- Volume 165, Issue 9, 2019
Volume 165, Issue 9, 2019
- Review
-
-
-
Phasevarions of bacterial pathogens – phase-variable epigenetic regulators evolving from restriction–modification systems
More LessPhase-variable DNA methyltransferases control the expression of multiple genes via epigenetic mechanisms in a wide variety of bacterial species. These systems are called phasevarions, for phase-variable regulons. Phasevarions regulate genes involved in pathogenesis, host adaptation and antibiotic resistance. Many human-adapted bacterial pathogens contain phasevarions. These include leading causes of morbidity and mortality worldwide, such as non-typeable Haemophilus influenzae , Streptococcus pneumoniae and Neisseria spp. Phase-variable methyltransferases and phasevarions have also been discovered in environmental organisms and veterinary pathogens. The existence of many different examples suggests that phasevarions have evolved multiple times as a contingency strategy in the bacterial domain, controlling phenotypes that are important in adapting to environmental change. Many of the organisms that contain phasevarions have existing or emerging drug resistance. Vaccines may therefore represent the best and most cost-effective tool to prevent disease caused by these organisms. However, many phasevarions also control the expression of current and putative vaccine candidates; variable expression of antigens could lead to immune evasion, meaning that vaccines designed using these targets become ineffective. It is therefore essential to characterize phasevarions in order to determine an organism’s stably expressed antigenic repertoire, and rationally design broadly effective vaccines.
-
-
-
-
Sensing and responding to diverse extracellular signals: an updated analysis of the sensor kinases and response regulators of Streptomyces species
Streptomyces venezuelae is a Gram-positive, filamentous actinomycete with a complex developmental life cycle. Genomic analysis revealed that S. venezuelae encodes a large number of two-component systems (TCSs): these consist of a membrane-bound sensor kinase (SK) and a cognate response regulator (RR). These proteins act together to detect and respond to diverse extracellular signals. Some of these systems have been shown to regulate antimicrobial biosynthesis in Streptomyces species, making them very attractive to researchers. The ability of S. venezuelae to sporulate in both liquid and solid cultures has made it an increasingly popular model organism in which to study these industrially and medically important bacteria. Bioinformatic analysis identified 58 TCS operons in S. venezuelae with an additional 27 orphan SK and 18 orphan RR genes. A broader approach identified 15 of the 58 encoded TCSs to be highly conserved in 93 Streptomyces species for which high-quality and complete genome sequences are available. This review attempts to unify the current work on TCS in the streptomycetes, with an emphasis on S. venezuelae .
-
- Microbe Profile
-
-
-
Microbe Profile: Streptomyces coelicolor: a burlesque of pigments and phenotypes
More LessThe streptomycetes are soil-dwelling bacteria that are found in soil everywhere on Earth: the molecule geosmin, which they produce as part of their life cycle, is what gives soil its familiar ‘earthy’ smell. The species is best known for the production of biologically active small molecules called ‘natural products’. These molecules are the source of most of our antibiotics and anti-fungals, as well as many other drugs. The streptomycetes have a filamentous form rather than the more familiar rod-shaped spirochete and coccoid forms. They exhibit a complex life cycle and sporulation mechanism involving several differentiated cell types, each having specific roles in the colony life history. Streptomyces coelicolor is an important model system for this genus – research on this bacterium has provided foundational information for all of these fascinating processes.
-
-
- Biotechnology
-
-
-
Identification and comparison of two closely related dextransucrases released by water kefir borne Lactobacillus hordei TMW 1.1822 and Lactobacillus nagelii TMW 1.1827
More LessDextransucrases are extracellular enzymes, which are exclusively expressed by lactic acid bacteria (LAB) and produce α−1→6 linked glucose polymers from sucrose. In this study, two dextransucrases derived from water kefir borne Lactobacillus hordei TMW 1.1822 and Lactobacillus nagelii TMW 1.1827 were identified and comparatively investigated. Differences between both proteins mainly arise from an additional C-terminal glucan-binding domain and the presence of a signal motif in the L. nagelii TMW 1.1827 dextransucrase. L. hordei TMW 1.1822 released the enzyme only in the presence of its substrate sucrose in contrast to L. nagelii TMW 1.1827, while both strains functionally expressed the dextransucrases independently of sucrose. Both enzymes could be recovered as crude protein extracts in culture supernatants, as they are not covalently bound to the cell surface. This enabled the formation of dextrans at equal reaction conditions as well as their subsequent structural analysis in terms of molecular structure and molecular weight. The volumetric transglycosylation and hydrolysis activities were distinctly different for both enzymes, which produced O3-branched dextrans with a comparable degree of branching. Moreover, identical oligosaccharides were obtained for both dextrans upon endo-dextranase digestion, while some differences in the polysaccharide fine structures could be identified from the varying portions of certain oligosaccharides. Dextrans synthesized by the dextransucrase released by L. nagelii exhibited an averaged molecular weight (M w) of 7.9×107 Da, while those produced by the dextransucrase released by L. hordei exhibited an M w of 6.1×107 Da. Moreover, glycosylation of glucansucrases by LAB was identified for the first time for the released dextransucrase of L. nagelii TMW 1.1827. Our study therefore reveals new molecular insights into how dextransucrases released by water kefir borne L. hordei TMW 1.1822 and L. nagelii TMW 1.1827 contribute to the complex formation of the traditional beverage water kefir.
-
-
-
-
Antimicrobial activity of green silver nanoparticles from endophytic fungi isolated from Calotropis procera (Ait) latex
Endophytes, a potential source of bioactive secondary metabolites, were isolated from the widely used medicinal plant Calotropis procera Ait. Approximately 675 segments from 15 Calotropis procera plants and 15 latex samples were assessed for the presence of endophytic fungi. Finally, eight fungal species were isolated and identified based on their macro- and micro-morphology. The endophytic fungal filtrates were screened for their antimicrobial activity against 11 important pathogenic micro-organisms. The filtrates of nanoparticles were from three of the eight isolated endophytic fungi, namely, Penicillium chrysogenum, Aspergillus fumigatus and Aspergillus flavus, and were highly effective against the tested bacteria, while the remaining endophytic fungal filtrates displayed low activity.
-
- Genomics and Systems Biology
-
-
-
Evolution of bacteria seen through their essential genes: the case of Pseudomonas aeruginosa and Azotobacter vinelandii
Pseudomonas aeruginosa is a metabolically versatile bacterium and also an important opportunistic pathogen. It has a remarkable genomic structure since the genetic information encoding its pathogenicity-related traits belongs to its core-genome while both environmental and clinical isolates are part of the same population with a highly conserved genomic sequence. Unexpectedly, considering the high level of sequence identity and homologue gene number shared between different P. aeruginosa isolates, the presence of specific essential genes of the two type strains PAO1 and PA14 has been reported to be highly variable. Here we report the detailed bioinformatics analysis of the essential genes of P. aeruginosa PAO1 and PA14 that have been previously experimentally identified and show that the reported gene variability was owed to sequencing and annotation inconsistencies, but that in fact they are highly conserved. This bioinformatics analysis led us to the definition of 348 P. aeruginosa general essential genes. In addition we show that 342 of these 348 essential genes are conserved in Azotobacter vinelandii , a nitrogen-fixing, cyst-forming, soil bacterium. These results support the hypothesis of A. vinelandii having a polyphyletic origin with a Pseudomonads genomic backbone, and are a challenge to the accepted theory of bacterial evolution.
-
-
- Host-microbe Interaction
-
-
-
Bacteriophage acquisition restores protective mutualism
More LessInsects are frequently infected with inherited facultative symbionts known to provide a range of conditionally beneficial services, including host protection. Pea aphids (Acyrthosiphon pisum) often harbour the bacterium Hamiltonella defensa , which together with its associated bacteriophage A. pisum secondary endosymbiont (APSE) confer protection against an important natural enemy, the parasitic wasp Aphidius ervi. Previous studies showed that spontaneous loss of phage APSE resulted in the complete loss of the protective phenotype. Here, we demonstrate that APSEs can be experimentally transferred into phage-free (i.e. non-protecting) Hamiltonella strains. Unexpectedly, trials using injections of phage particles alone failed, with successful transfer occurring only when APSE and Hamiltonella were simultaneously injected. After transfer, stable establishment of APSE fully restored anti-parasitoid defenses. Thus, phages associated with heritable bacterial symbionts can move horizontally among symbiont strains facilitating the rapid transfer of ecologically important traits although natural barriers may preclude regular exchange.
-
-
-
-
Regulation of hsnT, nodF and nodE genes in Rhizobium tropici CIAT 899 and their roles in the synthesis of Nod factors and in the symbiosis
Rhizobium tropici strain CIAT 899 possesses outstanding agronomic properties as it displays tolerance to environmental stresses, a broad host range and high effectiveness in fixing nitrogen with the common bean (Phaseolus vulgaris L.); in addition, it carries intriguing features such as five copies of the regulatory nodD gene, and the capacity to synthesize a variety of nodulation factors (NFs), even in a flavonoid-independent manner, when submitted to abiotic stresses. However, the roles of several nod genes of the repertoire of CIAT 899 remain to be determined. In this study, we obtained mutants for the hsnT, nodF and nodE genes of CIAT 899 and investigated their expression, NF structures and symbiotic properties. Either in the presence of the flavonoid apigenin, or of salt the expression of hsnT, nodF and nodE in wild-type CIAT 899 was highly up-regulated in comparison to the mutants of all five copies of nodD, indicating the roles that regulatory nodD genes play in the activation of hsnT, nodF and nodE; however, NodD1 was recognized as the main inducer. In total, 29 different NF structures were synthesized by wild-type CIAT 899 induced by apigenin, and 36 when induced by salt, being drastically reduced by mutations in hsnT, nodF and nodE, especially under osmotic stress, with specific changes related to each gene, indicating that the three genes participate in the synthesis of NFs. Mutations in hsnT, nodF and nodE affected differently symbiotic performance (nodule number and shoot dry weight), according to the host plant. Our results indicate that the expression of hsnT, nodF and nodE genes of CIAT 899 is mediated by nodD genes, and although these three genes do not belong to the main set of genes controlling nodulation, they contribute to the synthesis of NFs that will impact symbiotic performance and host specificity.
-
- Physiology and Metabolism
-
-
-
Mutational loss of carotenoids in alkaliphilic Bacillus pseudofirmus OF4 results in sensitivity to oxidative stress and growth at high pH
Alkaliphilic Bacillus pseudofirmus OF4, which has a broad pH growth range of 7.5 to above 10.5, is yellow-pigmented due to carotenoids. Carotenoids contribute to membrane rigidity and can alleviate cellular oxidative stress. This study was undertaken to gain insight into the roles carotenoids play in alkaliphile physiology. Carotenoid content was high in stationary phase and in cells grown nonfermentatively at pH 10.5 A colourless mutant was isolated by the in-frame deletion of a key carotenogenic gene, crtM. In cells grown to stationary phase in a pH 10.5 medium with a suboptimal concentration of Na+, the ∆crtM strain exhibited lower resistance to paraquat and hydrogen peroxide. Preincubation of the mutant in a nutrient-free pH 10.5 buffer revealed a pronounced sensitivity to hydrogen peroxide in growth at pH 7.5. In growth curves in media with optimal or suboptimal nutrient concentrations conducted at 37°, the mutant grew identically to the wild-type at pH 7.5 but its lag time was longer than the wild-type at pH 10.5 and growth was slower when the carbon source, malate, was limiting. When the temperature of the growth curves was lowered to 25°, the mutant no longer had a pH 10.5 phenotype, implicating the effect of carotenoids on membrane rigidity for the pH 10.5 growth phenotype. These results suggest that carotenoids in B. pseudofirmus OF4 play a role in managing oxidative stress when cells are adapting to other stressful conditions such as nutrient limitation while also helping to maintain membrane fluidity/rigidity balance for membrane-linked functions.
-
-
-
-
Understanding the role of the lysozyme-like domain of D29 mycobacteriophage-encoded endolysin in host cell lysis and phage propagation
More LessMycobacteriophages are viruses that infect and kill mycobacteria. The peptidoglycan hydrolase, lysin A (LysA), coded by one of the most potent mycobacteriophages, D29, carries two catalytic domains at its N-terminus and a cell wall-binding domain at its C-terminus. Here, we have explored the importance of the centrally located lysozyme-like catalytic domain (LD) of LysA in phage physiology. We had previously identified an R198A substitution that causes inactivation of the LD when it is present alone on a polypeptide. Here, we show that upon incorporation of the same mutation (i.e. R350A) in full-length LysA, the protein demonstrates substantially reduced activity in vitro, even in the presence of the N-terminal catalytic domain, and has less efficient mycobacterial cell lysis ability when it is expressed in Mycobacterium smegmatis . These data suggest that an active LD is required for the full-length protein to function optimally. Moreover, a mutant D29 phage harbouring this substitution (D29R350A) in its LysA protein shows significantly delayed host M. smegmatis lysis. However, the mutant phage demonstrates an increase in burst size and plaque diameter. Taken together, our data show the importance of an intact LD region in D29 LysA PG hydrolase, and indicate an evolutionary advantage over other phages that lack such a domain in their endolysins.
-
Volumes and issues
-
Volume 170 (2024)
-
Volume 169 (2023)
-
Volume 168 (2022)
-
Volume 167 (2021)
-
Volume 166 (2020)
-
Volume 165 (2019)
-
Volume 164 (2018)
-
Volume 163 (2017)
-
Volume 162 (2016)
-
Volume 161 (2015)
-
Volume 160 (2014)
-
Volume 159 (2013)
-
Volume 158 (2012)
-
Volume 157 (2011)
-
Volume 156 (2010)
-
Volume 155 (2009)
-
Volume 154 (2008)
-
Volume 153 (2007)
-
Volume 152 (2006)
-
Volume 151 (2005)
-
Volume 150 (2004)
-
Volume 149 (2003)
-
Volume 148 (2002)
-
Volume 147 (2001)
-
Volume 146 (2000)
-
Volume 145 (1999)
-
Volume 144 (1998)
-
Volume 143 (1997)
-
Volume 142 (1996)
-
Volume 141 (1995)
-
Volume 140 (1994)
-
Volume 139 (1993)
-
Volume 138 (1992)
-
Volume 137 (1991)
-
Volume 136 (1990)
-
Volume 135 (1989)
-
Volume 134 (1988)
-
Volume 133 (1987)
-
Volume 132 (1986)
-
Volume 131 (1985)
-
Volume 130 (1984)
-
Volume 129 (1983)
-
Volume 128 (1982)
-
Volume 127 (1981)
-
Volume 126 (1981)
-
Volume 125 (1981)
-
Volume 124 (1981)
-
Volume 123 (1981)
-
Volume 122 (1981)
-
Volume 121 (1980)
-
Volume 120 (1980)
-
Volume 119 (1980)
-
Volume 118 (1980)
-
Volume 117 (1980)
-
Volume 116 (1980)
-
Volume 115 (1979)
-
Volume 114 (1979)
-
Volume 113 (1979)
-
Volume 112 (1979)
-
Volume 111 (1979)
-
Volume 110 (1979)
-
Volume 109 (1978)
-
Volume 108 (1978)
-
Volume 107 (1978)
-
Volume 106 (1978)
-
Volume 105 (1978)
-
Volume 104 (1978)
-
Volume 103 (1977)
-
Volume 102 (1977)
-
Volume 101 (1977)
-
Volume 100 (1977)
-
Volume 99 (1977)
-
Volume 98 (1977)
-
Volume 97 (1976)
-
Volume 96 (1976)
-
Volume 95 (1976)
-
Volume 94 (1976)
-
Volume 93 (1976)
-
Volume 92 (1976)
-
Volume 91 (1975)
-
Volume 90 (1975)
-
Volume 89 (1975)
-
Volume 88 (1975)
-
Volume 87 (1975)
-
Volume 86 (1975)
-
Volume 85 (1974)
-
Volume 84 (1974)
-
Volume 83 (1974)
-
Volume 82 (1974)
-
Volume 81 (1974)
-
Volume 80 (1974)
-
Volume 79 (1973)
-
Volume 78 (1973)
-
Volume 77 (1973)
-
Volume 76 (1973)
-
Volume 75 (1973)
-
Volume 74 (1973)
-
Volume 73 (1972)
-
Volume 72 (1972)
-
Volume 71 (1972)
-
Volume 70 (1972)
-
Volume 69 (1971)
-
Volume 68 (1971)
-
Volume 67 (1971)
-
Volume 66 (1971)
-
Volume 65 (1971)
-
Volume 64 (1970)
-
Volume 63 (1970)
-
Volume 62 (1970)
-
Volume 61 (1970)
-
Volume 60 (1970)
-
Volume 59 (1969)
-
Volume 58 (1969)
-
Volume 57 (1969)
-
Volume 56 (1969)
-
Volume 55 (1969)
-
Volume 54 (1968)
-
Volume 53 (1968)
-
Volume 52 (1968)
-
Volume 51 (1968)
-
Volume 50 (1968)
-
Volume 49 (1967)
-
Volume 48 (1967)
-
Volume 47 (1967)
-
Volume 46 (1967)
-
Volume 45 (1966)
-
Volume 44 (1966)
-
Volume 43 (1966)
-
Volume 42 (1966)
-
Volume 41 (1965)
-
Volume 40 (1965)
-
Volume 39 (1965)
-
Volume 38 (1965)
-
Volume 37 (1964)
-
Volume 36 (1964)
-
Volume 35 (1964)
-
Volume 34 (1964)
-
Volume 33 (1963)
-
Volume 32 (1963)
-
Volume 31 (1963)
-
Volume 30 (1963)
-
Volume 29 (1962)
-
Volume 28 (1962)
-
Volume 27 (1962)
-
Volume 26 (1961)
-
Volume 25 (1961)
-
Volume 24 (1961)
-
Volume 23 (1960)
-
Volume 22 (1960)
-
Volume 21 (1959)
-
Volume 20 (1959)
-
Volume 19 (1958)
-
Volume 18 (1958)
-
Volume 17 (1957)
-
Volume 16 (1957)
-
Volume 15 (1956)
-
Volume 14 (1956)
-
Volume 13 (1955)
-
Volume 12 (1955)
-
Volume 11 (1954)
-
Volume 10 (1954)
-
Volume 9 (1953)
-
Volume 8 (1953)
-
Volume 7 (1952)
-
Volume 6 (1952)
-
Volume 5 (1951)
-
Volume 4 (1950)
-
Volume 3 (1949)
-
Volume 2 (1948)
-
Volume 1 (1947)