Propionate metabolism in a methanogenic enrichment culture. Direct reductive carboxylation and acetogenesis pathways

Abstract Serial dilutions of methanogenic sludges in propionate medium gave a methanogenic non-acetoclastic enrichment degrading 1 mol of propionate to 1.6 mol of acetate and 0.17 mol of methane, with a transient accumulation of butyrate. NMR recordings showed the conversion of [2-¹³C]- and [3-¹³C]-propionate to [3-¹³C]- and [4-¹³C]-butyrate, respectively, thus demonstrating a reductive carboxylation of propionate to butyrate. The labelling found in the accumulated acetate and fermentation balances also suggested that reductive carboxylation was the major pathway involved in propionate conversion to acetate.     

Occurrence of isopropylthio compounds in the aquatic ecosystem (Lake Neusiedl, Austria) as a chemical marker for Microcystis flos-aquae

Abstract Volatile organic sulfur compounds occuring during a bloom of different species of Microcystis in Lake Neusiedl, Austria, were analyzed by gas chromatography and mass spectrometry. In open water diisopropyl disulfide and diisopropyl tri-sulfide were the only sulphur compounds to be found. It was shown that Microcystis flos-aquae was the causative agent for the generation of these sulphur compounds, since high concentrations of these substances were found both in the floating scum of cyanobacteria taken from open lake and in axenic cultures of five isolated strains of M. flos-aquae . Strains isolated from colonies of Microcystis aeruginosa were not able to synthesize isopropylthio compounds. Alternatively, methylthio compounds were released. The rather unusual formation of the isopropylthio group can be used as a chemical marker to differentiate between M. flos-aquae and M. aeruginosa as two separate species which hitherto have been regarded as formae. In a canal passing through the reed belt of Lake Neusiedl where Microcystis was missing, these compounds were not detected. Different sulfur compounds (dimethyl disulfide, dimethyl trisulfide, dibutyl sulfide and bis(methylthio) methane) which in part have not yet been reported for freshwater ecosystems occurred at this site. Their origin, however, remains obscure.     

Dimethyl sulfide metabolism in salt marsh sediments

Abstract Anoxic sediment slurries prepared from Spartina salt marsh soils contained dimethyl sulfide (DMS) at concentrations ranging from 1 to 10 μM. DMS was produced in slurries over the initial 1–24 h incubation. After the initial period of production, DMS decreased to undetectable levels and methane thiol (MSH) was produced. Inhibition of methanogenesis caused a 20% decrease in the rate of DMS consumption, while inhibition of sulfate reduction caused a 80% decrease in DMS consumption. When sulfate reduction and methanogenesis were simultaneously inhibited, DMS did not decrease. DMS contributed about 28% to the methane production rate, while DMS probably contributed only 1% or less to the sulfate reduction rate. Incubation of the sediment slurries under an atmosphere of air resulted in similar DMS consumption compared to anaerobic incubations, but MSH and CH₄ were not evolved.
Sediments from the marsh released significant quantities of DMS when treated with cold alkali, indicating that potentially significant sources of DMS existed in the sediments. Values of base-hydrolyzable DMS as high as 190 μmol per liter of sediment were observed near the sediment surface, and values always decreased with depth in the sediment. Simple flux experiments with small intact sediment cores, showed that DMS was emitted from the marsh surface when cores were injected with glutaraldehyde or molybdate and 2-bromoethanesulfonate (BES), but nit when cores were left uninhibited. These results showed that DMS was readily metabolized by microbes in marsh sediments and that this metabolism may be responsible for reducing the emission of DMS from the marsh surface.     

飞蝗复眼生理和结构上的节律变化

采用细胞内记录和光镜方法研究了飞蝗(Locusta migratoria)夜间和日间在暗适应和明适应状态下小网膜细胞角敏感度以及晶锥和小网膜细胞之间区域结构上的变化.结果表明小网膜细胞角敏感度的变化不仅仅由于晶锥周围主色素细胞色素颗粒的移动,而且也由于小眼感杆束结构上的节律变化.     

棕色固氮菌产生的钼配位化合物——Ⅱ.功能的初步探讨

棕色固氮菌在正常培养过程中所产生的含肽物质,有络合特征峰出现。含肽物质与钼(V)络合的EPR信号g值为1.94。与钼酸盐的络合稳定常数K为2.5×10~9。棕色固氮菌变种UW1(Av1~-,Av2~-),UW38(Av1~-,Av2~ )和UW91(Av1~ ,Av2~-)都能产生类似的含肽物质。培养基中钼的存在是含肽物质产生和分泌所必需的,含肽物质排出的量与培养基中钼的水准呈正相关。不能积累钼的变种UW71在高钼培养基中只能限量地分泌含肽物质。氨培养条件下仍能产生和分泌含肽物质。这种含肽物质与该菌粗提液中的某种成分(除固氮酶组分外)具同源性,它既能从菌体中分泌出来,又能进入菌体,在菌体和培养液之间往返运行,可能在该菌钼酸盐运输中起载体作用。     

Catalysis by heteropentalenes of electron transfer to oxygen from ferredoxin-NADP oxidoreductase reduced by NADPH

A range of heteropentalene and bipyridinium compounds have been tested as catalysts of electron transfer to oxygen from spinach ferredoxin-NADP⁺ oxidoreductase reduced by NADPH. For a particular class of compound, the rate of oxygen reduction increased with increasing midpoint potential of the compound under conditions in which reduction of the compound was rate-limiting. Compounds with similar midpoint potentials from different structural classes showed marked differences in rate, attributed to specificity in the interaction with ferredoxin-NADP⁺ oxidoreductase.     

Membrane turnover in crab photoreceptors studied by high-resolution scanning electron microscopy and by a new technique of thick-section transmission electron microscopy

Summary Crab photoreceptors were examined after treatment by the osmium-DMSO-osmium method for high-resolution scanning electron microscopy. This technique of specimen preparation was also adapted for transmission electron microscopy, enabling sections up to 1 urn thick to be viewed in a conventional microscope at 75 kV. With appropriate pretreatment, some cytoskeletal elements can be visualised by both techniques. The methods were then used to investigate some of the daily changes known to occur in photoreceptor cell structure. Striking differences were found in the structure of Golgi bodies present in retinula cells during the synthesis and breakdown phases of the daily cycle of photoreceptor membrane turnover. Cyclic changes were also noticed in the mitochondria of retinula cells, and additional evidence was found for a previously proposed model of rhabdomeral microvillus formation.     

Stereoisomeric flavour compounds XXXV: Chiral aroma compounds of sherry I. Optically pure stereoisomers of solerone and solerole

The enantioseparation of the sherry aroma components 5-oxo-4-hydroxyhexanoic acid γ-lactone (solerone) and 4,5-dihydroxyhexanoic acid γ-lactone (solerole) is achieved, using Chiraspher (Merck) as the chiral HPLC phase and the optical purity ascertained directly by HRGC with heptakis(3-O-acetyl-2,6-di-O-pentyl)-β-cyclodextrin (Lipodex D) as the chiral stationary phase. The absolute configurations of 4,5-dihydroxyhexanoic acid γ-lactones are assigned by ¹H-NMR spectral data of diastereomeric α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) esters, according to Mosher's model. Sensory qualities of the isomers are given.     

夜蛾复眼转化速度与光暗适应的时间关系

夜行蛾类的复眼,随光、暗适应时间而逐步转化,这种转化是可逆的.以屏蔽色素分布范围的大小为指标来判断复眼的转化速度得以下结果:1.从亮眼到暗眼:亮眼进入暗适应后其屏蔽色素随暗适应时间的增加而逐步向远心端方向集中.屏蔽色素的移动是减速进行的.暗适应开始后的前3分钟,每分钟移动百分率为10.7,当暗到10—15分钟时每分钟移动百分率为4.6,再暗到60—150分钟时每分钟移动百分率为0.7.屏蔽色素移动的速度个体间差异较大,完成全过程大多数个体需150分钟,少数个体只需60分钟,另有个别个体经过270分钟暗适应仍尚未完成全过程.2.从暗眼到亮眼:暗眼受光后,其屏蔽色素随光适应时间的增加而向近心端方向扩散,色素移动速度随时间的增加而减缓.转化全过程约需60分钟.     

A telescopic method for photographing within 8×8 cm minirhizotrons

The volatile organic compounds produced during a sequence of soil incubations under controlled conditions, with either added NH₄ ⁺-N or NO₃ ^--N, were collected and identified. The nature and relative amounts of the volatile organic compounds produced by the microorganisms in the soils were remarkably reproducible and consistent.