Dot assay for determining adhesive interactions between yeasts and bacteria under controlled hydrodynamic conditions

Candida belongs to the normal human microflora and are found adhering to a number of human body tissues as well as to a variety of biomaterials implants. Often, yeasts adhere in association with bacteria, but to date there is no definitive assay to investigate adhesive interactions between yeasts and bacteria adhering on surfaces. Although we recently described the use of a parallel plate flow chamber to this purpose [Millsap, K.W., Bos, R., Van der Mei, H.C., Busscher, H.J., 1998. Adhesive interactions between medically important yeasts and bacteria. FEMS Microbiol. Rev. 21, 321–336], the method was slow and evaluation of a large number of strains showed major biological variation between experiments. Here, we describe a new assay for the simultaneous determination of the adhesive interactions between yeasts and different bacterial strains on a surface under controlled hydrodynamic conditions. On an acrylic surface, the presence of adhering bacteria suppressed adhesion of Candida albicans ATCC 10261 to various degrees, depending on the bacterial strain involved. Suppression of C. albicans ATCC 10261 adhesion was strongest by Actinomyces naeslundii T14V-J1, while adhering Streptococcus gordonii NCTC 7869 caused the weakest suppression of yeast adhesion. When adhering yeasts and bacteria were challenged with the high detachment force of a passing liquid–air interface, the majority of the yeasts detached, while C. albicans adhering on the control, bare polymethylmethacrylate surface formed aggregates. Summarizing, this study presents a new method to determine suggested adhesive interactions between yeasts and adhering bacteria under controlled hydrodynamic conditions. However, the results seem to indicate that these adhesive interactions may well not exist, but that instead different bacterial strains have varying abilities to discourage yeast adhesion.     

Bioconversion of biodiesel refinery waste in the bioemulsifier by Trichosporon mycotoxinivorans CLA2

ABSTRACT: BACKGROUND: The microbial bioemulsifiers was surface active compounds, are more effective in stabilizing oil-in-water emulsions. The yeasts have been isolated to produce bioemulsifiers from vegetable oils and industrial wastes. RESULTS: Trichosporon mycotoxinivorans CLA2 is bioemulsifier-producing yeast strain isolated from effluents of the dairy industry, with ability to emulsify different hydrophobic substrates. Bioemulsifier production (mg/L) and the emulsifying activity (E24) of this strain were optimized by response surface methodology using mineral minimal medium containing refinery waste as the carbon source, which consisted of diatomaceous earth impregnated with esters from filters used in biodiesel purification. The highest bioemulsifier production occurred in mineral minimal medium containing 75 g/L biodiesel residue and 5 g/L ammonium sulfate. The highest emulsifying activity was obtained in medium containing 58 g/L biodiesel refinery residue and 4.6 g/L ammonium sulfate, and under these conditions, the model estimated an emulsifying activity of 85%. Gas chromatography and mass spectrometry analysis suggested a bioemulsifier molecule consisting of monosaccharides, predominantly xylose and mannose, and a long chain aliphatic groups composed of octadecanoic acid and hexadecanoic acid at concentrations of 48.01% and 43.16%, respectively. The carbohydrate composition as determined by GC-MS of their alditol acetate derivatives showed a larger ratio of xylose (49.27%), mannose (39.91%), and glucose (10.81%). 1 H NMR spectra confirmed by COSY suggested high molecular weight, polymeric pattern, presence of monosaccharide's and long chain aliphatic groups in the bioemulsifier molecule. CONCLUSIONS: The biodiesel residue is an economical substrate, therefore seems to be very promising for the low-cost production of active emulsifiers in the emulsification of aromatics, aliphatic hydrocarbons, and kerosene.     

Bacterial Indigo Reduction

We have examined bacterial indigo reduction to provide a basis for the development of a sustainable alternative to the present chemical methods used to reduce indigo for denim dyeing. Indigo was reduced by Clostridium isatidis, but not by the related Clostridium aurantibutyricum, Clostridium celatum nor Clostridium papyrosolvens. However C. papyrosolvens could, like C. isatidis, reduce the soluble dye, indigo carmine. Of the bacteria examined only the supernatant from C. isatidis cultures decreased indigo particle size. An anthraquinone-rich madder root extract, the soluble anthraquinone-2,6-disulfonic acid and humic acid all stimulated the reduction of indigo by C. isatidis, without affecting the redox potential of the cultures. C. isatidis cultures generated redox potentials from -476 to -602 mV vs SCE, which were about 100 mV more negative than those of the other bacteria examined. The mechanism of bacterial indigo reduction remains unknown, but the unique features of the indigo-reducing C. isatidis indicate possible mechanisms.     

Adenine nucleotide translocation in yeast mitochondria. Effect of inhibitors of mitochondrial biogenesis on the ADP translocase

1. Optimal test conditions for adenine nucleotide translocation in Candida utilis mitochondria are a standard medium, consisting of 0.63 M mannitol, 2 mM EDTA (or ethylene glycol tetraacetic acid, EGTA), 10 mM morpholinopropane sulfonic acid (pH 6.8), and a temperature of 0 °C.

2. Adenine nucleotide translocation in C. utilis mitochondria is an exchange-diffusion process. The whole pool of internal adenine nucleotides is exchangeable, ADP being the most readily exchangeable nucleotide. The rate of mitochondrial ADP exchange, but not the K_m value, depends on growth conditions. At 0 °C, the rate is about 3 to 4 nmoles ADP/min per mg protein for mitochondria obtained from yeast grown in the presence of 1.5% glucose; it rises to 11.5 nmoles when glucose is replaced by 3% ethanol in the growth medium. The K_m value for ADP is 2 μM. The Q₁₀ is about 2 between 0 and 20 °C. Among other exchangeable adenine nucleotides are ATP, dADP and the methylene and the hypophosphate analogues of ADP. Unlike mammalian mitochondria, C. utilis mitochondria are able to transport external UDP by a carboxyatractyloside-sensitive process.

3. Under conditions of oxidative phosphorylation (phosphate and substrate present in an aerated medium), added ADP is exchanged with internal ATP. A higher ATP/ADP ratio was found in the extramitochondrial space than in the intramito-chondrial space. The difference between the calculated phosphate potentials in the two spaces was 0.9–1.7 kcal/mole.

4. Atractyloside, carboxyatractyloside, bongkrekic acid and palmityl-CoA inhibit mitochondrial adenine nucleotide translocation in C. utilis as they do in mammalian mitochondria, but 2 to 4 times less efficiently. The inhibition due to atractyloside or palmityl-CoA is competitive with respect to ADP whereas that due to bongkrekic acid and carboxyatractyloside is non-competitive. Carboxyatractyloside and atractyloside inhibitions are additive. The apparent K_d for the binding of [³⁵S]-carboxyatractyloside and [¹⁴C]bongkrekic acid is 10–15 nM and the concentration of sites 0.4–0.6 nmole/mg protein in both cases. [³⁵S]Carboxyatractyloside binding is competitively displaced by atractyloside and vice versa.

5. Binding of [¹⁴C]ADP has been carried out with mitochondria depleted of their endogenous adenine nucleotides by incubation with phosphate and Mg²⁺ at 20 °C. The amount of bound [¹⁴C]ADP which is atractyloside removable is 0.08–0.16 nmole/mg protein.

6. The rate of ADP transport is quite different in mitochondria isolated from C. utilis, according to whether it is grown on glucose, or on ethanol or in the presence of chloramphenicol; for instance, it decreases by 10 times when 3% ethanol in the growth medium is replaced by 10% glucose and by 5 times when chloramphenicol is added to the medium. These variations are accompanied by parallel variations in cytochrome aa₃. The number of atractyloside-sensitive ADP binding sites is not modified by the above conditions of culture, nor the number of [³⁵S]carboxyatractyloside binding sites. The affinity for ADP is apparently not significantly modified, nor the size of the endogenous adenine nucleotide pool. In contrast to glucose repression or chloramphenicol inhibition, semi-anaerobiosis in C. utilis lowers significantly the mitochondrial binding capacity for carboxyatractyloside. Strict anaerobiosis in S. cerevisiae results in a practical loss of the cytochrome oxidase activity, and also of the carboxyatractyloside and ADP binding capacity. Transition from anaerobiosis to aerobiosis restores the cytochrome oxidase activity and the ADP and carboxyatractyloside binding capacities.     

Impact of sixteen chemical pesticides on conidial germination of two entomophthoralean fungi: Conidiobolus thromboides and Pandora nouryi

Effects of sixteen chemical pesticides on conidial germination of C. thromboides and P. nouryi were investigated at two concentrations (R and 0.2R, where R=the lowest manufacture's recommended concentration for field use). Of the fungicides tested, propamocarb hydrochloride did not significantly affect conidial germination of C. thromboides, but at R it completely inhibited conidial germination of P. nouryi. At 0.2R of procymidone, iprodione, haloxyfop-methyl and fenoxaprop-p-ethyl, conidia of C. thromboides had some germination after 24 h, although they entirely restricted conidial germination of the fungus at the concentration of R. Tribenuron-methyl, one herbicide, had no adverse effect on conidial germination of C. thromboides and P. nouryi after 6 h at the two concentrations, whereas the other seven herbicides were strongly antagonistic to P. nouryi, except for carfentrazone-ethyl at 0.2R.     

Production of a peptidoglycolipid bioemulsifier by Pseudomonas aeruginosa grown on hydrocarbon

A strain of Pseudomonas aeruginosa isolated from a polluted soil was found to produce an extracellular bioemulsifier when cultivated on hexadecane as sole carbon source. The emulsifier was precipitated with acetone and redissolved in sterile water. Dodecane, crude oil and kerosene were found to be good substrates for emulsification by the bioemulsifier. Growth and bioemulsifier production reached the optimal levels on the fourth and fifth day, respectively. Emulsifying activity was observed over a pH range of 3.5 to 10.0 with a maximum at pH 7.0. The activity of the bioemulsifier was heat stable up to 70 degrees C while about 50 percent of its activity was retained at 100 degrees C. The components of the bioemulsifier were determined, it was found to contain carbohydrate, protein and lipid. The protein complex was precipitated with ammonium sulphate and fractionated on a Sephadex G-100. Gel electrophoresis of the bioemulsifier showed a single band whose molecular weight was estimated as 14,322 Da. The bioemulsifier was classified as a peptidoglycolipid. Certain strains of P. aeruginosa produce peptidoglycolipid in place of rhamnolipid.     

海南岛不同林龄木麻黄凋落物内外细菌多样性及其化感潜力

凋落物在生态系统中具有重要作用。为了对比凋落物内外微生物的多样性和群落结构,选取海南省海口市桂林洋海滨区3个林龄木麻黄凋落物为研究对象,采用Illumina Miseq高通量测序,对凋落物内外微生物的多样性和组成进行分析。结果表明: 凋落物外生细菌的多样性高于内生细菌,中龄林凋落物内外细菌多样性和丰富度均最高,其次是幼龄林,成熟林最低。菌群群落组成分析表明: 在门分类水平上,变形菌门和放线菌门最为丰富(约占总数的80%);属水平上,短小杆菌属、Jatrophihabitans、分支杆菌属、放线孢菌属、Mucilaginibacter、假单孢菌属等在不同林龄间表现出显著差异。主坐标分析(PCoA)表明,凋落物内生细菌受林龄的影响较大,而外生细菌受环境因子的影响较大;解淀粉芽孢杆菌发酵液对木麻黄种子化感潜力最强,且其中含有2,2′-亚甲基双-(4-甲基-6-叔丁基苯酚)等化感物质,表明解淀粉芽孢杆菌参与了化感物质的合成。凋落物微生物群落多样性对木麻黄的化感作用有一定影响,这为探讨微生物在木麻黄凋落物降解过程中作用的研究奠定基础。     

蛹虫草线粒体基因型快速检测体系的构建及线粒体遗传稳定性的初步研究

本研究的目的是建立一种快速确定蛹虫草菌株线粒体基因型的技术体系,并探讨蛹虫草连续传代培养后线粒体的遗传稳定性。从已知线粒体基因组的蛹虫草菌株中扩增线粒体内含子位点,将扩增产物混合并制作出两套DNA分子量标准,即在8个内含子位点分别具有内含子的8条扩增条带组成的M-I和在6个内含子位点分别缺失内含子的6条扩增条带组成的M-II。从待检测的蛹虫草菌株（包括3个已知和2个未知线粒体基因组的菌株）中扩增同样的（假定）内含子位点,然后通过琼脂糖凝胶电泳分别与制备好的两个DNA分子量标准进行比较,能够准确判断蛹虫草菌株的线粒体内含子分布模式,从而验证了所构建的线粒体基因型快速检测体系的有效性。选择10个蛹虫草组织分离菌株和8个单分生孢子菌株连续转接培养15代,没有发现线粒体内含子分布模式发生改变。本研究成功构建了快速检测蛹虫草线粒体基因型的技术体系,并发现蛹虫草线粒体具有很高的遗传稳定性,为开展蛹虫草线粒体遗传规律的研究奠定了基础。     

Estimation of soluble β-glucan content of yeast cell wall by the sensitivity to Glucanex 200G treatment

The soluble β-glucan contents in the cell wall of yeasts were estimated by treating cells with Glucanex^® 200G that contained mainly β1,3-glucanase and some β1,6-glucanase. The sensitivity of cell walls of 11 yeasts to various concentrations of β-glucanase was compared. The yeasts that are resistant to β-glucanase treatment are expected to contain higher β-glucan content and those that are sensitive to the β-glucanase treatment are expected to contain lower β-glucan content. Two yeast strains were selected for further study by comparing the sensitivity of cell wall to β-glucanase; Candida bombicola and Candida albicans. Candida bombicola was more resistant and C. albicans was more sensitive to the Glucanex^® 200G treatment. The results of enzyme sensitivity tests were verified by quantification of soluble β-glucan content purified from the yeasts. Much larger amount of soluble β-glucan was obtained from the cell walls of C. bombicola (0.08 g g⁻¹ dried cell) than C. albicans (0.025 g g⁻¹ dried cell).     

西藏马鹿与同域野生有蹄类、家畜草青期食性比较

西藏马鹿为我国特有种,曾一度被认定为野外灭绝。在其生境中有多种食性相近的野生有蹄类及家畜同域分布,探究青藏高原特殊环境下西藏马鹿与这些有蹄类的食物资源种间竞争与共存关系十分必要。2013年和2014年8—9月,采用粪便显微分析法确定了桑日县西藏马鹿自然保护区西藏马鹿、白唇鹿、藏原羚、牦牛、山羊草青期食物组成,并比较分析了西藏马鹿与同域野生有蹄类、家畜之间的食物重叠和分化状况。结果表明: 西藏马鹿与其他有蹄类具有相似的可食植物种类组成,但所占食谱比例不同。西藏马鹿主要可食植物多为其他有蹄类次要可食植物,其中弱小火绒草为西藏马鹿(在动物食谱中的百分比为11.2%)与牦牛(10.2%)共同的主要食物,西藏柳为西藏马鹿(9.6%)和白唇鹿(11.4%)共同的主要食物。从科级水平来看,豆科植物为西藏马鹿(21.4%)与藏原羚(42.5%)的共同主要可食植物,莎草科植物为白唇鹿(49.2%)、牦牛(33.4%)、山羊(50.3%)的共同主要可食植物。菊科植物作为西藏马鹿(29.6%)的主要可食植物,也是白唇鹿(7.6%)、藏原羚(11.6%)、牦牛(17.3%)和山羊(14.1%)的次要可食植物。禾本科植物作为西藏马鹿(7.1%)次要可食植物,较其他4种有蹄类(白唇鹿13.6%、藏原羚12.3%、牦牛11.5%、山羊16.0%)所占比例低。西藏马鹿与其他有蹄类食物重叠度均高于0.5,与牦牛的重叠度最高(0.65)。西藏马鹿食物多样性指数(1.32)、均匀度指数(0.37)和生态位宽度指数(15.79)均较高。与2007—2008年相比,西藏马鹿食物组成变化较大,豆科植物比例增大,莎草科植物比例降低,食物质量总体有所提高。西藏马鹿与家畜之间存在较高的食物资源竞争,这将进一步影响西藏马鹿的分布范围和生存空间。     

Screening of bioemulsifier-producing micro-organisms isolated from oil-contaminated sites

Eighty-eight micro-organisms were isolated from oil-contaminated soils and checked for their extracellular bioemulsifier producing potential. The micro-organisms were screened on the basis of oil spread, drop collapse and emulsification index. Most efficient strains were characterized as Lysinibacillus sp. SP1025 and Bacillus cereus SP1035. In Lysinibacillus sp. SP1025, the E-24 index, surface tension and production of crude bioemulsifier were found to be 83.3 % with diesel, 34.20?±?0.03 mN/m and 3.07?±?0.62 g/L, respectively, whereas in the case of Bacillus cereus SP1035, the E-24 index, surface tension and production of crude bioemulsifier recorded were 76.5 % with diesel, 43.42?±?0.03 mN/m and 3.90?±?0.3 g/L. Crude biomemulsifier produced by selected micro-organisms was stable, withstanding a wide temperature and pH range with an E-24 Index value greater than 50 %. All emulsions formed were oil-in-water type. Emulsions formed with tested aliphatic and aromatic hydrocarbons, except those formed with ester based oils, were 100 % stable with the entire organic layer converted into emulsion. To the best of our knowledge this is the first report for bioemulsifier production from the genus Lysinibacillus.     

薹草属少花薹草组（莎草科）小坚果形态和微形态及其分类学意义

利用扫描电镜对少花薹草组（Carex sect. Paniceae）27种及4变种（东亚14种4变种,北美13种）小坚果形态与微形态特征进行比较观察。结果表明（：1）所有材料小坚果的形状为倒卵球形和钝三棱状,组内很一致,长度为1.53～3.59 mm,同种不同居群个体差异不显著（P>0.05）。（2）表皮细胞一般为五至七边形,偶有四边形或八边形,丝柄薹草（C. rouyana）不同个体间有变异;垂周璧式样直或微波状;硅质台平,偶有凹或略凸,具1个中心体,C. filipes var. kuzakaiensis和C. filipes var. tremula中偶见2个中心体,无卫星体,这些性状种内稳定。（3）利用表皮细胞形状、硅质台凹凸情况和中心体个数对于区分近似种具有价值,如白马薹草（C. baimaensis）和线柄薹草（C. filipes）,且可以区分一些种下等级,如线柄薹草及其变种var. kuzakaiensis、var. oligostachys和var. tremula。（4）sect. Paniceae s.s.和sect. Laxiflorae小坚果形态和微形态...     

撕裂蜡孔菌在开放体系中对甲基橙染料的静态脱色研究

为了评价撕裂蜡孔菌处理偶氮染料的应用潜力,用性能稳定的甲基橙染料为材料,采用批次试验在开放性体系中研究了染料初始浓度、菌丝生物量、温度、pH等因素对该菌脱色能力的影响,运用菌丝体反接、染液光谱扫描、菌丝体显微观察等方法探讨了菌丝体脱色的可能机制,利用植物萌发试验进行了染料和脱色后溶液的毒性测试。结果表明,撕裂蜡孔菌在开放的静止体系中能够对甲基橙高效脱色,其最适脱色温度为35℃,最佳脱色pH值在6左右。菌丝对甲基橙的脱色表现在吸附和产酶降解两个方面,脱色过程中染料对菌丝体本身的影响较少。植物毒性分析显示撕裂蜡孔菌脱色48h后的产物对植物的毒性比甲基橙本身更强,若要彻底降解可能需要较长时间。本研究可为染料脱色工艺提供新的菌种。     

Variations in chromosome size and organization in Candida albicans and Candida stellatoidea

Candida albicans and the closely related species Candida stellatoidea are medically important diploid asexual yeasts. Clinical isolates frequently show variant electrophoretic karyotypes, apparently due largely to chromosomal translocations. These translocations seem to occur at hot spots characterized by the repeated DNA sequence RSP1. A programmed karyotypic rearrangement occurs in C. stellatoidea. Karyotypic rearrangement may serve as a source of genetic variation in these asexual yeasts.     

Delineation of Chondrus (Gigartinales, Florideophyceae) in China and the origin of C. crispus inferred from molecular data

Complete nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences were obtained for 18 Chondrus populations collected at 15 sites from eight countries worldwide. Pairwise comparisons with the multiple alignment revealed that intraspecific divergences of ITS sequences ranged from 0.3 to 1.8% in C. crispus Stackhouse (except for the entity SVLH from France) and from 0.0 to 0.6% in C. ocellatus Holmes, whereas interspecific divergences in Chondrus varied from 1.4 to 5.0%. Three phylogenetic methods (neighbour joining, maximum parsimony and maximum likelihood) confirmed three main lineages: the North Atlantic lineage containing entities of C. crispus from Canada, France, Germany, England, Portugal, Ireland and Wales; a second lineage comprising three species: C. sp. 1, C. armatus (Harvey) Yamada et Mikami, and C. pinnulatus (Harvey) Okamura from the Northern Pacific; and a third lineage containing just one species: C. ocellatus from the Northern Pacific. Chondrus yendoi Yamada et Mikami separated from other Chondrus species singly. nrDNA ITS data indicate that a previous assignment of C. sp. 2 to Mazzaella japonica (Mikami) Hommersand may be incorrect, and additional evidence is needed to resolve the generic placement of this entity. It is inferred from the nrDNA ITS data that three Chondrus species are presently known in China with two, C. ocellatus and C. nipponicus, in Qingdao and two, C. armatus and C. nipponicus, in Dalian. We hypothesize that the ancestor of North Atlantic C. crispus had a Pacific origin, and that the present distribution of C. crispus in the Atlantic Ocean correlates with a trans-Arctic dispersal and vicariance events associated with Pleistocene glaciation maxima.     

Influence of oxygen on ethanol and xylitol production by xylose fermenting yeasts

The behaviour of Pichia stipitis, Pachysolen tannophilus, Candida shehatae and Candida parapsilosis was investigated to select the most suitable yeast to convert xylose either to ethanol or to xylitol, with little or no formation of by-products. The aeration rate was used as a variable parameter. P. stipitis and C. parapsilosis were the most effective producers or ethanol and xylitol, respectively, both reaching productivities at very low levels of oxygenation. With P. stipitis, better ethanol productivity was attained under microaerobic conditions (K_La = 4·8 h⁻¹) while with C. parapsilosis high yields and rates of xylitol production were detected at K_La values of about 16·3 h⁻¹. P. tannophilus and C. shehatae showed lower performances under all conditions used while changes in oxygenation modified the ratio of ethanol to xylitol produced by these yeasts, suggesting that they are more dependent on the oxygen power input than P. stipitis and C. parapsilosis. The influence of oxygen transfer rates on ethanol and xylitol formation with the best producers is discussed.     

Bioemulsifier production by Streptomyces sp. S22 isolated from garden soil

Out of 45 actinomycetes isolated from garden soil, pond water and air; fifteen showed good emulsification activity. Streptomyces sp. S22 isolated from garden soil produced maximum bioemulsifier with 0.5% (v/v) sunflower oil during stationary phase at 37 degrees C, pH 6 and 250 rev/min. Emulsification activity was maximum (320 EU/ml) with sunflower oil as substrate. Partially purified bioemulsifier from Streptomyces sp. S22 was a peptidoglycolipid containing lipid (51.25%), protein (30%), non-reducing sugar (17.75%) and reducing sugar (1%). The yield of partially purified bioemulsifier was 1.6 g/l and reduced the surface tension of water by 23.09 mN/m. The bioemulsifier produced by Streptomyces sp. S22 was stable at room temperature for seven days.     

风车草(Cyperus alternifolius)人工湿地系统氮去除及氮转化细菌研究

研究了风车草人工湿地污水处理系统TN去除率及氮转化细菌的数量。结果表明:风车草人工湿地对TN的去除率为73.8%,与无植物人工湿地系统相比较,去除率提高了17.4%。风车草人工湿地氨化细菌为7.98×10⁵cfu·g^-1(细砂),硝化细菌为1.95×10⁵MPN·g^-1(细砂),反硝化细菌为5.89×10⁴1.95×10⁴MPN·g^-1(细砂)。与无植物系统氮转化细菌相比,氨化细菌无明显差异,硝化细菌及反硝化细菌均高出1个数量级。     

Evaluation of bioemulsifier mediated Microbial Enhanced Oil Recovery using sand pack column

Bacillus licheniformis K125, isolated from an oil reservoir, produces an effective bioemulsifier. The crude bioemulsifier showed 66% emulsification activity (E(24)) and reduced the surface tension of water from 72 to 34 mN/m. It contains substantial amount of polysaccharide, protein and lipid. This bioemulsifier is pseudoplastic non-Newtonian in nature. It forms oil in water emulsion which remains stable at wide range of pH, temperature and salinity. It gave 43+/-3.3% additional oil recovery upon application to a sand pack column designed to simulate an oil reservoir. This is 13.7% higher than that obtained from crude lipopeptide biosurfactants produced by the standard strain, Bacillus mojavensis JF2 and 8.5% higher than hot water spring isolate, Bacillus licheniformis TT42. The increased oil recovery obtained by using the crude bioemulsifier can be attributed to its combined surface and emulsification activity. Its mechanism of oil recovery must be similar to the mechanism exhibited by surfactant-polymer flooding process of chemical enhanced oil recovery.     

桃小食心虫和梨小食心虫幼虫肠道细菌多样性

为明确桃小食心虫和梨小食心虫幼虫肠道细菌的结构和多样性,本研究利用Illumina HiSeq技术对饲喂金冠苹果的桃小食心虫和梨小食心虫幼虫肠道细菌的16S rRNA V4变异区进行测序与分析.结果表明: 共获得桃小食心虫幼虫肠道细菌229043条reads,聚类为2112个OTUs,注释得到27个门,65个纲,124个目,205个科,281个属;共获得梨小食心虫幼虫肠道细菌240389条reads,聚类为957个OTUs,注释得到22个门,46个纲,89个目,145个科,180个属.桃小食心虫幼虫肠道细菌以变形菌门(87.98%±5.29%)、厚壁菌门(3.91%±1.19%)和放线菌门(1.04%±0.47%)为主;梨小食心虫肠道细菌以变形菌门(50.06%±19.56%)、厚壁菌门(32.02%±8.48%)和蓝细菌门(25.24%±10.28%)为主.两种食心虫在门、纲、目、科、属、种水平上均存在显著差异.从本研究结果看,即使均以苹果为寄主,两种食心虫幼虫肠道细菌结构和多样性也存在显著差异,桃小食心虫幼虫肠道细菌多样性比梨小食心虫丰富,这可能与两者不同的取食特性和消化机制有关.本研究结果为后期揭示肠道微生物与两种食心虫相互作用关系奠定了基础.