Localized electron transfer rates and microelectrode-based enrichment of microbial communities within a phototrophic microbial mat

Abstract

Phototrophic microbial mats frequently exhibit sharp, light-dependent redox gradients that regulate microbial respiration on specific electron acceptors as a function of depth. In this work, a benthic phototrophic microbial mat from Hot Lake, a hypersaline, epsomitic lake located near Oroville in north-central Washington, was used to develop a microscale electrochemical method to study local electron transfer processes within the mat. To characterize the physicochemical variables influencing electron transfer, we initially quantified redox potential, pH, and dissolved oxygen gradients by depth in the mat under photic and aphotic conditions. We further demonstrated that power output of a mat fuel cell was light-dependent. To study local electron transfer processes, we deployed a microscale electrode (microelectrode) with tip size ~20 μm. To enrich a subset of microorganisms capable of interacting with the microelectrode, we anodically polarized the microelectrode at depth in the mat. Subsequently, to characterize the microelectrode-associated community and compare it to the neighboring mat community, we performed amplicon sequencing of the V1–V3 region of the 16S gene. Differences in Bray-Curtis beta diversity, illustrated by large changes in relative abundance at the phylum level, suggested successful enrichment of specific mat community members on the microelectrode surface. The microelectrode-associated community exhibited substantially reduced alpha diversity and elevated relative abundances of Prosthecochloris, Loktanella, Catellibacterium, other unclassified members of Rhodobacteraceae, Thiomicrospira, and Limnobacter, compared with the community at an equivalent depth in the mat. Our results suggest that local electron transfer to an anodically polarized microelectrode selected for a specific microbial population, with substantially more abundance and diversity of sulfur-oxidizing phylotypes compared with the neighboring mat community.

Species-level bacterial community profiling of the healthy sinonasal microbiome using Pacific Biosciences sequencing of full-length 16S rRNA genes

“…Previous applications of PacBio to sequencing the 16S rRNA gene were initially hampered by higher error rates and insufficient polymerase processivity to leverage circular consensus sequencing [19,20]. Subsequent improvements in PacBio sequencing chemistry have mostly overcome this [21,22], and more recent efforts have shown the value of FL16S sequencing by PacBio for and identified the major considerations needed for handling PacBio instead of Illumina 16S reads [23][24][25]. This work extends and improves upon previous efforts in several ways:…”

“…This increases taxonomic and phylogenetic resolution by increasing the number of informative sites sequenced, while continuing to use a well-studied pan-bacterial marker gene. Initial applications of Pacific Biosciences (PacBio) single-molecule real-time (SMRT) sequencing were hampered by the technology's high intrinsic error rate [19][20][21], but improvements to the chemistry have since allowed for the generation of high-quality "circular consensus sequence" (CCS) reads, in which individual 16S rRNA genes are sequenced many times using circularized library templates combined with highly processive polymerases that provide for single-molecule, consensus-sequence error correction [22]. Recent studies evaluating FL16S sequencing by PacBio have found that, with appropriate processing and filtering, CCS reads of FL16S genes can be generated that are of sufficiently high quality to offer higher taxonomic resolution than partial 16S rRNA sequences [23][24][25][26].…”

Syntrophic anaerobic photosynthesis via direct interspecies electron transfer

“…However, neither the mechanisms nor the phototrophs responsible for electron exchange with electrodes have yet been identified, leaving an open question of whether other phototrophs can also capture electrons directly from a solid electrode for photosynthesis. In a previous study on electron transfer in a microbial mat harvested from Hot Lake—an episomitic lake in northern Washington (WA, USA)—we found the green sulfur bacterium Prosthecochloris aestuarii to predominate at the tip of a carbon microelectrode inserted into the illuminated mat13. In subsequent experiments, a pure culture of P. aestuarii was isolated.…”

Autonomous Device for Evaluating the Field Performance of Microbial Fuel Cells in Remote Areas

“…Previous reports documented that Hot Lake conditions undergo daily cycles in redox potential caused by variations in light energy input and metabolic interactions among the microbial species associated with a well-developed benthic phototrophic mat. 28,30 The large magnitude of daily oscillations of SMFC power suggests that the power generated is directly or indirectly coupled to the photosynthesis in the Hot Lake microbial mat or photosynthetic organisms in the overlying water column. The data set provided in Figure 5 illustrates that the RSMFCT provides enough temporal resolution for monitoring the transient daily changes in SMFC behavior, which are an important design parameter for the reliable use of SMFCs as a power source.…”