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PubMed2005

Nitrogen turnover in drying sediments of an Amazon floodplain lake.

In the Amazon floodplain large areas are subject to annual cycles of drying and rewetting. The turnover of nitrogen in the periodically drying sediments is an important regulator of floodplain fertility. In the present study the transition of a lake sediment from flooded to dry conditions was studied with respect to microbial nitrogen turnover. Soil nitrogen pools, as well as the activity and abundance of denitrifying and nitrifying bacteria, were investigated during one dry season. During the first weeks after drying, most of the inorganic nitrogen vanished from the sediment. The process was inhibited by a nitrification inhibitor, showing that coupled nitrification-denitrification was responsible for the nitrogen loss. Assimilation by plants or microbes, as well as leaching, were not important mechanisms of nitrogen loss. During a period of only 10 days, 59% of the total denitrification and 94% of the total N2O emission during the dry period occurred. Cell numbers of denitrifiers were not correlated with activities. Denitrification was not correlated with other sediment variables but was regulated by the patchy distribution of reduced and oxidized zones in the uppermost centimeters of the sediment. This heterogeneity was probably introduced by the bioturbation of small insects, which was restricted to a rather short time period shortly after drying.

Bacteria↗
PubMed1999

Effect of Introduced Pseudomonas fluorescens Strains on Soil Nematode and Protozoan Populations in the Rhizosphere of Wheat and Pea.

Previous studies have shown that inoculation of pea seeds with Pseudomonas fluorescens strains F113lacZY or F113G22 increased mineralization of organic nitrogen in the rhizosphere. In contrast, inoculation of the same strains onto wheat seeds reduced mineralization of N from organic residues incorporated into soil. In the present study, we report on a likely explanation of this phenomenon, which appears to be governed by the effect of plant-microbe interactions on bacterial-feeding nematodes and protozoa. In soil microcosm tests, inoculation of pea seeds with Pseudomonas fluorescens strains F113lacZY or F113G22 resulted in an increase in the number of nematodes and protozoa in the rhizosphere as compared to noninoculated controls. This trend was repeated using a model sand system into which the bacteriophagous nematode Caenorhabditis elegans was introduced. It was subsequently found that non-inoculated germinating pea seeds exerted a nematicidal effect on C. elegans, which was remedied by inoculation with either strain F113lacZY or F113G22. This suggests that nematicidal compounds released by the germinating pea seeds were metabolized by the microbial inoculants before they affected nematode populations in the spermosphere or rhizosphere of pea. In contrast, inoculation of wheat plants resulted in significantly lower nematode populations in the rhizosphere, whereas protozoan numbers were unaffected. No nematicidal effects of inoculated or noninoculated wheat seeds could be found, suggesting that microfaunal populations were affected at a later stage during plant growth. Because of their key roles in accelerating the turnover of microbially immobilized N and organic matter, plants that support a larger microfaunal population are likely to benefit from a higher availability of inorganic nitrogen. Therefore, an understanding of plant-microbe interactions and their effects on soil microfaunal populations is essential in order to assess the effects of microbial inocula on plant mineral nutrition.

Journal Article↗
PubMed2006

Structure of microbial communities performing the simultaneous reduction of Fe(II)EDTA.NO2- and Fe(III)EDTA -.

BioDeNOx is a combined physicochemical and biological process for the removal of nitrogen oxides (NOx) from flue gas. In the present study, two anaerobic bioreactors performing BioDeNOx were run consecutively (RUN-1 and RUN-2) at a dilution rate of 0.01 h(-1) with Fe(II)EDTA.NO(2-) and Fe(III)EDTA(-) as electron acceptors and ethanol as electron donor. The measured protein concentration of the reactor biomass of both runs was 120 mg/l. Different molecular methods were used to determine the identity and abundance of the bacterial populations in both bioreactors. Bacillus azotoformans strain KT-1 was recognized as a key player in Fe(II)EDTA.NO(2-) reduction. PCR-denaturing gradient gel electrophoresis analysis of the reactor biomass showed a greater diversity in RUN-2 than in RUN-1. Enrichments of Fe(II)EDTA.NO(2-) and Fe(III)EDTA(-) reducers and activity assays were conducted using the biomass from RUN-2 as an inoculum. The results on substrate turnover, overall microbial diversity, and enrichments and finally activity assays confirmed that ethanol was used as electron donor for Fe(II)EDTA.NO(2-) reduction. In addition, the Fe(III)EDTA(-) reduction rate of the microbial community proved to be feasible enough to run the bioreactors, ruling out the chemical reduction of Fe(III)EDTA(-) with sulfide as was proposed by other researchers.

Anaerobiosis↗
PubMed2004

Use of stable isotopes to measure de novo synthesis and turnover of amino acid-C and -N in mixed micro-organisms from the sheep rumen in vitro.

Protein synthesis and turnover in ruminal micro-organisms were assessed by stable-isotope methods in order to follow independently the fate of amino acid (AA)-C and -N in different AA. Rumen fluid taken from sheep receiving a grass hay-concentrate diet were strained and incubated in vitro with starch-cellobiose-xylose in the presence of NH3 and 5 g algal protein hydrolysate (APH)/l, in incubations where the labels were (15)NH3, [(15)N]APH or [(13)C]APH. Total (15)N incorporation was calculated from separate incubations with (15)NH3 and [(15)N]APH, and net N synthesis from the increase in AA in protein-bound material. The large difference between total and net AA synthesis indicated that substantial turnover of microbial protein occurred, averaging 3.5 %/h. Soluble AA-N was incorporated on average more extensively than soluble AA-C (70 v. 50 % respectively, P=0.001); however, incorporation of individual AA varied. Ninety percent of phenylalanine-C was derived from the C-skeleton of soluble AA, whereas the incorporation of phenylalanine-N was 72 %. In contrast, only 15 % aspartate-C+asparagine-C was incorporated, while 45 % aspartate-N+asparagine-N was incorporated. Deconvolution analysis of mass spectra indicated substantial exchange of carboxyl groups in several AA before incorporation and a condensation of unidentified C2 and C4 intermediates during isoleucine metabolism. The present results demonstrate that differential labelling with stable isotopes is a way in which fluxes of AA synthesis and degradation, their biosynthetic routes, and separate fates of AA-C and -N can be determined in a mixed microbial population.

Amino Acids↗
PubMed2000

Carbon monoxide production is not enhanced by nitrogenase activity.

A diverse group of nitrogen-fixing bacteria and two heme degraders were grown with and without fixed nitrogen sources under oxic and suboxic conditions, with and without addition of heme-containing compounds. Several of the strains produced carbon monoxide (CO) under one or more of these conditions, but nitrogenase activity did not stimulate rates of production relative to controls. Although nitrogenase can reduce CO(2) to CO in vitro in the absence of N(2), this process likely contributes minimally to CO production in soils under in situ conditions. In contrast, myoglobin or hematin addition under oxic conditions significantly stimulated CO production by the heme degraders. However, estimates of CO production from microbial heme turnover suggest that this too is likely to be only a small source of CO in soils in situ.

Journal Article↗
PubMed2005

Influence of flavomycin on microbial numbers, microbial metabolism and gut tissue protein turnover in the digestive tract of sheep.

Flavomycin is an antibiotic that promotes growth in ruminant and non-ruminant livestock. The aim of this study was to determine the mechanism of action of flavomycin in sheep by measuring microbial numbers, microbial metabolism and gut tissue protein turnover at different sites in the digestive tract. Two weight-matched groups (n 5) of male castrate lambs (30 kg) received 800 g grass cubes/d for 6 weeks, with one group receiving 20 mg/d flavomycin during the last 2 weeks. Samples of digesta and gut tissue segments were obtained immediately post mortem, 90 min after a flood-dose of [ring-D5]phenylalanine. Viable bacterial counts and volatile fatty acid concentrations were highest in ruminal digesta, followed by the colon and caecum, then the duodenum and ileum. The only effect of flavomycin was an increased bacterial count in the rumen (3.5 v. 1.2 x 10(9) per g; P=0.04). Acetate was proportionally greater and propionate and butyrate were lower in the caecum and colon than the rumen. Flavomycin had no effect on volatile fatty acid proportions or ammonia concentrations. Bacteria growing on peptides as sole C source were not affected by flavomycin. Proteolytic, peptidolytic and amino acid deamination activities were similar in the rumen, caecum and colon; they tended to be lower in animals receiving flavomycin. Protein turnover in ruminal wall and duodenal tissues, measured by a flood-dose technique, decreased with flavomycin (P=0.075 and 0.027, respectively). Thus, flavomycin differs from ionophores in its mode of action. It may influence protein metabolism of both digesta and tissue throughout the ruminant digestive tract.

Ammonia↗
PubMed2005

Heterotrophic fixation of CO(2) in soil.

The occurrence of heterotrophic CO(2) fixation by soil microorganisms was tested in several mineral soils differing in pH and two artificial soils (a mixture of silica sand, alfalfa powder, and nutrient medium inoculated with a soil suspension). Soils were incubated at ambient ( approximately 0.05 vol%) and elevated ( approximately 5 vol%) CO(2) concentrations under aerobic conditions for up to 21 days. CO(2) fixation was detected using either a technique for determining the natural abundance of (13)C or by measuring the distribution of labeled (14)C-CO(2) in soil and bacteria. The effects of elevated CO(2) on microbial biomass (direct counts, chloroform fumigation extraction method), composition of microbial community (phospholipid fatty acids), microbial activity (respiration, dehydrogenase activity), and turnover rate were also measured. Heterotrophic CO(2) fixation was proven in all soils under study, being higher in neutral soils. The main portion of the fixed CO(2) (98-99%) was found in extracellular metabolites while only approximately 1% CO(2) was incorporated into microbial cells. High CO(2) concentration always induced an increase in microbial activity, changes in the composition of the microbial community, and a decrease in microbial turnover. The results suggest that heterotrophic CO(2) fixation could be a widespread process in soils.

Bacteria↗
PubMed1995

Reassessing the manipulation of protein synthesis by rumen microbes.

Protein synthesis by rumen microbes plays an important role in ruminant nutrition. Microbial proteins that are not recycled flow out of the rumen and account for more than 50% of the total proteins entering the intestines. Determination of microbial nitrogen in digesta is based on the isolation of a representative sample of rumen microbes and on the use of specific markers (purine bases, RNA, 15N incorporation). This review discusses the reliability of microbial markers and examines current methods for assessing differences in turnover rate and microbial composition among liquid and particulate compartments. Four groups of factors acting on microbial synthesis, which are also adaptable to farm conditions, are considered: I) modification of protozoal population; II) modification of liquid and solid phase kinetics in the rumen; III) balance in the components of the diet; and IV) probiotics. The effects of these factors are discussed, considering their feasibility and their usefulness for the host.

Animal Nutritional Physiological Phenomena↗
PubMed2026

Low-pH sulfate reduction in acid mine drainage treatment systems: implications for acidophilic and acid-tolerant sulfate-reducing bacteria - a systematic review.

Acid mine drainage (AMD) is characterized by persistent acidity, high sulfate and dissolved metal concentrations. Sulfate-reducing bacteria (SRB) are attractive candidates for AMD remediation because dissimilatory sulfate reduction generates alkalinity while producing sulfide that can facilitate metal removal through precipitation. Extending these processes to acidic conditions has increased interest in acidophilic and acid-tolerant SRB (aSRB and atSRB), yet evidence from cultivation, molecular surveys and treatment systems has often been interpreted separately. This systematic review synthesized 53 culture-dependent, culture-independent, and treatment system studies from 2014 to 2024 to examine relationships among taxonomic occurrence, physiological capability, demonstrated low-pH sulfate reduction and treatment performance. Phylogenetic analysis showed that low-pH sulfate-reducing phenotypes were distributed across multiple lineages and 16S rRNA relatedness alone did not predict acid tolerance. Desulfosporosinus was the most consistently represented genus across studies, although its recurrence was influenced by cultivation strategies. Sulfate reduction was demonstrated below pH 3, with sustained low-pH activity most strongly supported by controlled reactor studies; approximately pH 4.0-5.5 emerged as a comparatively well-supported range, while activity at lower pH was more dependent on microbial physiology and experimental conditions. Low-pH sulfate reduction also emerged as a community-level process shaped by electron-donor use, metabolite turnover and complementary microbial functions, while treatment performance additionally depended on biomass retention, hydraulic conditions and sulfide management. The reviewed studies support a distinction between taxonomic presence, demonstrated activity and treatment contribution. Future work should prioritize standardized reporting of active sulfate-reduction conditions, stronger taxon-function validation and long-term field testing of low-pH sulfidogenic systems.

Sulfates↗
PubMed1998

Degradation of phthalate and Di-(2-Ethylhexyl)phthalate by indigenous and inoculated microorganisms in sludge-amended soil

The metabolism of phthalic acid (PA) and di-(2-ethylhexyl)phthalate (DEHP) in sludge-amended agricultural soil was studied with radiotracer techniques. The initial rates of metabolism of PA and DEHP (4.1 nmol/g [dry weight]) were estimated to be 731.8 and 25.6 pmol/g (dry weight) per day, respectively. Indigenous microorganisms assimilated 28 and 17% of the carbon in [14C]PA and [14C]DEHP, respectively, into microbial biomass. The rates of DEHP metabolism were much greater in sludge assays without soil than in assays with sludge-amended soil. Mineralization of [14C]DEHP to 14CO2 increased fourfold after inoculation of sludge and soil samples with DEHP-degrading strain SDE 2. The elevated mineralization potential was maintained for more than 27 days. Experiments performed with strain SDE 2 suggested that the bioavailability and mineralization of DEHP decreased substantially in the presence of soil and sludge components. The microorganisms metabolizing PA and DEHP in sludge and sludge-amended soil were characterized by substrate-specific radiolabelling, followed by analysis of 14C-labelled phospholipid ester-linked fatty acids (14C-PLFAs). This assay provided a radioactive fingerprint of the organisms actively metabolizing [14C]PA and [14C]DEHP. The 14C-PLFA fingerprints showed that organisms with different PLFA compositions metabolized PA and DEHP in sludge-amended soil. In contrast, microorganisms with comparable 14C-PLFA fingerprints were found to dominate DEHP metabolism in sludge and sludge-amended soil. Our results suggested that indigenous sludge microorganisms dominated DEHP degradation in sludge-amended soil. Mineralization of DEHP and PA followed complex kinetics that could not be described by simple first-order equations. The initial mineralization activity was described by an exponential function; this was followed by a second phase that was described best by a fractional power function. In the initial phase, the half times for PA and DEHP in sludge-amended soil were 2 and 58 days, respectively. In the late phase of incubation, the apparent half times for PA and DEHP increased to 15 and 147 days, respectively. In the second phase (after more than 28 days), the half time for DEHP was 2.9 times longer in sludge-amended soil assays than in sludge assays without soil. Experiments with radiolabelled DEHP degraders suggested that a significant fraction of the 14CO2 produced in long-term degradation assays may have originated from turnover of labelled microbial biomass rather than mineralization of [14C]PA or [14C]DEHP. It was estimated that a significant amount of DEHP with poor biodegradability and extractability remains in sludge-amended soil for extended periods of time despite the presence of microorganisms capable of degrading the compound (e.g., more than 40% of the DEHP added is not mineralized after 1 year).

Journal Article↗
PubMed2003

Species-specific measurements of ectomycorrhizal turnover under N-fertilization: combining isotopic and genetic approaches.

Ectomycorrhizal fungi play a significant role in the transfer of nutrients between plant and soil pools. Here we combine natural abundance (14)C measurements with restriction fragment length polymorphism (RFLP) to study the effects of nitrogen fertilization on the residence time of carbon within ectomycorrhizal species. We show that the carbon in ectomycorrhizal fungi turns over every 4-5 years, indicating that these fungi are relatively long-lived. Moreover, ectomycorrhizal fungi responded in a species-specific way to fertilization. Cenococcum geophilum contained younger carbon on average in nitrogen-fertilized plots than in control plots, even though turnover rates of the community as a whole did not shift significantly. Our results suggest that the response of ectomycorrhizal fungi to N availability is complex, and alterations in tissue turnover within this microbial pool may vary depending on community structure.

Carbon Radioisotopes↗
PubMed2003

A tripartite microbial reporter gene system for real-time assays of soil nutrient status.

Plant-derived carbon is the substrate which drives the rate of microbial assimilation and turnover of nutrients, in particular N and P, within the rhizosphere. To develop a better understanding of rhizosphere dynamics, a tripartite reporter gene system has been developed. We used three lux-marked Pseudomonas fluorescens strains to report on soil (1) assimilable carbon, (2) N-status, and (3) P-status. In vivo studies using soil water, spiked with C, N and P to simulate rhizosphere conditions, showed that the tripartite reporter system can provide real-time assessment of carbon and nutrient status. Good quantitative agreement for bioluminescence output between reference material and soil water samples was found for the C and P reporters. With regard to soil nitrate, the minimum bioavailable concentration was found to be greater than that analytically detectable in soil water. This is the first time that bioavailable soil C, N and P have been quantified using a tripartite reporter gene system.

Acyltransferases↗
PubMed2000

Are microorganisms more effective than plants at competing for nitrogen?

Plant scientists have long debated whether plants or microorganisms are the superior competitor for nitrogen in terrestrial ecosystems. Microorganisms have traditionally been viewed as the victors but recent evidence that plants can take up organic nitrogen compounds intact and can successfully acquire N from organic patches in soil raises the question anew. We argue that the key determinants of 'success' in nitrogen competition are spatial differences in nitrogen availability and in root and microbial distributions, together with temporal differences in microbial and root turnover. Consequently, it is not possible to discuss plant-microorganism competition without taking into account this spatiotemporal context.

Fungi↗
PubMed1996

Consequences of reduced fibre intake on digestion, rate of passage and caecal microbial activity in the young rabbit.

The present work was undertaken to study in vivo fibre degradation, rate of passage and caecal fermentation activity (CFA) in the young rabbit (7 weeks old) receiving ad lib. a control (C) or low-fibre (LF) diet (400 and 220 g neutral-detergent fibre (NDF)/kg respectively). As a consequence of the 50% reduction in the dietary fibre level, the voluntary food intake of the rabbits decreased by 25%, and the daily fibre intake was reduced by 60% (26.7 and 10.8 g NDF/d for groups C and LF, respectively). In spite of a longer mean retention time of the fibre particles, the quantity of fibre digested daily was significantly lower (P < 0.01) for the LF than for the C group (4.0 and 7.8 g NDF/d respectively). The circadian distribution of the faecal excretion (as a percentage of the total DM output) did not differ between diets (P = 0.52) and no interaction was found (P = 0.96) between diet and time of excretion. Also, variables describing the CFA showed no interactions between diet (C or LF) and time of sampling (during caecotrophy or during hard faeces excretion). Our results indicated no direct relationship between the quantity of fibre digested and the total short-chain fatty acid concentration in the caecum, but the fermentation pattern indicated lower proportions of acetate for the LF diet. Higher levels of diaminopimelic acid (DAPA) and ATP were found for the LF diet associated with an improved dietary fibre digestibility, suggesting a higher microbial activity. However, this effect was balanced by a lower caecal digesta turnover rate and the microbial biomass output estimated through the faecal DAPA output did not vary significantly.

Animals↗
PubMed2004

Belowground carbon dynamics in loblolly pine (Pinus taeda) immediately following diammonium phosphate fertilization.

Forest soils store an immense quantity of labile carbon (C) and a may be a large potential sink for atmospheric C. Forest management practices such as fertilization may enhance overall C storage in soils, yet changes in physiological processes following nutrient amendments have not been widely investigated. We intensively monitored belowground C dynamics for nearly 200 days following diammonium phosphate fertilization of pot-grown loblolly pine (Pinus taeda L.) seedlings in an effort to examine the short-term effects of fertilization on processes involved in soil C sequestration. Soil respiration rates initially increased in fertilized pots relative to controls, followed by a brief reversal in this trend and then a final sustained pattern of elevated rates of soil respiration in the fertilized treatment. Patterns in soil respiration rates over time reflected changes in autotrophic (root) and heterotrophic (microbial) components of soil respiration. Root respiration rates were greater in the fertilized treatment 49 days following fertilization and returned to control rates by the end of the study. In contrast, microbial respiration rates and microbial activity per soil C concentration remained depressed over the same time period. Compared with control seedlings, total root biomass was 27% greater in fertilized seedlings harvested at the end of the study, indicating that the elevated soil respiration rates observed toward the end of the study were a result of increased respiring root biomass. We conclude that fertilization, at least over the short-term, may increase soil C sequestration by increasing belowground biomass production and reducing microbial driven C turnover.

Biomass↗
PubMed1988

Effects of an abrupt diet change from hay to concentrate on microbial numbers and physical environment in the cecum of the pony.

Microbial numbers, pH, fluid volume, and turnover rate in the pony cecum were measured during an abrupt change from an all-forage to an all-concentrate diet, both fed at maintenance energy levels. Concentrate feeding resulted in increased (P less than 0.01) numbers of total viable anaerobic bacteria. The numbers of organisms growing on selective starch medium increased (P less than 0.01) when concentrate was fed, while numbers on xylan and pectin media decreased (P less than 0.025). Seven days after the diet change to concentrate, the number of bacteria growing on lactate medium increased (P less than 0.01), followed by a gradual decline. Cellulolytic bacteria occurred in low numbers, ranging from 1.1 x 10(4) to 4.4 x 10(4) per g of cecal contents. Feeding all concentrate decreased both the number of genera (P less than 0.01) and total protozoan numbers (P less than 0.01) in the cecum. Minimum cecal pH values of 6.4 and 5.8 were obtained when forage and concentrate, respectively, were fed, with the minimum pH occurring 6 h postfeeding. Dry-matter percentage of cecal contents followed a diurnal pattern which was the inverse of the pH curve. During forage feeding, the cecum contained an average of 2.2 liters (1.6 to 3.4 liters), which turned over 3.9 times per day. When concentrate was fed, cecal volume averaged 3.9 liters (0.6 to 8.6 liters), with a mean liquid turnover of 4.2 times per day. Microbial numbers and pH changes in the pony cecum associated with an abrupt change in diet from hay to concentrate resembled those which occur in the rumen under similar feeding conditions.

Animal Feed↗
PubMed2003

Microbial processes associated with roots of bulbous rush coated with iron plaques.

Bulbous rush (Juncus bulbosus) is a pioneer species in acidic, iron-rich, coal mining lakes in the eastern part of Germany. Juncus roots are coated with iron plaques, and it has been suggested that microbial processes under the iron plaques might be supportive for Juncus plant growth. The objectives of this work were to enumerate the microbes involved in the turnover of iron and organic root exudates in the rhizoplane, to investigate the effect of oxygen and pH on the utilization of these exudates by the rhizobacteria, and to study the ability of the root-colonizing microbiota to reduce sulfate. Enumeration studies done at pH 3 demonstrated that 10(6) Fe(III) reducers and 10(7) Fe(II) oxidizers g (fresh wt root)(-1) were associated with Juncus roots. When roots were incubated in goethite-containing medium without and with supplemental glucose, Fe(II) was formed at rates approximating 1.1 mmol g (fresh wt root) (-1) d(-1) and 3.6 mmol g (fresh wt root)(-1) d(-1) under anoxic conditions, respectively. These results suggest that a rapid microbially mediated cycling of iron occurs in the rhizosphere of Juncus roots under changing redox conditions. Most-probable-number estimates of aerobes and anaerobes capable of consuming root exudates at pH 3 were similar in the rhizosphere sediment and in Juncus roots, but numbers of aerobes were significantly higher than those of anaerobes. At pH 3, supplemental organic exudates were primarily subject to aerobic oxidation to CO2 and not subject to fermentation. However, at pH 4.5, root exudates were also rapidly utilized under anoxic conditions. Root-associated sulfate reduction was not observed at pH 3 to 4.5 but was observed at pH 4.9. The pH increased during all root-incubation studies both under oxic and anoxic conditions. Thus, as result of the microbial turnover of organic root exudates, pH and CO2 levels might be elevated at the root surface and favor Juncus plants to colonize acidic habitats.

Carbon Dioxide↗
PubMed1976

The effect of molybdenum on the conversion of sulphate to sulphide and microbial-protein-sulphur in the rumen of sheep.

1. [35S]sulphate was used to measure the apparent turnover of sulphate, sulphide and microbial-protein-S in the rumen contents of four sheep that were intraruminally infused with 10 g sodium sulphate/d alone, or together with 126 mg sodium molybdate (50 mg molybdenum). 2. Infusion of molybdate increased the concentration of sulphate in rumen fluid from 2.2 to 7.2 mug S/ml and decreased the rate of reduction of sulphate to sulphide by 50%. Although the rate of sulphide production was slower, the concentration of sulphide in the rumen is suggested to explain these changes. 3. In animals that were not infused with molybdate, only one-third of the S (3.0 g/d) that passed through the sulphate pool in rumen fluid was converted to sulphide, decreasing to one-sixth when molybdate was infused. 4. The turnover of S amino acids in microbial protein was not significantly affected by molybdate. Only 52-57% of the S amino acid content of microbial protein was synthesized de novo by way of the sulphide pool.

Amino Acids, Sulfur↗