Loss of Cytochrome cM Stimulates Cyanobacterial Heterotrophic Growth in the Dark

Abstract

Although cyanobacteria are photoautotrophs, they have the capability for heterotrophic metabolism that enables them to survive in their natural habitat. However, cyanobacterial species that grow heterotrophically in the dark are rare. It remains largely unknown how cyanobacteria regulate heterotrophic activity. The cyanobacterium Leptolyngbya boryana grows heterotrophically with glucose in the dark. A dark-adapted variant dg5 isolated from the wild type (WT) exhibits enhanced heterotrophic growth in the dark. We sequenced the genomes of dg5 and the WT to identify the mutation(s) of dg5. The WT genome consists of a circular chromosome (6,176,364 bp), a circular plasmid pLBA (77,793 bp) and two linear plasmids pLBX (504,942 bp) and pLBY (44,369 bp). Genome comparison revealed three mutation sites. Phenotype analysis of mutants isolated from the WT by introducing these mutations individually revealed that the relevant mutation is a single adenine insertion causing a frameshift of cytM encoding Cyt c(M). The respiratory oxygen consumption of the cytM-lacking mutant grown in the dark was significantly higher than that of the WT. We isolated a cytM-lacking mutant, ΔcytM, from another cyanobacterium Synechocystis sp. PCC 6803, and ΔcytM grew in the dark with a doubling time of 33 h in contrast to no growth of the WT. The respiratory oxygen consumption of ΔcytM grown in the dark was about 2-fold higher than that of the WT. These results suggest a suppressive role(s) for Cyt cM in regulation of heterotrophic activity.

Identification of a cis‐acting element in nitrogen fixation genes recognized by CnfR in the nonheterocystous nitrogen‐fixing cyanobacterium Leptolyngbya boryana

“…Leptolyngbya boryana (formerly Plectonema boryanum ) IAM‐M101 strain dg5 (Hiraide et al ., ) was used as the WT. NK4 is a mutant derived from dg5 , where the cnfR gene is disrupted by a kanamycin resistance cartridge (Tsujimoto et al ., ).…”

In vivo transposon tagging in the nonheterocystous nitrogen‐fixing cyanobacterium Leptolyngbya boryana

“…Recently, we reported that the cytM gene-encoding cytochrome c M has a function to suppress heterotrophic growth ability in the dark. A single adenine insertion in cytM was identified as the responsible mutation by comparison between genome sequences of the WT and a spontaneous variant dg5 showing faster heterotrophic growth [21]. This was confirmed by the phenotype of a cytM-disrupted mutant that was isolated through a targeted mutagenesis technique [21].…”

The Effect of Two Amino acid Residue Substitutions via RNA Editing on Dark-operative Protochlorophyllide Oxidoreductase in the Black Pine Chloroplasts

“…The cyanobacterial mutant YFB14 lacking chlB 26 was derived from Leptolyngbya boryana (formerly Plectonema boryanum ) strain dg5 36 , which was used as the host strain to overexpress chlB variants. YFB14 was cultivated in BG-11 medium with 15 µg ml −1 kanamycin under medium-intensity light conditions (40 µmol photon m −2 s −1 ) using fluorescent lamps as described previously 16 .…”