Transcriptomic and Physiological Insights into the Robustness of Long Filamentous Cells of Methanosaeta harundinacea, Prevalent in Upflow Anaerobic Sludge Blanket Granules

Abstract

bMethanosaeta spp. are widely distributed in natural environments, and their filamentous cells contribute significantly to sludge granulation and the good performance of anaerobic reactors. A previous study indicated that Methanosaeta harundinacea 6Ac displays a quorum sensing-regulated morphological transition from short to long filaments, and more acetate is channeled into methane production in long filaments, whereas more is channeled into biomass synthesis in short filaments. Here, we performed transcriptomic and physiological analysis to gain insights into active methanogenesis in long filaments of M. harundinacea 6Ac. Both RNA sequencing (RNA-seq) and quantitative reverse transcription-PCR indicated that transcription of the genes involved in aceticlastic methanogenesis and energy metabolism was upregulated 1.2-to 10.3-fold in long filaments, while transcription of the genes for the methyl oxidative shunt was upregulated in short filaments. [2-13 C]acetate trace experiments demonstrated that a relatively higher portion of the acetate methyl group was oxidized to CO 2 in short filaments than in long filaments. The long filaments exhibited higher catalase activity and oxygen tolerance than the short ones, which is consistent with increased transcription of the oxidant-scavenging genes. Moreover, transcription of genes for cell surface structures was upregulated in the long filaments, and transmission electron microscopy revealed a thicker cell envelope in the filaments. RNA-seq determined a >2-fold upregulation of a variety of antistress genes in short filaments, like those encoding chaperones and DNA repair systems, which implies that the short filaments can be stressed. This study reveals the genetic basis for the prevalence of the long filamentous morphology of M. harundinacea cells in upflow anaerobic sludge blanket granules. Methanogenic degradation of organic complexes is a widely used approach in wastewater treatment; it promotes the development of upflow anaerobic sludge blanket (UASB) reactors (1). Efficient mineralization of organic complexes to CH 4 and CO 2 in the UASB reactor is implemented by diverse microbes through a food chain mode, where methanogens implement the final chemical reaction producing CH 4 (2, 3). In UASB reactors and other ecosystems, acetate-derived methane (aceticlastic methanogenesis) contributes about 70% of the methane produced by either the generalist aceticlastic methanogens of the species Methanosarcina or the obligate aceticlastic methanogens of the species Methanosaeta (4, 5). Methanosaeta species are believed to be the key components in anaerobic digesters not only because of their ability to use very low concentrations of acetate (threshold, 5 to 20 M) (6) but also because of their fiber-like cells that serve as a scaffold for the attachment of other organisms to promote the formation of UASB granules (7), an essential self-immobilized organization of the functional microbes. It has been reported that Methanosaeta cells comprise one-third of the anaerobic migrating ...

Critical Biofilm Growth throughout Unmodified Carbon Felts Allows Continuous Bioelectrochemical Chain Elongation from CO2 up to Caproate at High Current Density

“…The role of H2 as electron mediator in MES systems has been extensively discussed (Blanchet et al, 2015;Jourdin et al, 2016b;LaBelle and May, 2017;Puig et al, 2017) and some biofilms were showed to be very effective at capturing it before it could escape the biofilm (Jourdin et al, 2016b). Some methanogens belonging to genera such as Methanosaeta and Methanospirillum were also showed to form long filaments over hundreds of micrometers in anaerobic granular sludge (Parshina et al, 2014;Li et al, 2015;Zhou et al, 2015). However, methanogenesis activity was inhibited in our reactors by continuously feeding a chemical inhibitor.…”

Perspectives for microbial community composition in anaerobic digestion: from abundance and activity to connectivity

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Biphasic Study to Characterize Agricultural Biogas Plants by High-Throughput 16S rRNA Gene Amplicon Sequencing and Microscopic Analysis

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