Search for: All records

Thalassospira species are ubiquitous marine bacteria with poorly understood ecology, and some have been implicated in iron corrosion. To better elucidate the mechanisms and ecological implications of extracellular electron transfer (EET) in oxidative processes, we conducted genomic and bioelectrochemical characterization of Thalassospira xiamenensis strain SN3, an obligate heterotroph isolated from coastal marine sediment cathode- oxidizing enrichments. Physiologic and genomic analyses indicate that SN3 lacks the capacity for lithoautotrophic growth and lacks homologs to genes canonically involved in EET. Bioelectrochemical characterization of SN3 cells shows that inward EET requires a terminal electron acceptor (respiration). Deletion of nitrate reductase catalytic subunit napA abolished current consumption and catalytic activity under nitrate-reducing conditions. Media exchange experiments demonstrate that inward EET in SN3 is facilitated by direct contact with the electrode, with a formal midpoint potential of 153 ± 16 mV vs. SHE. Through deletion of the formate dehydrogenase fdhABCD and electrochemical characterization of mutant cells, we show that inward EET is not a function of Fdh enzyme sorption to the electrode, as has been demonstrated for other organisms. This provides further evidence of a cell-mediated and contact-dependent EET mechanism. This work provides a foundation for investigating this metabolically versatile organism’s yet uncharacterized mechanism of EET. 

ABSTRACT We report the full genome sequence ofHalomonassp. strain M1, isolated from a continental high pH serpentinizing spring in northern California, USA. The 3.7 Mb genome has a G + C content of 54.13%, encodes 3,354 protein-coding genes, and provides insights into the metabolic potential for sulfur oxidation. 

ABSTRACT Here, we report the complete genome sequence forRoseinatronobactersp. S2, a sulfur-oxidizing heterotroph isolated from a serpentinizing system in Northern California. The S2 genome is 4.4 Mb and contains 4,570 protein-encoding genes. This organism contains the genes necessary for sulfur species oxidation and complete ethylmalonyl and pentose phosphate pathways. 

Terrestrial serpentinizing systems allow us insight into the realm of alkaliphilic microbial communities driven by geology in a way that is frequently more accessible than their deep subsurface or marine counterparts. However, these systems are also marked by geochemical and microbial community variation due to the interactions of serpentinized fluids with host geology and the surface environment. To separate the transient from the endemic microbes in a hyperalkaline environment, we assessed the Ney Springs terrestrial serpentinizing system microbial community and geochemistry at six time points over the span of a year. Using 16S rRNA gene surveys we observed 93 amplicon sequence variants (ASVs) that were found at every sampling event. This is compared to ~17,000 transient ASVs that were detected only once across the six sampling events. Of the resident community members, 16 of these ASVs were regularly greater than 1% of the community during every sampling period. Additionally, many of these core taxa experienced statistically significant changes in relative abundance with time. Variation in the abundance of some core populations correlated with geochemical variation. For example, members of the Tindallia group, showed a positive correlation with variation in levels of ammonia at the spring. Investigating the metagenome assembled genomes of these microbes revealed evidence of the potential for ammonia generation via Stickland reactions within Tindallia . This observation offers new insight into the origin of high ammonia concentrations (>70 mg/L) seen at this site. Similarly, the abundance of putative sulfur-oxidizing microbes like Thiomicrospira , Halomonas , and a Rhodobacteraceae species could be linked to changes observed in sulfur-oxidation intermediates like tetrathionate and thiosulfate. While these data supports the influence of core microbial community members on a hyperalkaline spring’s geochemistry, there is also evidence that subsurface processes affect geochemistry and may impact community dynamics as well. Though the physiology and ecology of these astrobiologically relevant ecosystems are still being uncovered, this work helps identify a stable microbial community that impacts spring geochemistry in ways not previously observed in serpentinizing ecosystems. 

Extracellular electron transfer (EET) – the process by which microorganisms transfer electrons across their membrane(s) to/from solid-phase materials – has implications for a wide range of biogeochemically important processes in marine environments. Though EET is thought to play an important role in the oxidation of inorganic minerals by lithotrophic organisms, the mechanisms involved in the oxidation of solid particles are poorly understood. To explore the genetic basis of oxidative EET, we utilized genomic analyses and transposon insertion mutagenesis screens (Tn-seq) in the metabolically flexible, lithotrophic Alphaproteobacterium Thioclava electrotropha ElOx9 T . The finished genome of this strain is 4.3 MB, and consists of 4,139 predicted ORFs, 54 contain heme binding motifs, and 33 of those 54 are predicted to localize to the cell envelope or have unknown localizations. To begin to understand the genetic basis of oxidative EET in ElOx9 T , we constructed a transposon mutant library in semi-rich media which was comprised of >91,000 individual mutants encompassing >69,000 unique TA dinucleotide insertion sites. The library was subjected to heterotrophic growth on minimal media with acetate and autotrophic oxidative EET conditions on indium tin oxide coated glass electrodes poised at –278 mV vs. SHE or un-poised in an open circuit condition. We identified 528 genes classified as essential under these growth conditions. With respect to electrochemical conditions, 25 genes were essential under oxidative EET conditions, and 29 genes were essential in both the open circuit control and oxidative EET conditions. Though many of the genes identified under electrochemical conditions are predicted to be localized in the cytoplasm and lack heme binding motifs and/or homology to known EET proteins, we identified several hypothetical proteins and poorly characterized oxidoreductases that implicate a novel mechanism(s) for EET that warrants further study. Our results provide a starting point to explore the genetic basis of novel oxidative EET in this marine sediment microbe.