degraded more of the alkanes fraction than the aromatics fraction of both crude oils. GC fingerprinting of alkane fraction showed major degradation of heptadecane (C₁₇), octadecane (C₁₈), nonadecane (C₁₉), eicosane (C₂₀), docosane (C₂₂), tricosane (C₂₃) and tetracosane (C₂₄) of crude oil, while the Alc. odorans P20 degraded alkanes and aromatics equally. The asphaltenic component increased in both types of crude oil after biodegradation. The two strains grew very well on n -alkane up to C₃₃ as well as on pristane (branched-chain alkane) but could not grow on cycloalkanes. Acinetobacter calcoaceticus S30 could not grow on pure polycyclic aromatic hydrocarbon (PAH) compounds except naphthalene but Alc. odorans P20 could grow on anthracene, phenanthrene, dibenzothiophene, fluorene, fluoranthene, pyrene and chrysene.     

Flash pyrolysis of the outer cortical tissues in Lower Devonian Psilophyton dawsonii

Coalified residues of the xylem and peripheral structure tissues (stereomc) from perminei alized (CaCO₃) Lower Devonian Psilophyton dawsomi have been analysed by Hash pyrolysis-gas chromatography-mass spectrometry. Both yielded C₁-C₃ alkylphenols, C₁-C₃ alkylbenzenes, C₁-C₃ alkylnaphthalenes, although with varying relative abundances. The stereomc also generated a scries of n -alk-1-cries and H-alkanes (C₃C₂₄, maximum at C₁₀) which is believed to be derived from the cuticle. The sources of the aromatic compounds are discussed, and while it is concluded that those in the xylem are derived from lignin, the macromolecule having been degraded by diagencsis and thermal maturation, the molecular sources of those from the stereomc may also include a wide range of substances including simple phenolic acids, flavonoids and non-lignin polyphenolics. Possible functions for the stereome are discussed.     

Molecular biology of bacterial methanol oxidation

Abstract A detailed understanding of the mechanism of methanol oxidation in bacteria is a prerequisite for the future construction of new strains carrying this trait, or the improvement of industrial processes which employ methylotrophic bacteria. Recent advances in the isolation of mutants and the characterization of cloned genes involved in C₁ metabolism have expanded the biochemical data obtained in previous years, and indirectly stimulate research on electron transport and bacterial oxidases. Due to the heterogeneity of the physiology and genetic background of methylotrophs, classical genetic techniques are not readily applicable. The adaptation of these methods requires a detailed understanding of both bacterial metabolism and the principles of the genetic techniques involved. The results obtained to date from a limited number of methylotrophic organisms, using recombinant techniques, may facilitate future research in other organisms that have proved refractory to classical genetic analysis.     

Behaviour of Staphylococcus aureus strains, producers of enterotoxins C1 or C2, during the manufacture and storage of Burgos cheese

Burgos cheese was manufactured from pasteurized ewes milk inoculated with Staphylococcus aureus strains FRI 137 and FRI 361, at levels of ca 10³ and 10⁵ cfu/ml and stored at 4°, 10° and 15°C and at room temperature (10°-15°C). Populations of Staph. aureus and mesophilic aerobes, pH, and production of thermonuclease and enterotoxins C₁ and C₂ were investigated. Aerobic counts increased during cheese-making and storage. With both test strains, important growth was observed only during the storage period, the larger levels corresponding to the higher temperatures. Although Staph. aureus strains attained populations of over 10⁸ cfu/g, no enterotoxin was detected. Strain FRI 361 reached 10⁷ cfu/g without production of a detectable amount of thermonuclease. With strain FRI 137, the minimal population associated with enzyme activity was influenced by the inoculum size. Staphylococcus aureus counts are better indicators of staphylococcal growth in Burgos cheese than the thermonuclease test.     

Enhanced degradation of petrol (Slovene diesel) in an aqueous system by immobilized Pseudomonas fluorescens

The rate of degradation of n -alkanes C₁₂-C₁₈, in petrol (Slovene diesel) in an aqueous system, by free and immobilized Pseudomonas fluorescens in shaking flasks was investigated. Cells were immobilized to a biosupport, Biofix, and a biosorbant, Drizit. Analysis of cellular growth of the free and immobilized bacteria over 8 d of incubation with diesel as the sole carbon source, showed a reduction in the lag phase in the immobilized cultures in comparison to the free system. The free system degraded 52·3% of C₁₂ and 11·6% of C₁₃, but C₁₄-C₁₈ were not degraded. In comparison to the free system and diesel which had not been exposed to experimental conditions (unexposed), the immobilized systems degraded significantly more of C₁₃-C₁₈. Biofix-immobilized cells degraded 14·8% of C₁₂ and an average of 53·5% of C₁₃-C₁₈. Drizit-immobilized cells degraded 24·5% of C₁₂, 52·4% of C₁₃ and an average of 91·2% of C₁₄-C₁₈. This study shows the successful use of immobilized bacteria technology to enhance the degradation of diesel in an aqueous system.     

Enzymes and pathways of polyamine breakdown in microorganisms

Abstract The information currently available on the breakdown of spermidine and putrescine by microorganisms is reviewed. Two major metabolic routes have been described, one for the free bases via δ¹-pyrroline (4-aminobutyraldehyde), the other via N -acetyl derivatives. In both pathways oxidases or aminotransferases are the key enzymes in removing the nitrogen atoms. The two routes converge at 4-aminobutyrate, which is then metabolized via succinate. The degradation of putrescine in Escherichia coli has been well characterized at both genetic and biochemical levels, but for other bacteria much less information is available. The C₃ moiety of spermidine is broken down via β-alanine, but the metabolism of this compound and its precursors is poorly understood. In yeasts, a catabolic route for spermidine and putrescine via N -acetyl derivatives has been described in Candida boidinii , and the evidence for its occurrence in other species is reviewed. Except for the terminal step of this pathway, the same group of enzymes can metabolize both the C₃ and C₄ moieties of spermidine. It is likely that other routes of polyamine catabolism also exist in both bacteria and yeasts.     

An Escherichia coli S1-like ribosomal protein is immunologically conserved in Gram-negative bacteria, but not in Gram-positive bacteria

Abstract A study was made of the enzymology of primary and intermediary pathways of C₁ metabolism in three strains of non-motile obligately methylotrophic bacteria. Each uses a variant of the ribulosemonophosphate (RMP) cycle of formaldehyde fixation which involves the Entner-Doudoroff route for hexose-phosphate cleavage and transaldolase/transketolase mode of rearrangement. The organisms possess high levels of hexulose-phosphate synthase and NAD(P)-linked glucose-6-phosphate and 6-phosphogluconate dehydrogenases. In addition they contain small activities of dye-linked methanol and methylamine dehydrogenases, PMS- and NAD-linked formaldehyde and formate dehydrogenases. This indicates cyclic rather than direct oxidation of formaldehyde derived from methanol or methylamine. The tricarboxylic acid cycle is defective in 2-ketoglutarate dehydrogenase and the glyoxylate shunt is not operating because of the absence of malate synthase. Oxaloacetate is regenerated by (phosphoenol) pyruvate carboxylases. NH⁺ ₄ is assimilated mainly by glutamate dehydrogenase. The results show metabolic similarities between motile and non-motile obligate methanol and methylamine utilizers.     

Evidence for the occurrence of the alternative, vanadium-containing nitrogenase in the cyanobacterium Anabaena variabilis

Abstract Anabaena variabilis can be grown with dependence on either molybdenum (Mo) or vanadium (V) in the medium with essentially the same growth rates. Vanadium cultures reduce C₂H₂ to C₂H₄ and partly (to 2–3%) to C₂H₆. These C₂H₄ and C₂H₆ formations can be shown to be strictly light dependent, proving that the gases are formed by the cyanobacterium. C₂H₄ and C₂H₆ productions are accompanied by a H₂ formation which is much higher than in Mo cultures. Maximal C₂H₂-formation rates are 2/3 lower in V-grown cells compared to Mo control cultures. This is the first demonstration of a light-dependent ethane formation and of the occurrence of the alternative nitrogenase in any phototroph.     

Effect of H2 evolution on 15N2 fixation, C2H2 reduction and relative efficiency of leguminous symbionts

The (C₂H₄+ H_2(C2H₂))/¹⁵N₂ ratios of 15 clover- Rhizobium symbionts. soybean, and black medick symbionts were measured. Relative efficiency based on the C2H4 production and on ¹⁵N₂ incorporation were compared, and in most symbionts there was little difference between the two measures of relative efficiency. Total measurable electron flux through nitrogenase during acetylene reduction and ¹⁵N₂ incorporation were nearly equal for most symbionts studied. The relative efficiency and the (C₂H₄+ H_2(C2H₂))/¹⁵N₂ ratio showed an inverse correlation. Use of this ratio appears preferable to use of the ratio of C2H2 reduction/N₂ reduction. Some evolution of H₂ was observed in the presence of C₂H₂.