rfaP mutants of Salmonella typhimurium

Salmonella typhimurium rfaP mutants were isolated and characterised with respect to their sensitivity towards hydrophobic antibiotics and detergents, and their lipopolysaccharides were chemically analysed. The rfaP mutants were selected after diethylsulfate mutagenesis or as spontaneous mutants. The mutation in two independent mutants SH7770 (line LT2) and SH8551 (line TML) was mapped by cotransduction with cysE to the rfa locus. The mutants were sensitive to hydrophobic antibiotics (clindamycin, erythromycin and novobiocin) and detergents (benzalkoniumchloride and sodium dodecyl sulfate). Analysis of their lipopolysaccharides by chemical methods and by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed that their saccharide portion was, to a large extent, of chemotype Rc with small proportions of material containing a more complete core oligosaccharide and O-specific chains. Only 2.5 mol phosphate/mol lipopolysaccharide was found whereas the phosphate content of the lipopolysaccharide of a galE mutant strain was 4.8 mol. Thus the rfaP mutant lipopolysaccharides lacked more than two phosphate residues. Assessment of the location of phosphate groups in rfaP lipopolysaccharides revealed the presence of at least 2 mol phosphate in lipid A, indicating that the core oligosaccharide was almost devoid of phosphate. The chemical, physiological and genetic data obtained for these mutants are in full agreement with those reported earlier for rfaP mutants of Salmonella minnesota.     

Isolation of a replication region of a large lactococcal plasmid and use in cloning of a nisin resistance determinant

The replication region of a 28-kilobase-pair (kbp) cryptic plasmid from Lactococcus lactis subsp. lactis biovar diacetylactis SSD207 was cloned in L. lactis subsp. lactis MG1614 by using the chloramphenicol resistance gene from the streptococcal plasmid pGB301 as a selectable marker. The resulting 8.1-kbp plasmid, designated pVS34, was characterized further with respect to host range, potential cloning sites, and location of replication gene(s). In addition to lactococci, pVS34 transformed Lactobacillus plantarum and, at a very low frequency, Staphylococcus aureus but not Escherichia coli or Bacillus subtilis. The 4.1-kbp ClaI fragment representing lactococcal DNA in pVS34 contained unique restriction sites for HindIII, EcoRI, XhoII, and HpaII, of which the last three could be used for molecular cloning. A region necessary for replication was located within a 2.5-kbp fragment flanked by the EcoRI and ClaI restriction sites. A 3.8-kbp EcoRI fragment derived from a nisin resistance plasmid, pSF01, was cloned into the EcoRI site of pVS34 to obtain a nisin-chloramphenicol double-resistance plasmid, pVS39. From this plasmid, the streptococcal chloramphenicol resistance region was subsequently eliminated. The resulting plasmid, pVS40, contains only lactococcal DNA. Potential uses for this type of a nisin resistance plasmid are discussed.     

Comparison of arbitrarily primed polymerase chain reaction and ribotyping for subtyping Actinobacillus actinomycetemcomitans

This study investigated the compatibility of arbitrarily primed polymerase chain reaction (AP-PCR) and ribotyping in the characterization of Actinobacillus actinomycetemcomitans , a major pathogen in the mixed anaerobic microflora of human periodontitis. AP-PCR was performed directly on lysed bacterial colonies using a random-sequence 10-base oligonucleotide primer. Ribotyping was carried out by using purified bacterial chromosomal DNA digested with BglI. DNA fragments were separated electrophoretically, blotted onto a nylon membrane and hybridized with the plasmid pKK3535 containing the rRNA operon of Escherichia coli. The two genetic methods were evaluated on isolates from single individuals and from family members. Twelve AP-PCR types and 47 ribotypes were distinguished among 76 A. actinomycetemcomitans isolates of different serotypes. AP-PCR typing and ribotyping gave compatible results in 18 of 20 comparisons. Although AP-PCR detected less genetic heterogeneity in A. actinomycetemcomitans than ribotyping, the rapid and relatively simple AP-PCR technique seems to be sufficiently discriminative to be used in large scale epidemiological studies which preclude the application of the more laborious ribotyping technique.     

Effect of some natural pesticides on entomogenous muscardine fungi.

Five commercial preparations of natural pesticides were tested for in vitro compatibility with muscardine fungi, Beauveria brongniartii and Metarhizium anisopliae. Neemark (azadirachtin) was found compatible with both the fungi. Phytoallexin, the natural fungicide, significantly inhibited the growth of both the fungi, while other natural pesticides showed moderate to severe inhibition.     

Conditions affecting direct gene transfer into rodent muscle in vivo.

This report extends our previous findings that mouse muscle cells in situ can take up naked DNA injected intramuscularly in vivo. Various conditions such as needle type, speed of injection, volume of injection fluid, tonicity of injection fluid, type of solute, type of muscle, physiologic condition of the muscle and age of the animals were appraised for their effect on the levels of luciferase activity expressed from the pRSVL plasmid. Specific conditions such as the use of normal saline as an injection fluid increased the efficiency of expression. The implantation of DNA pellets was an effective way to deliver DNA to muscle, especially for smaller muscle groups. Also, newborn and adult rat muscles expressed plasmid DNA delivered intramuscularly.     

Chemical regulators of carotenogenesis by Blakeslea trispora

The activation of the carotene biosynthetic pathway in Blakeslea trispora was found to occur by trisporic acid and many other compounds such as abscisic acid, β-ionone, α-ionone and vitamin A which share significant structural similarity with trisporic acid. The magnitude of stimulatory activities of these effectors was in the order trisporic acid > abscisic acid > β-ionone > α-ionone > vitamin A. Comparison of structures and stimulatory activities of all the effectors indicated that the short length of the side chain and the presence of a keto group in the ring structure of the trisporic acid molecule contributed significantly to the biological activity towards carotenogenesis.     

Seasonal shifts in the assembly dynamics of benthic macroinvertebrate and diatom communities in a subtropical river

Identifying seasonal shifts in community assembly for multiple biological groups is important to help enhance our understanding of their ecological dynamics. However, such knowledge on lotic assemblages is still limited. In this study, we used biological traits and functional diversity indices in association with null model analyses to detect seasonal shifts in the community assembly mechanisms of lotic macroinvertebrates and diatoms in an unregulated subtropical river in China. We found that functional composition and functional diversity (FRic, FEve, FDis, MNN, and SDNN) showed seasonal variation for macroinvertebrate and diatom assemblages. Null models suggested that environmental filtering, competitive exclusion, and neutral process were all important community assembly mechanisms for both biological groups. However, environmental filtering had a stronger effect on spring macroinvertebrate assemblages than autumn assemblages, but the effect on diatom assemblages was the same in both seasons. Moreover, macroinvertebrate and diatom assemblages were shaped by different environmental factors. Macroinvertebrates were filtered mainly by substrate types, velocity, and COD_Mn, while diatoms were mainly shaped by altitude, substrate types, and water quality. Therefore, our study showed (a) that different biological assemblages in a river system presented similarities and differences in community assembly mechanisms, (b) that multiple processes play important roles in maintaining benthic community structure, and (c) that these patterns and underlying mechanisms are seasonally variable. Thus, we highlight the importance of exploring the community assembly mechanisms of multiple biological groups, especially in different seasons, as this is crucial to improve the understanding of river community changes and their responses to environmental degradation.     

The importance of metacommunity ecology for environmental assessment research in the freshwater realm

Most bioassessment programs rest on the assumption that species have different niches, and that abiotic environmental conditions and changes therein determine community structure. This assumption is thus equivalent to the species sorting perspective (i.e. that species differ in their responses to environmental variation) in metacommunity ecology. The degree to which basing bioassessment on the species sorting perspective is reasonable is likely to be related to the spatial extent of a study and the characteristics of the organism groups (e.g. dispersal ability) with which the effects of anthropogenic changes are assessed. Recent findings in metacommunity research have stressed that community structure is determined not only by local abiotic environmental conditions but also by biotic interactions and dispersal‐related effects. For example, dispersal limitation may prevent community structure recovery from the effects of a putative stressor, as organisms may not be able to disperse to all sites in a region. Mass effects (i.e. the presence of species in environmentally suboptimal sites due to high dispersal rates from environmentally suitable sites) may, in turn, obscure the effects of a stressor, as dispersal from source sites (e.g. an unaltered site) allows persistence at sink sites (e.g. an anthropogenically altered site). Better bioassessment should thus take both niche‐ and dispersal‐related processes simultaneously into consideration, which can be accomplished by explicitly modelling spatial location as a proxy for dispersal effects. Such an integrated approach should be included in bioassessment programs using general multivariate approaches, predictive modelling, and multimetric indices.     

Burden of Giardia duodenalis Infection and Its Adverse Effects on Growth of Schoolchildren in Rural Malaysia

Background

Giardia duodenalis infection and malnutrition are still considered as public health problems in many developing countries especially among children in rural communities. This study was carried out among Aboriginal (Orang Asli) primary schoolchildren in rural peninsular Malaysia to investigate the burden and the effects of Giardia infection on growth (weight and height) of the children.

Methods/Findings

Weight and height of 374 children aged 7–12 years were assessed before and after treatment of Giardia infection. The children were screened for Giardia parasite using trichrome staining technique. Demographic and socioeconomic data were collected via face-to-face interviews using a pre-tested questionnaire. Overall, 22.2% (83/374) of the children were found to be infected with Giardia. Nutritional status of children was assessed and the results showed that the mean weight and height were 23.9 kg (95% CI = 23.3, 24.5) and 126.6 cm (95% CI = 125.6, 127.5), respectively. Overall, the prevalence of severe underweight, stunting and wasting were 28.3%, 23.8% and 21.0%, respectively. Multiple linear regression analyses showed sex, Giardia infection and household monthly income as the significant determinants of weight while sex and level of mother''s education were the significant determinants of height. Weight and height were assessed at 3 and 6 months after treatment of Giardia infection. It was found that Giardia infection has a significant association with the weight of children but not with height.

Conclusions/Significance

This study reveals high prevalence of Giardia infection and malnutrition among Aboriginal children in rural Malaysia and clearly highlights an urgent need to identify integrated measures to control these health problems in the rural communities. Essentially, proper attention should be given to the control of Giardia infection in Aboriginal communities as this constitutes one of the strategies to improve the nutritional status of Aboriginal children.     

Association of Weather and Anthropogenic Factors for Transmission of Japanese Encephalitis in an Endemic Area of India

Weather and anthropogenic factors are important determinants for Japanese encephalitis (JE) transmission. During 2008–2010, an increasing trend of JE was observed in Dibrugarh district of Northeast India. The JE cases were found to be clustered between June to October in each year. Monthly minimum temperature and rainfall were significantly associated with JE transmission at 1 and 2 months lagged. However, the relationship was more prominent at a lag of 1 month than that of two. Regression analysis suggested that rainfall, minimum and maximum temperature, and relative humidity at 6:00 h are significant predictors (P < 0.05) of quarterly occurrence of JE cases. Additional anthropogenic risk factors including the conditions such as pig sty/cattle shed around and lower part of the houses and proximity of rice field to the dwelling houses (P < 0.05) were also found to be predictors for JE occurrence. Meteorological and anthropogenic risk factors can be used to forecast JE outbreaks in Assam which in turn can help the local health authorities to protect communities in JE prone areas.