Microbial acceleration of aerobic pyrite oxidation at circumneutral pH.

Pyrite (FeS2 ) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite-bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin-Benson-Bassham CO2 fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30-50 nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X-ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro-organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral-pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite-associated metals.

Iron isotope fractionation during microbial dissimilatory iron oxide reduction in simulated Archaean seawater.

The largest Fe isotope excursion yet measured in marine sedimentary rocks occurs in shales, carbonates, and banded iron formations of Neoarchaean and Paleoproterozoic age. The results of field and laboratory studies suggest a potential role for microbial dissimilatory iron reduction (DIR) in producing this excursion. However, most experimental studies of Fe isotope fractionation during DIR have been conducted in simple geochemical systems, using pure Fe(III) oxide substrates that are not direct analogues to phases likely to have been present in Precambrian marine environments. In this study, Fe isotope fractionation was investigated during microbial reduction of an amorphous Fe(III) oxide-silica coprecipitate in anoxic, high-silica, low-sulphate artificial Archaean seawater at 30 °C to determine if such conditions alter the extent of reduction or isotopic fractionations relative to those observed in simple systems. The Fe(III)-Si coprecipitate was highly reducible (c. 80% reduction) in the presence of excess acetate. The coprecipitate did not undergo phase conversion (e.g. to green rust, magnetite or siderite) during reduction. Iron isotope fractionations suggest that rapid and near-complete isotope exchange took place among all Fe(II) and Fe(III) components, in contrast to previous work on goethite and hematite, where exchange was limited to the outer few atom layers of the substrate. Large quantities of low-δ(56)Fe Fe(II) (aqueous and solid phase) were produced during reduction of the Fe(III)-Si coprecipitate. These findings shed new light on DIR as a mechanism for producing Fe isotope variations observed in Neoarchaean and Paleoproterozoic marine sedimentary rocks.

The impact of splenectomy on outcome after resection for colorectal cancer: a multicenter, nested, paired cohort study.

PURPOSE: This study was designed to determine whether incidental splenectomy for iatrogenic injury affects long-term cancer-specific survival in patients having resection of an adenocarcinoma of the sigmoid or rectum. METHODS: A retrospective case-matched review of patients undergoing surgery for colorectal cancer with incidental splenectomy between January 1, 1990 and December 31, 1999 was undertaken. Data were analysed for age, American Society of Anesthesiologists physical status, gender, disease stage, operation type, and outcome. These cases were matched with patients from the same center, of the same age and gender, with the same stage of disease and operation, who did not require a splenectomy at the time of their surgery. RESULTS: Fifty-five patients were identified who had an iatrogenic splenectomy. Matched gender, stage, and American Society of Anesthesiologists-matched controls were identified. Follow-up from time of surgery to death or last follow-up ranged from 2 to 205 (median, 43) months. A Kaplan-Meier survival analysis using the Cox proportional hazards model to define the statistical significance found a significant difference between the groups favoring those without splenectomy (hazard ratio, 1.8; 95 percent confidence interval (CI), 1-3.3; P=0.0399). Cancer-specific survival at five years was 70 vs. 47 percent and at ten years was 55 vs. 38 percent. DISCUSSION: Patients with colorectal cancer who had splenectomy as a result of iatrogenic damage of the spleen while undergoing resection of the sigmoid or rectum for adenocarcinoma had a significantly worse prognosis.

Local invasion of the bladder with colorectal cancers: surgical management and patterns of local recurrence.

PURPOSE: Colorectal cancers may be adherent to the urinary bladder. To achieve oncologic clearance of the cancer, en bloc bladder resection should be performed. This study describes the multicenter experiences of en bloc bladder resection for colorectal cancer in the major New Zealand public hospitals. METHODS: A retrospective database of patients undergoing surgery for colorectal cancer adherent to the bladder between 1984 and 1999 was constructed. Data was analyzed for age, gender, disease stage, and outcome (local recurrence and survival). RESULTS: Fifty-three patients were identified: International Union Against Cancer and American Joint Committee on Cancer Stage 1=0; Stage 2=23; Stage 3=22; Stage 4=6; unknown=2. Forty-five had en bloc partial cystectomy performed, four en bloc total cystectomy, and four had the adhesions disrupted and no bladder resection. The most common site of the primary colorectal cancer is sigmoid colon, with local invasion into the dome of the bladder. All patients who did not have en bloc resection developed local recurrence and died from their disease. Mean follow-up was 62 months. The extent of bladder resection did not seem important in determining local recurrence. CONCLUSIONS: En bloc resection of the urinary bladder should be performed if the patient is to be offered an optimal oncologic resection for adherent colorectal cancer. The decision to perform total rather than partial cystectomy should be based on the anatomic location of the tumor. Because the sigmoid is usually the primary site, most patients will not have received preoperative radiation. Therefore, postoperative radiotherapy may reduce local recurrence in these patients.

Misconceptions about the colonic J-pouch: what the accumulating data show.

INTRODUCTION: Since 1986 when the colonic J-pouch-anal anastomosis was first described, it has gained increasing acceptance as the operation of choice for low rectal cancer surgery. However, there still exist several misconceptions about its use, namely anastomotic complications, alterations in anorectal physiology, and functional outcome. METHODS: All relevant articles derived from MEDLINE databases from 1986 to the present were reviewed. Emphasis was placed on reviewing the features that are claimed to make the colonic J-pouch-anal anastomosis superior to a straight anastomosis. RESULTS AND CONCLUSIONS: The colonic J-pouch has a role in ultra-low rectal cancer surgery, with an apparent reduction in the incidence of anastomotic leaks and reduced bowel frequency. Continence is unchanged and defecatory difficulties can be reduced by constructing a small pouch (< or =5 cm).

Priority access criteria for elective cholecystectomy: a comparison of three scoring methods.

AIM: To compare two priority access criteria scoring methods for elective cholecystectomy, with a score based on clinical judgement obtained using a linear analogue scale. METHODS: Patients placed on the waiting list for elective laparoscopic cholecystectomy between June and October 1997 were prioritised using the three methods. RESULTS: Data were obtained for 22 patients. The distributions of scores were different but there was a significant correlation between them. However, limits of agreement analysis demonstrated little agreement between them with a difference of +/- 30 points (out of a 100) between scores obtained with each method. CONCLUSION: The proposed methods for establishing priority access to elective cholecystectomy are poor tools, require validation and bear little relation to expert clinical judgement.

Generic surgical priority criteria scoring system: the clinical reality.

AIMS: To assess the 'generic surgical priority criteria' (GSPC) introduced into Auckland Hospital by the Northern Division of the Transitional Health Authority in 1997 and compare it with a score based on clinical judgement obtained using a linear analogue scale (LAS). METHODS: From the time of introduction in June 1997 all patients being placed on the general surgical waiting list have been scored using both the GSPC and the LAS. After two months the scores given to 209 patients were reviewed and compared. Correlation and limits of agreement analysis were performed for grouped data, cancer and benign groups. RESULTS: The data showed wide variation and poor agreement between the surgeons' clinical judgement in assessing priority for surgery and the score patients obtained using the GSPC. CONCLUSION: The GSPC has poor diagnostic discrimination as it failed to identify reliably a cancer diagnosis as high priority, with benign diagnoses scoring consistently higher. This highlights the need for clinical involvement in designing priority criteria and for formal validation of such tools.

Noradrenaline excites neurons in the guinea pig cerebellar vermis in vitro.

Noradrenaline (NA) was applied to the solution bathing the cavy cerebellar vermis in vitro and the responses of 98 neurons were recorded extracellularly. Two thirds (23/35) of the responses were excitations and the remaining third were inhibitions. The lowest concentration of NA with which responses could be obtained was 10(-11) M NA. Responses were generally transient and occurred with a mean latency of 61 +/- 8 sec. The excitation was generally direct as most responses (9/11) survived synaptic blockade. The excitations were thought to be mediated by alpha 1 receptors because they could be mimicked by phenylephrine and antagonised by prazozin.