Application of the Microbiology Concept Inventory to improve programmatic curriculum.

The Microbiology Concept Inventory is an assessment tool derived from the fundamental statements created by the American Society for Microbiology. This two-tier, multiple-choice question inventory requires students to choose the most correct answer for each question and provide a brief justification of their reasoning. Educators can utilize this tool to identify common misconceptions held by students and adjust curriculum to address and prevent the persistence of student misconceptions. Over the course of 5 years, the Microbiology Concept Inventory was annually administered to undergraduate students enrolled in entry-level, mid-level, and senior capstone microbiology courses at a mid-western rural university. Analysis was completed to compare course, year, majors and minors, gender, ethnicity, and cumulative GPA. Results of this study showed a significant difference in Microbiology Concept Inventory scores between students with high cumulative GPAs (3.5-4.0) and students with comparatively lower cumulative GPAs (2.5-2.99, 3.0-3.49). Results between the other demographic categories revealed statistically different scores in favor of white students, but no differences in scores between genders. The results suggest evidence of ethnic bias, but no gender bias as measured by the Microbiology Concept Inventory. Additionally, significant differences in scores across cohorts are indicative of improvements in the curricula due to prior targeted changes. Analysis of concept inventory results can guide curriculum changes for course instructors. Implementation of curriculum changes can enrich students' academic success.

Shifting effects of host physiological condition following pathogen establishment.

Understanding host persistence with emerging pathogens is essential for conserving populations. Hosts may initially survive pathogen invasions through pre-adaptive mechanisms. However, whether pre-adaptive traits are directionally selected to increase in frequency depends on the heritability and environmental dependence of the trait and the costs of trait maintenance. Body condition is likely an important pre-adaptive mechanism aiding in host survival, although can be seasonally variable in wildlife hosts. We used data collected over 7 years on bat body mass, infection and survival to determine the role of host body condition during the invasion and establishment of the emerging disease, white-nose syndrome. We found that when the pathogen first invaded, bats with higher body mass were more likely to survive, but this effect dissipated following the initial epizootic. We also found that heavier bats lost more weight overwinter, but fat loss depended on infection severity. Lastly, we found mixed support that bat mass increased in the population after pathogen arrival; high annual plasticity in individual bat masses may have reduced the potential for directional selection. Overall, our results suggest that some factors that contribute to host survival during pathogen invasion may diminish over time and are potentially replaced by other host adaptations.

Sex-biased infections scale to population impacts for an emerging wildlife disease.

Demographic factors are fundamental in shaping infectious disease dynamics. Aspects of populations that create structure, like age and sex, can affect patterns of transmission, infection intensity and population outcomes. However, studies rarely link these processes from individual to population-scale effects. Moreover, the mechanisms underlying demographic differences in disease are frequently unclear. Here, we explore sex-biased infections for a multi-host fungal disease of bats, white-nose syndrome, and link disease-associated mortality between sexes, the distortion of sex ratios and the potential mechanisms underlying sex differences in infection. We collected data on host traits, infection intensity and survival of five bat species at 42 sites across seven years. We found females were more infected than males for all five species. Females also had lower apparent survival over winter and accounted for a smaller proportion of populations over time. Notably, female-biased infections were evident by early hibernation and likely driven by sex-based differences in autumn mating behaviour. Male bats were more active during autumn which likely reduced replication of the cool-growing fungus. Higher disease impacts in female bats may have cascading effects on bat populations beyond the hibernation season by limiting recruitment and increasing the risk of Allee effects.

The gut microbiome of wild American marten in the Upper Peninsula of Michigan.

Carnivores are ecologically important and sensitive to habitat loss and anthropogenic disruption. Here we measured trophic level and gut bacterial composition as proxies of carnivore ecological status across the Upper Peninsula, Michigan, for wild American marten (Martes americana; hereafter marten). In contrast to studies that have focused on omnivorous and herbivorous species, we find that marten, like other carnivore species without a cecum, are dominated by Firmicutes (52.35%) and Proteobacteria (45.31%) but lack Bacteroidetes. Additionally, a majority of the 12 major bacterial genera (occurring at ≥1%) are known hydrogen producers, suggesting these taxa may contribute to host energy requirements through fermentative production of acetate. Our study suggests that live trapping and harvest methods yield similar marten gut microbiome data. In addition, preserving undisturbed forest likely impacts marten ecology by measurably increasing marten trophic level and altering the gut microbiome. Our study underscores the utility of the gut microbiome as a tool to monitor the ecological status of wild carnivore populations.

Wildlife exposure to SARS-CoV-2 across a human use gradient

The spillover of SARS-CoV-2 into humans has caused one of the most devastating pandemics in recorded history. Human-animal interactions have led to transmission events of SARS-CoV-2 from humans to wild and captive animals. However, many questions remain about how extensive SARS-CoV-2 exposure is in wildlife, the factors that influence wildlife transmission risk, and whether sylvatic cycles can generate novel variants with increased infectivity and virulence. We sampled 18 different wildlife species in the Eastern U.S. and detected widespread exposure to SARS-CoV-2 across wildlife species. Using quantitative reverse transcription polymerase chain reaction and whole genome sequencing, we conclusively detected SARS-CoV-2 in the Virginia opossum and had equivocal detections in six additional species. Species considered human commensals like squirrels, and raccoons had high seroprevalence, ranging between 62%-71%, and sites with high human use had three times higher seroprevalence than low human-use areas. SARS-CoV-2 genomic data from an infected opossum and molecular modeling exposed previously uncharacterized changes to amino acid residues observed in the receptor binding domain (RBD), which predicts improved binding between the spike protein and human angiotensin-converting enzyme (ACE2) compared to the dominant variant circulating at the time of isolation. These mutations were not identified in human samples at the time of collection. Overall, our results highlight widespread exposure to SARS-CoV-2 in wildlife and suggest that areas with high human activity may serve as important points of contact for cross-species transmission. Furthermore, this work highlights the potential role of wildlife in fueling de novo mutations that may eventually appear in humans.

Analysis of rabbit anti-thymocyte globulin vs basiliximab induction in pediatric liver transplant recipients.

Literature is limited comparing induction immunosuppression in pediatric liver transplant (LTx) recipients. This is a single-center, retrospective cohort study of primary pediatric liver transplants at our center between 2005 and 2016 who received either basiliximab (BSX) or rabbit anti-thymocyte globulin (rATG) induction. Maintenance immunosuppression consisted of tacrolimus ± a corticosteroid taper. Exclusions included receipt of an ABO-incompatible graft, retransplantation, and multi-organ transplantation. Primary outcomes were incidence of treated biopsy-proven acute rejection (tBPAR) and PTLD within the first year and infections within 90 days of LTx. Secondary outcomes included graft and patient survival, time to first tBPAR, and incidence of steroid-resistant rejection (SRR) within the first year post-LTx. A total of 136 patients were included in the final analysis of which 57 patients (42%) received BSX induction. Patients who received rATG induction with or without a 2-week corticosteroid taper experienced significantly more tBPAR compared to those who received BSX induction with a 6-month corticosteroid taper (55.7% vs 33.3%, P = .01). There were no differences in the incidence of PTLD, infections, SRR, graft or patient survival, or time to first tBPAR between the two groups. Induction with rATG either with or without a short corticosteroid taper was associated with significantly more tBPAR in primary pediatric LTx recipients when compared to BSX induction with a prolonged corticosteroid taper in the setting of maintenance immunosuppression with tacrolimus.

Conformal Ultrathin Film Metal-Organic Framework Analogues: Characterization of Growth, Porosity, and Electronic Transport.

Thin-film formation and transport properties of two copper-paddlewheel metal-organic framework (MOF) -based systems (MOF-14 and MOF-399) are investigated for their potential integration into electrochemical device architectures. Thin-film analogs of these two systems are fabricated by the sequential, alternating, solution-phase deposition of the inorganic and organic ligand precursors that result in conformal films via van der Merwe-like growth. Atomic force microscopy reveals smooth film morphologies with surface roughnesses determined by the underlying substrates and linear film growth of 1.4 and 2.2 nm per layer for the MOF-14 and MOF-399 systems, respectively. Electrochemical impedance spectroscopy is used to evaluate the electronic transport properties of the thin films, finding that the MOF-14 analog films demonstrate low electronic conductivity, while MOF-399 analog films are electronically insulating. The intrinsic porosities of these ultrathin MOF analog films are confirmed by cyclic voltammetry redox probe characterization using ferrocene. Larger peak currents are observed for MOF-399 analog films compared to MOF-14 analog films, which is consistent with the larger pores of MOF-399. The layer-by-layer deposition of these systems provides a promising route to incorporate MOFs as thin films with nanoscale thickness control and low surface roughness for electrochemical devices.

A Drosophila Genome-Wide Screen Identifies Regulators of Steroid Hormone Production and Developmental Timing.

Steroid hormones control important developmental processes and are linked to many diseases. To systematically identify genes and pathways required for steroid production, we performed a Drosophila genome-wide in vivo RNAi screen and identified 1,906 genes with potential roles in steroidogenesis and developmental timing. Here, we use our screen as a resource to identify mechanisms regulating intracellular levels of cholesterol, a substrate for steroidogenesis. We identify a conserved fatty acid elongase that underlies a mechanism that adjusts cholesterol trafficking and steroidogenesis with nutrition and developmental programs. In addition, we demonstrate the existence of an autophagosomal cholesterol mobilization mechanism and show that activation of this system rescues Niemann-Pick type C1 deficiency that causes a disorder characterized by cholesterol accumulation. These cholesterol-trafficking mechanisms are regulated by TOR and feedback signaling that couples steroidogenesis with growth and ensures proper maturation timing. These results reveal genes regulating steroidogenesis during development that likely modulate disease mechanisms.

UPRT, a suicide-gene therapy candidate in higher eukaryotes, is required for Drosophila larval growth and normal adult lifespan.

Uracil phosphoribosyltransferase (UPRT) is a pyrimidine salvage pathway enzyme that catalyzes the conversion of uracil to uridine monophosphate (UMP). The enzyme is highly conserved from prokaryotes to humans and yet phylogenetic evidence suggests that UPRT homologues from higher-eukaryotes, including Drosophila, are incapable of binding uracil. Purified human UPRT also do not show any enzymatic activity in vitro, making microbial UPRT an attractive candidate for anti-microbial drug development, suicide-gene therapy, and cell-specific mRNA labeling techniques. Nevertheless, the enzymatic site of UPRT remains conserved across the animal kingdom indicating an in vivo role for the enzyme. We find that the Drosophila UPRT homologue, krishah (kri), codes for an enzyme that is required for larval growth, pre-pupal/pupal viability and long-term adult lifespan. Our findings suggest that UPRT from all higher eukaryotes is likely enzymatically active in vivo and challenges the previous notion that the enzyme is non-essential in higher eukaryotes and cautions against targeting the enzyme for therapeutic purposes. Our findings also suggest that expression of the endogenous UPRT gene will likely cause background incorporation when using microbial UPRT as a cell-specific mRNA labeling reagent in higher eukaryotes.

Comparison of two methods for evaluating the quality of stored drinking water in Abidjan, Côte d'lvoire, and review of other comparisons in the literature.

Membrane filtration, multiple tube fermentation (the standard methods) and Colilert are techniques available for assessing drinking water quality, but there are no published comparisons of Colilert to standard methods in a developing country laboratory. We reviewed the published literature on Colilert and standard methods and conducted a study to compare Colilert with membrane filtration for the detection and enumeration of total coliforms and fecal coliforms (Escherichia coli bacteria) using 35 stored drinking water samples from households in Abidjan, Côte d'lvoire. Our study results are consistent with previous published studies conducted in developed countries. Results from Colilert and membrane filtration correlated for both total coliforms (r2 = 0.81) and E. coli (r2 = 0.93). Colilert is an acceptable method to measure the presence and quantity of coliforms in water samples in a developing country setting.

Effect of selective capsulorrhaphy on the passive range of motion of the glenohumeral joint.

BACKGROUND: Capsulorrhaphy of the glenohumeral joint is a common surgical procedure for the treatment of instability caused by increased capsular laxity. The effect of capsulorrhaphy on the range of motion of the shoulder is poorly understood. METHODS: We simulated localized capsular contractures by selective capsular plications in eight human cadaveric shoulders and studied the effect of such plications on the passive range of glenohumeral abduction, flexion, and external and internal rotation in different degrees of abduction. A 0.5 or 1-N-m torque was applied to the humerus, and the range of glenohumeral motion was measured with electronic goniometers in three planes and compared with those of the intact shoulder. RESULTS: Anterosuperior capsular plication most markedly affected external rotation of the adducted arm, decreasing it by a mean of 30.1 degrees (p < 0.0001). Anteroinferior plication significantly reduced abduction by a mean of 19.4 degrees (p < 0.0001) and external rotation by a mean of 20.6 degrees (p = 0.0046). Posterosuperior plication mostly limited internal rotation of the adducted arm (mean decrease, 16.1 degrees, p = 0.0045). On the average, total anterior and total posterior plication each limited flexion by approximately 20 degrees (p = 0.005) and abduction by >or=15 degrees (p < 0.005), whereas total anterior plication limited external rotation by >30 degrees (p 20 degrees (p < 0.0001). Total inferior capsular plication restricted abduction (by a mean of 27.7 degrees, p = 0.0001), flexion, and rotation. Total superior plication restricted external rotation and flexion. CONCLUSIONS AND CLINICAL RELEVANCE: Localized plications of the glenohumeral joint capsule lead to predictable patterns of loss of glenohumeral mobility. If plication is planned, losses of movement can be anticipated. The findings of this study may assist surgeons in identifying the parts of the capsule that are contracted and that may need lengthening.

The effect of rotational malunion of the radius and the ulna on supination and pronation.

We have assessed the influence of isolated and combined rotational malunion of the radius and ulna on the rotation of the forearm. Osteotomies were made in both the radius and the ulna at the mid-diaphyseal level of five cadaver forearms and stabilised with intramedullary metal implants. Malunion about the axis of the respective forearm bone was produced at intervals of 10 degrees. The ranges of pronation and supination were recorded by a potentiometer under computer control. We examined rotational malunions of 10 degrees to 80 degrees of either the radius or ulna alone and combined rotational malunions of 20 degrees to 60 degrees of both the radius and ulna. Malunion of the ulna in supination had little effect on rotation of the forearm. Malunion of either the radius or of the ulna in pronation gave a moderate reduction of rotation of the forearm. By contrast, malunion of the radius in supination markedly reduced rotation of the forearm, especially with malunion greater than 60 degrees. Combined rotational malunion produced contrasting results. A combination of rotational malunion of the radius and ulna in the same direction had an effect similar to that of an isolated malunion of the radius. A combination in the opposite direction gave the largest limitation of the range of movement. Clinically, rotational malunion may be isolated or part of a complex angular/rotational deformity and rotational malunion may lead to marked impairment of rotation of the forearm. A reproducible method for assessing rotational malunion is therefore needed.

Latex sensitivity in a macaque (Macaca mulatta).

UNLABELLED: BACKGROUND AND HISTORY: An adult Macaca mulatta was examined because of a history of multiple episodes of conjunctivitis and an acute, pruritic, dermatitic eruption that affected the axillary and inguinal regions, forearms, thorax, and neck. METHODS AND RESULTS: Results of corneal staining, examination of skin scrapings and feces, fungal culture, CBC, and a thyroid profile (thyroxine/triiodothyronine concentrations) were negative or normal, with the exception of eosinophilia (1,040/mm3). Examination of a punch biopsy specimen of the skin indicated chronic, nonsuppurative eosinophilic dermatitis. Skin patch testing against 25 contact allergens was negative for a delayed-type hypersensitivity reaction. Allergen-specific IgE testing, using six monkey chow additives, also yielded negative results, but testing against latex revealed a strong positive result (0.74 KU/L) consistent with a latex allergy. A skin prick test performed by use of a latex supernatant revealed significant inflammation at the latex site at 72 h and one week. Vinyl gloves were substituted for latex gloves, and that resulted in a marked decrease in erythema, pruritus, and lichenification with no flares of dermatitis for four years. Repeat skin biopsy fourteen weeks after the original biopsy revealed normal epidermis; however, mild chronic active nonsuppurative, perifolliculitis persisted. CONCLUSION: Latex can induce allergic dermatitis in nonhuman primates and should be included in the differen tial diagnosis for atopic dermatitis.

Anisocoria and middle cerebral artery saccular (berry) aneurysm in a rhesus macaque (Macaca mulatta).

A 27-year-old female rhesus macaque (Macaca mulatta) developed anisocoria. The left pupil was dilated and unresponsive to light. The macaque was euthanized because of unrelated reasons and the body was submitted for necropsy. On gross examination, a berry aneurysm of the right middle cerebral artery causing marked compression of the right optic tract was found. Arteriosclerotic changes were observed microscopically in the right middle cerebral and in the internal carotid arteries. The left iris was markedly degenerated, with atrophy of the constrictor muscle. Compression of the right optic tract may cause homonimus hemianopsia. A dilated and unresponsive left pupil indicated a lesion in the ipsilateral parasympathetic efferent pathway. In the absence of appreciable lesions of the left oculomotor nerve, the most likely cause of mydriasis was the iridic lesion. Intracranial aneurysms are common in humans (2 to 5%), but not in other species. Only about 10% of unruptured aneurysms are associated with neurologic deficits related to mechanical compression, such as visual deficits or anisocoria. Meticulous investigation of the ocular vascular and neural pathways led us to conclude that the anisocoria was unrelated to the aneurysm. To our knowledge, this report represents the first documented case of a naturally occurring intracranial aneurysm in nonhuman primates.

Use of guanfacine to control self-injurious behavior in two rhesus macaques (Macaca mulatta) and one baboon (Papio anubis).

BACKGROUND AND PURPOSE: Self-injurious behavior (SIB) affects 0.8 to 10% of individually housed non-human primates, and is a substantial threat to their health and well being. The potential for SIB to involve multiple neurotransmitters and the complex variations in response to external stressors complicate case management. Modulation of the adrenergic system by use of guanfacine, an alpha2A-adrenergic receptor agonist, was assessed as a novel therapeutic strategy for SIB. METHODS: The efficacy of guanfacine against SIB was evaluated in 11 self-biting episodes among two rhesus macaques (Macaca mulatta) and one baboon (Papio cynocephalus anubis). Affected animals were given guanfacine IM or PO at 0.5 mg/kg of body weight twice daily (rhesus) or 0.3 mg/kg (baboon) for 5 to 10 days, followed by gradual reduction of the dose to 0.25 mg/kg (rhesus) or 0.15 mg/kg (baboon) once daily over an average of 33 days. RESULTS: The 0.5 mg/kg twice daily regimen of guanfacine halted all self-biting, whereas reducing the dose to 0.25 mg/kg given twice daily or 0.5 mg/kg given once daily resulted in reversion to self-biting in four of the 11 episodes. Recurrence was controlled by returning to twice daily 0.5 mg/kg dosing for one aggressive episode, and resolved in the three milder episodes without dose or frequency being increased. Self-biting after discontinuation of therapy recurred six times over five years in case 1, three times over 1.5 years in case 2, and three times over one year in case 3. Clinical assessment suggested that guanfacine therapy decreased agitation without overt side effects associated with alpha2-agonists, such as profound sedation. CONCLUSION: The mechanism for guanfacine inhibition of self-biting is unclear, but could result from strengthening of prefrontal cortex inhibitory functions. Guanfacine therapy provides an effective psychological stabilizing tool that alleviates self-biting, and provides time to assess and address external stressors and triggers.

Dual infection with Pneumocystis carinii and Pasteurella pneumotropica in B cell-deficient mice: diagnosis and therapy.

BACKGROUND AND PURPOSE: The clinical presentation, diagnosis, histopathologic findings, and elimination of dual respiratory tract infection with Pasteurella pneumotropica and Pneumocystis carinii were studied in 100 adult barrier-reared C.B17 and MRL- lpr mice homozygous for a targeted mutation of the JH region of the immunoglobulin heavy chain. METHODS: Necropsy, aerobic bacteriologic culture of hematogenous and pulmonary tissues, histochemical staining of pulmonary tissues, polymerase chain reaction analysis of pulmonary tissues and feces, and viral serologic testing were performed on 19 clinically affected mice and 8 clinically normal mice, then later on antibiotic-treated and caesarian re-derived mice. Therapeutic strategies included sequential administration of trimethoprim/ sulfamethoxazole and enrofloxacin or enrofloxacin administration and caesarian rederivation. RESULTS: Clinically affected mice had diffuse, nonsuppurative, interstitial pneumonia with superimposed pyogranulomatous lobar pneumonia that was detected microscopically. Affected lung tissue yielded pure culture of P. pneumotropica. Aged-matched, clinically normal mice of both genotypes had interstitial histiocytic pneumonia without lobar pneumonia, and P. pneumotropica was not isolated. Histochemical staining of lung tissues from normal and clinically affected mice revealed scattered cysts consistent with P. carinii, principally in the interstitium. Treatment with sulfamethoxazole/trimethoprim and enrofloxacin eliminated bacteriologic detection of P. pneumotropica, decreased mortality from 50% to 6%, and improved breeding performance. CONCLUSION: A successful antibiotic therapy and rederivation approach, incorporating enrofloxacin, cesarian section, and isolator rearing, was developed for B cell-deficient mice with opportunistic infections.

Cloning and sequencing of the genes encoding the periplasmic-cytochrome B-containing selenate reductase of Thauera selenatis.

The periplasmic selenate reductase (Ser) of Thauera selennatis is a component of the electron transport chain catalyzing selenate reduction with acetate as the electron donor (i.e., selenate respiration). The purified enzyme consists of three subunits (SerA, SerB and SerC). Using transposon (i.e., Tn5) mutagenesis selenate reductase mutants were isolated. Junction fragments of DNA adjacent to the integrated Tn5 were used, together with oligonucleotides derived from the N-termini of SerA and SerB, to clone from a gene bank a DNA fragment that contained the corresponding genes. After sequencing, serA, serB and serC were identified by sequence comparison with the N-termini of the three subunits. The genes are arranged in the order serA, serB, serC; a fourth open reading frame (serD) in between, but overlapping serB and serC, is also present. The serA gene product contains an apparent leader peptide with a twin-arginine motif. The remainder of the translated amino acid sequence is similar to that of a number of prokaryotic molybdenum-containing enzymes (e.g., nitrate reductases and formate dehydrogenases of Escherichia coli). The serB gene product contains four cysteine clusters and is similar to various iron-sulfur protein subunits. The serC gene product contains a putative Sec-dependent leader peptide, but there are no similarities between the remainder of the translated protein and other protein subunits. The SerC contains two histidine and four methionine residues, and these may noncovalently bind heme b--which is a component of the active selenate reductase. The serD gene product encodes a putative protein that shows no significant sequence similarities to other proteins. However, the location of the serD within the other ser genes is similar to that of narJ within the E. coli narGHJI operon (nitrate reductase A); thus suggesting that the role of SerD may be similar to that of NarJ, which is a system-specific chaperone protein.

Expanded polytetrafluoroethylene entubulation of the rabbit inferior alveolar nerve.

OBJECTIVE: The purpose of this study was to evaluate the use of an expanded polytetrafluoroethylene conduit in the treatment of a 6. 0-mm gap in the rabbit inferior alveolar nerve and compare the results with those of an autogenous interpositional tibial nerve graft. STUDY DESIGN: The inferior alveolar nerves of 5 adult New Zealand White female rabbits (10 nerves) were exposed bilaterally, and a 6-mm segment of each nerve was resected. On one side, chosen at random, the gap was immediately bridged through use of an 8.0 x 2. 0-mm expanded polytetrafluoroethylene conduit; on the other side, the gap was grafted with an autogenous tibial nerve graft. Two randomly selected nerves served as sham-dissected controls. At 15 weeks after surgery, the animals were killed and the entire nerve segments were harvested and prepared according to standard fixation and embedding techniques. The sections were examined histomorphometrically to quantify the degree of axonal regeneration through definition of fascicular number, total fascicular surface area, axonal density, and mean axonal diameter at 3 locations along the repair site. RESULTS: Light microscopic examination revealed the presence of disorganized neural tissue in both groups, with slightly more fibrovascular interfascicular tissue in the expanded polytetrafluoroethylene group. Histomorphometric analysis revealed no significant differences between groups for most of the measured variables. The mean axonal diameter varied between groups, and the fascicular number was greater in the expanded polytetrafluoroethylene group at the middle site. CONCLUSIONS: This study demonstrates that regeneration of the inferior alveolar nerve can occur across a 6.0-mm gap through an expanded polytetrafluoroethylene tube with results comparable to those of an autogenous nerve graft, significant donor site morbidity being avoided. The significant differences between groups were probably due to greater containment of regenerating axonal fibers in the expanded polytetrafluoroethylene group.

A new chemolithoautotrophic arsenite-oxidizing bacterium isolated from a gold mine: phylogenetic, physiological, and preliminary biochemical studies.

A previously unknown chemolithoautotrophic arsenite-oxidizing bacterium has been isolated from a gold mine in the Northern Territory of Australia. The organism, designated NT-26, was found to be a gram-negative motile rod with two subterminal flagella. In a minimal medium containing only arsenite as the electron donor (5 mM), oxygen as the electron acceptor, and carbon dioxide-bicarbonate as the carbon source, the doubling time for chemolithoautotrophic growth was 7.6 h. Arsenite oxidation was found to be catalyzed by a periplasmic arsenite oxidase (optimum pH, 5.5). Based upon 16S rDNA phylogenetic sequence analysis, NT-26 belongs to the Agrobacterium/Rhizobium branch of the alpha-Proteobacteria and may represent a new species. This recently discovered organism is the most rapidly growing chemolithoautotrophic arsenite oxidizer known.

Two new arsenate/sulfate-reducing bacteria: mechanisms of arsenate reduction.

Two sulfate-reducing bacteria, which also reduce arsenate, were isolated; both organisms oxidized lactate incompletely to acetate. When using lactate as the electron donor, one of these organisms, Desulfomicrobium strain Ben-RB, rapidly reduced (doubling time = 8 h) 5.1 mM arsenate at the same time it reduced sulfate (9.6 mM). Sulfate reduction was not inhibited by the presence of arsenate. Arsenate could act as the terminal electron acceptor in minimal medium (doubling time = 9 h) in the absence of sulfate. Arsenate was reduced by a membrane-bound enzyme that is either a c-type cytochrome or is associated with such a cytochrome; benzyl-viologen-dependent arsenate reductase activity was greater in cells grown with arsenate/sulfate than in cells grown with sulfate only. The second organism, Desulfovibrio strain Ben-RA, also grew (doubling time = 8 h) while reducing arsenate (3.1 mM) and sulfate (8.3 mM) concomitantly. No evidence was found, however, that this organism is able to grow using arsenate as the terminal electron acceptor. Instead, it appears that arsenate reduction by the Desulfovibrio strain Ben-RA is catalyzed by an arsenate reductase that is encoded by a chromosomally-borne gene shown to be homologous to the arsC gene of the Escherichia coli plasmid, R773 ars system.