Isolation and characterization of actinobacteria ectosymbionts from Acromyrmex subterraneus brunneus (Hymenoptera, Formicidae)

The ectosymbiont actinobacterium Pseudonocardia was isolated from the integument of Acromyrmex leaf-cutter ants and seems to play a crucial role in maintaining asepsis of the nest. Currently, there has been an intensive search for Pseudonocardia associated with several attine species, but few studies have indicated that other actinobacteria may be associated with these ants as well. We therefore characterized the culturable actinobacteria community associated with the integument of the fungus-growing ant Acromyrmex subterraneus brunneus Forel, 1893 (Hymenoptera: Formicidae). Ectosymbionts were isolated using four different media and characterized by morphological and molecular (16S rDNA) methods. A total of 20 strains were isolated, of which 17 were characterized as Streptomyces spp., and one isolate each as Pseudonocardia, Kitassatospora and Propionicimonas. Unlike other Acromyrmex species, A. subterraneus brunneus is associated with a diversity of actinobacteria. Even though Pseudonocardia is present on this leaf-cutting ant’s integument, the number and diversity of Streptomyces spp. found differs from those of previous studies with other attine ants and suggest that different culturing approaches are needed to characterize the true diversity of microbes colonizing the integument of attine ants. Moreover, understanding the diversity of the culturable actinobacteria associated with A. subterraneus brunneus should increase our knowledge of the evolutionary relationship of this intricate symbiotic association.     

Variations du taux d'amp cyclique et des activités spécifiques de l'adénylate cyclase et de l'amp cyclique-phosphodiestérase pendant le cycle cellulaire d'un actinomycète

The variations in the concentrations of intra- and extracellular cyclic AMP and in the specific activities of adenylate cyclase (EC 4.6.1.1) and cyclic AMP phosphodiesterase (EC 3.1.4.17) have been monitored in synchronized culture of Nocardia restricta, a prokaryote belonging to the group of Actinomycetes. At the beginning of the cell cycel, during a first period of RNA and protein synthesis, there is an increasing synthesis of adenylate cyclase which can be suppressed in the presence of chloramphenicol or rifampicin. Simultaneously, the specific activity of cyclic AMP phosphodiesterase decreases and the concentrations of intra- and extracellular cyclic AMP rise. After the end of DNA replication, during a second period of RNA and protein synthesis, the specific activity of cyclic AMP phosphodiesterase increases; during the same time, the specific activity of adenylate cyclase and the level of intracellular cyclic AMP drop. It appears that the overall metabolism of cyclic AMP is coordinated so that the cyclic AMP level will be high at the beginning of DNA replication and will fall thereafter. The results are discussed in comparison with known data about the variations of cyclic AMP during the cell cycle of mammalian cells in cultures.     

Occurrence of Myrica-nodulating Frankia in Hawaiian volcanic soils

The ability of Hawaiian volcanic soils to nodulate actinorhizal Myrica cerifera, Casuarina equisetifolia, and Alnus glutinosa was determined using a host-plant bioassay. Myrica-nodulating Frankia occurred in five volcanic deposits with depositional ages ranging from 20 to 162 years before present. The oldest deposit had a mean estimated nodulation capacity from 450 to 1200 times greater than those of the younger deposits. Only the oldest deposit had high moisture content, high organic matter content, and increased vegetative cover, including an abundance of actinorhizal M. faya. Casuarina- and Alnus-nodulating Frankia were not detected in any of these volcanic deposits.     

白蚁共生放线菌研究进展

白蚁与微生物的共生关系是目前较受关注的研究热点,其肠道及巢内的共生微生物在降解木质纤维素的过程中扮演着重要的角色。放线菌是这些共生微生物中的重要一类,广泛存在于肠道、蚁巢及其周围土壤中,目前已探明共生放线菌在参与白蚁碳氮循环及保护巢群免受外来病菌侵染等方面发挥着极大的作用。近年来,人们利用分子生物学技术鉴定了部分共生放线菌的类群,发现了许多具应用前景的新放线菌及相关酶和代谢产物。因此,研究与白蚁相关的放线菌不仅有助于人们了解白蚁共生菌群落间的互作及其与宿主间的关系,而且对人类开发自然资源也有较大的帮助。本文对白蚁共生放线菌的研究进展作一综述,供同行参考。     

产甾体皂甙华重楼内生真菌、放线菌的分离与筛选

目的:研究重楼内生菌的次生代谢产物的医用价值。方法:从产自四川彭州的华重楼(Paris polyphylla vat．chinensis Franch)地下块茎中分离、筛选内生菌,采用PDA液体培养基26℃发酵培养;发酵液分别经泡沫反应、Salkowski反应、Liberman反应及以薯蓣皂甙元为标准对照的薄层层析分析。结果:表明其中编号为SNUF-1的真菌和编号为SNUA-1、SNUA-2的放线菌菌株均能分泌甾体皂甙或其类似化合物。结论:华重楼内生菌发酵液具有产生宿主药用活性的成份。     

Genus Pseudonocardia: What we know about its biological properties,abilities and current application in biotechnology

The genus Pseudonocardia belongs to a group of Actinomycetes, and is a member of the family Pseudonocardiacea. The members of this genus are aerobic, Gram-positive, non-motile bacteria that are commonly found in soil, plant and environment. Although this genus has a low clinical significance; however, it has an important role in biotechnology due to the production of secondary metabolites, some of which have anti-bacterial, anti-fungal and anti-tumour effects. The use of phenotypic tests, such as gelatinase activity, starch hydrolysis, catalase and oxidase tests, as well as molecular methods, such as polymerase chain reaction, are necessary for Pseudonocardia identification at the genus and species levels.     

In vivo analysis of straight-chain and branched-chain fatty acid biosynthesis in three actinomycetes

Abstract The starter units for branched-chain and straight-chain fatty acid biosynthesis was investigated in vivo in three actinomycetes using stable isotopes. Branched-chain fatty acids, which constitute the majority of the fatty acid pool, were confirmed to be biosynthesized using the amino acid degradation products methylbutyryl-CoA and isobutyryl-CoA as starter units. Straight-chain fatty acids were shown to be constructed using butyryl-CoA as a starter unit. Isomerization of the valine catabolite isobutyryl-CoA was shown to be only a minor source of this butyryl-CoA.     

Mutational analysis of primary alcohol metabolism in the methylotrophic actinomycete Amycolatopsis methanolica

Abstract Mutants of the methylotrophic actinomycete Amycolatopsis methanolica unable to grow on methanol as carbon source were isolated and characterized. Mutants specifically affected in methanol utilization were deficient in formaldehyde assimilation. Mutants blocked in the first step of primary alcohol oxidation (C1–C4) had lost activity of the tetrazolium-dependent alcohol dehydrogenase, a three-component enzyme complex. This complex, or individual components, thus play a crucial role in utilization of primary alcohols in A. methanolica .     

Studies of two strains of Actinopolyspora halophila,an extremely halophilic actinomycete

Actinopolyspora halophila is an extremely halophilic actinomycete requiring a minimum salt concentration of 12% (w/v) for growth in liquid media at 37°C. During antibiotic sensitivity testing of the organism, an erythromycin-resistant phenotypic variant designated A. halophila ER, was isolated. This strain was approximately 60-fold more resistant to erythromycin than the wild-type strain, and, moreover, was capable of growth in 6% sodium chloride. Optimal growth of both strains in liquid media was observed in 20% salt.After resuspension in water for up to 20 days, the organism exhibited good growth in fresh salt-containing media. Cultures resuspended in salt-containing media, however, were subject to extensive cellular autolysis.In addition to resistance to -lactam antibiotics which was mediated by cellular and exocellular -lactamases, the organism was insensitive to all other tested antibiotics except amakacin, chloramphenicol, kanamycin, gentamycin, naladixic acid, streptomycin, and tetracycline. No plasmids were detected in either strain. A. halophila possessed high cellular levels of catalase, -lactamase, and -glucosidase. A variety of exocellular enzymes including protease, -lactamase, xylanase, and carboxymethyl cellulase, were secreted maximally into growth media containing 15% NaCl.Issued as NRCC 25148     

Cell walls from Actinopolyspora halophila,an extremely halophilic actinomycete

Cell wall components were prepared from Actinopolyspora halophila (strain wt), an extremely halophilic actinomycete requiring a minimum 12% NaCl concentration for growth, and from an erythromycin-resistant strain of A. halophila (strain ER) that required only 6% NaCl for growth. Both cell wall preparations contained glutamic acid, alanine, and diaminopimelic acid in a 1:2:1 molar ratio. On the basis of muramic acid content, peptidoglycans from the wt and ER strains contained 255 and 245 disaccharide units per mg dry weight respectively. In addition, both cell wall preparations contained from 10 to 20% more glucosamine than muramic acid, and equimolar amounts of d-galactose and d-arabinose. Analysis of cell walls before and after digestion with Myxobacter AL-1 protease indicated that nearly all glycan disaccharide units were peptide-substituted and that peptide cross-bridging was facilitated by direct peptide linkages between N-diaminopimelic acid and C-terminal alanine. While the peptidoglycan of A. halophila wt was 50% peptide cross-linked, that from A. halophila ER was approximately 67% peptide cross-linked. Chemical modifications involving substitution of non-N-acetylated hexosamines of the cell walls greatly enhanced their sensitivity to lysozyme. Although differences in peptidoglycan structure between the two strains of A. halophila were observed, these probably do not account for the reduced salt requirement for growth of the erythromycin-resistant strain.Issued as NRCC 25165