A new perspective on water quality: Exploring spatial and temporal patterns of impaired waters

Managing surface water quality is a global challenge, and understanding spatial and temporal patterns of water quality is a key component to effective management. However, analysis of spatiotemporal patterns of impaired waters over broad areas is sparse due to disparate water quality data and variable water quality standards. Thus, here we leverage the Alabama 303(d) List of impaired waters to present a new perspective for investigating spatiotemporal water quality patterns. Every two years, each state in the United States is required to assess its surface water quality and compile a list of impaired waterbodies, meaning waters that do not meet water quality standards for their designated usage - referred to as the 303(d) List. The purpose of the 303(d) List is to identify impaired waters so that corrective action can be taken to reduce pollutant loads and, ultimately, improve water quality. Using GIS, a space time cube was created to analyze and visualize spatiotemporal patterns of the impaired rivers added to the Alabama 303(d) Lists from 1996 to 2022. For this analysis, the percentage of river length impaired out of the total river length, and number of times each impairment cause was listed, were summarized within Alabama sub-basins (Hydrologic Unit Code 8) (n = 51). Trend and hot spot analyses were conducted on the river impairment and causes. There was an up trend in river impairment for eight sub-basins across the state and a downtrend in one sub-basin. Over half of the sub-basins with an up trend in impairment also had an up trend in the number of times pathogens was listed as a cause of impairment. Additionally, coastal sub-basins were found to be a hot spot for river impairment. Interestingly, there was a down trend in the number of times nutrients, ammonia, and siltation were listed as a cause of impairment at the state and sub-basin scales of analysis. Altogether, these findings show the use of spatiotemporal pattern analysis of impaired waters and can indicate where, both spatially and by pollutant, management should prioritize water quality improvement efforts.

Development of the Groundwater Concept Inventory to Measure Groundwater Knowledge in a General Audience

Groundwater is a critical resource globally, and understanding groundwater processes is vital to ensure sustainable management practices. However, there are many widely held misconceptions and inaccuracies about groundwater, and we currently lack tools to measure groundwater knowledge across large populations and measure how groundwater knowledge relates to management decisions or behaviors. Here, we present a survey instrument, the Groundwater Concept Inventory (GWCI), that has been designed for general audiences to measure groundwater knowledge comparable to that in an introductory geoscience curriculum. The GWCI was developed using ∼1200 responses using an online platform, Amazon Mechanical Turks, to represent a general population. Responses were evaluated using the Rasch model that configures a relationship between person-ability and item-difficulty. We found that the study population displayed similar misconceptions about groundwater compared with previous literature, and that age and education were not strong predictors of GWCI scores. The GWCI can be used by researchers to understand links between knowledge and behavior, and also by other stakeholders to quantify misconceptions about groundwater and target resources for a more informed public.

Investigating the Relationship between Surface Water Pollution and Onsite Wastewater Treatment Systems

Onsite wastewater treatment systems (OWTSs) are important nonpoint sources (NPSs) of pollution to consider in watershed management. However, limited OWTS data availability makes it challenging to account for them as an NPS of water pollution. In this study, we succeeded in obtaining OWTS permits and integrated them with environmental data to model the pollution potential from OWTSs at the watershed scale using GIS-based multicriteria decision analysis. Then, in situ water quality parameters─Escherichia coli (E. coli), total nitrogen, total phosphorus, temperature, and pH─were measured along the main tributary at base-flow conditions. Three general linear models were developed to relate E. coli to water quality parameters and OWTS pollution indicators. It was found that the model with the OWTS pollution potential had the lowest corrected Akaike information criterion (AICc) value (35.01) compared to the models that included classified OWTS pollution potential input criteria (AICc = 36.76) and land cover (AICc = 36.74). These results demonstrate that OWTSs are a significant contributor to surface water pollution, and future efforts should be made to improve access to OWTS data (i.e., location and age) to account for these systems as an NPS of water pollution.

Honey bee colony loss linked to parasites, pesticides and extreme weather across the United States

Honey bee (Apis mellifera) colony loss is a widespread phenomenon with important economic and biological implications, whose drivers are still an open matter of investigation. We contribute to this line of research through a large-scale, multi-variable study combining multiple publicly accessible data sources. Specifically, we analyzed quarterly data covering the contiguous United States for the years 2015-2021, and combined open data on honey bee colony status and stressors, weather data, and land use. The different spatio-temporal resolutions of these data are addressed through an up-scaling approach that generates additional statistical features which capture more complex distributional characteristics and significantly improve modeling performance. Treating this expanded feature set with state-of-the-art feature selection methods, we obtained findings that, nation-wide, are in line with the current knowledge on the aggravating roles of Varroa destructor and pesticides in colony loss. Moreover, we found that extreme temperature and precipitation events, even when controlling for other factors, significantly impact colony loss. Overall, our results reveal the complexity of biotic and abiotic factors affecting managed honey bee colonies across the United States.

Spatial distribution and mass transport of Perfluoroalkyl Substances (PFAS) in surface water: A statewide evaluation of PFAS occurrence and fate in Alabama

Per- and polyfluoroalkyl substances (PFAS) have been previously detected near suspected sources in Alabama, but the overall extent of contamination across the state is unknown. This study evaluated the spatial distribution of 17 PFAS within the ten major river basins in Alabama and provided insights into their transport and fate through a mass flux analysis. Six PFAS were identified in 65 out of the 74 riverine samples, with mean ∑₆PFAS levels of 35.2 ng L^-1. The highest ∑₆PFAS concentration of 237 ng L^-1 was detected in the Coosa River, a transboundary river that receives discharges from multiple sources in Alabama and Georgia. PFAS distribution was not observed to be uniform across the state: while the Coosa, Alabama, and Chattahoochee rivers presented relatively high mean ∑₆PFAS concentrations of 191, 100 and 28.8 ng L^-1, respectively, PFAS were not detected in the Conecuh, Escatawpa, and Yellow rivers. Remaining river systems presented mean ∑₆PFAS concentrations between 7.94 and 24.7 ng L^-1. Although the short-chain perfluoropentanoic acid (PFPeA) was the most detected analyte (88%), perfluorobutanesulfonic acid (PFBS) was the substance with the highest individual concentration of 79.4 ng L^-1. Consistent increases in the mass fluxes of PFAS were observed as the rivers flowed through Alabama, reaching up to 63.3 mg s^-1, indicating the presence of numerous sources across the state. Most of the mass inputs would not have been captured if only aqueous concentrations were evaluated, since concentration is usually heavily impacted by environmental conditions. Results of this study demonstrate that mass flux is a simple and powerful complementary approach that can be used to broadly understand trends in the transport and fate of PFAS in large river systems.

GIS interpolation is key in assessing spatial and temporal bioremediation of groundwater arsenic contamination

Arsenic (As) contamination in groundwater is a global crisis that is known to cause cancers of the skin, bladder, and lungs, among other health issues, and affects millions of people around the world. Due to the time and financial constraints associated with establishing in-depth monitoring programs, it is difficult to monitor and map arsenic concentrations over time and across large areas. The goal of this study was to determine the most accurate Geographic Information Systems (GIS) interpolation method for mapping the effects of bioremediation on groundwater arsenic sequestration across a local-scale study area in northwest Florida (~900 m²) over the duration of a nine-month period (pre-injection, one-month post-injection, and nine-months post-injection). We used groundwater data collected from 2018 to 2019 to visualize arsenic contamination over time. Measured arsenic concentrations from 23 wells were grouped into three categories: (1) decreasing, (2) fluctuating, or (3) largely unaffected by the bioremediation procedure. The accuracy of three interpolation methods was also investigated: Inverse Distance Weighted (IDW), Ordinary Kriging (OK), and Empirical Bayesian Kriging (EBK). Statistical results using the leave-one-out cross validation (LOOCV) process showed that OK consistently provided the most accurate predictions of arsenic concentrations across space and time ([Root Mean Square Error (RMSE) = 0.265] and accurately predicted regulatory arsenic concentrations below 0.05 mg/L in nine of 11 wells, while IDW and EBK only accurately predicted four and five wells, respectively. While it was shown that OK tends to underpredict arsenic maxima, this did not affect the overall accuracy of the interpolation compared to results from EBK (RMSE = 0.297) and IDW (RMSE = 0.272). Overall, these interpolations aided in the interpretation of the extent of bioremediation, revealing the need for repeated injections to continuously remove arsenic from the groundwater. The study will provide guidance and evaluation methods for international and governmental organizations, industrial companies, and local communities on how to understand spatial and temporal distributions of arsenic contamination and inform bioremediation efforts at various scales in the future.

Seno-destructive smooth muscle cells in the ascending aorta of patients with bicuspid aortic valve disease

Background

Ascending aortic aneurysms constitute an important hazard for individuals with a bicuspid aortic valve (BAV). However, the processes that degrade the aortic wall in BAV disease remain poorly understood.

Methods

We undertook in situ analysis of ascending aortas from 68 patients, seeking potentially damaging cellular senescence cascades. Aortas were assessed for senescence-associated-ß-galactosidase activity, p16^Ink4a and p21 expression, and double-strand DNA breaks. The senescence-associated secretory phenotype (SASP) of cultured-aged BAV aortic smooth muscle cells (SMCs) was evaluated by transcript profiling and consequences probed by combined immunofluorescence and circular polarization microscopy. The contribution of p38 MAPK signaling was assessed by immunostaining and blocking strategies.

Findings

We uncovered SMCs at varying depths of cellular senescence within BAV- and tricuspid aortic valve (TAV)-associated aortic aneurysms. Senescent SMCs were also abundant in non-aneurysmal BAV aortas but not in non-aneurysmal TAV aortas. Multivariable analysis revealed that BAV disease independently associated with SMC senescence. Furthermre, SMC senescence was heightened at the convexity of aortas associated with right-left coronary cusp fusion. Aged BAV SMCs had a pronounced collagenolytic SASP. Moreover, senescent SMCs in the aortic wall were enriched with surface-localized MMP1 and surrounded by weakly birefringent collagen fibrils. The senescent-collagenolytic SMC phenotype depended on p38 MAPK signaling, which was chronically activated in BAV aortas.

Interpretation

We have identified a cellular senescence-collagen destruction axis in at-risk ascending aortas. This novel “seno-destructive” SMC phenotype could open new opportunities for managing BAV aortopathy.

Fund

Canadian Institutes of Health Research, Lawson Health Research Institute, Heart and Stroke Foundation of Ontario/Barnett-Ivey Chair.

Ku70 Serine 155 mediates Aurora B inhibition and activation of the DNA damage response

The Ku heterodimer (Ku70/Ku80) is the central DNA binding component of the classical non-homologous end joining (NHEJ) pathway that repairs DNA double-stranded breaks (DSBs), serving as the scaffold for the formation of the NHEJ complex. Here we show that Ku70 is phosphorylated on Serine 155 in response to DNA damage. Expression of Ku70 bearing a S155 phosphomimetic substitution (Ku70 S155D) in Ku70-deficient mouse embryonic fibroblasts (MEFs) triggered cell cycle arrest at multiple checkpoints and altered expression of several cell cycle regulators in absence of DNA damage. Cells expressing Ku70 S155D exhibited a constitutive DNA damage response, including ATM activation, H2AX phosphorylation and 53BP1 foci formation. Ku70 S155D was found to interact with Aurora B and to have an inhibitory effect on Aurora B kinase activity. Lastly, we demonstrate that Ku and Aurora B interact following ionizing radiation treatment and that Aurora B inhibition in response to DNA damage is dependent upon Ku70 S155 phosphorylation. This uncovers a new pathway where Ku may relay signaling to Aurora B to enforce cell cycle arrest in response to DNA damage.

Allelic imbalance at the DNA mismatch repair loci, hMSH2, hMLH1, hPMS1, hPMS2 and hMSH3, in squamous cell carcinoma of the head and neck

BACKGROUND

Squamous cell carcinoma of the head and neck (SCCHN) is one of the 10 most frequently occurring cancers in the world. Defective mismatch repair, as exhibited by the phenomenon of microsatellite instability, has been observed in SCCHN although no reports of mismatch repair gene mutations or altered protein expression have been published. In a variety of microsatellite instability (MSI) positive cancers where mutations in the mismatch repair (MMR) genes were not observed, allelic imbalance at the loci of the MMR genes was prevalent.

OBJECTIVE

To investigate whether allelic imbalance at the MMR genetic loci contributes to the development of SCCHN.

MATERIALS AND METHODS

35 matched normal/tumour SCCHN pairs were studied using 29 microsatellite markers located within and adjacent to six known DNA mismatch repair genes. In addition, mutational analysis and protein expression of hMSH2 and hMLH1 were investigated.

RESULTS AND CONCLUSIONS

We demonstrated that 36 and 17% of the analysed SCCHN specimens exhibited allele imbalance at the hMLH1 and hMSH3 genetic loci, respectively. Allelic instability at these two loci was found to be correlated with the MSI status of the SCCHN tumours. Allelic instability was found to be uncommon at the other MMR gene loci analysed. One mutation was found in hMSH2 and none in hMLH1 in this series of tumours. 23 of 24 (96%) of the examined SCCHN tumours showed reduced expression of either hMSH2 or hMCH1 genes. Allelic instability in the MMR genes, hMLH1 and hMSH3, is proposed to be involved in the aetiology of SCCHN tumours.

Elimination and biochemical responses to intravenous alendronate in postmenopausal osteoporosis

Postmenopausal women with established vertebral osteoporosis were studied for 2 years to determine the terminal elimination half-life and the duration of response to treatment with intravenous alendronate (30 mg) given over 4 days. The urinary excretion of alendronate followed a multiexponential decline. Approximately 50% of the total dose was excreted over the first 5 days, and a further 17% was excreted in the succeeding 6 months. Thereafter, there was a much slower elimination phase with an estimated mean terminal half-life of greater than 10 years (n = 11). Urinary excretion of hydroxyproline and calcium decreased significantly from pretreatment values by day 3, reaching a nadir by 1 week (40% and 67% decrease, respectively). Thereafter, hydroxyproline remained suppressed for the following 2 years. In contrast, urinary calcium excretion returned gradually toward pretreatment values over the first year and during the second year was comparable to pretreatment values. Serum activity of alkaline phosphatase activity decreased over 3 months (23% reduction), increased gradually thereafter, and returned to pretreatment values at month 24. Bone mineral density measured at the spine increased by approximately 5% during the first year and remained significantly higher than pretreatment values at 2 years. We conclude that a short course of high doses of intravenous alendronate is associated with a prolonged skeletal retention of the agent. This open study also suggests that this regimen has a sustained effect on bone turnover persisting for at least 1 year.

Effects of tryptophan supplementation to a maize-based diet on lipid metabolism in laying hens

1. Experiments were conducted with laying hens to determine the effects of supplementing 0, 1.0, 2.0 and 3.0 or 4.0 g trp/kg diet to a maize and soyabean meal-based laying ration (basal tryptophan = 1.66 g/kg) on tissue lipid concentrations. 2. Plasma cholesterol, triglycerides and nonesterified fatty acids were increased by supplementing the diet with 1.0 g trp/kg diet and decreased with 3.0 or 4.0 g trp/kg diet. A significant quadratic effect of supplemental tryptophan was observed on plasma lipids in most cases. The observed effects diminished with time. No consistent changes were observed in plasma glucose concentrations. 3. Total liver lipids were reduced by supplemental tryptophan at all concentrations.

Effect of tryptophan supplementation on aflatoxicosis in laying hens

Two experiments were conducted to determine the relationship of supplemental Trp on liver fat accumulation and egg production during aflatoxicosis in laying hens. In Experiment 1, two levels of Trp (0 and 2,000 ppm; basal = .16% Trp) and two levels of aflatoxin (AFLA) (0 and 10 ppm) were supplemented to a complete layer ration. In Experiment 2, a third level of AFLA (5 ppm) was added to the design. Single Comb White Leghorn hens (58 and 68 wk old) were fed the diets for 3 wk for Experiments 1 and 2, respectively. Henday production and egg weights were measured daily. Feed intake was measured weekly. Liver weights, liver moisture, and liver total lipids were determined at the end of each trial. In Experiment 1, supplemental Trp by itself caused a significant (P less than .01) reduction in total liver lipids compared to the controls (no Trp or AFLA). Adding trp and AFLA increased total liver lipids and caused a significant (P less than .05) decrease in egg production compared with adding AFLA alone. Total liver lipids were 41.1, 32.8, 54.8, and 62.4% (dry weight basis) for 0 Trp:0 AFLA, 2,000 Trp:0 AFLA, 0 Trp:10 AFLA, and 2,000 Trp:10 AFLA, respectively. Similar results were observed in Experiment 2. It was concluded that supplemental Trp by itself caused a reduction in total liver lipids, but when supplemented to a diet containing AFLA, Trp caused an increased severity of lesions associated with aflatoxicosis in layers.

The influence of dietary tryptophan on broiler chick growth and lipid metabolism as mediated by dietary protein levels

Three experiments were conducted to determine how dietary protein and tryptophan influence the lipid metabolism of growing broiler chicks. A diet-dilution method (corn-corn gluten meal-gelatin summit/corn starch basal) was used in three factorial experiments. Various levels of protein and tryptophan were fed in each experiment: protein from 16 to 28% and tryptophan from .34 to 2.74% of protein. Gain was maximized when the dietary levels of tryptophan were .83 +/- .03, 77 +/- .04, 77 +/- .05, and .78 +/- .05% of the protein for 16, 20, 24, and 28% dietary protein, respectively. The requirement estimates for feed efficiency and gain were similar. Liver lipids significantly decreased as the level of dietary tryptophan increased at each protein level (P less than .0001). Dietary tryptophan did not significantly alter the concentration of total plasma lipid in the chicks or in the carcass lipid content (P greater than .2399). Tryptophan supplementation significantly increased the concentration of plasma linoleic acid and plasma free tryptophan. The requirement of the chicks for tryptophan was estimated to be .80 +/- .01% of the dietary protein for the growing chick. Increased liver lipid and decreased plasma tryptophan are diagnostic lesions suggesting a tryptophan deficiency.

Galactose as a regulatory factor of its own metabolism by rat liver

As part of a series of studies to assess the regulation of hepatic galactose-metabolizing enzymes, galactokinase, galactose-1-phosphate uridyltransferase, and UDPgalactose-4-epimerase, the effect of feeding a high galactose-containing diet to normal adult and pregnant female rats was examined. Sixteen days of galactose exposure of adult virgin females produced a different response in the specific activity of each of the enzymes, that of galactokinase being lower, transferase higher, and epimerase transiently elevated. Galactose feeding increased the specific activity of transferase in pregnant rat liver above the elevated level that already exists in the pregnant state but failed to influence the enzyme of the developing fetal liver. Galactose added to liver homogenates did not activate transferase. The increased activity in liver of adult, fed animals was not associated with a change in isoenzyme patterns examined by isoelectric gel electrophoresis but was characterized on kinetic analysis by an increase in Vmax for UDPglucose. The changes in enzyme specific activity in liver of animals fed galactose appear to have physiologic significance because hepatocytes isolated from galactose exposed livers take up more galactose and convert more to glucose and lactate than cells from control animals.

Activity of hepatic galactose-metabolizing enzymes in the pregnant rat and fetus

The sp act of hepatic galactose-metabolizing enzymes, galactokinase, galactose-1-phosphate uridyltransferase, and uridine diphosphate-4-epimerase were measured in female rats during pregnancy and lactation as well as in fetuses and pups after parturition. Sp act for transferase and epimerase in pregnant rat liver are about 50% higher than that of virgin females, and with the increase in organ size during pregnancy the total hepatic activity is double that of nonpregnant animals. Galactokinase activity decreases somewhat during pregnancy, but total activity is 25% higher than in virgin liver. A Michaelis-Menten kinetic analysis of liver transferase indicates an increase in the maximum velocity of the reaction without a change in Km. Isoelectricfocusing on a high-resolution IEF gel demonstrated similar isozyme patterns. The sp act of the fetal liver enzymes increase to about twice that of the maternal tissue, but total activities are low due to the very small fetal liver size. Sp act of these enzymes in maternal liver fall after delivery, but sp act of galactokinase and transferase are programmed to increase in liver of the growing neonatal animals, reaching levels almost 5-fold higher than found in nonpregnant adult liver. An understanding of factors contributing to the enhanced transferase activity of the liver of pregnant and neonatal rats may contribute to possible ways of augmenting the residual transferase activity of patients with transferase-deficient galactosemia as a therapeutic strategy.

The comparative effects of azathioprine and cyclosporin on some gingival health parameters of renal transplant patients. A longitudinal study

The periodontal health of 24 adult renal transplant patients was investigated in a longitudinal study. Post-transplant patients were receiving either azathioprine or cyclosporin to prevent graft rejection. No significant difference (P greater than 0.05) was observed for plaque scores on gingival inflammation, either between treatment groups or throughout the investigation period. However, patients on cyclosporin therapy had significantly more gingival hyperplasia and probing sites greater than 3 mm than those on azathioprine (P less than 0.05). In the cyclosporin group, a significant increase in hyperplasia and probing sites greater than 3 mm was observed at 3 and 6 months post-transplant. A significant correlation (rs = 0.55, P less than 0.05) was observed between mean plasma concentrations of cyclosporin throughout the 6-month investigation period and the increase in gingival hyperplasia. The finding from this study would suggest that azathioprine has no unwanted effects on the periodontal health of post-renal transplant patients. Cyclosporin therapy caused an increase in gingival hyperplasia, which may be related to plasma concentrations of the drug.

Influence of choline and sulfate on copper and toxicity and substitution of and antagonism between methionine and copper supplements to chick diets

Studies were conducted to determine if the deleterious affects on chick growth of the primary antagonism between methionine and copper involves the homocysteine moiety or labile methyl group of methionine. A .1% choline supplement resulted in performance response similar to that of a .2% L-methionine supplement in the absence but not in the presence of 500 mg/kg copper from cupric sulfate. Similar results were observed when the levels of methionine and choline were doubled. Sulfate, with or without choline, had little effect in the presence of cupric sulfate. When cupric acetate was used instead of cupric sulfate, a small but nearly significant (P = .08) response to potassium sulfate was observed. Maximum performance with .29% supplemental methionine and 188 mg/kg Cu was predicted from a response surface analysis. The methionine requirement was increased by feeding copper. However, the increase in methionine requirement was accompanied by an improvement in growth rate and feed efficiency. This may explain why levels used of methionine and total sulfur-containing amino acids appear to be higher under field conditions (with pharmacological levels of copper) than in laboratory conditions (without pharmacological levels of copper). The primary antagonism between methionine and copper involves the homocysteine moiety, not the labile methyl groups.

The use of biofeedback techniques in occupational therapy for persons with chronic pain

The use of biofeedback in occupational therapy to aid the person with chronic pain in the resumption of his daily functional activities is discussed. The chronic pain syndrome and how it disrupts performance of activities is examined, as well as occupational therapy strategies for assessment and treatment using biofeedback, and indications for evaluating treatment outcomes. The authors assume readers have basic familiarity with biofeedback theory, equipment and its operation.

Galactose and glucose metabolism in the isolated perfused suckling and adult rat liver

The development of the technique for the perfusion of the immature liver has enabled us to characterize metabolic differences in carbohydrate metabolism in the suckling versus adult rat livers. Livers of fasted suckling and adult rats were perfused with 4 mM galactose or 4 mM glucose. Galactose uptake was the same for both age groups during the first 35 min. The adult liver maintained the initial rate of uptake after this period while the immature liver began to take up galactose more rapidly. By the end of the experimental period, on a weight basis, uptake by the young liver was three times that of the adult. Analysis of the livers at the end of the 90 min perfusion showed hepatic galactose concentrations to be one-half of circulating media levels. Glucose output was observed in each group during perfusion with either galactose or glucose. In the immature liver, galactose perfusion stimulated more glucose output than did the glucose perfusion. In the adult, however, both sugars resulted in the same levels of glucose output. Galactose perfusion resulted in glucose levels in young liver being higher than the media; while in the adult, the level was lower than the media. Galactose perfused livers of the suckling and adult contained significantly more uridine-5'-diphosphogalactose than the glucose perfused livers of each age.

Role of iron deposition in Sphaerotilus discophorus

Various physiological aspects of the process of iron deposition in Sphaerotilus discophorus were examined to elucidate its role. The values of iron/protein ratios suggested that a direct relationship existed between the iron concentration of the media and the magnitude of final iron deposition. Saturation of the organism's iron deposition system occurred at a 2.0 mM iron concentration, at a value of 0.6 mg of ferric ion per mg of cell protein. Laboratory data indicated that the strain's very low capacity for iron deposition observed at low external iron concentrations makes it unlikely that it is significant in limiting iron in the natural milieu. Under optimal iron concentrations, however, strain SS1 caused precipitation of iron (adsorbed to cellular material) in broth cultures, which was 10 to 100 times that mediated by some "non-iron" microorganisms. The strain's iron requirement, which was found to be between 0.003 and 0.02 mM, is commensurate with that of other microbes. One hundred micrograms of Mn(II) per ml and possibly 10 mug of either Co(II) or Ni(II) per ml could inhibit iron uptake in the deposition system. Sphaerotilus, when tested for its ability to withstand toxic concentrations of certain trace elements (Co, Cu, Mn, Ni, and Cd), demonstrated no exceptional resistance with respect to several other common microorganisms. Final cell yields were not affected by a varying iron concentration for Sphaerotilus growing under conditions of limiting carbon and nitrogen.

Measurement of growth and iron deposition in Sphaerotilus discophorus

Aspects of the physiology of iron deposition of an iron-precipitating strain of Sphaerotilus were investigated in laboratory culture to characterize the process. Measurement of growth (incorporated L-[3H]alanine) and iron deposition (incorporated 59Fe) demonstrated that Sphaerotilus exhibit a characteristic temporal pattern of iron deposition, which is delayed until the latter portion of the exponential or the onset of the stationary growth phase. The growth rate (mu=0.17 h-1) was apparently independent of the iron concentration in the medium. There was, furthermore, no direct correlation between the iron concentration and final cell protein yield. It was concluded from experiments involving growth on artificial substrata (glass cover slips) that sessile populations derived no phsiological advantage (manifested as differences in growth rates) over free-living cells. There was no difference in the rate or onset of iron deposition of attached compared to suspended cells. Blocking of protein synthesis by the addition of chloramphenicol suggested that, once iron deposition was initiated, continued protein synthesis was not required for full expression of this capability. The results suggested that iron deposition may be possibly mediated by certain of the constituents of the organism's sheath.