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Comparison of the evolutionary dynamics of symbiotic and housekeeping loci: a case for the genetic coherence of rhizobial lineages 总被引:6,自引:1,他引:5
In prokaryotes, lateral gene transfer across chromosomal lineages may be
mediated by plasmids, phages, transposable elements, and other accessory
DNA elements. However, the importance of such transfer and the evolutionary
forces that may restrict gene exchange remain largely unexplored in native
settings. In this study, tests of phylogenetic congruence are employed to
explore the range of horizontal transfer of symbiotic (sym) loci among
distinct chromosomal lineages of native rhizobia, the nitrogen-fixing
symbiont of legumes. Rhizobial strains isolated from nodules of several
host plant genera were sequenced at three loci: symbiotic nodulation genes
(nodB and nodC), the chromosomal housekeeping locus glutamine synthetase II
(GSII), and a portion of the 16S rRNA gene. Molecular phylogenetic analysis
shows that each locus generally subdivides strains into the same major
groups, which correspond to the genera Rhizobium, Sinorhizobium, and
Mesorhizobium. This broad phylogenetic congruence indicates a lack of
lateral transfer across major chromosomal subdivisions, and it contrasts
with previous studies of agricultural populations showing broad transfer of
sym loci across divergent chromosomal lineages. A general correspondence of
the three rhizobial genera with major legume groups suggests that host
plant associations may be important in the differentiation of rhizobial nod
and chromosomal loci and may restrict lateral transfer among strains. The
second major result is a significant incongruence of nod and GSII
phylogenies within rhizobial subdivisions, which strongly suggests
horizontal transfer of nod genes among congenerics. This combined evidence
for lateral gene transfer within, but not between, genetic subdivisions
supports the view that rhizobial genera are "reproductively isolated" and
diverge independently. Differences across rhizobial genera in the
specificity of host associations imply that the evolutionary dynamics of
the symbiosis vary considerably across lineages in native settings.
相似文献
95.
Karl Rumbold Hugo JJ van Buijsen Karin M Overkamp Johan W van Groenestijn Peter J Punt J van der Mari?t Werf 《Microbial cell factories》2009,8(1):64
Background
Increasingly lignocellulosic biomass hydrolysates are used as the feedstock for industrial fermentations. These biomass hydrolysates are complex mixtures of different fermentable sugars, but also inhibitors and salts that affect the performance of the microbial production host. The performance of six industrially relevant microorganisms, i.e. two bacteria (Escherichia coli and Corynebacterium glutamicum), two yeasts (Saccharomyces cerevisiae and Pichia stipitis) and two fungi (Aspergillus niger and Trichoderma reesei) were compared for their (i) ability to utilize monosaccharides present in lignocellulosic hydrolysates, (ii) resistance against inhibitors present in lignocellulosic hydrolysates, (iii) their ability to utilize and grow on different feedstock hydrolysates (corn stover, wheat straw, sugar cane bagasse and willow wood). The feedstock hydrolysates were generated in two manners: (i) thermal pretreatment under mild acid conditions followed by enzymatic hydrolysis and (ii) a non-enzymatic method in which the lignocellulosic biomass is pretreated and hydrolyzed by concentrated sulfuric acid. Moreover, the ability of the selected hosts to utilize waste glycerol from the biodiesel industry was evaluated. 相似文献96.
Vytautas Galvanauskas Oskars Grigs Juris Vanags Konstantins Dubencovs Valerija Stepanova 《Engineering in Life Science》2013,13(2):172-184
A model‐based approach for optimization and cascade control of dissolved oxygen partial pressure (pO2) and maximization of biomass in fed‐batch cultivations is presented. The procedure is based on the off‐line model‐based optimization of the optimal feeding rate profiles and the subsequent automatic pO2 control using a proposed cascade control technique. During the model‐based optimization of the process, feeding rate profiles are optimized with respect to the imposed technological constraints (initial and maximal cultivation volume, cultivation time, feeding rate range, maximal oxygen transfer rate and pO2 level). The cascade pO2 control is implemented using activation of cascades for agitation, oxygen enrichment, and correction of the preoptimized feeding rate profiles. The proposed approach is investigated in two typical fed‐batch processes with Escherichia coli and Saccharomyces cerevisiae. The obtained results show that it was possible to achieve sufficiently high biomass levels with respect to the given technological constraints and to improve controllability of the investigated processes. 相似文献
97.
Background
Genetic disruption of an important phenotype should favor compensatory mutations that restore the phenotype. If the genetic basis of the phenotype is modular, with a network of interacting genes whose functions are specific to that phenotype, compensatory mutations are expected among the genes of the affected network. This perspective was tested in the bacteriophage T3 using a genome deleted of its DNA ligase gene, disrupting DNA metabolism. 相似文献98.
99.
Tineke E Buffart Melanie Louw Nicole CT van Grieken Marianne Tijssen Beatriz Carvalho Bauke Ylstra Heike Grabsch Chris JJ Mulder Cornelis JH van de Velde Schalk W van der Merwe Gerrit A Meijer 《BMC medical genomics》2011,4(1):7
Background
Infection with H. pylori is important in the etiology of gastric cancer. Gastric cancer is infrequent in Africa, despite high frequencies of H. pylori infection, referred to as the African enigma. Variation in environmental and host factors influencing gastric cancer risk between different populations have been reported but little is known about the biological differences between gastric cancers from different geographic locations. We aim to study genomic instability patterns of gastric cancers obtained from patients from United Kingdom (UK) and South Africa (SA), in an attempt to support the African enigma hypothesis at the biological level.Methods
DNA was isolated from 67 gastric adenocarcinomas, 33 UK patients, 9 Caucasian SA patients and 25 native SA patients. Microsatellite instability and chromosomal instability were analyzed by PCR and microarray comparative genomic hybridization, respectively. Data was analyzed by supervised univariate and multivariate analyses as well as unsupervised hierarchical cluster analysis.Results
Tumors from Caucasian and native SA patients showed significantly more microsatellite instable tumors (p < 0.05). For the microsatellite stable tumors, geographical origin of the patients correlated with cluster membership, derived from unsupervised hierarchical cluster analysis (p = 0.001). Several chromosomal alterations showed significantly different frequencies in tumors from UK patients and native SA patients, but not between UK and Caucasian SA patients and between native and Caucasian SA patients.Conclusions
Gastric cancers from SA and UK patients show differences in genetic instability patterns, indicating possible different biological mechanisms in patients from different geographical origin. This is of future clinical relevance for stratification of gastric cancer therapy.100.
Justin J. Yerbury Dane Gower Laura Vanags Kate Roberts Jodi A. Lee Heath Ecroyd 《Cell stress & chaperones》2013,18(2):251-257
Amyotrophic lateral sclerosis is a devastating neurodegenerative disease. The mechanism that underlies amyotrophic lateral sclerosis (ALS) pathology remains unclear, but protein inclusions are associated with all forms of the disease. Apart from pathogenic proteins, such as TDP-43 and SOD1, other proteins are associated with ALS inclusions including small heat shock proteins. However, whether small heat shock proteins have a direct effect on SOD1 aggregation remains unknown. In this study, we have examined the ability of small heat shock proteins αB-crystallin and Hsp27 to inhibit the aggregation of SOD1 in vitro. We show that these chaperone proteins suppress the increase in thioflavin T fluorescence associated with SOD1 aggregation, primarily through inhibiting aggregate growth, not the lag phase in which nuclei are formed. αB-crystallin forms high molecular mass complexes with SOD1 and binds directly to SOD1 aggregates. Our data are consistent with an overload of proteostasis systems being associated with pathology in ALS. 相似文献