Explaining the coexistence of competing species is a major challenge in community ecology. In bacterial systems, competition is often driven by the production of bacteriocins, which are narrowspectrum proteinaceous toxins that serve to kill closely related species, providing the producer better access to limited resources. Bacteriocin producers have been shown to competitively exclude sensitive, nonproducing strains. However, the dynamics between bacteriocin producers, each lethal to its competitor, are largely unknown. In this study, we used in vitro, in vivo and in silico models to study competitive interactions between bacteriocin producers. Two Escherichia coli strains were generated, each carrying a DNA-degrading bacteriocin (colicins E2 and E7). Using reporter-gene assays, we showed that each DNase bacteriocin is not only lethal to its opponent but, at lower doses, can also induce the expression of its opponent's toxin. In a well-mixed habitat, the E2 producer outcompeted its adversary; however, in structured environments (on plates or in mice colons), the two producers coexisted in a spatially 'frozen' pattern. Coexistence occurred when the producers were initiated with a clumped spatial distribution. This suggests that a 'clump' of each producer can block invasion of the other producer. Agent-based simulation of bacteriocin-mediated competition further showed that mutual exclusion in a structured environment is a relatively robust result. These models imply that colicin-mediated colicin induction enables producers to successfully compete and defend their niche against invaders. This suggests that localized interactions between producers of DNA-degrading toxins can lead to stable coexistence of heterogeneously distributed strains within the bacterial community and to the maintenance of diversity.

BackgroundEvolutionary arms race plays a major role in shaping biological diversity. In microbial systems, competition often involves chemical warfare and the production of bacteriocins, narrow-spectrum toxins aimed at killing closely related strains by forming pores in their target’s membrane or by degrading the target’s RNA or DNA. Although many empirical and theoretical studies describe competitive exclusion of bacteriocin-sensitive strains by producers of bacteriocins, the dynamics among producers are largely unknown.Methodology/Principal findingsWe used a reporter-gene assay to show that the bacterial response to bacteriocins’ treatment mirrors the inflicted damage Potent bacteriocins are lethal to competing strains, but at sublethal doses can serve as strong inducing agents, enhancing their antagonists’ bacteriocin production. In contrast, weaker bacteriocins are less toxic to their competitors and trigger mild bacteriocin expression. We used empirical and numerical models to explore the role of cross-induction in the arms race between bacteriocin-producing strains. We found that in well-mixed, unstructured environments where interactions are global, producers of weak bacteriocins are selectively advantageous and outcompete producers of potent bacteriocins. However, in spatially structured environments, where interactions are local, each producer occupies its own territory, and competition takes place only in “no man’s lands” between territories, resulting in much slower dynamics.Conclusion/SignificanceThe models we present imply that producers of potent bacteriocins that trigger a strong response in neighboring bacteriocinogenic strains are doomed, while producers of weak bacteriocins that trigger a mild response in bacteriocinogenic strains flourish. This counter-intuitive outcome might explain the preponderance of weak bacteriocin producers in nature. However, the described scenario is prolonged in spatially structured environments thus promoting coexistence, allowing migration and evolution, and maintaining bacterial diversity.

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The present study was conducted to estimate the prevalence of Giardia lamblia infection in some regions of Baghdad city, the relationship of source of drinking water with the prevalence of this intestinal protozoal parasite had been evaluate, The study revealed that the total rate of G.lamblia infection in humans was 68/375 (18.13%) according to three diagnostic methods, there was significant relation (p≤0.01) between infectivity rate (25%) of this parasite and persons who consumed tap water as a source of drinking water as compared to other source of drinking water. RT-PCR tpi gene application was able to detected and genotyping G.lamblia to assemblage A and B, since mix infection of assemblage (A+B) are more prevalent in fecal samples than others, while in environmental samples the assemblage A, assemblage B showed in 1/4 (25%), 2/4(50%) respectively and mixed assemblage (A+B) showed in 1/4 (25%) of samples. K e y w o r d s Giardia lamblia,Genotyping, infectivity rate, RT-PCR tpi gene.

Majeed H., Jamshaid Qazi H., Safdar W., Fang Z. (2013): Microencapsulation can be a Novel tool in wheat flour with micronutrients fortification: Current trends and future applications -a review. Czech J. Food Sci., 31: 527-540.Wheat flour fortification can be a novel and effective food based approach to improve effective micronutrient deficiencies that affect millions of people worldwide especially in the developing countries. Wheat is an important cereal crop grown worldwide and its per capita consumption is high even in the developing countries. Being a most popular dietary food component, fortification of wheat flour with micronutrients like iron, vitamin A, folic acid, zinc, and iodine is expected to be the most effective strategy to overcome the related deficiencies and, if mandated, could be helpful in achieving the international health goals. However, on the other hand food fortification (Direct mixing) with micronutrients might cause unwanted sensory changes and interaction with food components resulting in a lower bioavailability. Microencapsulation may be helpful to prevent unwanted sensory changes and diminish micronutrients interactions with wheat flour components. The current review will focus on the technical issues related to the fortification (Direct mixing) of wheat flour and prospects of microencapsulation technology in fortification.