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Sulfur has many redox states and is a major metabolite in suboxic and anaerobic environments including, but not restricted to, marine and marginal marine sediments, the water column of oxygen minimum zones, salt marshes and oil wells. Microbially mediated redox cycling of sulfur typically comprises dissimilatory sulfate reduction (MSR), sulfide reoxidation, disproportionation and the oxidation and reduction of sulfur redox intermediates. These processes contribute to the degradation of organic matter, link the cycles of sulfur and carbon, control the production and consumption of methane and are critical for the long term budget of O2 in the atmosphere. Microbial and abiotic processes at redox interfaces also connect the sulfur cycle to the redox cycles of nitrogen, iron and other elements, producing distinctive geochemical and molecular signatures. Studies that couple microbiology with stable isotope geochemistry have informed interpretations of microbial sulfur cycling in modern and past environments. Laboratory-based studies and models of MSR have sought to understand the physiological and environmental controls of the magnitude of sulfur isotope fractionation. The fractionations of stable sulfur and oxygen isotopes during MSR are also used to track enzymatic activity during MSR and processes that oxidize sulfide in the presence of environmental oxidants. Outstanding questions in the field concern the importance of oxidative processes within the natural environment, the delivery of oxidants and carbon sources to the zones of sulfate reduction and the ability to detect or reconstruct oxidative processes from the chemical, isotopic, metagenomic, transcriptomic, proteomic and metabolomics profiles in the environment. Recent studies have emphasized the complex connections between sulfur and methane, iron, nitrogen and other elements. These links may involve the redox cycling of species that occur at concentrations difficult to detect by standard geochemical techniques or that are cycled at very rapid rates (cryptic cycles). Of particular interest is the use of isotope geochemistry to quantify links among various electron acceptors, including sulfate, ferric iron, and nitrate, during the anaerobic methane oxidation. For example, recent geochemical measurements have hinted that microbial sulfate reduction coupled to organic matter oxidation is mechanistically different to when sulfate reduction is coupled to methane oxidation. Recent studies have also suggested a possible contribution of a number of previously uncultured microbial groups in sulfur cycling in sulfidic environments, inspiring further studies of these organisms and their partnerships in anaerobic environments. This Research Topic highlights studies of microbial interactions, processes and communities that couple the sulfur cycle to the cycles of other elements in aphotic environments.

issimilatory sulfate reduction (MSR) --- subsurface sulfur cycle --- sulfur

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Sulfur has many redox states and is a major metabolite in suboxic and anaerobic environments including, but not restricted to, marine and marginal marine sediments, the water column of oxygen minimum zones, salt marshes and oil wells. Microbially mediated redox cycling of sulfur typically comprises dissimilatory sulfate reduction (MSR), sulfide reoxidation, disproportionation and the oxidation and reduction of sulfur redox intermediates. These processes contribute to the degradation of organic matter, link the cycles of sulfur and carbon, control the production and consumption of methane and are critical for the long term budget of O2 in the atmosphere. Microbial and abiotic processes at redox interfaces also connect the sulfur cycle to the redox cycles of nitrogen, iron and other elements, producing distinctive geochemical and molecular signatures. Studies that couple microbiology with stable isotope geochemistry have informed interpretations of microbial sulfur cycling in modern and past environments. Laboratory-based studies and models of MSR have sought to understand the physiological and environmental controls of the magnitude of sulfur isotope fractionation. The fractionations of stable sulfur and oxygen isotopes during MSR are also used to track enzymatic activity during MSR and processes that oxidize sulfide in the presence of environmental oxidants. Outstanding questions in the field concern the importance of oxidative processes within the natural environment, the delivery of oxidants and carbon sources to the zones of sulfate reduction and the ability to detect or reconstruct oxidative processes from the chemical, isotopic, metagenomic, transcriptomic, proteomic and metabolomics profiles in the environment. Recent studies have emphasized the complex connections between sulfur and methane, iron, nitrogen and other elements. These links may involve the redox cycling of species that occur at concentrations difficult to detect by standard geochemical techniques or that are cycled at very rapid rates (cryptic cycles). Of particular interest is the use of isotope geochemistry to quantify links among various electron acceptors, including sulfate, ferric iron, and nitrate, during the anaerobic methane oxidation. For example, recent geochemical measurements have hinted that microbial sulfate reduction coupled to organic matter oxidation is mechanistically different to when sulfate reduction is coupled to methane oxidation. Recent studies have also suggested a possible contribution of a number of previously uncultured microbial groups in sulfur cycling in sulfidic environments, inspiring further studies of these organisms and their partnerships in anaerobic environments. This Research Topic highlights studies of microbial interactions, processes and communities that couple the sulfur cycle to the cycles of other elements in aphotic environments.

issimilatory sulfate reduction (MSR) --- subsurface sulfur cycle --- sulfur

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Igneous oceanic crust is one of the largest potential habitats for life on earth, and microbial activity supported by rock-water-microbe reactions in this environment can impact global biogeochemical cycles. However, our understanding of the microbiology of this system, especially the subsurface “deep biosphere” component of it, has traditionally been limited by sample availability and quality. Over the past decade, several major international programs (such as the Center for Dark Energy Biosphere Investigations, the current International Ocean Discovery Program and its predecessor Integrated Ocean Drilling Program, and the Deep Carbon Observatory) have focused on advancing our understanding of life in this cryptic, yet globally relevant, biosphere. Additionally, many field and laboratory research programs are examining hydrothermal vent systems –a seafloor expression of seawater that has been thermally and chemically altered in subseafloor crust – and the microbial communities supported by these mineral-rich fluids. The Frontiers in Microbiology 3 September 2017 | Recent Advances in Geomicrobiology of the Ocean Crust papers in this special issue bring together recent discoveries of microbial presence, diversity and activity in these dynamic ocean environments. Cumulatively, the articles in this special issue serve as a tribute to the late Dr. Katrina J. Edwards, who was a pioneer and profound champion of studying microbes that “rust the crust”. This special issue volume serves as a foundation for the continued exploration of the subsurface ocean crust deep biosphere.

IODP --- deep biosphere --- hydrothermal vents --- Geomicrobiology --- ocean crust --- iron oxidation --- sulfate reduction

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Deep subsurface microbiology is a highly active and rapidly advancing research field at the interface of microbiology and the geosciences; it focuses on the detection, identification, quantification, cultivation and activity measurements of bacteria, archaea and eukaryotes that permeate the subsurface biosphere of deep marine sediments and the basaltic ocean and continental crust. The deep subsurface biosphere abounds with uncultured, only recently discovered and – at best - incompletely understood microbial populations. In spatial extent and volume, Earth’s subsurface biosphere is only rivaled by the deep sea water column. So far, no deep subsurface sediment has been found that is entirely devoid of microbial life; microbial cells and DNA remain detectable at sediment depths of more than 1 km; microbial life permeates deeply buried hydrocarbon reservoirs, and is also found several kilometers down in continental crust aquifers. Severe energy limitation, either as electron acceptor or donor shortage, and scarcity of microbially degradable organic carbon sources are among the evolutionary pressures that have shaped the genomic and physiological repertoire of the deep subsurface biosphere. Its biogeochemical role as long-term organic carbon repository, inorganic electron and energy source, and subduction recycling engine continues to be explored by current research at the interface of microbiology, geochemistry and biosphere/geosphere evolution. This Research Topic addresses some of the central research questions about deep subsurface microbiology and biogeochemistry: phylogenetic and physiological microbial diversity in the deep subsurface; microbial activity and survival strategies in severely energy-limited subsurface habitats; microbial activity as reflected in process rates and gene expression patterns; biogeographic isolation and connectivity in deep subsurface microbial communities; the ecological standing of subsurface biospheres in comparison to the surface biosphere – an independently flourishing biosphere, or mere survivors that tolerate burial (along with organic carbon compounds), or a combination of both? Advancing these questions on Earth’s deep subsurface biosphere redefines the habitat range, environmental tolerance, activity and diversity of microbial life.

Microbiology & Immunology --- Biology --- Health & Biological Sciences --- marine sediment --- Methane --- deep biosphere --- acetogenesis --- subseafloor sediment --- Hydrogen --- deep subsurface --- ocean crust --- sulfate reduction --- Peru margin

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This book represents the latest research on microbiota axes, with a special focus on the gut-skin axis and the role of microbial breast bacteria on human health communication. This book also contains discussions of the microorganism-derived products that can directly or indirectly be signals for our organs and systems. Gut dysbiosis, representing a disruption of intestinal integrity, can create aberrant physiological conditions (including immunological disorders, intestinal stress, and anxiety-like behavior), as well as high serum levels of microbial metabolites increasing oxidative stress dysfunctions and generalized inflammation. Much research in this field has been carried out in animal models, and establishing whether those findings translate to humans will be crucial but challenging. On the other hand, several studies conducted on humans have evaluated the link between fecal microbiota composition and quality of life by recruiting thousands of participants. As well as identifying bacterial genera associated with higher quality of life, they carried out metagenomic analyses that indicated that the potential of microorganisms to synthesize certain active metabolites, and especially their interrelation, may also correlate with general wellbeing. It is clear that many axes can influence our lives; the most important include “the gut-brain axis” and the “skin-gut-breast axis”. Together, the studies presented in this book have laid the foundations for a better understanding of the effects of gut microbiota on skin and on our body in general. The mechanisms that underlie them may represent the ideal focus for the initial efforts to explore the relevance of these axes for human wellbeing.

small–large intestine axis --- hydrogen sulfide --- Desulfovibrio --- bowel disease --- colitis --- gut microbiota --- microbiome --- maternal–fetal interface --- newborn --- child --- pediatric disease --- dysbiosis --- microbiota --- schizophrenia --- olanzapine administration --- weight gain --- sulfate reduction --- microbiota axis --- oral microbiota arthritis --- joint inflammation --- otitis media --- upper respiratory tract --- adenoid --- middle ear --- microbiota axes