09:15 〜 09:30
[AHW24-02] 琵琶湖の温暖化に伴う湖底境界層におけるMOB叢の空間変異
キーワード：メタン酸化細菌、温暖化、低酸素
Introduction
There is a big concern that global warming-induced by climate changes has an impact on the biota living in the lake bottom where oxygen is depleted. Fatty acid and stable isotope analysis using micro or macro biota at hypoxia layer in the lake can support to give the information of oxygen condition. However, we have poorly understood depressed oxygen condition impact on lake biodiversity, especially hypoxia-sensitive species.
Methane-oxidizing bacteria< MOB> are regarded as key players in aquatic ecosystems, which can mitigate greenhouse gas emissions to the atmosphere. They are classified into two major groups, type I and type II. Another group of MOB, ´Candidatus Methylomirabilis oxyfera´, and its close relatives have also been detected in various environments. In Taiwan, Feitsui Reservoir is a subtropical reservoir situated, where the predominance of ´M. oxyfera´-like the phylotypes in a planktonic MOB community were first reported. At the point of geographical proximity from Taiwan to Japan, it is expected that Lake Biwa also has´M. oxyfera´-like phylotypes in a planktonic MOB community induced by low oxygen condition.
Our objective is to demonstrate how planktonic MOB <´M. oxyferaʼ-like and type I>community change in lake Biwa, where it is not known well that depressed oxygen impacts on MOB community with oxidation-reduction information. Additionally, we use fatty acid and stable isotope analysis to support MOB community information using sediment samples.
Materials and Methods
We conducted synoptic monitoring for lake bottom environments and benthic macroinvertebrates at 15 offshore sites, whose depths ranged from 3.6 to 91.2 m, in the south and north basins during 4-15 October 2021. Water and sediment samples for catalyzed reporter deposition-fluorescence in situ hybridization and methane concentration analysis were taken from bottom layers October 2020, November, and December 2021. These samples were fixed with paraformaldehyde and were stored in a cooler box until filtration. Three-milliliter samples were passed through polycarbonate membrane filters and the filters were stored at –30℃ until further processing. CARD-FISH was performed by following a protocol previously described with some modifications. The specific probe DBACT-1027 was used to detect the ʻM. oxyferaʼ-like organisms. The probes were labeled with horseradish peroxidase. The hybridization was performed for 15 h at 37℃ with mild agitation. The hybridized cells were counted under a fluorescence microscope. The cells positive for the MOB-specific probes were enumerated.
Results and Discussion
The cells of ʻM. oxyferaʼ-like phylotype mainly occurred in the deep layers where methane concentrations were relatively higher. We will discuss stable isotope and fatty acid analysis can help to identify MOB abundance in an anoxic layer in the future.
There is a big concern that global warming-induced by climate changes has an impact on the biota living in the lake bottom where oxygen is depleted. Fatty acid and stable isotope analysis using micro or macro biota at hypoxia layer in the lake can support to give the information of oxygen condition. However, we have poorly understood depressed oxygen condition impact on lake biodiversity, especially hypoxia-sensitive species.
Methane-oxidizing bacteria< MOB> are regarded as key players in aquatic ecosystems, which can mitigate greenhouse gas emissions to the atmosphere. They are classified into two major groups, type I and type II. Another group of MOB, ´Candidatus Methylomirabilis oxyfera´, and its close relatives have also been detected in various environments. In Taiwan, Feitsui Reservoir is a subtropical reservoir situated, where the predominance of ´M. oxyfera´-like the phylotypes in a planktonic MOB community were first reported. At the point of geographical proximity from Taiwan to Japan, it is expected that Lake Biwa also has´M. oxyfera´-like phylotypes in a planktonic MOB community induced by low oxygen condition.
Our objective is to demonstrate how planktonic MOB <´M. oxyferaʼ-like and type I>community change in lake Biwa, where it is not known well that depressed oxygen impacts on MOB community with oxidation-reduction information. Additionally, we use fatty acid and stable isotope analysis to support MOB community information using sediment samples.
Materials and Methods
We conducted synoptic monitoring for lake bottom environments and benthic macroinvertebrates at 15 offshore sites, whose depths ranged from 3.6 to 91.2 m, in the south and north basins during 4-15 October 2021. Water and sediment samples for catalyzed reporter deposition-fluorescence in situ hybridization and methane concentration analysis were taken from bottom layers October 2020, November, and December 2021. These samples were fixed with paraformaldehyde and were stored in a cooler box until filtration. Three-milliliter samples were passed through polycarbonate membrane filters and the filters were stored at –30℃ until further processing. CARD-FISH was performed by following a protocol previously described with some modifications. The specific probe DBACT-1027 was used to detect the ʻM. oxyferaʼ-like organisms. The probes were labeled with horseradish peroxidase. The hybridization was performed for 15 h at 37℃ with mild agitation. The hybridized cells were counted under a fluorescence microscope. The cells positive for the MOB-specific probes were enumerated.
Results and Discussion
The cells of ʻM. oxyferaʼ-like phylotype mainly occurred in the deep layers where methane concentrations were relatively higher. We will discuss stable isotope and fatty acid analysis can help to identify MOB abundance in an anoxic layer in the future.