Diverse type I and type II methanotrophs cultivated from an Indian freshwater wetland habitat

Wetlands are the main natural sources of methane emissions, which make up a significant portion of greenhouse gas emissions. Such wetland patches serve as rich habitats for aerobic methanotrophs. Limited knowledge of methanotrophs from tropical wetlands widens the scope of study from these habitats. In the present study, a freshwater wetland in a tropical region in India was sampled and serially diluted to obtain methanotrophs in culture. This was followed by the isolation of methanotrophs on agarose-containing plates, incubated under methane: air atmosphere. Methanotrophs are difficult to cultivate, and very few cultures of methanotrophs are available from tropical wetlands. Our current study reports the cultivation of a diverse community of methanotrophs from six genera, namely, Methylomonas, Methylococcus, Methylomagnum, Methylocucumis (type I methanotrophs) along with Methylocystis, Methylosinus (type II methanotrophs). A high abundance of methanotrophs (106–1010 methanotrophs/g fresh weight) was observed in the samples. A Methylococcus strain could represent a putative novel species that was also isolated. Cultures of Methylomagnum and Methylocucumis, two newly described type I methanotrophs exclusively found in rice fields, were obtained. A large number of Methylomonas koyamae strains were cultured. Our study is pioneering in the documentation of culturable methanotrophs from a typical tropical wetland patch. The isolated methanotrophs can act as models for studying methanotroph-based methane mitigation from wetland habitats and can be used for various mitigation and valorization applications. (AU)

Response of Anaerobic Protozoa to Oxygen Tension in Anaerobic System

The effect of oxygen on anaerobic protozoa was studied in anaerobic batch reactors inoculated with sludge and protozoa cultures. Among the protozoa genera, Metopus, Brachonella, Plagiopyla, Trepomonas, and Vanella were more sensitive to oxygen compared to other genera. Protozoa genera Menoidium, Rhynchomonas, Cyclidium, Spathidium, and Amoeba were found to survive under aerobic conditions, and the growth rate was slightly higher or similar to anaerobic condition. O2 tension resulted in the loss of free and endosymbiotic methanogens in anaerobic system, while methanogens were observed inside the protozoan cysts. Survival of anaerobic protozoa declined considerably when the O2 tension exceeded 1% atm. sat. and showed chemosensory behavior in response to O2 exposure. Superoxide dismutase activity was detected in survived protozoa cells under O2 tension. Facultative anaerobic protozoa with SOD activity can provide a mechanism to overcome possible occurrence of oxygen toxicity in the treatment of wastewater in anaerobic reactor

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The association between a positive lactulose methane breath test and rectocele in constipated patients

Objectives: Rectocele with constipation might be related to methane (CH4) producing intestinal bacteria. We investigated the breath CH4 levels and the clinical characteristics of colorectal motility in constipated patients with rectocele. Methods: A database of consecutive female outpatients was reviewed for the evaluation of constipation according to the Rome III criteria. The patients underwent the lactulose CH4 breath test (LMBT), colon marker study, anorectal manometry, defecography and bowel symptom questionnaire. The profiles of the lactulose breath test (LBT) in 33 patients with rectocele (with size ≥ 2 cm) and 26 patients with functional constipation (FC) were compared with the breath test results of 30 healthy control subjects. Results: The mean size of rectocele was 3.52 ± 1.06 cm. The rate of a positive LMBT (LMBT+) was significantly higher in patients with rectocele (33.3%) than in those with FC (23.1%) or healthy controls (6.7%) (p = 0.04). Breath CH4 concentration was positively correlated with rectosigmoid colon transit time in rectocele patients (γ = 0.481, p < 0.01). A maximum high pressure zone pressure > 155 mmHg was a significant independent factor of LMBT+ in rectocele patients (OR = 8.93, 95% CI = 1.14-71.4, p = 0.04). Conclusions: LMBT+ might be expected in constipated patients with rectocele. Moreover, increased rectosigmoid colonic transit or high anorectal pressure might be associated with CH4 breath levels. Breath CH4 could be an important therapeutic target for managing constipated patients with rectocele (AU)

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