Bacterium lacking a known gene for retinal biosynthesis constructs functional rhodopsins

Yu Nakajima, Keiichi Kojima, Yuichiro Kashiyama, Satoko Doi, Ryosuke Nakai, Yuki Sudo, Kazuhiro Kogure, Susumu Yoshizawa

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Microbial rhodopsins, comprising a protein moiety (rhodopsin apoprotein) bound to the light-absorbing chromophore retinal, function as ion pumps, ion channels, or light sensors. However, recent genomic and metagenomic surveys showed that some rhodopsin-possessing prokaryotes lack the known genes for retinal biosynthesis. Since rhodopsin apoproteins cannot absorb light energy, rhodopsins produced by prokaryotic strains lacking genes for retinal biosynthesis are hypothesized to be non-functional in cells. In the present study, we investigated whether Aurantimicrobium minutum KNCT, which is widely distributed in terrestrial environments and lacks any previously identified retinal biosynthesis genes, possesses functional rhodopsin. We initially measured ion transport activity in cultured cells. A light-induced pH change in a cell suspension of rhodopsin-possessing bacteria was detected in the absence of exogenous retinal. Furthermore, spectroscopic analyses of the cell lysate and HPLC-MS/MS analyses revealed that this strain contained an endogenous retinal. These results confirmed that A. minutum KNCT possesses functional rhodopsin and, hence, produces retinal via an unknown biosynthetic pathway. These results suggest that rhodopsin-possessing prokaryotes lacking known retinal biosynthesis genes also have functional rhodopsins.

Original languageEnglish
Article numberME20085
Pages (from-to)1-7
Number of pages7
JournalMicrobes and Environments
Issue number4
Publication statusPublished - 2020


  • Phylum Actinobacteria
  • Retinal biosynthesis
  • Rhodopsin

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Soil Science
  • Plant Science


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