Find the odd man out with respect to chemoautotrophs
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CLS Aipmt 17 18 XIII Zoo Study Package 4 SET 1 Chapter 14
The unique geochemistry of marine shallow-water hydrothermal systems promotes the establishment of diverse microbial communities with a range of metabolic pathways. In contrast to deep-sea vents, shallow-water vents not only support chemosynthesis, but also phototrophic primary production due to the availability of light. However, comprehensive studies targeting the predominant biogeochemical processes are rare, and consequently a holistic understanding of the functioning of these ecosystems is currently lacking.
To this end, we combined stable isotope probing of lipid biomarkers with an analysis of the bacterial communities to investigate if chemoautotrophy, in parallel to photoautotrophy, plays an important role in autotrophic carbon fixation and to identify the key players.
Analysis of the bacterial diversity revealed Anaerolineae of the Chloroflexi as the most abundant bacterial class.
Furthermore, the presence of key players involved in iron cycling generally known from deep-sea hydrothermal vents e. Relatively increased 13 C-incorporation in the dark allowed the classification of ai C , C , and i C as potential lipid biomarkers for bacterial chemoautotrophy in this ecosystem. Highest total 13 C-incorporation into fatty acids took place at the sediment surface, but chemosynthesis was found to be active down to 8 cm sediment depth.
In conclusion, this study highlights the relative importance of chemoautotrophy compared to photoautotrophy in a shallow-water hydrothermal system, emphasizing chemosynthesis as a prominent process for biomass production in marine coastal environments influenced by hydrothermalism. Chemoautotrophic microorganisms in hydrothermal systems are able to assimilate inorganic carbon into biomass and effectively transfer the energy from the geothermal source to higher trophic levels e.
The general knowledge of chemoautotrophy at deep-sea hydrothermal vents has advanced considerably over the last years e. However, hydrothermal systems can harbor heterogeneous microbial habitats e. Thus, there are still significant gaps in relation to the microbial biogeochemistry of hydrothermal systems in determining the function of different community members and the relevance of the metabolic pathways carried out by them e.
Hydrothermal systems occur over a wide depth range in the oceans, from the intertidal to the abyss e. Energy sources for primary production in these systems become available when the hot, reduced hydrothermal fluids mix with the cold, oxygenated seawater e.
In contrast to deep-sea vents, shallow-water vents not only support chemosynthetic processes, but also primary production by photosynthesis due to the availability of light Tarasov et al. Accordingly, shallow-water systems are generally characterized by a higher input of autochthonous organic matter compared to deep-sea vents, where new biomass is thought to be exclusively produced by chemosynthesis Jannasch and Mottl, Furthermore, the additional input of allochthonous organic matter generated on land, in the vicinity of the vents, or in the water column above the vents may sustain heterotrophic processes e.
Marine shallow-water hydrothermal systems have been investigated using geochemical approaches e. However, comprehensive studies targeting the predominant biogeochemical processes at shallow-water hydrothermal systems are rare, and a holistic understanding of the functioning of these ecosystems is currently lacking.
Several isotope-based methods have been introduced in recent years for cultivation-independent characterization of active microorganisms in environmental samples e. The analysis of lipid signatures in natural environments offers a unique approach, as they provide quantitative information about the community structure without the necessity of culturing, as well as revealing information about the adaptation of microbes to varying environmental conditions e.
In hydrothermal environments, lipids have been used to decipher carbon flow at deep-sea vents e. Approaches utilizing substrates labeled with stable isotopes such as 13 C in combination with mass spectrometric determination of the labeled fatty acids have been furthermore widely used for the detection and quantitative assessment of physiologically active bacteria in complex microbial communities e. Recent studies concluded that dark carbon fixation can be a major process in coastal sediments not influenced by hydrothermal activity, representing nearly half of global chemoautotrophy in the ocean and being predominantly performed by Gammaproteobacteria Middelburg, ; Boschker et al.
However, the analysis of lipid signatures has not yet been applied to elucidate the relative importance of chemosynthesis for primary production in marine shallow-water hydrothermal systems.
The aim of the present study was to investigate the relative contribution of chemoautotrophy for total microbial carbon fixation in a light-exposed, iron-enriched marine shallow-water hydrothermal system, where the continuous supply of reduced substances from below may support chemoautotrophy, while the presence of light sustains photoautotrophy.
Dominica belongs to the Lesser Antilles islands, which represents one of only two active arc systems in the Atlantic Ocean. Although most of these islands have a single volcanic center e. Therefore, Dominica has been the most volcanically active island in the Lesser Antilles arc over the last , years and one of the most active worldwide Wadge, ; Lindsay et al.
Study area and experimental set up of this study. Maps were created using Ocean Data View R. Submarine photo courtesy of A.
Geochemistry values taken from Gomez-Saez et al. B SIP-experiment to evaluate the effect of light with incubations under light and dark conditions. C SIP-experiment to investigate different redox interfaces under dark conditions as a function of incubation time 6 to 48 h and sediment depth at five intervals 0—2, 2—4, 4—6, 6—8, and 8—10 cm. Identification of locations where hot fluids percolate through the sediment was carried out by SCUBA diving using previously described in situ temperature probes e.
The pH and salinity were measured in situ at the point of fluid discharge from the sediments, using a WTW pH meter with Mic-D electrode. Fluid samples for geochemical analyses were collected with a funnel at the point of discharge out of the sediments, channeling the fluid into a food-grade large volume nylon bag as described previously Gomez-Saez et al.
The sediment from the cores was sliced at five different depths 0—2, 2—4, 4—6, 6—8, and 8—10 cm. Two SIP-experiments were carried out immediately upon arrival in the laboratory.
Furthermore, half of the samples were incubated with 13 C-bicarbonate addition to set a final concentration of 6. The second SIP-experiment investigated different redox interfaces under dark conditions. Twelve sediment cores were sampled from the same venting area and a mixture of 13 C-bicarbonate and hydrothermal fluid was injected into eight sediment cores at five different depth layers 0—2, 2—4, 4—6, 6—8, and 8—10 cm to set a final concentration of 6.
The bacterial diversity of the five sediment depth layers 0—2, 2—4, 4—6, 6—8, and 8—10 cm was analyzed from one of the cores incubated in the dark for 48 h, which might bias the results if interpreted as natural community composition. DNA was extracted from 0. Sequences processing, including alignment, quality control, dereplication, clustering and classification, was done with the SILVAngs analysis pipeline 1. Sequences were clustered in operational taxonomic units OTU 0.
All downstream statistical analyses were done in R R Core Team, , using the vegan package Oksanen et al. All analyses were done excluding OTU 0. Prior to this, the data were normalized to the sample with the least number of sequences 8—10 cm depth; 28, sequences. Data interpretation was based on the relative abundances of the sequences classified at the class or genus level. DNA-based analysis of bacterial diversity. A The percentage of classified and unclassified phyla, classes and genera.
B,C Relative sequences abundances at the phylum and class level, respectively. Genera identified as the most characteristic of the given taxonomical class and their relative abundance are presented in C. Total lipids were extracted from freeze-dried sediment samples following a protocol based on Bligh and Dyer and modified by Sturt et al. An aliquot of the total lipid extract was saponified following Elvert et al. This method includes a base saponification using potassium hydroxide in methanol, base extraction of the neutral lipids and acid extraction of the free fatty acids.
Prior to analysis, fatty acids were derivatized using boron trifluoride BF 3 in methanol Merck , leading to fatty acid methylesters. Identification of fatty acids was performed by gas chromatography — mass spectrometry GC-MS combining an Agilent N gas chromatograph with an Agilent N mass selective detector. The total running time was 60 min.
Helium was used as carrier gas with a flow-rate of 1. The reference gas was CO 2 and squalane was used as injection standard to check for internal precision. Incorporation of 13 C in the SIP experiments is reflected as an excess compared to the amount of 13 C in background samples and is expressed in terms of total uptake as described by Middelburg et al.
Total uptake of 13 C was calculated as the product of excess 13 C E and concentration of the respective compound. E was the difference between the fraction F of the sample and background:.
A non-metric multidimensional scaling NMDS analysis was performed in order to assess how incubated samples during 6—48 h in the dark were similar or differ from each other based on the incorporation of 13 C-bicarbonate into different fatty acids.
Dissimilarity among samples was calculated based on the Bray-Curtis dissimilarity index. Bacterial community analysis of the incubated samples revealed variations in the taxonomical composition as a function of sediment depth.
The abundance of potential iron-oxidizers was highest in the surface layer. The likely natural isotopic composition of fatty acids was inferred from incubations without tracer addition, averaging — Uptake of 13 C-bicarbonate into lipid biomarkers under light and dark conditions. Total uptake of 13 C-bicarbonate into fatty acids after incubations under light yellow and dark black conditions including standard deviations of repeated measurements.
B Absolute 13 C-bicarbonate uptake into the different bacterial fatty acids. C Total quantified 13 C-incorporation in fatty acids. The total uptake under light conditions which is attributed to chemoautotrophy is indicated by the dashed area. Uptake of 13 C-bicarbonate into lipid biomarkers under dark conditions as a function of incubation time and sediment depth. A Total uptake of 13 C-bicarbonate into different fatty acids after sediment core incubations under dark conditions as a function of time 6, 12, 24, or 48 h and sediment depth intervals 0—2, 2—4, 4—6, 6—8, or 8—10 cm.
B Non-metric multidimensional scaling analysis NMDS based on total 13 C uptake into each fatty acid in all depths and of incubation times, identifying the presence of two groups of samples that are statistically different from each other. Into this category, we also included those fatty acids with at least five times more 13 C-uptake under light than under dark conditions, i. Incorporation of 13 C into bacterial fatty acids differed as a function of light availability, supporting the classification of fatty acids being dominantly produced during chemo- or photoautotrophy in shallow-water hydrothermal systems.
In addition, fatty acids that were linked to chemoautotrophy included the fatty acids 10Me- C 0. Ratios between dark and light incubations of the absolute 13 C-uptake into fatty acids.
Color code indicates which fatty acids were more likely to be indicative of chemoautotrophy red or photoautotrophy green. Incubations in the dark as a function of time 6, 12, 24, or 48 h and sediment depth 0—2, 2—4, 4—6, 6—8, or 8—10 cm were performed to obtain further insights into the chemosynthetic activity at different redox interfaces.
This suggests that microbially mediated iron cycling plays an important role in the biogeochemistry of the Dominica shallow hydrothermal system, which would be in accordance with other iron-enriched shallow-water hydrothermal systems off Santorini Greece or Tutum Bay Papua New Guinea Handley et al.
The most well documented marine iron oxidizer is Mariprofundus ferrooxydans belonging to the Zetaproteobacteria Emerson et al.
This is in accordance with the cultivation conditions of Mariprofundus , which grows as an oxygen-dependent obligate lithotroph at a pH range of 5. Iron-oxidizing Zetaproteobacteria have previously been found mainly at deep-sea hydrothermal vents Emerson and Moyer, ; Kato et al. In addition to iron-oxidizers, we could also identify numerous taxa potentially capable of reducing iron, mainly Deltaproteobacteria.
Although Shewanellaceae of the Gammaproteobacteria are among the most commonly identified iron-reducing bacteria Zhang et al. In contrast, the thermophilic genus Geothermobacter , originally isolated from a deep-sea hydrothermal vent Kashefi et al.
Geothermobacter was among the five most abundant genera of the whole dataset, indicating its importance for iron cycling at the studied vent system. We further detected other less abundant iron-reducing taxa that are also known to be able to use sulfur as electron acceptor, like Deferribacteres, Desulfobulbus , and Desulfuromonas.
This is in accordance with previous studies of hydrothermal ecosystems, including shallow-water vents Takai et al. Other highly abundant chemolithotrophic genera that obtain energy via oxidation of reduced chemical species other than iron were detected in our study. In line with these findings, all of these taxa have been previously found at thermally active sites or deep-sea hydrothermal vents e.
The autotrophic bacterial community composition of the Dominica shallow-water vents varied with sediment depth, with a clear dominance of a mixed photo- and chemoautotrophic community in the surface layer and exclusively chemoautotrophic microorganisms in the deeper layers.
Solved Examples(Set 1) - Series - Odd Man Out
Origin of earth dates back to 1 10,—15, million years ago 2 — million years ago 3 — million years ago 4 — million years ago Sol. Who finally refuted the theory of spontaneous generation and experimentally disproved it? Answer 3 Louis Pasteur disproved it by Swan neck experiment. An experiment to prove that organic compounds were the basis of life, was performed by 1 Van Helmont 2 Oparin 3 S. Miller 4 Fox Sol.
In every competitive exam, Odd Man Out type questions are very common. In odd man out problems all the items given in the question except one follow a certain pattern or a group. That means out of the all given elements, one will not fall into the group due to some difference in the property. That is the odd element. Hence, it is the odd one.
Reasoning - Odd Man Out
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Green  and stars James Mason and Robert Newton. It followed upon wartime action by the IRA in Belfast, in consequence of which Northern Ireland undertook its first and only execution of an Irish Republican , year old Tom Williams. The film's opening intertitle reads: "This story is told against a background of political unrest in a city of Northern Ireland.
Bacteria, Bacteriophages, and Fungi
The unique geochemistry of marine shallow-water hydrothermal systems promotes the establishment of diverse microbial communities with a range of metabolic pathways. In contrast to deep-sea vents, shallow-water vents not only support chemosynthesis, but also phototrophic primary production due to the availability of light. However, comprehensive studies targeting the predominant biogeochemical processes are rare, and consequently a holistic understanding of the functioning of these ecosystems is currently lacking. To this end, we combined stable isotope probing of lipid biomarkers with an analysis of the bacterial communities to investigate if chemoautotrophy, in parallel to photoautotrophy, plays an important role in autotrophic carbon fixation and to identify the key players.
Diversities of life among the microbes make up 18 generally lively essays by Postgate that—for the general reader—waver on the edge of opacity. Twenty-five years ago, Postgate wrote a well- received Science essayists usually write on natural phenomenon that are observable animal behavior or subjects that are widely reported, such as DNA. Postgate, author of the classic Microbes and Man The Outer Reaches of Life.
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