Rhodopsin-mediated nutrient uptake by cultivated photoheterotrophic Verrucomicrobiota

Area of Science:

• Microbiology
• Marine Biology
• Biochemistry

Background:

• Rhodopsins are light-harvesting pigments found in diverse marine microbes.
• Their function in Verrucomicrobiota, an understudied phylum, remains largely unknown.
• Metagenomic data suggested rhodopsin presence, but in vivo roles were uncharacterized.

Purpose of the Study:

• Investigate the distribution and diversity of rhodopsins in the Verrucomicrobiota phylum.
• Characterize the physiology of the first cultivated rhodopsin-containing Verrucomicrobiota strains.
• Determine the ecological role of rhodopsin phototrophy in Verrucomicrobiota.

Main Methods:

• Genomic analysis of 2916 Verrucomicrobiota genomes to identify rhodopsin genes.
• Isolation and cultivation of two Verrucomicrobiota strains containing proteorhodopsin and xanthorhodopsin.
• Physiological experiments under controlled laboratory conditions, including carbon starvation and light exposure.
• 16S rRNA gene amplicon sequencing to assess strain abundance in environmental samples.

Main Results:

• Rhodopsins were identified in over 7% of analyzed Verrucomicrobiota genomes.
• Two novel strains, one with proteorhodopsin and one with xanthorhodopsin, were successfully cultivated.
• Rhodopsin phototrophy was observed to support sugar transport and cellular energy generation during carbon starvation.
• Strain abundance peaked at the deep chlorophyll maximum during winter and spring.

Conclusions:

• Photoheterotrophic Verrucomicrobiota utilize rhodopsins to harness light energy.
• This energy supports essential functions like motility and organic matter degradation.
• Verrucomicrobiota may occupy a niche where light energy facilitates nutrient acquisition and survival.
• Rhodopsin phototrophy is a key adaptation for Verrucomicrobiota in light-rich marine environments.