Colonization factors of diarrheagenicE. coli and their intestinal receptors

WhileEscherichia coli is common as a commensal organism in the distal ileum and colon, the presence of colonization factors (CF) on pathogenic strains ofE. coli facilitates attachment of the organism to intestinal receptor molecules in a species- and tissue-specific fashion. After the initial adherence, colonization occurs, and the involvement of additional virulence determinants leads to illness. EnterotoxigenicE. coli (ETEC) is the most extensively studied of the five categories ofE. coli that cause diarrheal disease, and has the greatest impact on health worldwide. ETEC can be isolated from domestic animals and humans. The biochemistry, genetics, epidemiology, antigenic characteristics, and cell and receptor binding properties of ETEC have been extensively described. Another major category, enteropathogenicE. coli (EPEC), has virulence mechanisms, primarily effacement and cytoskeletal rearrangement of intestinal brush borders, that are distinct from ETEC. An EPEC CF receptor has been purified and characterized as a sialidated transmembrane glycoprotein complex directly attached to actin, thereby associating CF-binding with host-cell response. Three, additional categories ofE. coli diarrheal disease, their colonization factors and their host cell receptors are discussed. It appears that biofilms exist in the intestine in a manner similar to oral bacterial biofilms, and thatE. coli is part of these biofilms as both commensals and pathogens.Abbreviations CF colonization factor - CFA Colonization Factor Antigen - CS coli-surface-associated antigen - EAggEC enteroaggregativeE. coli - ECDD E. coli diarrheal disease - EHEC enterohemorrhagicE. coli - EIEC enteroinvasiveE. coli - EPEC enteropathogenicE. coli - ETEC enterotoxigenicE. coli - Gal galactose - GalNAc N-acetyl galactosamine - LT heat-labile toxin - NeuAc N-acetyl neuraminic acid - PCF Putative colonization factor - RBC red blood cells - SLT Shiga-like toxin - ST heat-stable toxin     

The industrial chemical bisphenol A (BPA) interferes with proliferative activity and development of steroidogenic capacity in rat Leydig cells

The presence of bisphenol A (BPA) in consumer products has raised concerns about potential adverse effects on reproductive health. Testicular Leydig cells are the predominant source of the male sex steroid hormone testosterone, which supports the male phenotype. The present report describes the effects of developmental exposure of male rats to BPA by gavage of pregnant and lactating Long-Evans dams at 2.5 and 25 μg/kg body weight from Gestational Day 12 to Day 21 postpartum. This exposure paradigm stimulated Leydig cell division in the prepubertal period and increased Leydig cell numbers in the testes of adult male rats at 90 days. Observations from in vitro experiments confirmed that BPA acts directly as a mitogen in Leydig cells. However, BPA-induced proliferative activity in vivo is possibly mediated by several factors, such as 1) protein kinases (e.g., mitogen-activated protein kinases or MAPK), 2) growth factor receptors (e.g., insulin-like growth factor 1 receptor-beta and epidermal growth factor receptors), and 3) the Sertoli cell-secreted anti-Mullerian hormone (also called Mullerian inhibiting substance). On the other hand, BPA suppressed protein expression of the luteinizing hormone receptor (LHCGR) and the 17beta-hydroxysteroid dehydrogenase enzyme (HSD17B3), thereby decreasing androgen secretion by Leydig cells. We interpret these findings to mean that the likely impact of deficits in androgen secretion on serum androgen levels following developmental exposure to BPA is alleviated by increased Leydig cell numbers. Nevertheless, the present results reinforce the view that BPA causes biological effects at environmentally relevant exposure levels and its presence in consumer products potentially has implication for public health.     

Glomeromycotan mycorrhizal fungi from tropical Australia III. Measuring diversity in natural and disturbed habitats

Aims and Background

The aim was to investigate the diversity and distribution of Glomeromycotan fungi forming arbuscular mycorrhizal associations (AMF) in undisturbed and disturbed habitats in the vicinity of Kakadu National Park in tropical Australia. This is a tropical region with a 7–9 month dry season and a monsoonal wet season. Complimentary methods of fungus detection were used to investigate the diversity and relative dominance of AMF at a regional scale.

Methods

Soils were sampled from 32 sites, representing eucalypt savanna woodlands, wetlands, sandstone escarpment, rainforest, and disturbed mine waste rock dumps (overburden or spoil). Populations of AMF were identified and quantified using spores from soil. Morphology patterns of fungi colonising bait plant roots were examined and isolates were obtained by four complimentary pot-culturing methods.

Results

Different methods of detecting fungi produced different answers about which AMF were most important in the tested soils. In particular, spore surveys apparently underestimated the importance of Glomus species and overestimated the activity of Acaulospora species with numerous small spores, while calculated spore biovolumes overestimated the importance of Scutellospora and Gigaspora species with large spores, relative to inoculum levels of these fungus categories measured in bioassays. Spore surveys revealed 15 species of fungi and 8 additional fungi were recovered from the same soil samples using pot-culture isolation methods. Pot-cultures were especially important for detecting Glomus species that had high inoculum levels, but rarely produced spores in soils. Spores of AMF increased in abundance as vegetation developed in mine habitats reaching a peak that was higher than in undisturbed plant communities. Spore numbers (but not biovolumes) were well correlated with bioassay measurements of inoculum levels.

Conclusions

Most AMF species were widespread, but several were restricted to disturbed habitats or wetland soils. Undisturbed sites had a substantially higher diversity of AMF than partially vegetated mine waste rock dumps. It is recommended that AMF population surveys should not be based entirely on spore occurrence data, to avoid overlooking important fungi that sporulate infrequently. These fungi could be detected by bioassays or pot culture isolation from soil. Major variations in the detectability of AMF correspond to different life history strategies and can mask variations in their abundance.     

Structural studies on a low oxygen affinity hemoglobin from mammalian species: Sheep (Ovis aries)

Hemoglobin (Hb) is in equilibrium between low affinity Tense (T) and high affinity Relaxed (R) states associated with its unliganded and liganded forms, respectively. Mammalian species can be classified into two groups on the basis of whether they express ‘high’ and ‘low’ oxygen affinity Hbs. Although Hbs from former group have been studied extensively, a limited number of structural studies have been performed for the low oxygen affinity Hbs. Here, the crystal structure of low oxygen affinity sheep methemoglobin (metHb) has been determined to 2.7 Å resolution. Even though sheep metHb adopts classical R state like quaternary structure, it shows localized quaternary and tertiary structural differences compared with other liganded Hb. The critical group of residues in the “joint region”, shown as a major source of quaternary constraint on deoxyHb, formed unique interactions in the α1β2/α2β1 interfaces of sheep metHb structure. In addition, the constrained β subunits heme environment and the contraction of N-termini and A-helices of β subunits towards the molecular dyad are observed for sheep metHb structure. These observations provide the structural basis for a low oxygen affinity and blunt response to allosteric effector of sheep Hb.     

In vitro propagation of Stackhousia tryonii Bailey (Stackhousiaceae): a rare and serpentine-endemic species of central Queensland, Australia

Stackhousia tryonii Bailey, a rare species whichhyperaccumulates nickel and with a potential to be exploited inphytoremediation/phytomining, is difficult to propagate via seeds. This studyinvestigated the development of a micropropagation protocol for the productionof large stocks of S. tryonii. Disinfested shoot tips andnodal buds were precultured on Gamborg's (B₅) basal medium toobtain aseptic shoots for the optimisation of the protocol. 6-Benzyl aminopurine(BAP) at 1.0 mg l^–1 produced the highest number ofshoots per explant in B₅ medium. Comparison betweenB₅ and MS media showed similar responses, but with marked influenceof BAP concentration on shoot numbers. Transfer of shoots from MS(multiplication) medium to MS medium supplemented with indole-3-acetic acid(IAA) and indole-3-butyric acid (IBA), individually or in combination, indicatedthat a combination of IAA and IBA (0.75 mg l^–1each) is required to produce roots on young shoots (75%) compared to IBA(15–45%) or IAA (0–10%) alone. This study demonstrated that by usingthis protocol, a high multiplication rate (up to 18 shoots per explant) could be produced within 4 weeks, andthey can be readily hardened (98% survival) in a glasshouse by transplantingthem into a potting mixture of sand and perlite (4:1).     

Tissue Culture Studies of Tomato (Lycopersicon esculentum)

Tomato is a major vegetable crop that has achieved tremendous popularity over the last century. It is grown in almost every country of the world. Development of protocols for in vitro selection can provide new advances for the production of stress tolerant cultivars. Techniques have been optimised for the production of haploids and somatic hybrids. Attempts have also been made to transfer the higher regenerative ability of wild varieties to cultivated tomatoes. Although, some information is available on the morphogenesis of tomato, the techniques have not been developed to a level at which they can be utilised in large-scale multiplication of commercially important cultivars. The morphogenesis response seems to be highly dependent PGRs used in the media, which is again cultivar and genotypic specific. Somatic embryogenesis in tomato is still at its infancy, and efficient procedures for large-scale production via somatic embryogenesis are yet to be developed. Genetic stability of the tissue culture raised tomato plants also needs to be addressed. The use of a combination of molecular and conventional breeding techniques could be the option for the development of cultivars resistant to biotic and abiotic stresses. This paper reviews the advances made in various aspects of tissue culture in tomato. It also discusses the issues that still need to be addressed to utilise the full potential of plant tissue culture techniques in genetic improvement and mass propagation of tomato.     

TP53 codon 72 polymorphism and type 2 diabetes: a case–control study in South Indian population

Molecular Biology Reports - TP53 functions primarily as a tumor suppressor, controlling a myriad of signalling pathways that prevent a cell from undergoing malignant transformation. This tumor...