Thiorhodovibrio frisius and Trv. litoralis spp. nov., Two Novel Members from a Clade of Fastidious Purple Sulfur Bacteria That Exhibit Unique Red-Shifted Light-Harvesting Capabilities

Abstract

In the pursuit of cultivating anaerobic anoxygenic phototrophs with unusual absorbance spectra, a purple sulfur bacterium was isolated from the shoreline of Baltrum, a North Sea island of Germany. It was designated strain 970, due to a predominant light harvesting complex (LH) absorption maximum at 963–966 nm, which represents the furthest infrared-shift documented for such complexes containing bacteriochlorophyll a. A polyphasic approach to bacterial systematics was performed, comparing genomic, biochemical, and physiological properties. Strain 970 is related to Thiorhodovibrio winogradskyi DSM 6702T by 26.5, 81.9, and 98.0% similarity via dDDH, ANI, and 16S rRNA gene comparisons, respectively. The photosynthetic properties of strain 970 were unlike other Thiorhodovibrio spp., which contained typical LH absorbing characteristics of 800–870 nm, as well as a newly discovered absorption band at 908 nm. Strain 970 also had a different photosynthetic operon composition. Upon genomic comparisons with the original Thiorhodovibrio strains DSM 6702T and strain 06511, the latter was found to be divergent, with 25.3, 79.1, and 97.5% similarity via dDDH, ANI, and 16S rRNA gene homology to Trv. winogradskyi, respectively. Strain 06511 (=DSM 116345T) is thereby described as Thiorhodovibrio litoralis sp. nov., and the unique strain 970 (=DSM 111777T) as Thiorhodovibrio frisius sp. nov.

Calcium and the ecology of photosynthesis in purple sulfur bacteria

“…Thiorhodovibrio frisius (Table 1) exhibits the most red-shifted (lowest energy) Q y absorption of all known BChl a-containing phototrophs (Kimura et al, 2023). This significantly lowered LH1-Q y transition energy provides the largest "uphill" energy gap between LH1 and the RC yet observed (Methner et al, 2023;Permentier et al, 2001;Rücker et al, 2012). A study of this unusual purple bacterium revealed a major role for Ca 2+ in expanding its spectral reach and a minor role in conferring thermostability on its Core photocomplex (Imanishi et al, 2019).…”

“…Not surprisingly, Trv. frisius (Figures 10 and 11) also originated from an intertidal sandy sediment habitat (Methner et al, 2023).…”

“…vinosum . The former species displays the most red‐shifted LH1 absorbance of any known purple bacterium (Methner et al, 2023; Permentier et al, 2001), whereas the latter—the archetypal purple sulfur bacterium—shows spectral features nearly identical to those of Alc. tepidum .…”

“…This is particularly relevant for Trv. frisius because it lacks a peripheral (LH2) photocomplex (Methner et al, 2023) and therefore must rely on a single LH complex for funnelling energy to its RC.…”

“…strain 970, recently described as a new species Trv. frisius (Methner et al, 2023; Permentier et al, 2001; Rücker et al, 2012). All four of these PSB contain Bchl a , although each displays a unique absorption spectrum (Kimura et al, 2023, and see later figure).…”