DNA Throughout the Single Mitochondrion of a Kinetoplastid Flagellate: Observations on the Ultrastructure of Cryptobia vaginalis (Hesse, 1910)

SYNOPSIS. Cryptobia vaginalis (Hesse 1910) occurs as long thin and short broad forms in the vagina of the gnathobdelliform leeches Haemopis sanguisuga (Linnaeus) and Hirudo medicinalis Linnaeus. Cytochemical staining for DNA and transmission electron microscopy of sectioned material indicate that in the thin forms the kinetoplast DNA (kDNA) is dispersed irregularly through the mitochondrial network ( pankinetoplastic condition) rather than concentrated in the adbasal region of the mitochondrion ( eukinetoplastic condition) as in trypanosomatids and most other kinetoplastid flagellates. Light-microscopic studies on the rare broad forms, however, suggest that these have conventional adbasal location of the kinetoplast. Binary fission appears to occur in the thin forms, suggesting that the dispersed kinetoplast is either highly polyenergid or lacks a genetic function. In other features of its microanatomy, C. vaginalis is a conventional kinetoplastid. The flagellate has an incomplete corset of pellicular microtubules which may have a role in the cortical contractility characteristic of the genus Cryptobia . Feeding is by pinocytosis of vaginal colloids through a microtubule-lined cytopharynx, possibly after binding to a prominent filament-coated preoral ridge. A pulsatile (contractile) vacuole is present and appears to be responsible for defecation as well as osmoregulation. Some individuals have elongate bacterial epibionts attached to the body in parallel with the cortical microtubules. All individuals have 2–8 spheroplast-like endobiotic bacteria in the prenuclear cytoplasm.     

Electrophoretic protein patterns of Geotrichum and its teleomorphs

Total patterns of water-soluble proteins of 35 strains (7 species) of Galactomyces and Dipodascus strains with their respective Geotrichum anamorphs are compared. Quantitative differences among a number of species are found with iso-electric focusing; bands that characterize species are selected. Qualitative differences are found between the teleomorph genera.     

Yeast-like symbiotes as a sterol source in anobiid beetles (Coleoptera,Anobiidae): possible metabolic pathways from fungal sterols to 7-dehydrocholesterol

Insects are unable to synthesize sterols and require exogenous sterol sources for their normal development and reproduction. A few exceptions are insects associated with symbiotic yeasts or fungi. We analyzed sterols by GC-MS in two anobiid beetles (Lasioderma serricorne and Stegobium paniceum), their intracellular yeast-like symbiotes (YLS), and their diets in order to clarify the sterols synthesized by YLS and the metabolic pathways of the sterols in the beetles. Several C(27), C2(8), and C(29) saturated and unsaturated sterols were identified; the predominant sterols were cholesterol and 7-dehydrocholesterol in the anobiid beetles and ergosterol in the YLS. Most sterols detected in YLS were those known in the late pathway of the ergosterol biosynthesis in yeasts and most of the sterols in the beetles appear to be intermediate metabolites from YLS sterols to 7-dehydrocholesterol. The anobiid beetles appear to use ergosterol and 5-dihydroergosterol as sources for 7-dehydrocholesterol.     

耐辐射的产黑色素酵母状真菌

从1945年7月美国第一次核试验至今,全世界已进行了几千次的核试验,对周边环境造成了不同程度的污染,对人类及其生存环境造成了极大危害。而耐辐射微生物因其惊人的耐辐射能力,以及特殊的生命现象和生理机制,使其不仅成为研究生命起源、物种进化等理论科学的重要材料,而且也在环境工程、人类健康、生物技术等方面具有极大的应用前景,从而成为世界各国竞相发掘的重要资源。     

褐飞虱体内酵母类共生菌的形态观察

试验采用冷冻切片技术结合显微摄像系统观察研究了褐飞虱雌成虫体内酵母类共生菌的形态特性和在寄主虫体内的存在状态.光学显微镜观察证实,褐飞虱雌成虫的头部和胸部均未观察到共生菌,在其腹部脂肪体中却发现大量酵母类共生菌的存在,且有大量的菌胞出现.菌胞已经成为褐飞虱特有的细胞器,其发育可划分为发育初期、共生菌增殖适应期、对数增殖期(高峰期)、释放期和衰竭期5个阶段.按照形态划分,褐飞虱体内的酵母类共生菌有4大类型,即长梭形、杆状、卵形和球状.其中,长梭形和杆状个体最多、占绝大多数,卵形和球状个体很少见.此外,还发现具假膈梭形和不规则共生菌的存在.同时观察到该类共生菌通过多边芽殖进行无性繁殖,且以顶端芽殖(包括两端芽殖)为主.     

三种稻飞虱成虫体内酵母类共生菌的形态差异

试验采用冷冻切片技术结合显微摄像系统观察法研究了酵母类共生菌在3种稻飞虱成虫体内的存在状态、形态特性以及种类和组成.光学显微镜观察证实,3种稻飞虱成虫的头部和胸部均未观察到共生菌,在其腹部脂肪体中有大量酵母类共生菌,且以出芽进行无性繁殖,并伴有菌胞的出现.3种稻飞虱成虫体内共生菌的形态和组成明显不同.其中,褐飞虱体内的共生菌个体较大,以梭形、杆状和卵形为主,分别占共生菌总数的30.7%、53.5%和15.1%;灰飞虱和白背飞虱体内的共生菌个体较小,以卵形为主,分别占共生菌总数的93.4%和94.7%.此外,褐飞虱成虫体内的各类共生菌都显著大于灰飞虱和白背飞虱成虫体内的同种类型个体,且灰飞虱和白背飞虱体内的同种共生菌个体大小之间也存在一定差异.     

Increased rates of sequence evolution in endosymbiotic bacteria and fungi with small effective population sizes

Mutualistic, maternally transmitted endosymbiotic microorganisms undergo severe population bottlenecks at each host generation, resulting in a reduction in effective population size (Ne). Previous studies of Buchnera, the primary endosymbiont of aphids, and of several other species of endosymbiotic bacteria have shown that these species exhibit an increase in the rate of substitution of slightly deleterious mutations, among other predicted effects of increased drift due to small Ne, such as reduced codon bias. However, these studies have been limited in taxonomic scope, and it was therefore not clear whether the increase in rate is a general feature of endosymbiont lineages. Here, we test the prediction that a long-term reduction in Ne causes an increase in substitution rate using DNA sequences of the 16S rRNA gene from 13 phylogenetically independent comparisons between taxonomically diverse endosymbiotic microorganisms and their free-living relatives. Maximum likelihood and distance-based methods both indicate a significant increase in substitution rate in a wide range of bacterial and fungal endosymbionts compared to closely related free-living lineages. We use the same data set to test whether 16S genes from endosymbionts display increased A + T content, another indicator of increased genetic drift, and find that there is no significant difference in base composition between endosymbiont and nonendosymbiont 16S genes. However, analysis of an additional data set of whole bacterial genomes demonstrates that, while host-dependent bacteria have significantly increased genomic A + T content, the base content of the 16S gene tends to vary less than that of the whole genome. It is possible that selection for stability of rRNA is strong enough to overcome the effects of drift toward increased A + T content in endosymbiont 16S genes, despite the reduced effective population sizes of these organisms.     

Multiple symbiotes in larval black flies (Diptera: Simuliidae): associations of trichomycete fungi with ichthyosporeans, mermithid nematodes, and microsporidia

Studies of the interactions between two or more species of symbiotic microorganisms in a single host animal have lagged behind those involving interactions between hymenopteran or dipteran parasitoids. We screened the larvae of four species of black flies (Cnephia ornithophilia, Simulium furculatum, Simulium innoxium, and Simulium vandalicum) to determine if the colonization and prevalence of trichomycete fungi were influenced by ichthyosporeans, mermithid nematodes, microsporidia, or other species of trichomycetes. Differences in the layering of the peritrophic matrix of microsporidian-infected larvae, compared with that of uninfected larvae, were associated with greater levels of colonization by the midgut-inhabiting trichomycete Harpella melusinae. Colonization levels of different species of trichomycetes were significantly correlated with one another in only 2 of 11 cases. Aside from the consistent attachment of the trichomycete Simuliomyces microsporus to the ichthyosporean Paramoebidium chattoni, we found little evidence that prevalence and colonization levels of trichomycetes were influenced by other symbiotes, including other trichomycetes. This trend might reflect the physical separation of trichomycetes, which are gut specific, from other symbiotes. In addition, any combinations of symbiotes that were wholly incompatible would not have been observed in our field-collected material.     

褐飞虱不同致害性种群体内共生菌18S rDNA部分序列比较

分离纯化了褐飞虱3种不同致害性种群体内类酵母共生菌 (yeast-like symbionts, YLS),并对其18S rDNA基因序列进行了比较。结果表明,褐飞虱3种不同致害性种群体内类酵母共生菌18S rDNA均扩增出600 bp左右的片断。依据获得的18S rDNA特异性序列,结合已知真菌的18S rDNA部分序列,构建了不同宿主的YLS分子系统树。结果显示, 褐飞虱3种不同致害性种群体内的YLS同属子囊菌亚门（Ascomycotina）的核菌纲（Pyrenomycetes）,并与此纲中的Hypomyces chrysospermus亲缘关系相对最近。     

云南5个地区戟叶酸模花中酵母菌和类酵母的多样性

[目的]研究云南5个地区(晋宁、祥云、程海、泸沽湖、洱海)的戟叶酸模(Rumex hastatus)花中的酵母菌和类酵母.[方法]采用涂布平板法对5个地区的戟叶酸模花中酵母菌和类酵母进行分离,通过26S rDNA Dl/D2区域序列分析并结合形态观察对分离获得的酵母菌和类酵母进行鉴定;采用胞外酶定性筛选培养基进行产酶筛选;用苏丹黑B染色法筛选产油脂菌株.[结果]从戟叶酸模花中分离得到82株酵母菌和99株类酵母;82株酵母菌鉴定为6个属16个种和1个潜在新种,99株类酵母鉴定为短梗霉属(Aureobasidium)的普鲁兰类酵母(A.pullulans)及3个变种;戟叶酸模花中的优势属是类酵母短梗霉属,其次为红酵母属(Rhodotorula)和隐球酵母属(Cryptococcus);筛选到134株具有产胞外酶活性和83株产油脂的酵母菌和类酵母.[结论]研究结果显示5个地区的戟叶酸模花中酵母菌和类酵母种类多样性较为丰富,并具有产淀粉酶、蛋白酶、纤维素酶、脂肪酶和油脂的特点,有潜在的应用前景.