Physiological and morphological observations on Thiovulum sp.
Cell suspensions of Thiovulum sp., collected from enrichment cultures, were grown, maintained, and harvested for periods up to 7 months. In open-flow cultures run with aerated seawater, a continuous supply of hydrogen sulfide was provided by diffusion through a semipermeable membrane from either a live culture of Desulfovibrio esturaii, neutralized sodium sulfide, or a N2-H2S gas mixture. Attempts to grow Thiovulum in pure culture failed despite variation in concentrations of dissolved oxygen and hydrogen sulfide in stratified as well as in completely mixed systems. Uptake of 14CO2 and some organic compounds by purified cell suspensions was measured, and values were corrected for the activity of heterotrophic as well as autotrophic contaminants as determined in control experiments. Cell populations exhibited maximum uptake activities during formation of the characteristic veils. Substantial uptake of CO2 in air-saturated seawater was coincident with an optimal concentration of hydrogen sulfide of about 1 mM. Glutamate and a selection of vitamins (B12M biotin, and thiamine) did not significantly affect the uptake of CO2. No substantial uptake of carbon from acetate, glutamate, mannitol, and Casamino Acids was found. Within the range of error indicated, the data are consistent with acceptance of a chemolithotrophic nature of Thiovulum. (+info)
Roots as a site of hydrogen sulfide uptake in the hydrocarbon seep vestimentiferan Lamellibrachia sp.
Vestimentiferan tubeworms have no mouth or gut, and the majority of their nutritional requirements are provided by endosymbiotic bacteria that utilize hydrogen sulfide oxidation to fix CO(2) into organic molecules. It has been assumed that all vestimentiferans obtain the sulfide, O(2) and CO(2) needed by the bacteria across the plume (gill) surface, but some live in locations where very little sulfide is available in the sea water surrounding the plume. We propose that at least some of these vestimentiferans can grow a posterior extension of their body and tube down into the sea-floor sediment, and that they can use this extension, which we call the 'root', to take up sulfide directly from the interstitial water. In this study of the vestimentiferan Lamellibrachia sp., found at hydrocarbon seeps in the Gulf of Mexico at depths of approximately 700 m, we measured seawater and interstitial sulfide concentrations in the hydrocarbon seep habitat, determined the structural characteristics of the root tube using transmission electron microscopy, characterized the biochemical composition of the tube wall, and measured the sulfide permeability of the root tube. We found that, while the sulfide concentration is less than 1 (micro)mol l(-)(1) in the sea water surrounding the gills, it can be over 1.5 mmol l(-)(1) at a depth of 10-25 cm in sediment beneath tubeworm bushes. The root tube is composed primarily of giant (&bgr;)-chitin crystallites (12-30 % of total mass) embedded in a protein matrix (50 % of total mass). Root tubes have a mean diameter of 1.4 mm, a mean wall thickness of 70 (micro)m and can be over 20 cm long. The tubeworm itself typically extends its body to the distal tip of the root tube. The root tube wall was quite permeable to sulfide, having a permeability coefficient at 20 degrees C of 0. 41x10(-)(3 )cm s(-)(1), with root tube being 2.5 times more permeable to sulfide than trunk tube of the same diameter. The characteristics of the root suggest that it reaches down to the higher sulfide levels present in the deeper sediment and that it functions to increase the surface area available for sulfide uptake in a manner analogous to a respiratory organ. (+info)
Long-term effects on the olfactory system of exposure to hydrogen sulphide.
OBJECTIVE: To study chronic effects of hydrogen sulphide (H2S) on cranial nerve I (nervi olfactorii), which have been only minimally described. METHODS: Chemosensations (smell and taste) were evaluated in eight men who complained of continuing dysfunction 2-3 years after the start of occupational exposure to H2S. Various bilateral (both nostrils) and unilateral (one nostril at a time) odour threshold tests with standard odorants as well as the Chicago smell test, a three odour detection and identification test and the University of Pennsylvania smell identification test, a series of 40 scratch and sniff odour identification tests were administered. RESULTS: Six of the eight patients showed deficits of various degrees. Two had normal scores on objective tests, but thought that they continued to have problems. H2S apparently can cause continuing, sometimes unrecognised olfactory deficits. CONCLUSION: Further exploration into the extent of such problems among workers exposed to H2S is warranted. (+info)
On the occurrence of anoxic microniches, denitrification, and sulfate reduction in aerated activated sludge.
A combination of different methods was applied to investigate the occurrence of anaerobic processes in aerated activated sludge. Microsensor measurements (O(2), NO(2)(-), NO(3)(-), and H(2)S) were performed on single sludge flocs to detect anoxic niches, nitrate reduction, or sulfate reduction on a microscale. Incubations of activated sludge with (15)NO(3)(-) and (35)SO(4)(2-) were used to determine denitrification and sulfate reduction rates on a batch scale. In four of six investigated sludges, no anoxic zones developed during aeration, and consequently denitrification rates were very low. However, in two sludges anoxia in flocs coincided with significant denitrification rates. Sulfate reduction could not be detected in any sludge in either the microsensor or the batch investigation, not even under short-term anoxic conditions. In contrast, the presence of sulfate-reducing bacteria was shown by fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes and by PCR-based detection of genes coding for the dissimilatory sulfite reductase. A possible explanation for the absence of anoxia even in most of the larger flocs might be that oxygen transport is not only diffusional but enhanced by advection, i.e., facilitated by flow through pores and channels. This possibility is suggested by the irregularity of some oxygen profiles and by confocal laser scanning microscopy of the three-dimensional floc structures, which showed that flocs from the two sludges in which anoxic zones were found were apparently denser than flocs from the other sludges. (+info)
Detoxification of hydrogen sulfide and methanethiol in the cecal mucosa.
Colonic bacteria liberate large quantities of the highly toxic gases hydrogen sulfide (H(2)S) and methanethiol (CH(3)SH). The colonic mucosa presumably has an efficient means of detoxifying these compounds, which is thought to occur through methylation of H(2)S to CH(3)SH and CH(3)SH to dimethylsulfide (CH(3)SCH(3)). We investigated this detoxification pathway by incubating rat cecal mucosal homogenates with gas containing H(2)S, CH(3)SH, or CH(3)SCH(3). Neither CH(3)SH nor CH(3)SCH(3) was produced during H(2)S catabolism, whereas catabolism of CH(3)SH liberated H(2)S but not CH(3)SCH(3). Thus, H(2)S and CH(3)SH are not detoxified by methylation to CH(3)SCH(3). Rather, CH(3)SH is demethylated to H(2)S, and H(2)S is converted to nonvolatile metabolites. HPLC analysis of the homogenate showed the metabolite to be primarily thiosulfate. Analysis of cecal venous blood obtained after intracecal instillation of H(2)(35)S revealed that virtually all absorbed H(2)S had been oxidized to thiosulfate. The oxidation rate of H(2)S by colonic mucosa was 10,000 times greater than the reported methylation rate. Conversion to thiosulfate appears to be the mechanism whereby the cecal mucosa protects itself from the injurious effects of H(2)S and CH(3)SH, and defects in this detoxification possibly could play a role in colonic diseases such as ulcerative colitis. (+info)
The contribution of sulphate reducing bacteria and 5-aminosalicylic acid to faecal sulphide in patients with ulcerative colitis.
BACKGROUND: Butyrate oxidation within the colonocyte is selectively inhibited by hydrogen sulphide, reproducing the metabolic lesion observed in active ulcerative colitis. AIMS: To study generation of hydrogen sulphide by sulphate reducing bacteria (SRB) and the effects of 5-aminosalicylic acid (5-ASA) in patients with ulcerative colitis in order to identify a role of this noxious agent in pathogenesis. PATIENTS: Fresh faeces were obtained from 37 patients with ulcerative colitis (23 with active disease) and 16 healthy controls. METHODS: SRB were enumerated from fresh faecal slurries and measurements made of sulphate reducing activity, and sulphate and hydrogen sulphide concentrations. The effect of 5-ASA on hydrogen sulphide production was studied in vitro. RESULTS: All controls and patients with active ulcerative colitis carried SRB and total viable counts were significantly related to the clinical severity grade. SRB were of two distinct types: rapidly growing strains (desulfovibrios) which showed high sulphate reduction rates, present in 30% of patients with ulcerative colitis and 44% of controls; and slow growing strains which had little activity. In vitro, 5-ASA inhibited sulphide production in a dose dependent manner; in patients with ulcerative colitis not on these drugs faecal sulphide was significantly higher than in controls (0.55 versus 0.25 mM, p=0.027). CONCLUSIONS: Counts and carriage rates of SRB in faeces of patients with ulcerative colitis are not significantly different from those in controls. SRB metabolism is not uniform between strains and alternative sources of hydrogen sulphide production exist in the colonic lumen which may be similarly inhibited by 5-ASA. The evidence for hydrogen sulphide as a metabolic toxin in ulcerative colitis remains circumstantial. (+info)
Mucin secretion is modulated by luminal factors in the isolated vascularly perfused rat colon.
BACKGROUND: Mucins play an important protective role in the colonic mucosa. Luminal factors modulating colonic mucus release have been not fully identified. AIM: To determine the effect of some dietary compounds on mucus discharge in rat colon. METHODS: An isolated vascularly perfused rat colon model was used. Mucus secretion was induced by a variety of luminal factors administered as a bolus of 1 ml for 30 minutes in the colonic loop. Mucin release was evaluated using a sandwich enzyme linked immunosorbent assay supported by histological analysis. RESULTS: The three dietary fibres tested in this study (pectin, gum arabic, and cellulose) did not provoke mucus secretion. Luminal administration of sodium alginate (an algal polysaccharide used as a food additive) or ulvan (a sulphated algal polymer) induced a dose dependent increase in mucin discharge over the concentration range 1-25 mg/l (p<0.05 for 25 mg/l alginate and p<0.05 for 10 and 25 mg/l ulvan). Glucuronic acid and galacturonic acid, which are major constituents of a variety of fibres, produced significant mucin secretion (p<0.05). Hydrogen sulphide and mercaptoacetate, two sulphides produced in the colonic lumen by microbial fermentation of sulphated polysaccharides, did not modify mucin secretion. Among the short chain fatty acids, acetate (5-100 mM) induced a dose dependent release of mucus (p<0.05 for 100 mM acetate). Interestingly, butyrate at a concentration of 5 mM produced colonic mucin secretion (p<0.05), but increasing its concentration to 100 mM provoked a gradual decrease in mucus discharge. Propionate (5-100 mM) did not induce mucin release. Several dietary phenolic compounds (quercetin, epicatechin, resveratrol) did not provoke mucus discharge. CONCLUSIONS: Two algal polysaccharides (alginate and ulvan), two uronic acids (glucuronic acid and galacturonic acid), and the short chain fatty acids acetate and butyrate induce mucin secretion in rat colon. Taken together, these data suggest that some food constituents and their fermentation products may regulate the secretory function of colonic goblet cells. (+info)
Improved plating media for the detection of Salmonella species with typical and atypical hydrogen sulfide production.
The Salmonella detection ability of 2 surfactant-supplemental media, xylose-lysine-tergitol (Nia-proof) 4 (XLT4) and Miller-Mallinson (MM) agar, was compared against that of several commonly used plating media. XLT4 and MM appeared to be the most efficient in detecting Salmonella in meat products and food animal environments. MM was superior to XLT4 in detecting those increasingly more prevalent strains of Salmonella possessing weak to ultraweak H2S production characteristics. (+info)