The reactions of bacterial viruses with their host cells

The Botanical Review -     

Action of Bacillus sphaericus endopeptidases on bacterial peptidoglycans and peptidoglycan fragments

Two endopeptidases have been characterized in Bacillus sphaericus 9602: a gamma-D-glutamyl-(L) meso-diaminopimelate endopeptidase (endopeptidase I) and a gamma-D-glutamyl-L-diaminoacid endopeptidase (endopeptidase II). They are active on the peptide moieties of some bacterial peptidoglycans. Their specificities have been studied on peptides or monomeric glycopeptides derived from peptidoglycans. Their study was attempted on dimeric and polymeric fragments of a E. coli radioactive peptidoglycan. Those compounds are specifically labelled on the meso-diaminopimelate residues and are listed below.     

Adjuvant activity of monomeric bacterial cell wall peptidoglycans

We have previously shown that lysozyme solubilized cell walls of Mycobacteria or Nocardiae can replace whole mycobacterial cells or Wax D in Freund's complete adjuvant and it was found quite recently that hydrosoluble peptidoglycans, free of neutral sugars, are also adjuvant active. We show now that the simplest fragment tested — the disaccharide tetrapeptide (I) — increases circulating antibodies to ovalbumin and induces a delayed hypersensitivity toward this antigen. Similar compounds obtained from the basal layer of the cell wall of $\text{E. coli}$ are also active. Thus the immunoadjuvant activity of soluble cell wall peptidoglycans is a property of the monomeric unit and is not restricted to acid fast bacteria.     

Endogenous viruses: insights into viral evolution and impact on host biology

Recent studies have uncovered myriad viral sequences that are integrated or 'endogenized' in the genomes of various eukaryotes. Surprisingly, it appears that not just retroviruses but almost all types of viruses can become endogenous. We review how these genomic 'fossils' offer fresh insights into the origin, evolutionary dynamics and structural evolution of viruses, which are giving rise to the burgeoning field of palaeovirology. We also examine the multitude of ways through which endogenous viruses have influenced, for better or worse, the biology of their hosts. We argue that the conflict between hosts and viruses has led to the invention and diversification of molecular arsenals, which, in turn, promote the cellular co-option of endogenous viruses.     

Prokaryotic toxin-antitoxin systems--the role in bacterial physiology and application in molecular biology

Bacteria have developed multiple complex mechanisms ensuring an adequate response to environmental changes. In this context, bacterial cell division and growth are subject to strict control to ensure metabolic balance and cell survival. A plethora of studies cast light on toxin-antitoxin (TA) systems as metabolism regulators acting in response to environmental stress conditions. Many of those studies suggest direct relations between the TA systems and the pathogenic potential or antibiotic resistance of relevant bacteria. Other studies point out that TA systems play a significant role in ensuring stability of mobile genetic material. The evolutionary origin and relations between various TA systems are still a subject of a debate. The impact of toxin-antitoxin systems on bacteria physiology prompted their application in molecular biology as tools allowing cloning of some hard-to-maintain genes, plasmid maintenance and production of recombinant proteins.     

Gut bacterial communities in the Mediterranean fruit fly (Ceratitis capitata) and their impact on host longevity

Fruit flies (Diptera: Tephritidae) harbor stable bacterial communities in their digestive system, composed mainly of members of the Enterobacteriaceae. However, the Enterobacteriaceae are not the sole community in this habitat. We examined the hypothesis that Pseudomonas spp. form a cryptic community in the gut of Ceratitis capitata, the Mediterranean fruit fly (‘medfly’). Suicide polymerase restriction PCR (SuPER PCR), a novel culture-independent technique, revealed that Pseudomonas spp. form minor, common and stable communities within the medfly's gut. These include P. aeruginosa, a known pathogen of arthropods. Experimental inoculations with high levels of P. aeruginosa reduced the medfly's longevity while inoculations with members of the Enterobacteriaceae extended the fly's life.Accordingly, we suggest that in addition to their possible contribution to the fly's nitrogen and carbon metabolism, development and copulatory success (as shown in previous studies), the Enterobacteriaceae community within the medfly's gut may also have an indirect contribution to host fitness by preventing the establishment or proliferation of pathogenic bacteria.     

The effect of bacterial and synthetic peptidoglycans on the toxicity of a cell-free pertussis preparation

The influence of bacterial and synthetic peptidoglycans on the toxicity of acellular pertussis preparations (APP) has been studied in the mouse weight gain test and in the endotoxic shock development test on mice treated with Actinomycin D. The data obtained in these tests indicate that the immunomodulators (IM) under study are capable of changing (increasing or decreasing, depending on the dose) the toxic properties of APP. The antitoxic action of IM, established in this study, depends on the combination of the doses of IM and APP and the time elapsed from the time of immunization. The possibility of using these IM in a dose of 0.0001 microgram for reducing the LD50 of APP has been established. The use of IM belonging to the group of bacterial synthetic peptidoglycans for the development of acellular pertussis vaccines with reduced reactogenicity has been shown to hold much promise.     

Cassava biology and physiology

Cassava or manioc (Manihot esculenta Crantz), a perennial shrub of the New World, currently is the sixth world food crop for more than 500 million people in tropical and sub-tropical Africa, Asia and Latin America. It is cultivated mainly by resource-limited small farmers for its starchy roots, which are used as human food either fresh when low in cyanogens or in many processed forms and products, mostly starch, flour, and for animal feed. Because of its inherent tolerance to stressful environments, where other food crops would fail, it is often considered a food-security source against famine, requiring minimal care. Under optimal environmental conditions, it compares favorably in production of energy with most other major staple food crops due to its high yield potential. Recent research at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia has demonstrated the ability of cassava to assimilate carbon at very high rates under high levels of humidity, temperature and solar radiation, which correlates with productivity across all environments whether dry or humid. When grown on very poor soils under prolonged drought for more than 6 months, the crop reduce both its leaf canopy and transpiration water loss, but its attached leaves remain photosynthetically active, though at greatly reduced rates. The main physiological mechanism underlying such a remarkable tolerance to drought was rapid stomatal closure under both atmospheric and edaphic water stress, protecting the leaf against dehydration while the plant depletes available soil water slowly during long dry periods. This drought tolerance mechanism leads to high crop water use efficiency values. Although the cassava fine root system is sparse, compared to other crops, it can penetrate below 2 m soil, thus enabling the crop to exploit deep water if available. Leaves of cassava and wild Manihot possess elevated activities of the C₄ enzyme PEP carboxylase but lack the leaf Kranz anatomy typical of C₄ species, pointing to the need for further research on cultivated and wild Manihot to further improve its photosynthetic potential and yield, particularly under stressful environments. Moreover, a wide range in values of K _m (CO₂) for the C₃ photosynthetic enzyme Rubisco was found among cassava cultivars indicating the possibility of selection for higher affinity to CO₂, and consequently higher leaf photosynthesis. Several plant traits that may be of value in crop breeding and improvement have been identified, such as an extensive fine root system, long leaf life, strong root sink and high leaf photosynthesis. Selection of parental materials for tolerance to drought and infertile soils under representative field conditions have resulted in developing improved cultivars that have high yields in favorable environments while producing reasonable and stable yields under stress.     

Cassava biology and physiology

Cassava or manioc (Manihot esculenta Crantz), a perennial shrub of the New World, currently is the sixth world food crop for more than 500 million people in tropical and sub-tropical Africa, Asia and Latin America. It is cultivated mainly by resource-limited small farmers for its starchy roots, which are used as human food either fresh when low in cyanogens or in many processed forms and products, mostly starch, flour, and for animal feed. Because of its inherent tolerance to stressful environments, where other food crops would fail, it is often considered a food-security source against famine, requiring minimal care. Under optimal environmental conditions, it compares favorably in production of energy with most other major staple food crops due to its high yield potential. Recent research at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia has demonstrated the ability of cassava to assimilate carbon at very high rates under high levels of humidity, temperature and solar radiation, which correlates with productivity across all environments whether dry or humid. When grown on very poor soils under prolonged drought for more than 6 months, the crop reduce both its leaf canopy and transpiration water loss, but its attached leaves remain photosynthetically active, though at greatly reduced rates. The main physiological mechanism underlying such a remarkable tolerance to drought was rapid stomatal closure under both atmospheric and edaphic water stress, protecting the leaf against dehydration while the plant depletes available soil water slowly during long dry periods. This drought tolerance mechanism leads to high crop water use efficiency values. Although the cassava fine root system is sparse, compared to other crops, it can penetrate below 2 m soil, thus enabling the crop to exploit deep water if available. Leaves of cassava and wildManihotpossess elevated activities of the C₄ enzyme PEP carboxylase but lack the leaf Kranz anatomy typical of C₄ species, pointing to the need for further research on cultivated and wild Manihot to further improve its photosynthetic potential and yield, particularly under stressful environments. Moreover, a wide range in values of K _m (CO₂) for the C₃ photosynthetic enzyme Rubisco was found among cassava cultivars indicating the possibility of selection for higher affinity to CO₂, and consequently higher leaf photosynthesis. Several plant traits that may be of value in crop breeding and improvement have been identified, such as an extensive fine root system, long leaf life, strong root sink and high leaf photosynthesis. Selection of parental materials for tolerance to drought and infertile soils under representative field conditions have resulted in developing improved cultivars that have high yields in favorable environments while producing reasonable and stable yields under stress.     

The cell biology of Listeria monocytogenes infection: the intersection of bacterial pathogenesis and cell-mediated immunity

Listeria monocytogenes has emerged as a remarkably tractable pathogen to dissect basic aspects of cell biology, intracellular pathogenesis, and innate and acquired immunity. In order to maintain its intracellular lifestyle, L. monocytogenes has evolved a number of mechanisms to exploit host processes to grow and spread cell to cell without damaging the host cell. The pore-forming protein listeriolysin O mediates escape from host vacuoles and utilizes multiple fail-safe mechanisms to avoid causing toxicity to infected cells. Once in the cytosol, the L. monocytogenes ActA protein recruits host cell Arp2/3 complexes and enabled/vasodilator-stimulated phosphoprotein family members to mediate efficient actin-based motility, thereby propelling the bacteria into neighboring cells. Alteration in any of these processes dramatically reduces the ability of the bacteria to establish a productive infection in vivo.     

Characterisation of Legionella pneumophila phospholipases and their impact on host cells

Phospholipases are a diverse class of enzymes produced both by eukaryotic hosts and their pathogens. Major insights into action pathways of bacterial phospholipases have been provided during the last years. On the one hand bacterial phospholipases act as potent membrane destructors and on the other hand they manipulate and initiate host signalling paths, such as chemokine expression or the inflammatory cascade. Reaction products of bacterial phospholipases may potentially influence many more host cell processes, such as cell respreading, lamellopodia formation, cell migration and membrane traffic. Phospholipases play a dominant role in the biology of the lung pathogen Legionella pneumophila. So far, 15 different phospholipase A-encoding genes have been identified in the L. pneumophila genome. These phospholipases can be divided into three major groups, the GDSL, the patatin-like and the PlaB-like enzymes. The first two lipase families are also found in higher plants (such as flowering plants) and the second family shows similarities to eukaryotic cytosolic phospholipases A. Therefore, when those enzymes are injected or secreted by the bacterium into the host cell they may mimic eukaryotic phospholipases. The current knowledge on L. pneumophila phospholipases is summarised here with emphasis on their activity, mode of secretion, localisation, expression and importance for host cell infections.     

mkl基因在海分枝杆菌抵抗宿主免疫中的作用

本研究利用 MycoMarT7噬菌体建立了海分枝杆菌随机突变库,鉴定获得1株转座子插在基因MMAR＿0994（mkl）上的突变株。用野生株和突变株分别感染斑马鱼成鱼,通过观察斑马鱼的存活情况,研究 mkl基因对海分枝杆菌毒力的影响;利用尾静脉注射感染孵出48 h后的斑马鱼幼鱼,于荧光显微镜下观察突变株及野生株在幼鱼体内的播散情况,以检测 mkl基因在细菌与宿主天然免疫相互作用中的功能;将野生株和突变株分别感染小鼠来源巨噬细胞,检测其在巨噬细胞内的增殖。此外,还检测了突变株对酸性环境的耐受情况。结果显示,mkl基因突变株感染斑马鱼成鱼后25 d内没有鱼死亡;在斑马鱼幼鱼感染模型和细胞感染模型中,突变株的增殖明显减弱;突变株对酸性环境压力更敏感。以上结果提示,mkl基因在海分枝杆菌抵抗宿主免疫及致病中发挥重要作用。