Search results for "Obligate"

2015

Bacterial endosymbiosis is an important evolutionary process in insects, which can harbor both obligate and facultative symbionts. The evolution of these symbionts is driven by evolutionary convergence, and they exhibit among the tiniest genomes in prokaryotes. The large host spectrum of facultative symbionts and the high diversity of strategies they use to infect new hosts probably impact the evolution of their genome and explain why they undergo less severe genomic erosion than obligate symbionts. Candidatus Hamiltonella defensa is suitable for the investigation of the genomic evolution of facultative symbionts because the bacteria are engaged in specific relationships in two clades of in…

Role of Symbiosis in Evolution

2013

The biological relevance of the widespread prokaryote–eukaryote symbioses as a source of evolutionary innovation has been unveiled by the advent of the Genomic era, allowing deep knowledge on single or consortia uncultivable species. The establishment and maintenance of symbiosis are complex issues where partners’ fitness determines the evolutionary outcome. Comparative genomics allows to dissect the evolutionary process that begins with host invasion, takes the path from facultative to obligate symbiosis, and ends up in replacement or coexistence with new bacterial symbionts. Whole genomes of several intracellular bacterial symbionts have been sequenced, allowing the comparison among the d…

Complete Genome Sequence of “Candidatus Portiera aleyrodidarum” BT-QVLC, an Obligate Symbiont That Supplies Amino Acids and Carotenoids to Bemisia ta…

2012

ABSTRACT The genome of “ Candidatus Portiera aleyrodidarum,” the primary endosymbiont of the whitefly Bemisia tabaci (Mediterranean species), is reported. It presents a reduced genome (357 kb) encoding the capability to synthetize, or participate in the synthesis of, several amino acids and carotenoids, being the first insect endosymbiont capable of supplying carotenoids.

Molecular Systematics of Aphids and Their Primary Endosymbionts

2001

Abstract Aphids constitute a monophyletic group within the order Homoptera (i.e., superfamily Aphidoidea). The Aphidoidea originated in the Jurassic about 150 my ago from some aphidiform ancestor whose origin can be traced back to about 250 my ago. They exhibit a mutualistic association with intracellular bacteria ( Buchnera sp.) related to Escherichia coli. Buchnera is usually considered the aphids' primary endosymbiont. The association is obligate for both partners. The 16S rDNA-based phylogeny of Buchnera from four aphid families showed complete concordance with the morphology-based phylogeny of their aphid hosts, which pointed to a single original infection in a common ancestor of aphid…

Changes in the proton potential and the cellular energetics of Escherichia coli during growth by aerobic and anaerobic respiration or by fermentation.

1998

The energetic parameters of Escherichia coli were analyzed for the aerobic/anaerobic transition. The electrochemical proton potential (delta p) across the cytoplasmic membrane was determined in the steady state of respiration with O2, nitrate, fumarate, dimethylsulfoxide (Me2SO), and for fermentation. With O2, a proton potential of -160 mV was obtained. For anaerobic respiration with nitrate, fumarate or Me2SO, delta p decreased only slightly by about 20 mV in contrast to earlier assumptions, whereas delta p dropped by approximately 40 mV during fermentation. Under all conditions, the membrane potential (delta psi) contributed the major portion to delta p. The cellular ATP levels were highe…

Learning how to live together: genomic insights into prokaryote–animal symbioses

2008

Our understanding of prokaryote-eukaryote symbioses as a source of evolutionary innovation has been rapidly increased by the advent of genomics, which has made possible the biological study of uncultivable endosymbionts. Genomics is allowing the dissection of the evolutionary process that starts with host invasion then progresses from facultative to obligate symbiosis and ends with replacement by, or coexistence with, new symbionts. Moreover, genomics has provided important clues on the mechanisms driving the genome-reduction process, the functions that are retained by the endosymbionts, the role of the host, and the factors that might determine whether the association will become parasitic…

Evolution of Prokaryote-Animal Symbiosis from a Genomics Perspective

2010

Symbioses involving prokaryotes living in close relationship with eukaryotic cells have been widely studied from a genomic perspective, especially in the case of insects. In the process toward host accommodation, symbionts experience major genetic and phenotypic changes that can be detected in comparison with free-living relatives. But, as expected, several scenarios allowed the evolution of symbiotic associations, from the first stages of free-living bacteria, through secondary and facultative symbiosis, towards the final point of obligate primary endosymbiosis. Particular relevance has the association formed by the coexistence of several symbionts into a given host. A summary of findings …

Life History Trade-Offs and Relaxed Selection Can Decrease Bacterial Virulence in Environmental Reservoirs

2012

Pathogen virulence is usually thought to evolve in reciprocal selection with the host. While this might be true for obligate pathogens, the life histories of opportunistic pathogens typically alternate between within-host and outside-host environments during the infection-transmission cycle. As a result, opportunistic pathogens are likely to experience conflicting selection pressures across different environments, and this could affect their virulence through life-history trait correlations. We studied these correlations experimentally by exposing an opportunistic bacterial pathogen Serratia marcescens to its natural protist predator Tetrahymena thermophila for 13 weeks, after which we meas…

Stable isotopes challenge the perception of ocean sunfish Mola mola as obligate jellyfish predators

2011

Evidence is provided from stable isotope analysis that aggregations of small ocean sunfish Mola mola (total length <1 m) feed broadly within coastal food webs and their classification as obligate predators of gelatinous zooplankton requires revision.

Is the population genetic structure of complex life cycle parasites determined by the geographic range of the most motile host?

2010

Due to their particular way of life, dispersal of parasites is often mediated by their host's biology. Dispersal distance is relevant for parasites because high degree of dispersal leads to high gene flow, which counters the rate of parasite local adaptation in the host populations. Parasites with complex life cycles need to exploit sequentially more than one host species to complete their life cycle. Most trematode parasites have such complex life cycles involving invertebrate and vertebrate hosts. The spatial scales of invertebrate and vertebrate host populations are often different, which may decrease the probability that the parasite cycles locally in the intermediate host population. W…