Sulfate reducing bacteria (SRB) have existed throughout much of Earth's history and remain major contributors to carbon cycling in modern systems. Despite their importance, misconceptions about SRB ...are prevalent. In particular, SRB are commonly thought to lack oxygen tolerance and to exist only in anoxic environments. Through the last two decades, researchers have discovered that SRB can, in fact, tolerate and even respire oxygen. Investigations of microbial mat systems have demonstrated that SRB are both abundant and active in the oxic zones of mats. Additionally, SRB have been found to be highly active in the lithified zones of microbial mats, suggesting a connection between sulfate reduction and mat lithification. In the present paper, we review recent research on SRB distribution and present new preliminary findings on both the diversity and distribution of δ-proteobacterial SRB in lithifying and non-lithifying microbial mat systems. These preliminary findings indicate the unexplored diversity of SRB in a microbial mat system and demonstrate the close microspatial association of SRB and cyanobacteria in the oxic zone of the mat. Possible mechanisms and further studies to elucidate mechanisms for carbonate precipitation via sulfate reduction are also discussed.
ABSTRACT
Sulfate‐reducing bacteria (SRB) have been recognized as key players in the precipitation of calcium carbonate in lithifying microbial communities. These bacteria increase the alkalinity by ...reducing sulfate ions, and consuming organic acids. SRB also produce copious amounts of exopolymeric substances (EPS). All of these processes influence the morphology and mineralogy of the carbonate minerals. Interactions of EPS with metals, calcium in particular, are believed to be the main processes through which the extracellular matrix controls the precipitation of the carbonate minerals. SRB exopolymers were purified from lithifying mat and type cultures, and their potential role in CaCO3 precipitation was determined from acid‐base titrations and calcium‐binding experiments. Major EPS characteristics were established using infrared spectroscopy and gas chromatography to characterize the chemical functional groups and the sugar monomers composition. Our results demonstrate that all of the three SRB strains tested were able to produce large amounts of EPS. This EPS exhibited three main buffering capacities, which correspond to carboxylic acids (pKa = 3.0), sulfur‐containing groups (thiols, sulfonic and sulfinic acids – pKa = 7.0–7.1) and amino groups (pKa = 8.4–9.2). The calcium‐binding capacity of these exopolymers in solution at pH 9.0 ranged from 0.12gCa gEPS−1–0.15 gCa gEPS−1. These results suggest that SRB could play a critical role in the formation of CaCO3 in lithifying microbial mats. The unusually high sulfur content, which has not been reported for EPS before, indicates a possible strong interaction with iron. In addition to changing the saturation index through metabolic activity, our results imply that SRB affect the rock record through EPS production and its effect on the CaCO3 precipitation. Furthermore, EPS produced by SRB may account for the incorporation of metals (e.g. Sr, Fe, Mg) associated with carbonate minerals in the rock record.
•An inverse relationship between prolonged and chronic stress and normal reproductive efficiency has been observed in domestic animals.•The early effect of stress may stimulate GnRH/LH ...secretion.•Regulation of gonadotropin secretion under stress conditions may occur at the level of GnRH and GnRHR genes expression.•Stress-induced changes in the expression of GnRH and GnRHR are physiological state- and stressor duration-dependent.
Using an ELISA assay, the levels of GnRH and GnRHR were analysed in the preoptic area (POA), anterior (AH) and ventromedial hypothalamus (VM), stalk/median eminence (SME); and GnRHR in the anterior pituitary gland (AP) of non-breeding and breeding sheep subjected to short-term or prolonged stress. The ELISA study was supplemented with an analysis of plasma LH concentration. Short-term footshock stimulation significantly increased GnRH levels in hypothalamus in both seasons. Prolonged stress elevated or decreased GnRH concentrations in the POA and the VM, respectively during anoestrus, and lowered GnRH amount in the POA-hypothalamus of follicular-phase sheep. An up-regulation of GnRHR levels was noted in both, anoestrous and follicular-phase animals. In the non-breeding period, a prolonged stress procedure increased GnRHR biosynthesis in the VM and decreased it in the SME and AP, while in the breeding time the quantities of GnRHR were significantly lower in the whole hypothalamus. In follicular-phase ewes the fluctuations of GnRH and GnRHR levels under short-term and prolonged stress were reflected in the changes of LH secretion, suggesting the existence of a direct relationship between GnRH and GnRH-R biosynthesis and GnRH/LH release in this period.
The study showed that stress was capable of modulating the biosynthesis of GnRH and GnRHR; the pattern of changes was dependent upon the animal’s physiological state and on the time course of stressor application. The obtained results indicate that the disturbances of gonadotropin secretion under stress conditions in sheep may be due to a dysfunction of GnRH and GnRHR biosynthetic pathways.
This study was performed to explain how the molecular processes governing the biosynthesis of gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) in the hypothalamic–pituitary unit are ...reflected by luteinizing hormone (LH) secretion in sheep during anoestrous period and during luteal and follicular phases of the oestrous cycle. Using an enzyme-linked immunosorbent assay (ELISA), we analyzed the levels of GnRH and GnRHR in preoptic area (POA), anterior (AH) and ventromedial hypothalamus (VM), stalk–median eminence (SME), and GnRHR in the anterior pituitary gland (AP). Radioimmunoassay has also been used to define changes in plasma LH concentrations. The study provides evidence that the levels of GnRH in the whole hypothalamus of anoestrous ewes were lower than that in sheep during the follicular phase of the oestrous cycle (POA: p < 0.001, AH: p < 0.001, VM: p < 0.01, SME: p < 0.001) and not always than in luteal phase animals (POA: p < 0.05, SME: p < 0.05). It has also been demonstrated that the GnRHR amount in the hypothalamus–anterior pituitary unit, as well as LH level, in the blood in anoestrous ewes were significantly lower than those detected in animals of both cyclic groups. Our data suggest that decrease in LH secretion during the long photoperiod in sheep may be due to low translational activity of genes encoding both GnRH and GnRHR.
Celotno besedilo
Dostopno za:
DOBA, FSPLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
An intensive multi-year field study of the modern marine stromatolites at Highborae Cay, Bahamas has identified a variety of microbial communities that colonize the stromatolite surfaces. They ...include both bacterial and diatom dominated communities. The "classic" microbial communities are those described by Reid et al. (2000). They include Schizothrix mats, dominated by S. gebeleinii, which trap and bind ooid sand grains (Type 1 mat); biofilm mats, composed of sulfate reducing bacteria, which form thin crusts of microcrystalline carbonate (Type 2 mat); and Solentia mats, dominated by coccoid endolithic Solentia species, which create cemented layers of fused sand grains (Type 3 mat). Another bacterial mat, termed "pudding mat" due to its pudding-like texture, is dominated by thin filaments of Phormidium sp. and single filaments of S. gebeleinii, but may also be colonized by a unique species of coccoid cyanobacterium related to Cyanothece. The diatom mats include stalked diatoms and tube diatoms. The stalked diatom mats form as a thin (1-3 mm) surface pink fuzz comprised of Striatella unipunctata, or a yellow fuzz that may develop into a thick (0.5-1 cm) yellow fur with Licmophora remulus and Licmophora paradoxa. The tube diatom mats, which occur as discrete pustules that may coalesce to create uniform blankets, are formed by naviculid - like tube diatoms. These different mat types recognized based on field descriptions and light microscopy also show distinct differences based on microbial fingerprinting and carbohydrate fractionation. Denaturing gradient gel electrophoresis (DGGE) analyses show similarities between stalked diatom mat types and "classic" mat types 1 and 2; these mats cluster separately from tube diatom mats and pudding mats, which each form distinct clades. In addition, the carbohydrate fractions of classic mat types are composed mostly of structural extracellular polymeric secretions (EPS), whereas stalked diatom and pudding mats contain predominantly non-structural carbohydrates. Although the pudding mats and diatom communities can contribute to the trapping of ooids, the stabilization of the unconsolidated sediment ultimately requires binding by S. gebeleinii. The combination of carbohydrate composition and ability to rapidly rebound after burial result in the high erosion resistance exhibited by the "classic" mats. Conversely, the extremely sensitive nature of diatoms to burial results in the low erosion resistance of the diatom mats. Nevertheless, all may contribute to the biogenesis of the Highborne Cay stromatolites.
Contents
The effects of prolonged, intermittent infusion of β‐endorphin or naloxone into the third cerebral ventricle of follicular‐phase ewes on the expression of genes encoding GnRH and GnRHR in ...the hypothalamus and GnRHR in the anterior pituitary gland (AP) were examined by an enzyme‐linked immunoabsorbent assay. Activation or blockade of μ‐opioid receptors significantly decreased or increased the GnRH concentration and GnRHR abundance in the hypothalamus, respectively, and affected in the same way GnRHR quantity in the AP gland. The changes in the levels of GnRH and GnRHR after treatment with β‐endorphin as well as following action of naloxone were reflected in fluctuations of plasma LH concentrations. On the basis of these results, it is suggested that β‐endorphinergic system in the hypothalamus of follicular‐phase ewes affects directly or via β‐endorphin‐sensitive interneurons GnRH and GnRHR biosynthesis leading to suppression in secretory activity of the hypothalamic‐pituitary axis.
This study was performed to explain how the molecular processes governing the biosynthesis of gonadotropinreleasing hormone (GnRH) and GnRH receptor (GnRHR) in the hypothalamic-pituitary unit are ...reflected by luteinizing hormone (LH) secretion in sheep during anoestrous period and during luteal and follicular phases of the oestrous cycle. Using an enzyme-linked immunosorbent assay (ELISA), we analyzed the levels of GnRH and GnRHR in preoptic area (POA), anterior (AH) and ventromedial hypothalamus (VM), stalk-median eminence (SME), and GnRHR in the anterior pituitary gland (AP). Radioimmunoassay has also been used to define changes in plasma LH concentrations. The study provides evidence that the levels of GnRH in the whole hypothalamus of anoestrous ewes were lower than that in sheep during the follicular phase of the oestrous cycle (POA: p < 0.001, AH: p < 0.001, VM: p < 0.01, SME: p < 0.001) and not always than in luteal phase animals (POA: p < 0.05, SME: p < 0.05). It has also been demonstrated that the GnRHR amount in the hypothalamus-anterior pituitary unit, as well as LH level, in the blood in anoestrous ewes were significantly lower than those detected in animals of both cyclic groups. Our data suggest that decrease in LH secretion during the long photoperiod in sheep may be due to low translational activity of genes encoding both GnRH and GnRHR.
Celotno besedilo
Dostopno za:
DOBA, FSPLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Contents
The effects of prolonged, intermittent infusion of
β
‐endorphin or naloxone into the third cerebral ventricle of follicular‐phase ewes on the expression of genes encoding Gn
RH
and Gn
RHR
in ...the hypothalamus and Gn
RHR
in the anterior pituitary gland (AP) were examined by an enzyme‐linked immunoabsorbent assay. Activation or blockade of
μ
‐opioid receptors significantly decreased or increased the Gn
RH
concentration and Gn
RHR
abundance in the hypothalamus, respectively, and affected in the same way Gn
RHR
quantity in the AP gland. The changes in the levels of Gn
RH
and Gn
RHR
after treatment with
β
‐endorphin as well as following action of naloxone were reflected in fluctuations of plasma
LH
concentrations. On the basis of these results, it is suggested that
β
‐endorphinergic system in the hypothalamus of follicular‐phase ewes affects directly or via
β
‐endorphin‐sensitive interneurons Gn
RH
and Gn
RHR
biosynthesis leading to suppression in secretory activity of the hypothalamic‐pituitary axis.
Contents The effects of prolonged, intermittent infusion of beta-endorphin or naloxone into the third cerebral ventricle of follicular-phase ewes on the expression of genes encoding GnRH and GnRHR in ...the hypothalamus and GnRHR in the anterior pituitary gland (AP) were examined by an enzyme-linked immunoabsorbent assay. Activation or blockade of µ-opioid receptors significantly decreased or increased the GnRH concentration and GnRHR abundance in the hypothalamus, respectively, and affected in the same way GnRHR quantity in the AP gland. The changes in the levels of GnRH and GnRHR after treatment with beta-endorphin as well as following action of naloxone were reflected in fluctuations of plasma LH concentrations. On the basis of these results, it is suggested that beta-endorphinergic system in the hypothalamus of follicular-phase ewes affects directly or via beta-endorphin-sensitive interneurons GnRH and GnRHR biosynthesis leading to suppression in secretory activity of the hypothalamic-pituitary axis.
The RT-PCR (reverse transcription polymerase chain reaction) technique was used to analyze GnRH mRNA and GnRH-R mRNA in the preoptic area, anterior and ventromedial hypothalamus, and GnRH-R mRNA in ...the stalk/median eminence and anterior pituitary gland of follicular ewes subjected to short (3 h during one day) or prolonged (5 h daily during four consecutive days) footshock stimulation. To analyze relationship between expression of GnRH and GnRH-R genes with LH secretion the blood samples were collected at 10 min intervals to determine LH levels in control and stressed animals. The concentration of GnRH mRNA increased significantly in the preoptic area, anterior and ventromedial hypothalamus of ewes subjected to short stress. The prolonged stressful stimuli significantly decreased GnRH mRNA levels in all analyzed structures. In short stressed ewes the significant augmentation of mRNA encoding GnRH-R was detected in the preoptic area, entire hypothalamus, stalk/median eminence and anterior pituitary gland. The GnRH-R mRNA was significantly reduced in all tested structures of animals subjected to prolonged footshocking except for the preoptic area, where GnRH-R mRNA did not differ from control values. The changes in GnRH mRNA and GnRH-R mRNA levels under short or prolonged stress were associated with an increase or decrease of LH concentration in blood plasma, suggesting the existence of a direct relationship between GnRH mRNA and GnRH-R mRNA expression with LH secretion. The results indicate that the expression of both GnRH gene and GnRH-R gene, as well as LH secretion in ewes during the follicular phase of the estrous cycle, are dependent upon the kind of stress.
