MicrobiologyBytes

The immune system of plants can be unstable in the face of rapidly evolving micro-organisms, and pathogens that can evade recognition can spread with alarming speed through a plant population. In this article in Microbiology Today, Gail Preston and Dawn Arnold ask, what is the reason for this inherent instability, and how can disease control be improved?

Plants, unlike animals, lack an adaptive immune system that allows them to recognize and defend against novel pathogenic micro-organisms. Instead they rely on a heritable, innate immune system in which plant receptors recognize the presence or activity of microbial molecules known as elicitors. Plants exposed to infection can increase the effectiveness of their immune system by increasing the speed and strength of their defence mechanisms. However, pathogens that have the ability to evade recognition can spread rapidly through plant populations. The instability of receptor-dependent resistance in the face of rapid microbial evolution creates one of the most fundamental challenges in plant breeding. In this article we discuss why receptordependent resistance breaks down in the face of pathogen evolution and consider whether knowledge of pathogen evolution can provide insights to improve disease control.

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Related:

• Toxins for microbial attack and plant defence
• Bacteriophages for plant disease control

This article reviews recent research on Rift Valley fever virus (RVFV) infection, encompassing four main areas: epidemiology and outbreak prediction, viral pathogenesis, human diagnostics and therapeutics, and vaccine and therapeutic candidates. RVFV continues to extend its range in Africa and the Middle East. Better definition of RVFV-related clinical syndromes and human risk factors for severe disease, combined with early-warning systems based on remote-sensing, simplified rapid diagnostics, and tele-epidemiology, hold promise for earlier deployment of effective outbreak control measures. Advances in understanding of viral replication pathways and host cell-related pathogenesis suggest means for antiviral therapeutics and for more effective vaccination strategies based on genetically engineered virus strains or subunit vaccines. RVFV is a significant health and economic burden in many areas of Africa, and remains a serious threat to other parts of the world. Development of more effective methods for RVFV outbreak prevention and control remains a global health priority.

Advances in Rift Valley fever research: insights for disease prevention. Curr Opin Infect Dis. Jul 6 2010 doi: 10.1097/QCO.0b013e32833c3da6

Group A rotaviruses (RVs) are important pathogens that cause acute, dehydrating gastroenteritis in infants and young children. The burden of disease is severe, particularly in developing countries where RV infections lead to more than 500,000 deaths annually. RVs are non-enveloped, triple-layered icosahedral particles that enclose an eleven-segmented, double-stranded (ds) RNA genome. The genome encodes six structural proteins (VP1–VP4, VP6, and VP7) and five or six non-structural proteins (NSP1–NSP5, and sometimes NSP6). Individual RV strains have traditionally been classified into serotypes based on the antibody responses generated against the outermost structural proteins VP7 (G-serotypes) and VP4 (P-serotypes). Due to the ease of sequencing, RVs are now classified into G/P-genotypes based on the relatedness of the genes encoding VP7 and VP4.

Although the mechanism by which RV infection leads to immunological protection is not fully understood, G/P-type-specific neutralizing antibodies have been shown to play an important role. Strains with particular G/P-type combinations are the most prevalent causes of disease in humans worldwide, and these are the targets of the two currently licensed RV vaccines. RotaTeq (Merck) contains five live-attenuated, reassortant viruses with human VP7 genes in a predominantly bovine RV background. In contrast, Rotarix (GlaxoSmithKline) is a live-attenuated, human RV containing genotype 1 internal genes. Both vaccines have proven safe and effective at protecting against severe diarrheal disease in industrialized countries and Latin America. However, the efficacy of RotaTeq and Rotarix in developing countries is expected to be reduced, which may be related to viral serotype diversity among other factors. Additionally, the high monetary cost of these current vaccines may limit their availability in regions of the world where they are most needed. As a result, there is a global health initiative to develop new RV vaccines that can be manufactured on-site at a lower cost. Two vaccine candidates being considered are the live-attenuated human strains RV3 and 116E.

Complete genome sequence analysis of candidate human rotavirus vaccine strains RV3 and 116E. Virology. Jun 25 2010
Rotaviruses (RVs) cause severe gastroenteritis in infants and young children; yet, several strains have been isolated from newborns showing no signs of clinical illness. Two of these neonatal strains, RV3 (G3P[6]) and 116E (G9P[11]), are currently being developed as live-attenuated vaccines. In this study, we sequenced the eleven-segmented double-stranded RNA genomes of cell culture-adapted RV3 and 116E and compared their genes and protein products to those of other RVs. Using amino acid alignments and structural predictions, we identified residues of RV3 or 116E that may contribute to attenuation or influence vaccine efficacy. We also discovered residues of the VP4 attachment protein that correlate with the capacity of some P[6] strains, including RV3, to infect newborns versus older infants. The results of this study enhance our understanding of the molecular determinants of RV3 and 116E attenuation and are expected to aid in the ongoing development of these vaccine candidates.

Related:

• Rotavirus vaccines for the developing world
• Rotavirus Infection: A Systemic Illness?

Mycobacterium tuberculosis was first isolated more than 125 years ago. Although a huge amount of research has been devoted to it over this time, tuberculosis still represents a major public health threat in many countries. The main hindrances in fighting this disease include a lack of understanding of the human infection, its establishment and progression, as well as the host-pathogen interactions that determine the different outcomes. Furthermore, the treatment regimen of six months administration of up to four drugs has not evolved in more than four decades, and recent years have seen an alarming increase in multi-drug resistant (MDR) and extensively drug-resistant (XDR) strains. It is clear then that novel and imaginative approaches are needed to speed up both basic and translational research in tuberculosis, especially in the areas of vaccine and drug development.

Optimisation of Bioluminescent Reporters for Use with Mycobacteria. 2010 PLoS ONE 5(5): e10777. doi:10.1371/journal.pone.0010777
Mycobacterium tuberculosis, the causative agent of tuberculosis, still represents a major public health threat in many countries. Bioluminescence, the production of light by luciferase-catalyzed reactions, is a versatile reporter technology with multiple applications both in vitro and in vivo. In vivo bioluminescence imaging (BLI) represents one of its most outstanding uses by allowing the non-invasive localization of luciferase-expressing cells within a live animal. Despite the extensive use of luminescent reporters in mycobacteria, the resultant luminescent strains have not been fully applied to BLI.
One of the main obstacles to the use of bioluminescence for in vivo imaging is the achievement of reporter protein expression levels high enough to obtain a signal that can be detected externally. Therefore, as a first step in the application of this technology to the study of mycobacterial infection in vivo, we have optimised the use of firefly, Gaussia and bacterial luciferases in mycobacteria using a combination of vectors, promoters, and codon-optimised genes. We report for the first time the functional expression of the whole bacterial lux operon in Mycobacterium tuberculosis and M. smegmatis thus allowing the development of auto-luminescent mycobacteria. We demonstrate that the Gaussia luciferase is secreted from bacterial cells and that this secretion does not require a signal sequence. Finally we prove that the signal produced by recombinant mycobacteria expressing either the firefly or bacterial luciferases can be non-invasively detected in the lungs of infected mice by bioluminescence imaging.
While much work remains to be done, the finding that both firefly and bacterial luciferases can be detected non-invasively in live mice is an important first step to using these reporters to study the pathogenesis of M. tuberculosis and other mycobacterial species in vivo. Furthermore, the development of auto-luminescent mycobacteria has enormous ramifications for high throughput mycobacterial drug screening assays which are currently carried out either in a destructive manner using LuxAB or the firefly luciferase.

Related:

• Public health and bovine tuberculosis
• Origin and spread of Mycobacterium tuberculosis
• Tuberculosis – is the white plague winning?

Some of the most hyperthermophilic bacteria are found within the genus Thermotoga. This article in Microbiology Today explains how these properties could make these micro-organisms promising new sources of biofuels:

Thermotoga first attracted the attention of biotechnologists because of the variety of thermophilic enzymes found in the genus. These bacteria grow on different carbohydrates that are degraded into their sugar monomers before they are taken up and metabolized. It has therefore been possible to isolate, characterize and use a number of highly thermostable hydrolytic and other enzymes from Thermotoga.

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• Life’s a gas… and it’s hydrogen
• Some bacteria degrade explosives, others prefer boiling methanol

With an estimated annual incidence of over nine million cases, tuberculosis (TB) is believed to be responsible for more adult deaths each year than any other single infectious agent. The highest burden of disease is currently borne by the less developed countries of Africa and Asia where efforts to control TB are hampered by weak health systems and in some settings, by the high prevalence of co-infection with HIV. The recent emergence of multidrugresistant stains that cannot be cured with standard treatments has served to emphasize the urgency of the situation. Control of TB in high burden countries relies on the detection and treatment of infectious cases, most usually by testing patients attending a health clinic that report a cough of at least three weeks duration. The diagnostic tests available in these settings are sputum smear microscopy, an insensitive technique requiring a skilled practitioner and chest radiography, a technique lacking in specificity as well as sensitivity. World Health Organization estimates suggest that in 2006 there were 4 million individuals with undiagnosed tuberculosis. More effective interventions are required to detect and treat infectious cases earlier in the transmission chain, particularly in vulnerable communities with a high prevalence of HIV.

Mycobacterium tuberculosis, the causative agent is spread from person to person via infected aerosols created by patients with respiratory forms of the disease. Bacilli released into the airways following necrosis and destruction of lung tissue may be expelled from the lungs and if released in the form of aerosols may remain airborne and available for inhalation and infection of a new host. Despite being the major mode of transmission there is little data available regarding the exhalation of M. tuberculosis. This paper describes testing of a novel device that utilizes immunosensor and bio-optical technology to detect M. tuberculosis antigen in the breath of humans.

Field test of a novel detection device for Mycobacterium tuberculosis antigen in cough. BMC Infectious Diseases 2010, 10: 161 doi:10.1186/1471-2334-10-161
Tuberculosis is a highly infectious disease that is spread from person to person by infected aerosols emitted by patients with respiratory forms of the disease. We describe a novel device that utilizes immunosensor and bio-optical technology to detect M. tuberculosis antigen (Ag85B) in cough and demonstrate its use under field conditions during a pilot study in an area of high TB incidence.
The TB Breathalyzer device (Rapid Biosensor Systems Ltd) was field tested in the outpatient clinic of Adama Hospital, Ethiopia. Adults seeking diagnosis for respiratory complaints were tested. Following nebulization with 0.9% saline patients were asked to cough into a disposable collection device where cough aerosols were deposited. Devices were then inserted into a portable instrument to assess whether antigen was present in the sample. Demographic and clinical data were recorded and all patients were subjected to chest radiogram and examination of sputum by Ziehl-Nielsen microscopy. In the absence of culture treatment decisions were based on smear microscopy, chest x-ray and clinical assessment. Breathalyzer testing was undertaken by a separate physician to triage and diagnostic assessment.
Sixty individuals were each subjected to a breathalyzer test. The procedure was well tolerated and for each patient the testing was completed in less than 10 min. Positive breath test results were recorded for 29 (48%) patients. Of 31 patients with a diagnosis of tuberculosis 23 (74%) were found positive for antigen in their breath and 20 (64%) were smear positive for acid fast bacilli in their sputum. Six patients provided apparent false positive breathalyzer results that did not correlate with a diagnosis of tuberculosis.
We propose that the breathalyzer device described warrants further investigation as a tool for studying exhalation of M. tuberculosis. The portability, simplicity of use and speed of the test device suggest it may also find use as a tool to aid early identification of infectious cases. We recommend studies be undertaken to determine the diagnostic sensitivity and specificity of the device when compared to microbiological and clinical indicators of tuberculosis disease.

Related:

• Why is TB more common in men than in women?
• Origin and spread of Mycobacterium tuberculosis
• Public health and bovine tuberculosis

The ocean is teaming with sunken treasure and for some treasure hunters the sand itself is the target. In this article in Microbiology Today, Jem Stach tells how novel actinomycetes on the seabed could be a source of much-needed novel antimicrobial drugs:

For most, the search for sunken treasure evokes images of glistening gold discovered when a diver’s hand wafts away the sand. However, for another kind of treasure hunter, the bioprospector, the sand itself is the target, brought from the depths of the sea, to the laboratory bench. In this case, the bioprospector is interested in marine microbes and their potential to produce antimicrobial compounds. With global sales of these life-saving products set to exceed $100 billion by 2015, such micro-organisms could be worth more than their weight in gold.

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Related:

• The weird and wonderful actinobacteria
• An introduction to the actinobacteria

Malaria caused by Plasmodium falciparum is a disease that is responsible for 880,000 deaths per year worldwide. Vaccine development has proved difficult and resistance has emerged for most antimalarial drugs. To discover new antimalarial chemotypes, researchers have used a chemical genetic approach to assay 309,474 chemicals. Many chemicals in the library of compounds tested showed potent in vitro activity against drug-resistant P. falciparum strains. A reverse chemical genetic study identified 19 new inhibitors of 4 validated drug targets and 15 novel binders among 61 malarial proteins. Phylochemogenetic profiling in several organisms revealed similarities between Toxoplasma gondii and mammalian cell lines and dissimilarities between P. falciparum and related protozoans. One exemplar compound displayed efficacy in a mouse model. These findings provide the scientific community with new starting points for malaria drug discovery.

Chemical genetics of Plasmodium falciparum. Nature 465, 311–315 (2010) doi:10.1038/nature09099

Related:

• Drug discovery: Priming the antimalarial pipeline
• Nature Collections – Malaria
• New ways to beat malaria

Strategies to reduce emissions of carbon dioxide (CO₂) from fossil fuels, and hence mitigate climate change, include energy savings, development of renewable biofuels, and carbon capture and storage (CCS). For CCS, several scenarios are being considered. One approach is capture of point-source CO₂ from power plants or other industrial sources and subsequent injection of the concentrated CO₂ underground or into the ocean. An alternative to this point-source CCS method is expansion of biological carbon sequestration of atmospheric CO₂ by measures such as reforestation, changes in land use practices, increased carbon allocation to underground biomass, production of biochar, and enhanced biomineralization. In addition to geological or oceanic CO₂ injection, novel models for point-source CCS based on accelerated weathering and biomineralization are emerging, utilizing either abiotic or biotic processes. Biomineralization of CO₂ by calcium carbonate (CaCO3) precipitation is a common phenomenon in marine, freshwater, and terrestrial ecosystems and is a fundamental process in the global carbon cycle.

Employment of cyanobacteria in biomineralization of carbon dioxide by calcium carbonate precipitation offers novel and self-sustaining strategies for point-source carbon capture and sequestration. Although details of this process remain to be elucidated, a carbon-concentrating mechanism, and chemical reactions in exopolysaccharide or proteinaceous surface layers are assumed to be of crucial importance. Cyanobacteria can utilize solar energy through photosynthesis to convert carbon dioxide to recalcitrant calcium carbonate. Calcium can be derived from sources such as gypsum or industrial brine. A better understanding of the biochemical and genetic mechanisms that carry out and regulate cynaobacterial biomineralization should put us in a position where we can further optimize these steps by exploiting the powerful techniques of genetic engineering, directed evolution, and biomimetics.

Calcifying cyanobacteria-the potential of biomineralization for carbon capture and storage. Curr Opin Biotechnol. Apr 22 2010

Related:

• Growing Algae to Mop Up CO₂ off Antarctica
• Saturday Cinema: Cyanobacteria