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The symbioses between invertebrates and chemosynthetic bacteria allow both host and symbiont to colonize and thrive in otherwise inhospitable deep-sea habitats. Given the global distribution of the bathymodioline symbioses, this association is an excellent model for evaluating co-speciation and evolution of symbioses. Thus far, the methanotroph and chemoautotroph endosymbionts of mussels are tightly clustered within two independent clades of gamma Proteobacteria, respectively. Further physiological and genomic studies will elucidate the ecological and evolutionary roles that these bacterial clades play in the symbiosis and chemosynthetic community. Due to the overall abundance of the methanotrophic symbioses at hydrothermal vents and hydrocarbon seeps, they likely play a significant, but as of yet unquantified, role in the biogeochemical cycling of methane. With this in mind, the search for methanotrophic symbioses should not be restricted to these known deep-sea habitats, but rather should be expanded to include methane-rich coastal marine and freshwater environments inhabited by methanotrophs and bivalves. Our current understanding of the bathymodioline symbioses provides a strong foundation for future explorations into the origin, ecology, and evolution of methanotroph symbioses, which are now becoming possible through a combination of classical and advanced molecular techniques.

Recent years have witnessed a global increase in more intense, widespread and frequent fires that threaten human security and ecosystems and contribute to green house gas emissions which result in climate change with feed-backs on both fire patterns and land degradation. The interplay between fire weather-risk and land degradation is complex and involves several non linear inter-actions that influence trends in both fire patterns and land degradation processes. Majority of fires are lit by humans but the influence of humans on fire patterns is closely related to fire weather. Weather conditions are the main factors of fire readiness in a given fire prone area. Frequent and more intense fires reduce bio-mass supported in an area, affecting the productive soil layer which leads to soil erosion, change in species composition and a general decline in biodiversity and hence land degradation. In this regard fire is an agent of land degradation which is defined here as a persistent reduction in the capacity of ecosystems to supply services. In arid to semi-arid and dry sub-humid areas, extensive burning may be followed by low rainfall periods thus exposing soil to erosion agents such as heat, and wind and subsequent encroachment of the area by fast growing weeds when normal rainfall return which increases fire risk in that area than before.

Of major concern is how climate change will influence the interaction between fire weather and land degradation. Observations in different regions already link more intense fires witnessed in the past decade to climate change generated hotter and drier summer weather, in addition to fire suppression practices. Prolonged drought under climate change is likely to intensify land degradation due to land use pressure setting conditions for the spread of more fast growing highly flammable weeds during the onset of rainfall. Current evidence suggests that in arid to semi-arid lands, invasive highly flammable herbaceous species associated with degraded lands may out-compete native vegetation during abnormally wet periods under climate change. And with increased fire weather-risk, these areas will undergo increased hot fires facilitated by accumulated dry highly flammable biomass of these invasive species and hence putting the landscape under a perpetual cycle of increased susceptibility to land degradation and fire. Future land degradation studies need to put greater emphasis on the role of fire weather for a better assessment of burning conditions and interaction with land degradation processes.

The large number of symbioses among termite gut flagellates and prokaryotes, the high level of integration evidenced by the elaborate attachment structures or the intracellular location, and the large proportion of the prokaryotic gut microbiota that is associated with the protozoa suggest a major importance of such symbioses for the hindgut metabolism of lower termites.

Molecular tools allow the identification of the phylogeny of the partners involved in the symbioses, and although these investigations are still far from complete, it is apparent that the symbionts represent unusual and mostly unstudied phylogenetic groups. As a consequence of the unusual phylogenetic position and the complete lack of isolates, the metabolic capacities of the symbionts and their role in the symbiosis are still largely obscure.

In order to understand the hindgut metabolisms of lower termites, it will be essential to elucidate the metabolic relationship between the flagellates and their symbionts. It is reasonable to assume that the functional roles of the partners are less diverse than their phylogenetic diversity, and in view of the possible co-evolution of the partners, the symbioses between prokaryotes and gut flagellates are also excellent case studies in the microbial ecology and evolution.

In conclusion of old and new observations, the old killer symbionts of may rather be parasites than mutualists. However, this view does not completely do justice to the system. By coding for R bodies and presumably also for toxins, plasmids and phage genomes ensure the persistence of and of the plasmids / phages themselves in paramecia populations. -free populations of may develop under unfavorable conditions, e.g., in case of poor nutrients being the reason for low abundance of the ciliates. Only then paramecia without endocytobionts would survive, not being threatened by R body-bearing that are released by host cells. -free paramecia need less food and grow faster. Since, however, in many habitats the conditions are favorable for bacterial feeders like , R body-coding plasmids or phages ensure persistence of the killer symbioses, no matter whether is a mutualist or parasite. As always in microbially infected protozoa, host and endocytobiont are forming an entirely new unit facing selection.

Recent years have witnessed a global increase in more intense, widespread and frequent fires that threaten human security and ecosystems and contribute to green house gas emissions which result in climate change with feed-backs on both fire patterns and land degradation. The interplay between fire weather-risk and land degradation is complex and involves several non linear inter-actions that influence trends in both fire patterns and land degradation processes. Majority of fires are lit by humans but the influence of humans on fire patterns is closely related to fire weather. Weather conditions are the main factors of fire readiness in a given fire prone area. Frequent and more intense fires reduce bio-mass supported in an area, affecting the productive soil layer which leads to soil erosion, change in species composition and a general decline in biodiversity and hence land degradation. In this regard fire is an agent of land degradation which is defined here as a persistent reduction in the capacity of ecosystems to supply services. In arid to semi-arid and dry sub-humid areas, extensive burning may be followed by low rainfall periods thus exposing soil to erosion agents such as heat, and wind and subsequent encroachment of the area by fast growing weeds when normal rainfall return which increases fire risk in that area than before.

Of major concern is how climate change will influence the interaction between fire weather and land degradation. Observations in different regions already link more intense fires witnessed in the past decade to climate change generated hotter and drier summer weather, in addition to fire suppression practices. Prolonged drought under climate change is likely to intensify land degradation due to land use pressure setting conditions for the spread of more fast growing highly flammable weeds during the onset of rainfall. Current evidence suggests that in arid to semi-arid lands, invasive highly flammable herbaceous species associated with degraded lands may out-compete native vegetation during abnormally wet periods under climate change. And with increased fire weather-risk, these areas will undergo increased hot fires facilitated by accumulated dry highly flammable biomass of these invasive species and hence putting the landscape under a perpetual cycle of increased susceptibility to land degradation and fire. Future land degradation studies need to put greater emphasis on the role of fire weather for a better assessment of burning conditions and interaction with land degradation processes.

The symbioses between invertebrates and chemosynthetic bacteria allow both host and symbiont to colonize and thrive in otherwise inhospitable deep-sea habitats. Given the global distribution of the bathymodioline symbioses, this association is an excellent model for evaluating co-speciation and evolution of symbioses. Thus far, the methanotroph and chemoautotroph endosymbionts of mussels are tightly clustered within two independent clades of gamma Proteobacteria, respectively. Further physiological and genomic studies will elucidate the ecological and evolutionary roles that these bacterial clades play in the symbiosis and chemosynthetic community. Due to the overall abundance of the methanotrophic symbioses at hydrothermal vents and hydrocarbon seeps, they likely play a significant, but as of yet unquantified, role in the biogeochemical cycling of methane. With this in mind, the search for methanotrophic symbioses should not be restricted to these known deep-sea habitats, but rather should be expanded to include methane-rich coastal marine and freshwater environments inhabited by methanotrophs and bivalves. Our current understanding of the bathymodioline symbioses provides a strong foundation for future explorations into the origin, ecology, and evolution of methanotroph symbioses, which are now becoming possible through a combination of classical and advanced molecular techniques.

Hydrogenosomes are not the same. They evolved several times — independently — from mitochondria or the common ancestor of hydrogenosomes and mitochondria. This process, in general, involved the loss of the organellar genome together with the mitochondrial electron transport chain, and metabolic adaptations to anoxic environments such as the use of protons as terminal electron acceptors. Substantial differences in the physiological capacities of the various hydrogenosomes reflect their independent evolution through evolutionary tinkering. Notably, even the common denominator of these organelles, i.e., the production of hydrogen, can become marginal in certain hydrogenosomes.

The hydrogenosomal metabolism is crucial for the establishment of symbiotic associations, and sometimes differences in the host’s metabolism seem to be able to provide the clues for an understanding of the presence or absence of pears to be insufficient to explain the observations. Obviously, intrinsic properties of the various hosts and their symbionts play an important role, which are, at the moment, clearly not even beyond the level of a preliminary phenomenological description. Intensive efforts are required to analyse the elusive molecular basis of symbiotic associations. Many fascinating insights into the secrets of symbiotic associations await their discovery.

Tremendous advances in our understanding of the -legume symbioses have been made. The probable identification of NFR1 and NFR5 as Nod-factor receptors and the discovery of symbiotically relevant protein secretion systems in rhizobia, are but two of the milestones in this field of Probable commonalities between the infection of legumes by arbuscular mycorrhiza and rhizobia suggest similar evolutionary mechanisms. In the years that lay ahead, more parts of the symbiotic puzzle will be put together at an ever-increasing pace. research. Light is being shed on the fundamental role of SPS in symbiosis.

In conclusion of old and new observations, the old killer symbionts of may rather be parasites than mutualists. However, this view does not completely do justice to the system. By coding for R bodies and presumably also for toxins, plasmids and phage genomes ensure the persistence of and of the plasmids / phages themselves in paramecia populations. -free populations of may develop under unfavorable conditions, e.g., in case of poor nutrients being the reason for low abundance of the ciliates. Only then paramecia without endocytobionts would survive, not being threatened by R body-bearing that are released by host cells. -free paramecia need less food and grow faster. Since, however, in many habitats the conditions are favorable for bacterial feeders like , R body-coding plasmids or phages ensure persistence of the killer symbioses, no matter whether is a mutualist or parasite. As always in microbially infected protozoa, host and endocytobiont are forming an entirely new unit facing selection.

Hydrogenosomes are not the same. They evolved several times — independently — from mitochondria or the common ancestor of hydrogenosomes and mitochondria. This process, in general, involved the loss of the organellar genome together with the mitochondrial electron transport chain, and metabolic adaptations to anoxic environments such as the use of protons as terminal electron acceptors. Substantial differences in the physiological capacities of the various hydrogenosomes reflect their independent evolution through evolutionary tinkering. Notably, even the common denominator of these organelles, i.e., the production of hydrogen, can become marginal in certain hydrogenosomes.

The hydrogenosomal metabolism is crucial for the establishment of symbiotic associations, and sometimes differences in the host’s metabolism seem to be able to provide the clues for an understanding of the presence or absence of pears to be insufficient to explain the observations. Obviously, intrinsic properties of the various hosts and their symbionts play an important role, which are, at the moment, clearly not even beyond the level of a preliminary phenomenological description. Intensive efforts are required to analyse the elusive molecular basis of symbiotic associations. Many fascinating insights into the secrets of symbiotic associations await their discovery.