Fatty acid patterns of phospholipids and lipopolysaccharides in the characterisation of microbial communities in soil: a review

 This review discusses the analysis of whole-community phospholipid fatty acid (PLFA) profiles and the composition of lipopolysaccharides in order to assess the microbial biomass and the community structure in soils. For the determination of soil microbial biomass a good correlation was obtained between the total amount of PLFAs and the microbial biomass measured with methods commonly used for determinations such as total adenylate content and substrate-induced respiration. Generally, after the application of multivariate statistical analyses, whole-community fatty acid profiles indicate which communities are similar or different. However, in most cases, the organisms accounting for similarity or difference cannot be determined, and therefore artefacts could not be excluded. The fatty acids used to determine the biomass vary from those which determine the community structure. Specific attention has to be paid when choosing extraction methods in order to avoid the liberation of fatty acids from non-living organic material and deposits, and to exclude the non-target selection of lipids from living organisms, as well. By excluding the fatty acids which were presumed to be common and widespread prior to multivariate statistical analysis, estimates were improved considerably. Results from principal component analysis showed that determining the levels of fatty acids present in both low and high concentrations is essential in order to correctly identify microorganisms and accurately classify them into taxonomically defined groups. The PLFA technique has been used to elucidate different strategies employed by microorganisms to adapt to changed environmental conditions under wide ranges of soil types, management practices, climatic origins and different perturbations. It has been proposed that the classification of PLFAs into a number of chemically different subgroups should simplify the evaluating procedure and improve the assessment of soil microbial communities, since then only the subgroups assumed to be involved in key processes would be investigated. Received: 24 August 1998     

Effects of dietary medium-chain triacylglycerols (tricaprylin and tricaproin) and phospholipid supply on survival, growth and lipid metabolism in common carp (Cyprinus carpio L.) larvae

The present study investigated the interaction of dietary medium-chain fatty acids (MCFA) and phospholipids (PL) on survival, growth and lipid metabolism in common carp larvae. Nine diets based on casein and dextrin and with a variable lipid part were tested in triplicate for 22 days post first feeding. The 3×3 design consisted of three triacylglycerols (3% of diet) combined with three different lipid supplements. Tested triacylglycerols were triolein (TOL), tricaprylin (TC8) and tricaproin (TC6), and lipid supplements were 2% soybean oil (low-fat diets without PL), 2% soybean lecithin (low-fat diets with 2% PL) or both 2% soybean lecithin and 6% TOL (high-fat diets with 2% PL).

In the first step, both TC6 and TC8 resulted in improved survival and growth rates compared to TOL, irrespective of the PL supply. In the second step, TC8 decreased survival and growth rates, whereas the difference between TC6 and TOL became less. Histological signs of impaired intestinal absorption of neutral lipids were evidenced in larvae fed TOL without PL and also in high-fat diets with 2% PL. The latter diets also resulted in poorer growth rates compared to low-fat diets with 2% PL. These results suggest that the quantitative PL requirement of larvae increases as the dietary level of long-chain triacylglycerols increases. Larvae fed TC6 or TC8 showed enlarged liver and hepatocyte volume and a decreased level of body neutral lipids. Based on β-hydroxybutyrate (β-HBA) measurements in whole larvae, TC8 was found to be more ketogenic than TC6. TC6 and TC8 affected differently the fatty acid profile of larval body neutral lipids. TC6 did not induce the appearance of MCFA, whereas TC8 feeding resulted in a low level of 8:0 and relatively high levels of 10:0 (3.8% of total fatty acids). Neither 8:0 nor 10:0 were found in larval polar lipids.

This study confirmed the essentiality of PL in common carp larval diets and underlines differences in the utilization of TC6 and TC8, which both initially stimulate growth during the first week, but only temporarily in the case of TC8.     

饲料磷脂对仔稚鱼营养生理的研究进展

近年来,磷脂(Phospholipids,PL)在仔稚鱼营养生理所发挥的作用引起人们广泛重视。综述了近年来饲料磷脂对仔稚鱼生长表现、消化道、骨骼发育以及脂肪代谢等方面的影响,以期为磷脂在水产苗种饲料中合理添加与应用提供理论参考。     

Determination of phospholipid- and lipopolysaccharide-derived fatty acids as an estimate of microbial biomass and community structures in soils

Several soils subject to different cultivation and management practices were examined by analysis of fatty acid profiles derived from phospholipids and lipopolysaccharides, using an improved sequential method which is capable of measuring ester-linked and non-ester-linked phospholipid fatty acids (EL-PLFA, NEL-PLFA, respectively) and the hydroxy fatty acids in lipopolysaccharides. A good correlation was obtained (r>0.90) between the soil biomass and total EL-PLFA in the soils investigated, which ranged from forest soils to a variety of agricultural soils. Elucidation of the composition of the community structure was an additional task. Eukaryotes can be differentiated from bacteria by the presence of polyunsaturated and -hydroxy fatty acids, both of which were much more abundant in the OF layer of the forest soil than in the remaining samples. A relatively low proportion of monomethyl branched-chain saturated fatty acids was obtained in the forest OF horizon, these being indicators for Gram-positive bacteria and actinomycetes. Various subclasses of proteobacteria produce and mid-chain hydroxy fatty acids, which occur primarily in agricultural soils. The ratios between monounsaturated fatty acids and saturated fatty acids seem to be very useful parameters of soil environmental conditions. In addition, on the basis of the differences in composition of the NEL-PLFA and hydroxy fatty acids of lipopolysaccharides, clear indications for the community structure of various soils were obtained. In the forest soils much more abundant anaerobic micro-organisms and relatively less abundant proteobacteria were present than in the other soils. In the cultivated soils, however, the proportion of Gram-negative bacteria was considerably higher. Furthermore, eukaryotes appeared to be pre-dominant in the soils once used for a manure deposit site.     

钠基蒙脱石对菜籽油中磷脂的吸附行为研究

为了解钠基蒙脱石（sodium montmorillonite, Na-MMT）在油脂脱胶过程中的吸附行为以及吸附机理,采用钠化方法将钙基蒙脱石制备成Na-MMT,并对其进行X射线衍射和热重分析;利用Na-MMT对菜籽油中的磷脂（phospholipids, PL）进行吸附,探讨PL在Na-MMT上的静态吸附平衡、吸附动力学和吸附热力学。结果表明,Na-MMT对PL的最大理论吸附量为833.3mg/g;Na-MMT对PL的吸附是属于优惠吸附,吸热且自发进行。Freundlich吸附模型能够较好地拟合其静态吸附行为;同时拟二级吸附动力学模型适用于描述Na-MMT吸附PL的动力学特性。 [     

Phospholipids and wheat gluten blends: interaction and kinetics

A model system comprising of lysophosphatidylcholine (LPC) and isolated gluten were used help understand the positive effect of PL on bread-loaf volume. The kinetics of the effect of gluten on the thermal properties of LPC were determined using DSC. Blends of PL and 3, 6, and 10% gluten were heated from 0 to 70 °C at rates between 3 and 19 °C/min and cooled to 0 °C. The onset and peak temperatures and ΔH were recorded. The peak temperature was used to calculate the activation energy (E_a) and Z value. The transition for pure LPC vesicle formation was detectable by DSC in the presence of gluten. Gluten increased the activation energy of LPC during vesicle formation and disruption. The increase in gluten content from 3 to 6% and then to 10% had a slight effect on the activation energy value of LPC during vesicle disruption, whereas during formation a steady increase was noticed with higher gluten additions. Overall, the ΔH of the blends showed a decrease at higher heating rate. The change in the PL activation energy in the presence of gluten is indicative of a form of interaction.     

卵黄和低密度脂蛋白对冷冻保存绵羊精子胆固醇、磷脂含量的影响

为了探索绵羊冷冻精液受精率低的原因,在稀释液中用低密度脂蛋白代替卵黄冷冻绵羊精液,研究LDL对冷冻中精子脂类含量的影响。结果表明,以卵黄稀释液冷冻精液,精子胆固醇含量从鲜精的234．54nmol／10^9降低到163．76nmol／10^9精子,胆固醇与磷脂的比值（c／p）从0．54下降到0．36;以9g／100mL LDL代替卵黄,冷冻后胆固醇含量为243．73nmol／10^9精子,c／p值保持在0．50。研究得出在卵黄稀释液中冷冻绵羊精液,精子胆固醇流失,c／p值下降;以LDL代替卵黄,可有效保护精子胆固醇,避免流失,维持了精子c／p值。     

Effect of endotoxin on phospholipids of hepatic mitochondria membrane and cation A antagonism in rabbits

AIM: To investigate the effect of endotoxin on phospholipid of hepatic mitochondria membrane (MiM) and cation A (CA) antagonism in the model of endotoxemia in rabbits. METHODS: Forty-eight healthy Japanese big-ear rabbits were randomly divided into 3 groups: the normal control (groupⅠ), endotoxin treatment group (groupⅡ) and cation A and endotoxin treatment group (group Ⅲ). The contents of phosphatidylcholine (PC), phosphatidylethanolamin (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) in MiM of three groups were measured at the 3rd or 7th hour after corresponding treatment. RESULTS: The contents of the four phospholipids in groupⅡ were lower than those in groupⅠ during the experiment (P<0.01). A significant increase in the contents of four phospholipids in group Ⅲ was observed as compared to group Ⅱ (P<0.05, P<0.01). CONCLUSION: Endotoxin decreases the major membrane phospholipids in MiM, whereas CA has a prominent protective effect on injuries by endotoxin in MiM and provides a valuable evidence for the use of some drugs of endotoxin antagonist.     

新大豆及储存受害大豆的毛油中磷脂成分研究

大豆在储运中因温度和温度过高而受损害后,磷脂组份发生较大的化学变化,色谱分析表明,不可皂化部分（主要是甾醇）和ＰＡ含量增加,而主要磷脂成份ＰＥ、ＰＩ、ＰＣ含量减少。胺损害大豆毛油水化脱胶困难及脱胶后油中磷含量偏高均与磷脂组份发生化学变化有关。     

Lipid nutrition of juvenile Litopenaeus vannamei II. Active components of soybean lecithin

Two experiments were conducted to investigate the active components of soybean lecithin for juvenile Litopenaeus vannamei. The first experiment was conducted to determine the dietary phosphatidylcholine (PC) requirement of juvenile L. vannamei, and to investigate whether other phospholipids (PL), mainly phosphatidylethanolamine (PE) and phosphatidylinositol (PI) were the active fractions of soybean lecithin. Seven levels of PC (0%, 0.35%, 0.7%, 1.4%, 2.1%, 2.8%, 4.2%) extracted from soybean lecithin (PC purity 93%) were used to determine the PC requirement; also, PE and PI (in a 25:22 proportion) were tested at 0.84% and 1.68% levels with PC levels controlled at 0.35% and 0.52% of diet to investigate the combined PE and PI effects. Results showed that no dietary PC requirement was evident based on shrimp growth and survival. Increasing purified PC in the diet decreased total lipid, free fatty acid and other PL levels in shrimp hepatopancreas (mid-gut gland) and increased PC level in shrimp muscle. However, other PL, mainly PE and PI, showed significant enhancing effects on shrimp growth when PC was provided at 0.35% or 0.52% of diet.

Another 4×2 factorial experiment was concluded to reevaluate the requirement of shrimp for PC by including purified PC at 0%, 0.7%, 1.4 % and 2.8% of diet with or without 0.1% cholesterol in the diet. A diet containing 1.4% PC provided by deoiled lecithin also was tested for comparison. Results showed no interaction between PC and cholesterol on shrimp growth, survival and feed conversion ratio (FCR). Compared with the apparent growth-enhancing effect of dietary cholesterol, the effect of purified PC was negligible. With PC at 1.4% of diet, the presence of other PL from lecithin or 0.1% cholesterol significantly enhanced shrimp growth and FCR.

In summary, purified soybean PC showed different effects from deoiled lecithin on shrimp growth, lipid composition, and relationship with dietary cholesterol. Beneficial effects of soybean lecithin on growth of L. vannamei could be attributed to the presence of PL other than PC in the diet under the experimental conditions of this study.