“Candidatus Chlorobium masyuteum,” a Novel Photoferrotrophic Green Sulfur Bacterium Enriched From a Ferruginous Meromictic Lake

Abstract

Anoxygenic phototrophic bacteria can be important primary producers in some meromictic lakes. Green sulfur bacteria (GSB) have been detected in ferruginous lakes, with some evidence that they are photosynthesizing using Fe(II) as an electron donor (i.e., photoferrotrophy). However, some photoferrotrophic GSB can also utilize reduced sulfur compounds, complicating the interpretation of Fe-dependent photosynthetic primary productivity. An enrichment (BLA1) from meromictic ferruginous Brownie Lake, Minnesota, United States, contains an Fe(II)-oxidizing GSB and a metabolically flexible putative Fe(III)-reducing anaerobe. “Candidatus Chlorobium masyuteum” grows photoautotrophically with Fe(II) and possesses the putative Fe(II) oxidase-encoding cyc2 gene also known from oxygen-dependent Fe(II)-oxidizing bacteria. It lacks genes for oxidation of reduced sulfur compounds. Its genome encodes for hydrogenases and a reverse TCA cycle that may allow it to utilize H2 and acetate as electron donors, an inference supported by the abundance of this organism when the enrichment was supplied by these substrates and light. The anaerobe “Candidatus Pseudopelobacter ferreus” is in low abundance (∼1%) in BLA1 and is a putative Fe(III)-reducing bacterium from the Geobacterales ord. nov. While “Ca. C. masyuteum” is closely related to the photoferrotrophs C. ferroooxidans strain KoFox and C. phaeoferrooxidans strain KB01, it is unique at the genomic level. The main light-harvesting molecule was identified as bacteriochlorophyll c with accessory carotenoids of the chlorobactene series. BLA1 optimally oxidizes Fe(II) at a pH of 6.8, and the rate of Fe(II) oxidation was 0.63 ± 0.069 mmol day–1, comparable to other photoferrotrophic GSB cultures or enrichments. Investigation of BLA1 expands the genetic basis for phototrophic Fe(II) oxidation by GSB and highlights the role these organisms may play in Fe(II) oxidation and carbon cycling in ferruginous lakes.

Microbial habitability of early Mars lacustrine environments sustained by iron redox cycling

“…However, similar microbial communities have been isolated in natura. For example, an Fe(II)-oxidizing photoferrotroph, Candidatus Chlorobium masyuteum, and a putative Fe(III)-reducing bacterium, Candidatus Pseudopelobacter ferreus, were recently co-enriched from the ferruginous Brownie Lake in Minnesota, USA (e.g., Lambrecht et al, 2021). Acetate and formate detected in the chemocline of Brownie Lake suggests that the redox cycling of Fe occurs between these organisms, but it has not yet been confirmed.…”

Insights on biotic and abiotic 2,4‐dichlorophenoxyacetic acid degradation by anaerobic iron‐cycling bacteria

“…Co‐culture BLA1 (Lambrecht et al., 2021) was enriched from ferruginous meromictic Brownie Lake in Minneapolis, MN. Photosynthetic growth is observed with Fe(II), acetate, and H 2 as electron donors, and Fe(III) reduction occurs with 1 mM acetate as an electron donor (Lambrecht et al., 2021). BLA1 was anoxically cultivated on Fe(II)‐containing freshwater medium (FW) at 20°C.…”

“…A co‐culture containing " Candidatus Chlorobium masyuteum", which oxidizes Fe(II) photosynthetically under anoxic conditions, and “; Candidatus Pseudopelobacter ferreus”, which reduces Fe(III) with acetate in the absence of light was enriched from the anoxic and sunlit chemocline of a meromictic lake (Lambrecht et al., 2021). Neither Ca .…”

Natural products from reconstructed bacterial genomes of the Middle and Upper Paleolithic

“…S6) but was detected in the dental calculus of nine individuals (dataset S4). Known members of Chlorobium are photolithoautotrophic, obligate anaerobic green sulfur bacteria that typically perform photosynthesis in anoxic water columns ( 32 , 33 ). Five of those nine individuals returned a HQ Chlorobium MAG (EMN001, PES001, GOY005, PLV001, and RIG001), and their HQ Chlorobium MAGs had the highest completeness of all MAGs in the metagenome (Fig.…”