Growth phase dependence of the activation of a bacterial gene for carotenoid synthesis by blue light.

Abstract

Myxococcus xanthus responds to blue light by producing carotenoid pigments. A mutation at a gene named carC is known to block the metabolism of phytoene, a carotenoid precursor, and this gene has now been cloned and sequenced. We show here that gene carC, which is homologous to phytoene dehydrogenase genes from other organisms, is tightly regulated by light through a mechanism that operates only when the cells have reached the stationary phase or are starved of a carbon source. A genetic element that mediates the effect of the growth phase has been identified. Gene carC is integrated with another unlinked carotenogenic gene in a single ‘light regulon’ controlled by common trans‐acting genetic elements. A potential −35 site for the binding of sigma factors has been found upstream of the carC transcriptional start. However, the −10 region shows no similarity with analogous sites at promoters of other Gram‐negative bacteria.

A Cluster of Structural and Regulatory Genes for Light‐Induced Carotenogenesis in Myxococcus xanthus

“…Strain MR151 carries a mutation that causes synthesis of carotenoids in the dark (Martinez-Laborda et al, 1990). Strain MR7 carries the ultraviolet-induced mutation carAI, which affects light-regulation of car genes (MartinezLaborda and Murillo, 1989;Fontes et al, 1993). Media and culture conditions were as in Fontes et al (1993).…”

“…A Tn5 insertion at this gene (QMR478, Fig. 2) is known to cause the accumulation of the two carotene precursors, lycopene and 3,4-dehydro-rhodopin, which are the substrates for the cyclization reaction taking place at one or the other branch of the carotenoid pathway (Ruiz-Vazquez et al, 1993; Fig. 1).…”

“…The carA mutation (carAI) results in a complex phenotype: it causes expression of carB in the dark while greatly reducing light stimulation of the unlinked (phytoene dehydrogenase) gene carC. Thus, carA seemed to play a dual function, acting as a negative regulator of the curB promoter in the dark and a positive regulator of the carC promoter in the light (Balsalobre et al, 1987;Fontes et al, 1993).…”

“…Mutation carAI causes both constitutive expression from the curB promoter and reduced activation of the carC promoter (MartinezLaborda and Murillo, 1989;Fontes et al, 1993). According to the sequence analysis, two genes which presumably code for DNA-binding proteins are present at the 3' end of the carA-carE gene cluster.…”

Growth and Carotenoid Production ofThraustochytriumsp. CHN-1 Cultured under Superbright Red and Blue Light-emitting Diodes

“…and behavioral processes both in plants and in prokaryotic and eukaryotic micro-organisms. 12) More detailed examination of blue LED the effects on the mechanisms of astaxanthin production will be necessary in the future study. .…”