来源于Micrococcus luteus的复苏促进因子异源表达及其对活性污泥中休眠细菌的促生长作用

【背景】复苏促进因子(Resuscitation promoting factor,RPF)是由某些放线菌分泌的一类活性蛋白质,最初在Micrococcusluteus中被发现。它不但能够复苏休眠细菌恢复生长,而且对正常的细菌也有促生长效果。然而关于RPF对于环境样品中除原始宿主以外细菌的复苏促进作用研究还鲜有报道。【目的】以寻找新的菌种资源、开发环境功能菌角度研究了RPF对环境样品中潜在休眠菌群的复苏促进作用。【方法】首先对来源于Micrococcus luteus IAM 14879的RPF(Ml RPF)蛋白序列进行生物信息学分析和同源模建;随后克隆了Ml RPF编码基因并在大肠杆菌中异源表达;最后利用重组Ml RPF对活性污泥样品中潜在的休眠细菌开展了复苏促生长研究。【结果】Ml RPF在进化树上处于单独分支,远离其它RPF家族成员;模建结构分析表明Ml RPF具有与C型溶菌酶相似的催化结构域,这有助于解释RPF家族蛋白具有溶解酶活性;重组Ml RPF在大肠杆菌中获得了可溶性表达,它能够促进休眠态M. luteus IAM 14879生长,保留了其生理活性;利用重组Ml RPF从某污水厂活性污泥样品中分离获得了Dietzia、Paracoccus、Rhodococcus和Brevundimonas菌株。【结论】为环境样品中微生物多样性研究及特殊微生物资源的发掘提供新的方法,也为基于Ml RPF的废水生物强化处理技术研发提供理论依据。     

Involvement of Escherichia coli K-12 recombination functions in elimination of multicopy plasmid R6K by DNA-damaging agents

Abstract A neutral lipomannan has been isolated from the membranes of Micrococcus agilis . In contrast to the lipomannans from 2 strains of Micrococcus luteus , which contained succinic acid ranging from 5.1%–8.0%, the M. agilis lipomannan had no detectable succinyl residues and exhibited neutral behaviour on Concanavalin A-agarose rocket electrophoresis. As with the M. luteus lipomannans, mannose was the only sugar detectable (as alditol acetate) by GLC analysis in the purified M. agilis lipomannan. Fatty acids accounted for 2% of the M. agilis lipomannan and were predominantly C₁₅ branched-chain acids, with higher amounts of C₁₆ iso and C₁₇ anteiso than that found in the M. luteus polymers. Neither conditions of growth of the organism nor the method of membrane preparation appeared to be responsible for the absence of succinyl residues. This appears to be the first report of a neutral membrane amphiphile.     

NMR field-cycling relaxation spectroscopy of bovine serum albumin,muscle tissue,micrococcus luteus and yeast: 14N1H-quadrupole dips

The frequency dependence of the proton spin lattice relaxation time of bovine serum albumin, muscle tissue, Micrococcus luteus and yeast has been measured by the aid of the field-cycling technique. In all systems ¹⁴N¹H-quadrupole dips have been observed. The conclusion is that amide groups are the dominating relaxation centers up to approx. 10⁷Hz. This finding can be understood by the fact that protein backbone fluctuations and, if possible, tumbling of the whole molecule rather than side group motions are the relevant mechanisms in this frequency range. A proton relaxation scheme for cells and tissue is presented.     

Cell wall storage polysaccharides in cotyledons ofLupinus angustifolius L. II. Mobilization during germination and seedling development

Summary During germination and early seedling development, cotyledons of seeds ofLupinus angustifolius were modified from thick-walled, fleshy storage organs to leaf-like, expanded photosynthetic organs by the controlled collapse of groups of mesophyll cells.Cotyledon cell walls of imbibed seeds are PAS-negative, have a strong affinity for calcofluor, and a dense fibrillar ultrastructure. The first visible sign of the mobilization of cell wall polysaccharides occurs 5 days after imbibition, with the appearance of PAS-positive maculae in ordered rows on the inner surface of the thickened walls. These correspond in orientation and frequency with the folds and radial striations found in walls of mature seeds, and with areas with poor affinity for calcofluor. In the electron microscope, the maculae appear as electron-lucent, wedge-shaped areas of loosely-arranged fibrils which, as germination proceeds, spread throughout the walls. The evidence suggests that storage polysaccharides are mobilized from the matrix of the walls by the action of hydrolytic enzymes leaving a framework of structural components, and not by the erosion of cracks and fissures.Most of the experimental work was carried out at the former ARC Unit of Development Botany, Cambridge.     

Effects of cold shock on the susceptibility of white lupins to fungal diseases

Experiments in controlled environments tested interactions between freezing soil (a compost-vermiculite mixture) and below-ground infection of white lupins with each of three pathogenic fungi (Botrytis cinerea, Fusarium avenaceum or Pleiochaeta setosa) on plant disease and death. Whilst soil freezing (up to 4 days at – 1^oC) caused slight necrosis and increased the severity of disease symptoms, incidence of plant death was increased only after inoculation, before freezing, of the lower hypocotyl of the youngest plants (soil frozen at less than 17 days old) with P. setosa. It is concluded that the contribution of below-ground infection by pathogenic fungi to overwinter losses in autumn-sown white lupin crops is exacerbated to a negligible extent by soil freezing, the main primary cause of such losses.