Pseudoxanthoma-elasticum-like changes on the soft palate

Pseudoxanthoma elasticum (PXE) is an autosomal recessive genetic disorder characterized by aberrant fragmentation and calcification of elastic fibers, leading to characteristic cutaneous, ophthalmic, and cardiovascular manifestations. PXE demonstrates significant phenotypic variability; involvement of the oral mucosa may be the only clue to the diagnosis. Reports on mucous membrane involvement in PXE are scarce. Here, we present a case of PXE-like changes in the oral cavity. A 70-year-old male patient presented with a painless leukoplakic lesion on the soft palate. Biopsy revealed numerous degenerated fibers in the lamina propria. Verhoeff-van Gieson and von Kossa staining confirmed their identity as calcified elastic fibers. A histopathological diagnosis of PXE-like changes was made; the patient was referred to ophthalmology where angioid streaks were visualized fundoscopically. PXE-like changes in the absence of the characteristic genetic mutation have also been reported with or without systemic manifestations. Furthermore, PXE-like changes have been reported in up to 10% of oral biopsy specimens undertaken without clinical suspicion for PXE. Therefore, the significance of such changes in isolation is unclear. Clinicians and pathologists should be aware of the potential oral manifestations of PXE to facilitate prompt diagnosis and subspecialist referral.

Extramammary myofibroblastoma of the oral cavity

Myofibroblastoma is a rare, benign mesenchymal tumor first described as a neoplasm of the breast. Extramammary myofibroblastoma is a histopathologically and genetically identical lesion occurring outside the breast. Herein is presented a case of extramammary myofibroblastoma arising in the oral cavity. A 59-year-old woman presented with a 1.5 cm nodule on the buccal surface of the lower lip. Wide local excision was performed. Histopathologic examination revealed haphazard fascicles of monomorphic spindle cells with hyalinized collagen bundles without fat. The spindled cells were diffusely positive for CD34, and focally for progesterone receptor. Desmin, smooth muscle actin, estrogen receptor, androgen receptor, S100, and STAT6 were negative. Rb1 expression was lost in tumor cells. Thus, the diagnosis of extramammary myofibroblastoma was made. Differential diagnoses include spindle-cell lipoma and angiofibroma. All three tumors are members of the 13q14 deletion/RB1 loss family. Indolent but locally aggressive (solitary fibrous tumor, desmoid fibromatosis) and frankly malignant (low-grade peripheral nerve sheath tumor, dermatofibrosarcoma protuberans) entities can be excluded by immunohistochemistry and careful microscopic examination. Extensive sampling extramammary myofibroblastoma is important to exclude the possibility of malignancy. Clinicians and pathologists alike should be aware of this entity and its potential to arise rarely in unusual locations.

Artificial Intelligence and Melanoma: A Comprehensive Review of Clinical, Dermoscopic, and Histologic Applications

Melanoma detection, prognosis, and treatment represent challenging and complex areas of cutaneous oncology with considerable impact on patient outcomes and healthcare economics. Artificial intelligence (AI) applications in these tasks are rapidly developing. Neural networks with increasing levels of sophistication are being implemented in clinical image, dermoscopic image, and histopathologic specimen classification of pigmented lesions. These efforts hold promise of earlier and highly accurate melanoma detection, as well as reliable prognostication and prediction of therapeutic response. Herein, we provide a brief introduction to AI, discuss contemporary investigational applications of AI in melanoma, and summarize challenges encountered with AI.

Development of a core outcome set for clinical trials in facial aging: study protocol for a systematic review of the literature and identification of a core outcome set using a Delphi survey

Background

Facial aging is a concern for many patients. Wrinkles, loss of volume, and discoloration are common physical manifestations of aging skin. Genetic heritage, prior ultraviolet light exposure, and Fitzpatrick skin type may be associated with the rate and type of facial aging. Although many clinical trials assess the correlates of skin aging, there is heterogeneity in the outcomes assessed, which limits the quality of evaluation and comparison of treatment modalities. To address the inconsistency in outcomes, in this project we will develop a core set of outcomes that are to be evaluated in all clinical trials relevant to facial aging.

Methods/design

A long list of measureable outcomes will be created from four sources: (1) systematic medical literature review, (2) patient interviews, (3) other published sources, and (4) stakeholder involvement. Two rounds of Delphi processes with homogeneous groups of physicians and patients will be performed to prioritize and condense the list. At a consensus meeting attended by physicians, patients, and stakeholders, outcomes will be further condensed on the basis of participant scores. By the end of the meeting, members will vote and decide on a final recommended set of core outcomes. Subsequent to this, specific measures will be selected or created to assess these outcomes.

Discussion

The aim of this study is to develop a core outcome set and relevant measures for clinical trials relevant to facial aging. We hope to improve the reliability and consistency of outcome reporting of skin aging, thereby enabling improved evaluation of treatment efficacy and patient satisfaction.

Trial registration

Core Outcome Measures in Effectiveness Trials (COMET) Initiative, accessible at http://www.comet-initiative.org/studies/details/737. Core Outcomes Set Initiative, (CSG-COUSIN) accessible at https://www.uniklinikum-dresden.de/de/das-klinikum/universitaetscentren/zegv/cousin/meet-the-teams/project-groups/core-outcome-set-for-the-appearance-of-facial-aging. Protocol version date is 28 July 2016.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2104-3) contains supplementary material, which is available to authorized users.

Antisense oligonucleotide targeting eukaryotic translation initiation factor 4E reduces growth and enhances chemosensitivity of non-small-cell lung cancer cells

Elevated levels of eukaryotic translation initiation factor 4E (eIF4E) enhance translation of many malignancy-related proteins, such as vascular endothelial growth factor (VEGF), c-Myc and osteopontin. In non-small-cell lung cancer (NSCLC), levels of eIF4E are significantly increased compared with normal lung tissue. Here, we used an antisense oligonucleotide (ASO) to inhibit the expression of eIF4E in NSCLC cell lines. eIF4E levels were significantly reduced in a dose-dependent manner in NSCLC cells treated with eIF4E-specific ASO (4EASO) compared with control ASO. Treatment of NSCLC cells with the 4EASO resulted in decreased cap-dependent complex formation, decreased cell proliferation and increased sensitivity to gemcitabine. At the molecular level, repression of eIF4E with ASO resulted in decreased expression of the oncogenic proteins VEGF, c-Myc and osteopontin, whereas expression of β-actin was unaffected. Based on these findings, we conclude that eIF4E-silencing therapy alone or in conjunction with chemotherapy represents a promising approach deserving of further investigation in future NSCLC clinical trials.

Calcium influences cellular and extracellular product formation during biofilm-associated growth of a marine Pseudoalteromonas sp

Bacteria undergo a variety of physiological changes following a switch from planktonic growth to surface-associated biofilm growth. Here, it is shown that biofilm development of a marine isolate, Pseudoalteromonas sp. 1398, results in global changes in its cytosolic and extracellular proteomes. Calcium influences these proteome responses, and affects the amount of surface-associated biomass and extracellular matrix material produced by Pseudoalteromonas sp. 1398. Four extracellular proteins, characterized by N-terminal sequencing, showed increased abundances, while one protein, flagellin, showed reduced abundance at higher [Ca2+]. Immunoblotting and transmission-electron-microscopy analysis confirmed that higher [Ca2+] and surface-associated growth results in the repression of flagella production. Two-dimensional gel electrophoresis (2DGE) studies combined with cluster analysis of global proteome responses demonstrated that Ca2+ had a greater regulatory influence on Pseudoalteromonas sp. growing in biofilms than on planktonic cultures. Approximately 22 % of the total cytosolic proteins resolved by 2DGE had differing abundances in response to a switch from planktonic growth to surface-associated growth when the cells were cultivated in 1 mM Ca2+. At higher [Ca2+] this number increased to 38 %. Fifteen cellular proteins that were differentially expressed in response to biofilm growth and/or Ca2+ were analysed by N-terminal sequencing and/or MS/MS. These proteins were identified as factors involved in cellular metabolic functions, putative proteases and transport proteins, although there were several proteins that had not been previously characterized. These results indicate that Ca2+ causes global changes in matrix material, as well as in cellular and extracellular protein profiles of Pseudoalteromonas sp. 1398. These changes are more pronounced when the bacterium grows in biofilms than when it grows in planktonic culture.

Calcium-induced virulence factors associated with the extracellular matrix of mucoid Pseudomonas aeruginosa biofilms

Pseudomonas aeruginosa colonizes the pulmonary tissue of patients with cystic fibrosis (CF), leading to biofilm-associated infections. The pulmonary fluid of CF patients usually contains elevated concentrations of cations and may contain the P. aeruginosa redox-active pigment pyocyanin, which is known to disrupt calcium homeostasis of host cells. Since divalent cations are important bridging ions for bacterial polysaccharides and since they may play regulatory roles in bacterial gene expression, we investigated the effect of calcium ions on the extracellular matrix constituents of P. aeruginosa biofilms. For mucoid strain P. aeruginosa FRD1, calcium addition (1.0 and 10 mM as CaCl(2)) resulted in biofilms that were at least 10-fold thicker than biofilms without added calcium. Scanning confocal laser microscopy showed increased spacing between cells for the thick biofilms, and Fourier transform infrared spectroscopy revealed that the material between cells is primarily alginate. An algD transcriptional reporter demonstrated that calcium addition caused an eightfold increase in alg gene expression in FRD1 biofilms. Calcium addition also resulted in increased amounts of three extracellular proteases (AprA, LasB, and PrpL). Immunoblots of the biofilm extracellular material established that AprA was harbored within the biofilm extracellular matrix. An aprA deletion mutation and a mutation in gene for a putative P. aeruginosa calmodulin-like protein did not significantly affect calcium-induced biofilm structure. Two-dimensional gel electrophoresis showed increased amounts of phenazine biosynthetic proteins in FRD1 biofilms and in calcium-amended planktonic cultures. Spectrochemical analyses showed that the calcium addition causes a three- to fivefold increase in pyocyanin production. These results demonstrate that calcium addition affects the structure and extracellular matrix composition of mucoid P. aeruginosa biofilms, through increased expression and stability of bacterial extracellular products. The calcium-induced extracellular matrix of mucoid P. aeruginosa consists primarily of the virulence factor alginate and also harbors extracellular proteases and perhaps pyocyanin, a biomolecule that may further disrupt cellular calcium levels.

The myelin proteolipid protein gene modulates apoptosis in neural and non-neural tissues

Mutations of the myelin proteolipid protein gene (Plp) are associated with excessive programmed cell death (PCD) of oligodendrocytes. We show for the first time that PLP is a molecule ubiquitously expressed in non-neural tissues during normal development, and that the level of native PLP modulates the level of PCD. We analyze three non-neural tissues, and show that native PLP is expressed in trophoblasts, spermatogonia, and cells of interdigital webbing. The non-neural cells that express high levels of native PLP also undergo PCD. The level of PLP expression modulates the level of PCD because mice that overexpress native PLP have increased PCD and mice deficient in PLP have decreased PCD. We show that overexpression of native PLP causes a dramatic acidification of extracellular fluid that, in turn, causes increased PCD. These studies show that the level of native PLP modulates the amount of PCD during normal development via a pH-dependent mechanism.

Characterization of algG encoding C5-epimerase in the alginate biosynthetic gene cluster of Pseudomonas fluorescens

The organization of the alginate gene cluster in Pseudomonas fluorescens was characterized. A bank of genomic DNA from P. fluorescens was mobilized to a strain of Pseudomonas aeruginosa with a transposon insertion (algJ::Tn501) in the alginate biosynthetic operon that rendered it non-mucoid. Phenotypic complementation in this heterologous host was observed, and a complementing clone containing 32 kb of P. fluorescens DNA was obtained. Southern hybridization studies showed that genes involved in alginate biosynthesis (e.g. algD, algG, and algA) were approximately in the same order and position as in P. aeruginosa. When the clone was mobilized to a P. aeruginosa algG mutant that produced alginate as polymannuronate due to its C5-epimerase defect, complementation was observed and the alginate from the recombinant strain contained L-guluronate as determined by proton nuclear magnetic resonance spectroscopy. A sequence analysis of the P. fluorescens DNA containing algG revealed sequences similar to P. aeruginosa algG that were also flanked by algE- and algX-like sequences. The predicted AlgG amino acid sequence of P. fluorescens was 67% identical (80% similar) to P. aeruginosa AlgG and 60% identical (76% similar) to Azotobacter vinelandii AlgG. As in P. aeruginosa, AlgG from P. fluorescens appeared to have a signal sequence that would localize it to the periplasm where AlgG presumably acts as a C5-epimerase at the polymer level. Non-polar algG knockout mutants of P. fluorescens were defective in alginate production, suggesting a potential role for this protein in polymer formation.

Gene expression and protein levels of the stationary phase sigma factor, RpoS, in continuously-fed Pseudomonas aeruginosa biofilms

Bacteria growing in biofilms experience gradients of environmental conditions, including varying levels of nutrients and oxygen. Therefore, bacteria within biofilms may enter distinct physiological states, depending on the surrounding conditions. In this study, rpoS expression and RpoS levels were measured as indicators of stationary phase growth within thick continuously-fed Pseudomonas aeruginosa biofilms. The level of rpoS expression in a 3-day-old biofilm was found to be three-fold higher than the average expression in stationary phase planktonic culture. RpoS levels in biofilms, indicated by immunoblot analysis, were similar to levels in stationary phase planktonic cultures. In planktonic cultures, oxygen limitation did not lead to increased levels of RpoS, suggesting that oxygen limitation was not the environmental signal causing increased expression of rpoS. These results suggest that bacteria within P. aeruginosa biofilms may exhibit stationary phase characteristics even when cultured in flow conditions that continually replenish nutrients.

Role of alginate and its O acetylation in formation of Pseudomonas aeruginosa microcolonies and biofilms

Attenuated total reflection/Fourier transform-infrared spectrometry (ATR/FT-IR) and scanning confocal laser microscopy (SCLM) were used to study the role of alginate and alginate structure in the attachment and growth of Pseudomonas aeruginosa on surfaces. Developing biofilms of the mucoid (alginate-producing) cystic fibrosis pulmonary isolate FRD1, as well as mucoid and nonmucoid mutant strains, were monitored by ATR/FT-IR for 44 and 88 h as IR absorbance bands in the region of 2,000 to 1,000 cm(-1). All strains produced biofilms that absorbed IR radiation near 1,650 cm(-1) (amide I), 1,550 cm(-1) (amide II), 1,240 cm(-1) (P==O stretching, C---O---C stretching, and/or amide III vibrations), 1,100 to 1,000 cm(-1) (C---OH and P---O stretching) 1,450 cm(-1), and 1,400 cm(-1). The FRD1 biofilms produced spectra with an increase in relative absorbance at 1,060 cm(-1) (C---OH stretching of alginate) and 1,250 cm(-1) (C---O stretching of the O-acetyl group in alginate), as compared to biofilms of nonmucoid mutant strains. Dehydration of an 88-h FRD1 biofilm revealed other IR bands that were also found in the spectrum of purified FRD1 alginate. These results provide evidence that alginate was present within the FRD1 biofilms and at greater relative concentrations at depths exceeding 1 micrometer, the analysis range for the ATR/FT-IR technique. After 88 h, biofilms of the nonmucoid strains produced amide II absorbances that were six to eight times as intense as those of the mucoid FRD1 parent strain. However, the cell densities in biofilms were similar, suggesting that FRD1 formed biofilms with most cells at depths that exceeded the analysis range of the ATR/FT-IR technique. SCLM analysis confirmed this result, demonstrating that nonmucoid strains formed densely packed biofilms that were generally less than 6 micrometer in depth. In contrast, FRD1 produced microcolonies that were approximately 40 micrometer in depth. An algJ mutant strain that produced alginate lacking O-acetyl groups gave an amide II signal approximately fivefold weaker than that of FRD1 and produced small microcolonies. After 44 h, the algJ mutant switched to the nonmucoid phenotype and formed uniform biofilms, similar to biofilms produced by the nonmucoid strains. These results demonstrate that alginate, although not required for P. aeruginosa biofilm development, plays a role in the biofilm structure and may act as intercellular material, required for formation of thicker three-dimensional biofilms. The results also demonstrate the importance of alginate O acetylation in P. aeruginosa biofilm architecture.

Role of antibiotic penetration limitation in Klebsiella pneumoniae biofilm resistance to ampicillin and ciprofloxacin

The penetration of two antibiotics, ampicillin and ciprofloxacin, through biofilms developed in an in vitro model system was investigated. The susceptibilities of biofilms and corresponding freely suspended bacteria to killing by the antibiotics were also measured. Biofilms of Klebsiella pneumoniae were developed on microporous membranes resting on agar nutrient medium. The susceptibilities of planktonic cultures and biofilms to 10 times the MIC were determined. Antibiotic penetration through biofilms was measured by assaying the concentration of antibiotic that diffused through the biofilm to an overlying filter disk. Parallel experiments were performed with a mutant K. pneumoniae strain in which beta-lactamase activity was eliminated. For wild-type K. pneumoniae grown in suspension culture, ampicillin and ciprofloxacin MICs were 500 and 0.18 microgram/ml, respectively. The log reductions in the number of CFU of planktonic wild-type bacteria after 4 h of treatment at 10 times the MIC were 4.43 +/- 0.33 and 4.14 +/- 0.33 for ampicillin and ciprofloxacin, respectively. Biofilms of the same strain were much less susceptible, yielding log reductions in the number of CFU of -0.06 +/- 0.06 and 1.02 +/- 0.04 for ampicillin and ciprofloxacin, respectively, for the same treatment. The number of CFU in the biofilms after 24 h of antibiotic exposure was not statistically different from the number after 4 h of treatment. Ampicillin did not penetrate wild-type K. pneumoniae biofilms, whereas ciprofloxacin and a nonreactive tracer (chloride ion) penetrated the biofilms quickly. The concentration of ciprofloxacin reached the MIC throughout the biofilm within 20 min. Ampicillin penetrated biofilms formed by a beta-lactamase-deficient mutant. However, the biofilms formed by this mutant were resistant to ampicillin treatment, exhibiting a 0.18 +/- 0.07 log reduction in the number of CFU after 4 h of exposure and a 1.64 +/- 0.33 log reduction in the number of CFU after 24 h of exposure. Poor penetration contributed to wild-type biofilm resistance to ampicillin but not to ciprofloxacin. The increased resistance of the wild-type strain to ciprofloxacin and the mutant strain to ampicillin and ciprofloxacin could not be accounted for by antibiotic inactivation or slow diffusion since these antibiotics fully penetrated the biofilms. These results suggest that some other resistance mechanism is involved for both agents.

Modifiable templates facilitate customization of physician order entry

Physician order entry is a key factor in improving the quality of healthcare, while simultaneously reducing its cost. This paper describes an editor, a database, and a run-time system for creating and executing highly customized, user modifiable, order entry templates. The system allows non-programmers to create new order entry templates rapidly. Over the past 18 months, the templates have been used on over 2500 patients to enter over 40,000 separate orders.

Phylogeny and taxonomy of mesophilic Methanococcus spp. and comparison of rRNA, DNA hybridization, and phenotypic methods

The phylogeny and taxonomy of the mesophilic methane-producing archaea of the order Methanococcales were examined by DNA relatedness, 16S rRNA sequence analysis, cellular protein patterns, and phenotypic methods. The mesophilic species Methanococcus maripaludis, Methanococcus vannielii, Methanococcus voltaei, and "Methanococcus aeolicus" formed a deep group with 5 to 30% DNA relatedness and 92 to 96% 16S rRNA sequence similarity. Twenty-two additional isolates and Methanococcus deltae were similar to the type strain of either M. voltaei or M. maripaludis. Two isolates, strains A2 and A3, exhibited 37% DNA relatedness and 99.2% 16S rRNA sequence similarity to M. voltaei PS(T) (T = type strain). In the absence of phenotypic differences, these organisms were assigned to M. voltaei. Similarly, four autotrophic isolates, strains C5, C6, C7, and C8, exhibited 54 to 69% DNA relatedness and 99.2% 16S rRNA sequence similarity to M. maripaludis JJT and were assigned to M. Maripaludis. While these isolates were sufficiently genetically diverse to justify classification in novel species, few differences were apparent in the phenotypic properties available for measurement. Thus, the phenotypic properties of these lithotrophic archaea were highly conserved and poor indicators of genetic diversity. Partial sequencing of about 200 bases of both the 16S and 23S rRNAs of the isolates demonstrated allelic diversity within methanococcal species. This allelic diversity did not correlate with diversity measured by DNA relatedness, cellular protein pattern, and other methods. Similarly, antisera to whole cells of the type strains did not cross-react strongly to whole cells of strains that were genetically similar, and serological cross-reactivity was not a useful taxonomic method for methanococci. Lastly, on the basis of the results of 16S rRNA sequence analyses and biochemical data, the ancestor of the mesophilic methanococci may have been an autotrophic thermophile.

Identification of algI and algJ in the Pseudomonas aeruginosa alginate biosynthetic gene cluster which are required for alginate O acetylation

Mucoid strains of Pseudomonas aeruginosa overproduce alginate, a linear exopolysaccharide Of D-mannuronate and variable amounts of L-guluronate. The mannuronate residues undergo modification by C-5 epimerization to form the L-guluronates and by the addition of acetyl groups at the 0-2 and 0-3 positions. Through genetic analysis, we previously identified algF, located upstream of algA in the 18-kb alginate biosynthetic operon, as a gene required for alginate acetylation. Here, we show the sequence of a 3.7-kb fragment containing the open reading frames termed algI, algJ, and algF. An algI::Tn5O1 mutant, which was defective in algIJFA because of the polar nature of the transposon insertion, produced alginate when algA was provided in trans. This indicated that the algIJF gene products were not required for polymer biosynthesis. To examine the potential role of these genes in alginate modification, mutants were constructed by gene replacement in which each gene (algI, algJ, or algF) was replaced by a polar gentamicin resistance cassette. Proton nuclear magnetic resonance spectroscopy showed that polymers produced by strains deficient in algIJF still contained a mixture of D-mannuronate and L-guluronate, indicating that C-5 epimerization was not affected. Alginate acetylation was evaluated by a colorimetric assay and Fourier transform-infrared spectroscopy, and this analysis showed that strains deficient in algIJF produced nonacetylated alginate. Plasmids that supplied the downstream gene products affected by the polar mutations were introduced into each mutant. The strain defective only in algF expression produced an alginate that was not acetylated, confirming previous results. Strains missing only algJ or algI also produced nonacetylated alginates. Providing the respective missing gene (algI, algJ, or algF) in trans restored alginate acetylation. Mutants defective in algI or algJ, obtained by chemical and transposon mutagenesis, were also defective in their ability to acetylate alginate. Therefore, algI and algJ represent newly identified genes that, in addition to algF, are required for alginate acetylation.

Incidence of complications following laparoscopic hernioplasty

Smaller individual series on the outcome of laparoscopic hernioplasty techniques have been reported. This study reports on the complications of 3,229 laparoscopic hernia repairs performed by the authors in 2,559 patients. The TAPP (transabdominal preperitoneal) technique was the most frequently performed: 1,944 (60%). The totally preperitoneal technique was performed 578 (18%) times. The IPOM (intraperitoneal onlay mesh) repair was performed 345 (11%) times. The plug-and-patch technique was used 286 (9%) times and simple closure of the hernia defect without mesh was used in 76 (2%) repairs. Overall, there were 336 (10%) complications: 17 (0.5%) major and 265 (8%) minor. There were 54 (1.6%) recurrences, with a mean follow-up of 22 months. The TAPP technique had 19 (1%) recurrences and 141 (7%) complications. There were four bowel obstructions in this subgroup from herniation of small bowel through the peritoneal closure and trocar sites. The totally preperitoneal technique had no recurrence and 60 (10%) complications. The IPOM group had 7 (2%) recurrences and 47 (14%) complications. The plug-and-patch technique had 26 (9%) recurrences and 24 (8%) complications. The simple closure of the internal ring had 2 (3%) recurrences and 10 (13%) complications. Laparoscopic hernioplasty is not without complications. Laparoscopic hernioplasty is not without complications. Training, experience, and attention to technique will prevent some of these complications.

Pseudomonas aeruginosa AlgG is a polymer level alginate C5-mannuronan epimerase

Alginate is a viscous extracellular polymer produced by mucoid strains of Pseudomonas aeruginosa that cause chronic pulmonary infections in patients with cystic fibrosis. Alginate is polymerized from GDP-mannuronate to a linear polymer of beta-1-4-linked residues of D-mannuronate and its C5-epimer, L-guluronate. We previously identified a gene called algG in the alginate biosynthetic operon that is required for incorporation of L-guluronate residues into alginate. In this study, we tested the hypothesis that the product of algG is a C5-epimerase that directly converts D-mannuronate to L-guluronate. The DNA sequence of algG was determined, and an open reading frame encoding a protein (AlgG) of approximately 60 kDa was identified. The inferred amino terminus of AlgG protein contained a putative signal sequence of 35 amino acids. Expression of algG in Escherichia coli demonstrated both 60-kDa pre-AlgG and 55-kDa mature AlgG proteins, the latter of which was localized to the periplasm. An N-terminal analysis of AlgG showed that the signal sequence was removed in the mature form. Pulse-chase experiments in both E. coli and P. aeruginosa provided evidence for conversion of the 60- to the 55-kDa size in vivo. Expression of algG from a plasmid inan algG (i.e., polymannuronate-producing) mutant of P. aeruginosa restored production of an alginate containing L-guluronate residues. The observation that AlgG is apparently processed and exported from the cytoplasm suggested that it may act as a polymer-level mannuronan C5-epimerase. An in vitro assay for mannuronan C5 epimerization was developed wherein extracts of E. coli expressing high levels of AlgG were incubated with polymannuronate. Epimerization of D-mannuronate to L-guluronate residues in the polymer was detected enzymatically, using a L-guluronate-specific alginate lyase of Klebsiella aerogenes. Epimerization was also detected in the in vitro reaction between recombinant AlgG and poly-D-mannuronate, using high-performance anion-exchange chromatography. The epimerization reaction was detected only when acetyl groups were removed from the poly-D-mannuronate substrate, suggesting that AlgG epimerization activity in vivo may be sensitive to acetylation of the D-mannuronan residues. These results demonstrate that AlgG has polymer-level mannuronan C5-epimerase activity.

Identification of algF in the alginate biosynthetic gene cluster of Pseudomonas aeruginosa which is required for alginate acetylation

Mucoid strains of Pseudomonas aeruginosa produce a high-molecular-weight exopolysaccharide called alginate that is modified by the addition of O-acetyl groups. To better understand the acetylation process, a gene involved in alginate acetylation called algF was identified in this study. We hypothesized that a gene involved in alginate acetylation would be located within the alginate biosynthetic gene cluster at 34 min on the P. aeruginosa chromosome. To isolate algF mutants, a procedure for localized mutagenesis was developed to introduce random chemical mutations into the P. aeruginosa alginate biosynthetic operon on the chromosome. For this, a DNA fragment containing the alginate biosynthetic operon and adjacent argF gene in a gene replacement cosmid vector was utilized. The plasmid was packaged in vivo into lambda phage particles, mutagenized in vitro with hydroxylamine, transduced into Escherichia coli, and mobilized to an argF auxotroph of P. aeruginosa FRD. Arg+ recombinants coinherited the mutagenized alginate gene cluster and were screened for defects in alginate acetylation by testing for increased sensitivity to an alginate lyase produced by Klebsiella aerogenes. Alginates from recombinants which showed increased sensitivity to alginate lyase were tested for acetylation by a colorimetric assay and infrared spectroscopy. Two algF mutants that produced alginates reduced more than sixfold in acetyl groups were obtained. The acetylation defect was complemented in trans by a 3.8-kb XbaI-BamHI fragment from the alginate gene cluster when placed in the correct orientation under a trc promoter. By a merodiploid analysis, the algF gene was further mapped to a region directly upstream of algA by examining the polar effect of Tn501 insertions. By gene replacement, DNA with a Tn501 insertion directly upstream of algA was recombined with the chromosome of mucoid strain FRD1. The resulting strain, FRD1003, was nonmucoid because of the polar effect of the transposon on the downstream algA gene. By providing algA in trans under the tac promoter, FRD1003 produced nonacetylated alginate, indicating that the transposon was within or just upstream of algF. These results demonstrated that algF, a gene involved in alginate acetylation, is located directly upstream of algA.

Populations of Methanogenic Bacteria in a Georgia Salt Marsh

Methanogens represented about 0.5% of the total bacteria in sediments from a Georgia salt marsh in which Spartina alterniflora is the predominant vegetation. The population of methanogens was composed of at least two groups of nearly equal size. One group was represented by cocci which were able to utilize trimethylamine and were unable to use H 2 or acetate. The second group was composed of two subgroups which were able to utilize H 2 but were unable to use trimethylamine or acetate. The more common subgroup included rod- or plate-shaped methanogens which could utilize isopropanol in addition to H 2 and formate. The second subgroup included Methanococcus maripaludis, which utilized only H 2 and formate. Other groups of methanogens were also present, including Methanosarcina sp. which utilized acetate, H 2 , and methylamines. In addition to the overall variability in the types of methanogens, the numbers of methanogens in sediments also exhibited significant spatial variability both within and between tall- and short- Spartina zones.