Isolation and identification of methanogenic microorganism in Dark Earth ("Terra Preta") and floodplain soils (Gleissolo) of the Eastern Amazonian

Author(s)

Jeanedy Maria Pazinato

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2007-09-14

Examining board members

Tsai Siu Mui; Marli de Fatima Fiore; Jean Pierre Henry Balbaud Ometto; Vivian Helena Pellizari; Maria Bernadete Amancio Varesche Silva

• Advisor: Tsai Siu Mui

Abstract

Methane, as well as carbon dioxide and nitrous oxide, is an important atmospheric trace gas. The ability of methane to absorb infrared irradiation makes this gas 20 or 30 times more efficient than carbon dioxide for the global warming. The tropical floodplains are the major sources of environment methane, contributing up to 60% for the natural gas emissions. In the Amazonian Basin, they are the major methane sources, contributing to around 5% for the global gas emission. On the other hand, upland soils, especially from anthropogenic origin present high organic matter content, one of the main sources for microbial production of methane by a unique group of microorganisms which present unique enzymatic systems for their metabolism. Methane is produced by methanogenic Archaea, by anaerobic degradation of the organic matter. These microorganisms are found in a variety of environments associated to organic matter decomposition and/or biogeochemical activities. A modified-atmosphere (H2:CO2, 80:20) in combination with an anoxic growth environment for enhancing the methanogenic Archaea growth was established during 18 months in three Amazonian floodplain and three Anthropogenic Dark Earth ("Terra Preta") soils and backgrounds located within the region of Santarém – Pará (Eastern Amazonia). Molecular approaches based on the Archaea 16S ribosomal rRNA gene sequence analysis allowed direct investigation of 12 individual types of methanogenic Archaea while community diversity of 669 clone sequences from four clone libraries from one floodplain soil (Várzea 3) was addressed by examining partial 16S rRNA gene sequences. Cultivation-dependent assays - enrichment and growth, as well as monitoring of methane production, direct phase-contrast microscopy and scanning electron microscopy, detection of the mcr - methyl coenzyme reductase – gene were used as reference methods in the development and evaluation of the molecular methods. Among the isolates from the Várzea 3 the genus Methanosarcina was predominant, indicating its possible role on the methane production, detected throughout the in vitro cultivation. Among the 12 types isolated from the nine soils, 10 corresponded to a sequence of Methanobacterium isolated from the gut of termites from a tropical environment. In conclusion, our explorative molecular approach gave the first picture towards the understanding of the role of methanogenic Archaea in floodplain and upland soils from the Eastern Amazonian. (AU)