The relationship among (i ) the local incidence of cholera, (ii) the prevalence in the aquatic environment of Vibrio cholerae, and (iii) bacterial viruses that attack potentially virulent O1 and O139 serogroup strains of this organism (cholera phages) was studied in Dhaka, Bangladesh. Over nearly a 3-year period, we found that significantly more environmental water samples contained either a phage or a phage-susceptible V. cholerae strain than both (P < 0.00001). The number of cholera patients varied seasonally during this period and frequently coincided with the presence of pathogenic V. cholerae strains in water samples that otherwise lacked detectable cholera phages. Interepidemic periods were characterized by water samples containing cholera phages but no viable bacteria. Our data support the conclusion that cholera phages can influence cholera seasonality and may also play a role in emergence of new V. cholerae pandemic serogroups or clones.bacteriophage ͉ seasonality ͉ epidemiology ͉ emergence ͉ lysogeny E pidemics of cholera caused by toxigenic Vibrio cholerae belonging to the O1 or O139 serogroups are a major public health problem in many developing countries of Asia, Africa, and Latin America (1). Cholera epidemics occur with seasonal regularity in the Ganges delta region of Bangladesh and India. Epidemics usually occur twice during a year, with the highest number of cases just after the monsoon during September to December. A somewhat smaller peak of cholera cases also is observed during the spring, between March and May. Although V. cholerae is a human pathogen, these bacteria constitute part of the normal aquatic flora in estuarine environments, and water is clearly a vehicle for transmission of V. cholerae. Although the seasonality of cholera in Bangladesh and elsewhere has been temporally associated with numerous physical and biological parameters (2), these associations do not directly cause epidemics, nor do they end them. More than a century of public health experience has shown that toxigenic O1 and O139 V. cholerae cells cause cholera epidemics and that the elimination of these cells from drinking water ends cholera epidemics. The parameters that directly modulate the level of viable cells belonging to the pathogenic clones of V. cholerae O1 and O139 in the Ganges delta aquatic environment remain unknown. Furthermore, the fact that pathogenic strains of V. cholerae are clonally distinct from environmental, nonpathogenic V. cholerae strains (1) undermines proposed mechanisms of seasonality and pandemic spread that are based on data from studies measuring the abundance of all Vibrio species in the aquatic environment (2).Bacterial viruses (phages) are known to play a critical role in the evolution of pathogenic bacterial species, and V. cholerae in particular. For example, cholera toxin genes are transferred to nontoxigenic strains by means of a lysogenic filamentous phage, CTX⌽ (3). Here we show that the presence of bacterial viruses acting on V. cholerae O1 or O139 (cholera phages or vibriopha...

The enzymes of the family of tRNA synthetases perform their functions with high precision by synchronously recognizing the anticodon region and the aminoacylation region, which are separated by Ϸ70 Å in space. This precision in function is brought about by establishing good communication paths between the two regions. We have modeled the structure of the complex consisting of Escherichia coli methionyl-tRNA synthetase (MetRS), tRNA, and the activated methionine. Molecular dynamics simulations have been performed on the modeled structure to obtain the equilibrated structure of the complex and the cross-correlations between the residues in MetRS have been evaluated. Furthermore, the network analysis on these simulated structures has been carried out to elucidate the paths of communication between the activation site and the anticodon recognition site. This study has provided the detailed paths of communication, which are consistent with experimental results. Similar studies also have been carried out on the complexes (MetRS ؉ activated methonine) and (MetRS ؉ tRNA) along with ligand-free native enzyme. A comparison of the paths derived from the four simulations clearly has shown that the communication path is strongly correlated and unique to the enzyme complex, which is bound to both the tRNA and the activated methionine. The details of the method of our investigation and the biological implications of the results are presented in this article. The method developed here also could be used to investigate any protein system where the function takes place through longdistance communication.dynamic cross-correlations ͉ methionyl-AMP ͉ protein structure network ͉ shortest pathways of communication ͉ stacking A crucial step in the translation of the genetic code is the aminoacylation of tRNA, which involves the molecular recognition between the aminoacyl-tRNA synthetases (aaRS) and their cognate tRNA. Each synthetase consists of the catalytic domain and the anticodon domain that are separated by Ϸ70 Å. Each tRNA connects these two regions with its anticodon and the acceptor stems. The mechanism of differentiations between cognate and noncognate tRNAs depends on contacts of anticodon domain of synthetase and anticodon stem of tRNA. The efficiency of the selection mechanism controls the overall accuracy of protein synthesis (1, 2). Recognition of the protein (aaRS) and the tRNA is explained by using the induced-fit mechanism, which suggests conformational changes in protein, tRNA, or both, leading to the final bound complex (3). However, the details of communication between the anticodon region and the aminoacylation region are less understood.In all living cells, protein synthesis starts with methionine.

Under stress conditions, many species of bacteria enter into starvation mode of metabolism or a physiologically viable but non-culturable (VBNC) state. Several human pathogenic bacteria have been reported to enter into the VBNC state under these conditions. The pathogenic VBNC bacteria cannot be grown using conventional culture media, although they continue to retain their viability and express their virulence. Though there have been debates on the VBNC concept in the past, several molecular studies have shown that not only can the VBNC state be induced under in vitro conditions but also that resuscitation from this state is possible under appropriate conditions. The most notable advance in resuscitating VBNC bacteria is the discovery of resuscitation-promoting factor (Rpf), which is a bacterial cytokines found in both Gram-positive and Gram-negative organisms. VBNC state is a survival strategy adopted by the bacteria, which has important implication in several fields, including environmental monitoring, food technology, and infectious disease management; and hence it is important to investigate the association of bacterial pathogens under VBNC state and the water/foodborne outbreaks. In this review, we describe various aspects of VBNC bacteria, which include their proteomic and genetic profiles under the VBNC state, conditions of resuscitation, methods of detection, antibiotic resistance, and observations on Rpf.

Communication within and across proteins is crucial for the biological functioning of proteins. Experiments such as mutational studies on proteins provide important information on the amino acids, which are crucial for their function. However, the protein structures are complex and it is unlikely that the entire responsibility of the function rests on only a few amino acids. A large fraction of the protein is expected to participate in its function at some level or other. Thus, it is relevant to consider the protein structures as a completely connected network and then deduce the properties, which are related to the global network features. In this direction, our laboratory has been engaged in representing the protein structure as a network of non-covalent connections and we have investigated a variety of problems in structural biology, such as the identification of functional and folding clusters, determinants of quaternary association and characterization of the network properties of protein structures. We have also addressed a few important issues related to protein dynamics, such as the process of oligomerization in multimers, mechanism of protein folding, and ligand induced communications (allosteric effect). In this review we highlight some of the investigations which we have carried out in the recent past. A review on protein structure graphs was presented earlier, in which the focus was on the graphs and graph spectral properties and their implementation in the study of protein structure graphs/networks (PSN). In this article, we briefly summarize the relevant parts of the methodology and the focus is on the advancement brought out in the understanding of protein structure-function relationships through structure networks. The investigations of structural/biological problems are divided into two parts, in which the first part deals with the analysis of PSNs based on static structures obtained from x-ray crystallography. The second part highlights the changes in the network, associated with biological functions, which are deduced from the network analysis on the structures obtained from molecular dynamics simulations.

Molecular mechanisms of multidrug resistance in Vibrio cholerae belonging to non-O1, non-O139 serogroups isolated during 1997 to 1998 in Calcutta, India, were investigated. Out of the 94 strains examined, 22 strains were found to have class I integrons. The gene cassettes identified were dfrA1, dfrA15, dfrA5, and dfrA12 for trimethoprim; aac(6)-Ib for amikacin and tobramycin; aadA1 and aadA2 for streptomycin and spectinomycin; and ereA2 for erythromycin resistance. To our knowledge, this is the first report of the presence of dfrA5, dfrA12, aac(6)-Ib, and ereA2 cassettes in class I integrons of V. cholerae. Forty-three of 94 strains also had plasmids, and out of these, 14 contained both class I integrons and plasmids. Pulsed-field gel electrophoresis followed by Southern hybridization revealed that in the 14 plasmid-bearing strains, class I integrons resided either on chromosomes, on plasmids, or on both. Our results indicated that besides class I integrons and plasmids, a conjugative transposon element, SXT, possibly contributed to the multiple antibiotic resistance.Cholera is a serious epidemic disease caused by the gramnegative bacterium Vibrio cholerae. Only V. cholerae strains belonging to the O1 and O139 serogroups are thought to be capable of causing epidemic cholera. Strains belonging to serogroups other than O1 and O139, collectively referred to as non-O1, non-O139 strains, are ubiquitously found in the aquatic environs (19) and are also capable of causing sporadic diarrhea. In 1996, an inexplicable upsurge in the incidence of cholera strains belonging to serogroups other than O1 and O139 occurred in Calcutta, India. After extensive molecular characterization, these strains were found to be devoid of the ctx filamentous phage (CTX) (31) and some other virulence genes (27). Based on these findings, it was concluded that some strains of V. cholerae belonging to different serotypes can cause diarrhea clinically indistinguishable from that associated with cholera (5) by a mechanism that could be distinct from that employed by the toxigenic V. cholerae O1 and O139 strains. The nomenclature "enteropathogenic V. cholerae" (EPVC) was proposed to include these serotypes (27). The incidence of EPVC had shown an upward trend from 1997 that continued into 1998. In the months of July and August 1998, the EPVC strains constituted one-third of the V. cholerae strains isolated from hospitalized patients (12). Recently a comparative study of clinical and environmental isolates of non-O1, non-O139 V. cholerae strains belonging to matching serogroups from our laboratories revealed that, despite sharing the same serogroups, the environmental and clinical isolates were genetically heterogeneous and also that the resistance to multiple antibiotics was more common among the clinical isolates (5). Multiple-antibiotic-resistant isolates of non-O1, non-O139V. choelrae strains were identified in children with diarrhea in Bangkok, Thailand (7).Reports of drug-resistant V. cholerae strains are appearing with increasing frequency (2...

Apophysomyces elegans was considered a rare but medically important zygomycete. We analyzed the clinical records of eight patients from a single center in whom zygomycosis due to A. elegans was diagnosed over a span of 25 months. We also attempted a DNA-based method for rapid identification of the fungi and looked for interstrain polymorphism using microsattelite primers. Three patients had cutaneous and subcutaneous infections, three had isolated renal involvement, one had rhino-orbital tissue infection, and the final patient had a disseminated infection involving the spleen and kidney. Underlying illnesses were found in two patients, one with diabetes mellitus and the other with chronic alcoholism. A history of traumatic implantation was available for three patients. All except two of the patients responded to surgical and/or medical therapy; the diagnosis for the two exceptions was made at the terminal stage of infection. Restriction enzyme (MboI, MspI, HinfI) digestion of the PCR-amplified internal transcribed spacer region helped with the rapid and specific identification of A. elegans. The strains could be divided into two groups according to their patterns, with clustering into one pattern obtained by using microsatellite [(GTG) 5 and (GAC) 5 ] PCR fingerprinting. The study highlights the epidemiology, clinical spectrum, and diagnosis of emerging A. elegans infections.Zygomycosis is a serious and often rapidly fatal infection especially in immunocompromised patients. It is caused by sparsely septate filamentous, saprophytic fungi belonging to the class Zygomycetes and the order Mucorales.

Current limitations in quantitatively predicting biological behavior hinder our efforts to engineer biological systems to produce biofuels and other desired chemicals. Here, we present a new method for calculating metabolic fluxes, key targets in metabolic engineering, that incorporates data from 13C labeling experiments and genome-scale models. The data from 13C labeling experiments provide strong flux constraints that eliminate the need to assume an evolutionary optimization principle such as the growth rate optimization assumption used in Flux Balance Analysis (FBA). This effective constraining is achieved by making the simple but biologically relevant assumption that flux flows from core to peripheral metabolism and does not flow back. The new method is significantly more robust than FBA with respect to errors in genome-scale model reconstruction. Furthermore, it can provide a comprehensive picture of metabolite balancing and predictions for unmeasured extracellular fluxes as constrained by 13C labeling data. A comparison shows that the results of this new method are similar to those found through 13C Metabolic Flux Analysis (13C MFA) for central carbon metabolism but, additionally, it provides flux estimates for peripheral metabolism. The extra validation gained by matching 48 relative labeling measurements is used to identify where and why several existing COnstraint Based Reconstruction and Analysis (COBRA) flux prediction algorithms fail. We demonstrate how to use this knowledge to refine these methods and improve their predictive capabilities. This method provides a reliable base upon which to improve the design of biological systems.

Arbuscular mycorrhizal fungi (AMF) are considered as a potential biotechnological tool for improving phytostabilization efficiency and plant tolerance to heavy metal-contaminated soils. However, the mechanisms through which AMF help to alleviate metal toxicity in plants are still poorly understood. A greenhouse experiment was conducted to evaluate the effects of two AMF species (Funneliformis mosseae and Rhizophagus intraradices) on the growth, Pb accumulation, photosynthesis and antioxidant enzyme activities of a leguminous tree (Robinia pseudoacacia L.) at Pb addition levels of 0, 500, 1000 and 2000 mg kg-1 soil. AMF symbiosis decreased Pb concentrations in the leaves and promoted the accumulation of biomass as well as photosynthetic pigment contents. Mycorrhizal plants had higher gas exchange capacity, non-photochemistry efficiency, and photochemistry efficiency compared with non-mycorrhizal plants. The enzymatic activities of superoxide dismutase (SOD), ascorbate peroxidases (APX) and glutathione peroxidase (GPX) were enhanced, and hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents were reduced in mycorrhizal plants. These findings suggested that AMF symbiosis could protect plants by alleviating cellular oxidative damage in response to Pb stress. Furthermore, mycorrhizal dependency on plants increased with increasing Pb stress levels, indicating that AMF inoculation likely played a more important role in plant Pb tolerance in heavily contaminated soils. Overall, both F. mosseae and R. intraradices were able to maintain efficient symbiosis with R. pseudoacacia in Pb polluted soils. AMF symbiosis can improve photosynthesis and reactive oxygen species (ROS) scavenging capabilities and decrease Pb concentrations in leaves to alleviate Pb toxicity in R. pseudoacacia. Our results suggest that the application of the two AMF species associated with R. pseudoacacia could be a promising strategy for enhancing the phytostabilization efficiency of Pb contaminated soils.