Gold uptake by Chlorella vulgaris

This paper describes a study on the uptake of gold (III) ions by viable and treated cells of the unicellular alga, Chlorella vulgaris. Inactivating the algal cells by various physical/chemical treatments resulted in a considerable enhancement in the uptake capacity over the pristine cells. X-ray Photoelectron Spectroscopy (XPS) analyses confirmed the deposition of elemental gold, Au (O), on the cell surface, indicating that a reduction process has taken place. XPS results also suggested an increase in the oxidized carbon species, carboxyl species in particular, on the surfaces of the treated cells. FTIR spectroscopy results revealed that the carboxyl group was involved mainly in the binding of the gold on the surface of both the viable and treated cells.     

小球藻的玻璃化超低温保存法

先用含0.5 m01·L-1甘油和0.4 mol·L-1蔗糖的预处理液处理20min,然后用含30%蔗糖 15%乙二醇 10%二甲基亚砜 BBMG培养液的玻璃化液处理,在0℃下预冻60min后,将小球藻投入液氮.此法存活率较高,可达到60.14%,小球藻种质保存效果较好.通过试验初步建立了小球藻玻璃化法超低温保存的技术程序.     

Genetic transformation of Lactobacillus casei by electroporation

Lactobacillus casei IAM1045 was transformed with a plasmid pAM beta 1-1, a tra deleted derivative of pAM beta 1, by electroporation. Effective transformation was achieved in electroporation buffers of a wide range of pH values, and in all phases of cell growth tested, with highest frequency in the early log phase. Polyethylene glycol increased the transformation frequency, whereas divalent cations such as Mg2+, Ca2+ and Mn2+ at 0.25 mM decreased the frequency by 2 to 3 orders. Highly efficient transformation of approximately 10(-4)/viable cell was achieved under optimal conditions. A plasmid harboring the trpD, C, F, B and A genes from L casei RNL7 was introduced by electroporation into tryptophan auxotrophic L casei JCM1053. The resulting transformant was found to express the trp genes introduced.     

Metabolism of Urea by Chlorella vulgaris

Urea metabolism was studied with nitrogen-starved cells of Chlorella vulgaris Beijerinck var. viridis (Chodat), a green alga which apparently lacks urease. Incorporation of radioactivity from urea-(14)C into the alcohol-soluble fraction was virtually eliminated in cell suspensions flushed with 10% CO(2) in air. This same result was obtained when expected acceptors of urea carbon were replenished by adding ornithine and glucose with the urea. Several carbamyl compounds, which might be early products of urea metabolism and a source of the (14)CO(2), were not appreciably labeled. If cells were treated with cyanide at a concentration which inhibited ammonia uptake completely and urea uptake only slightly, more than half of the urea nitrogen taken up was found in the medium as ammonia. Cells under nitrogen gas in the dark were unable to take up urea or ammonia, but the normal rate of uptake was resumed in light. Since 3-(3,4-dichlorophenyl)-1,1-dimethylurea did not selectively inhibit this uptake, an active respiration supported by light-dependent oxygen evolution in these cells was ruled out. A tentative scheme for urea metabolism is proposed to consist of an initial energy-dependent splitting of urea into carbon dioxide and ammonia. This reaction in Chlorella is thought to differ from a typical urease-catalyzed reaction by the apparent requirement of a high energy compound, possibly adenosine triphosphate.     

Diacetyl and Acetoin Production by Lactobacillus casei

Agitation of broth cultures of Lactobacillus casei retarded cellular dry weight accumulation but enhanced production of both diacetyl and acetoin. Addition of pyruvate overcame this retardation, but addition of sulfhydryl-protecting reagents did not. Both pyruvate and citrate enhanced accumulated dry weight of L. casei incubated without agitation, but only pyruvate increased diacetyl accumulation. Both actively dividing cells and cells suspended in buffer converted pyruvate to diacetyl and acetoin. Maximum production of diacetyl and acetoin occurred during the late logarithmic or early stationary phases. Cells isolated from pyruvate- or citrate-containing cultures showed the greatest ability to convert pyruvate to diacetyl and acetoin. The optimum pH for diacetyl and acetoin formation by whole cells was in the range of 4.5 to 5.5. The presence of citrate or acetate enhanced diacetyl and acetoin formation by L. casei cells in buffer suspension.     

Macrophage activation by Lactobacillus casei in mice

Effects of Lactobacillus casei YIT 9018 (LC 9018), which has antitumor activities against allogeneic and syngeneic murine tumors, on macrophage functions were examined. By intraperitoneal (i.p.) injection of LC 9018, acid phosphatase activity and phagocytic activity of peritoneal macrophages were enhanced significantly compared with those of normal peritoneal macrophages. The phagocytic activities showed peaks 2-3 days after the LC 9018-injection. LC 9018 accelerated the phagocytic function of the reticuloendotherial system in ICR mice tested by the carbon clearance test. The cytostatic activity of peritoneal exudate cells (PEC) induced by i.p. injection of LC 9018 into C57BL/6 mice against EL4 cells was also enhanced. On the other hand, PEC induced by L. fermentum YIT 0159, which has no antitumor activity, did not have cytostatic activity. These observations showed that LC 9018 was able to activate macrophages in mice.     

Lactobacillus casei and Lactobacillus plantarum initiate catabolism of methionine by transamination

AIMS: To study the ability of Lactobacillus casei and Lact. plantarum strains to convert methonine to cheese flavour compounds. METHODS AND RESULTS: Strains were assayed for methionine aminotransferase and lyase activities, and amino acid decarboxylase activity. About 25% of the strains assayed showed methionine aminotransferase activity. The presence of glucose in the reaction mixture increased conversion of methionine to 4-methylthio-2-ketobutanoate (KMBA) and 4-methylthio-2-hydroxybutanoate (HMBA) in all strains. The methionine aminotransferase activity in Lact. plantarum and Lact. casei showed variable specificity for the amino group acceptors glyoxylate, ketoglutarate, oxaloacetate and pyruvate. None of the strains showed methionine lyase or glutamate and methionine decarboxylase activities. CONCLUSION: The presence of amino acid converting enzymes in lactobacilli is strain specific. SIGNIFICANCE AND IMPACT OF THE STUDY: The findings of this work suggest that lactobacilli can be used as adjuncts for flavour formation in cheese manufacture.     

Characteristics of Sulfite Transport by Chlorella vulgaris

The rate of short-term accumulation of [³⁵S]sulfite in Chlorellavulgaris cells was found to be strongly dependent on the pHof the medium. The rate increased with decreased pH, and theincrease in rate closely paralleled the increase in the concentrationof the un-ionized form of sulfite. When the pH of the mediumwas increased, fast accumulation ceased immediately. The rateof accumulation showed a strong temperature dependence, withan apparent temperature coefficient of 1.93 per 10°C rise,between 10 and 25°C. Because pK_a values of sulfite shiftwith temperature, the rates were corrected by dividing by theconcentration of the un-ionized form of sulfite present at therespective temperatures. The temperature coefficient was thenfound to decrease to 1.45. When cells which had been allowedto accumulate [³⁵S]sulfite for 20 min were transferred to amedium containing no sulfite, more than 50% of the accumulated[³⁵S] was released into the medium in 20 min. Our results arecompatible with a simple diffusion model of SO₂ transport intoChlorella cells. (Received September 26, 1996; Accepted January 20, 1997)     

The Assimilation of Acetate by Chlorella vulgaris

The acetate metabolism of autotrophically grown, acetate-adaptedand acetate-grown cells is compared. All oxidize acetate rapidlyand assimilate about half of the acetate added in short-termexperiments. Kinetic analysis of the incorporation of ¹⁴C-acetatereveals citrate as a primary product of acetate assimilationin all cells in darkness. Malate formed from acetate-I-¹⁴C byacetate-grown cells is asymmetrically labelled in a manner consistentwith a primary incorporation of acetate into malate by a malatesynthase reaction. The chief difference between autotrophic and acetate-grown cellsis the faster rate at which the latter incorporate acetate carboninto compounds outside the tricarboxylic acid cycle. In particular,incorporation into protein and carbohydrate is much faster inacetate-grown cells and it is suggested that enzymes catalysingreactions leading away from the tricarboxylic acid cycle mayincrease in activity in acetate-grown cells. Light greatly stimulates acetate incorporation into lipide andalso increases the synthesis of protein and carbohydrate.     

Differentiation of Lactobacillus casei, Lactobacillus paracasei and Lactobacillus rhamnosus by polymerase chain reaction

Lactobacillus casei, Lact. paracasei and Lact. rhamnosus form a closely related taxonomic group within the heterofermentative lactobacilli. These three species are difficult to differentiate using traditional fermentation profiles. We have developed polymerase chain reaction primers which are specific for each of these species based on differences in the V1 region of the 16S rRNA gene. Sixty-three Lactobacillus isolates from cheese were identified using these primers. The 12 Lact. rhamnosus and 51 Lact. paracasei identified in this way were also differentiated using a randomly amplified polymorphic DNA (RAPD) primer.     

Metabolism of 5-methyltetrahydrofolate by Lactobacillus casei.

The metabolism of 5-[Me-14 C]methyltetrahydrofolate in Lactobacillus casei proceeded oxidatively with incorporation of label into purine and thymidylate derivatives. No labelled methionine was formed. (l)-5-Methyltetrahydrofolate, the natural isomer, was not a substrate for the L. casei folylpoly-gamma-glutamate synthetase although the unnatural (d)-isomer was slowly metabolized to the diglutamate form.