P. S. Dhanaraj

Manipulations of Catabolic Genes for the Degradation and Detoxification of Xenobiotics

Publisher Summary This chapter describes the manipulations of catabolic genes for the degradation and detoxification of xenobiotics. In vitro strain construction requires detailed genetic and biochemical information on the degradation pathways of xenobiotics. The control of catabolic pathways can also be modified by placing key biodegradation enzymes that require inducers, some of which are pollutants themselves, under the control of new regulatory systems. For example, genetic engineering has been used to uncouple the Pseudomonas mendocina toluene monoxygenase from toluene induction to derive Pseudomoms transconjugants that constitutively express the 2,4-D degradation pathway and to derive E. coli recombinant strains to enhance PCBs degradative activity in the presence of exogenous catabolite repressor substance. The cloning of genes for modified enzymes that have useful catabolic properties (such as relaxed substrate specificities or enhanced induction) provides an important repository of genetic diversity for future research.

Cellular aspects of microbe―insecticide interactions

Publisher Summary This chapter discusses the cellular aspects of the interactions between microbe insecticides. In higher organisms, such as insects and mammals the sites of action of insecticides have been clearly identified. Organochlorine insecticides interfere by impairing the ionic permeability of nerve cell membranes, producing an unstable state in which spurious nerve impulses induce uncontrolled activity in the whole organism. The organophosphorus and carbamate insecticides owe their insecticidal properties to phosphorylation or carbamylation of the enzyme acetylcholinesterase. This poisons the enzyme so that it cannot catalyze the hydrolysis of acetylcholine at the synapse (which permits the continuous transmission of nerve impulses) and effective nerve coordination breaks down, the insects or mammals suffer convulsions, and finally death occurs. By contrast, microorganisms display a multitude of potential targets for insecticide action. The chapter presents an illustrative table on cytological and biochemical effects of insecticides on microorganisms. In Dunaliella bioculata , lindane at 10 ppm altered the number of cellular organelles and caused degeneration of nuclear apparatus. Most of the insecticides have low water solubility. Hence they are incorporated in lipid-rich cellular structures. Therefore, biomembranes are good candidates as targets of insecticide action. In autotrophic microorganisms insecticides alter the structure of chloroplast and interfere with photophosphorylation in the light reaction of photosynthesis, which may be responsible for the reduction in CO 2 fixation and a decrease in the amount of soluble sugars.

Exploring bacterial diversity from contaminated soil samples from river Yamuna

The Yamuna is the source of key water supply in the national capital region of India. Due to its immense importance, the pollution of Yamuna has become an imperative issue of study. Various initiatives have been taken by the Indian Government to decontaminate this river, but so far no possible outcome has been obtained. Therefore bioremediation may seem to be a promising approach. To assess the bioremediation potential of the microbes at river Yamuna, study of microbial diversity was carried out. Escherichia, Pseudomonas, Bacillus, Thermomicrobium, Azoarcus, Nitrosomonas and Shigella were the dominant genera present at the contaminated river coastal zone. The presence of Escherichia and Shigella indicated the sewage contamination in the river. On the other hand, the presence of Pseudomonas and Bacillus indicated the existence of indigenous bacterial communities capable of de-polluting the river, thus providing a promising approach to decontaminate Yamuna by natural means.

Bioconcentration and metabolism of aldrin and phorate by the blue-green algae Anabaena (ARM 310) and Aulosira fertilissima (ARM 68)

Abstract Anabaena sp. and Aulosira fertilissima showed marked ability to bioconcentrate aldrin and phorate from culture medium. Uptake was directly related to the insecticide concentration in the medium and was inversely related to the water solubility of the insecticides. Bioconcentration of aldrin in Anabaena sp. and A. fertilissima ranged from 3.9 to 247.5 μg g −1 , respectively. Maximum concentration of aldrin in the blue-green algae was reached after 8–16 h and that of phorate after 16–32 h. Aldrin was metabolised to dieldrin by both blue-green algae but no metabolism was noticed in the case of phorate.

From dengue to Zika: the wide spread of mosquito-borne arboviruses

The worldwide invasion of arthropod-borne viruses (arboviruses) in recent decades is responsible for emerging public health threats. Some factors like climate change, urbanisation and uncontrolled population growth are fuelling their widespread. Arboviruses incorporate a vast collection of genetically diverse viral pathogens including that of dengue, Zika and chikungunya. These viruses are peculiar as they are zoonotic and are a serious harm to the society, with no particular therapy to neutralise their effect. So it is the need of the hour to develop an effective treatment against infections caused by them. This review focuses on some of the common families of mosquito-borne arboviruses and their most known members that are a threat to mankind and discusses their genome organisation, worldwide spread and negative influence on public health.

Identification of genus Campylobacter up to species level using internal features of 16S rRNA gene sequences

Introduction: 16S rRNA sequencing of novel isolates is one of the preliminary steps in characterization of bacteria, especially when the isolates are of medical relevance. The genus Campylobacter belongs to Class ε-proteobacteria under the Phylum Proteobacteria. It represents economically important species which are gastrointestinal pathogens in humans and livestock animals. Currently, more than 400 16S rDNA sequences belonging to 28 species of this genus are present in the RDP database. But heterogeneity has led to the misplacement of many of these sequences within wrong species. Also, various sequences belonging to Campylobacter have been deposited as orphans. The current study aimed to explore the internal features of 16S rRNA gene sequences in order to develop methods for identification of Campylobacter up to species level. Methods: 428 16S rRNA sequences of 28 species of Campylobacter were analyzed. 392 sequences (>1200 nucleotides, nts) of 16 species were considered for (i) phylogenetic framework analysis and (ii) in silico restriction digestion. 28 uncharacterized sequences present in the database were also investigated in the present study. Results: Phylogenetic framework analysis allowed the identification of genetic variability within Campylobacter species and helped to segregate certain uncharacterized sequences up to species level. 12 out of the 16 species under study showed homogenous behavior, but heterogeneity was observed between C. jejuni and C. coli and C. helveticus and C. upsaliensis respectively. Unique restriction enzymes were identified for six species. Conclusions: The present approach clearly showed that internal features of 16S rRNA is a useful tool for characterization of novel isolates up to the species level. Studies have revealed that niche overlap and consequent increase in the horizontal gene transfer between C. coli and C. jejuni, due to anthropogenic factors, maybe the reason for their heterogeneous nature. This explains the difficulties faced in segregation of the members of these species. 16S rRNA gene proved to be a viable and excellent marker for characterizing the uncharacterized Campylobacter strains leading to a significant diminution in database redundancy. Further, the approaches used in the study might assist in easier identification of the various Campylobacter sequences present in the database.