Light induction of gene expression in Myxococcus xanthus

Abstract

The synthesis of carotenoids by Myxococcus xanthus requires illumination with blue light. Mutations at two loci (carA and carR) remove the blue-light requirement and cause constitutive production of carotenoids. Mutations at a different locus (car@) prevent carotenogenesis in both wild-type and constitutive mutant strains. We describe here three independent car mutations induced by insertion of Tn5 kac, a transposon that carries a transcriptional probe for exogenous promoters. All three transposon insertions block carotenogenesis even in constitutive mutant strains. One insertion is in a previously unknown cargene and the other two are in the carB locus. One ofthe carB insertions expresses -galactosidase at very low levels in the dark but is strongly activated by light. When this TnS. Iac insertion is introduced in carA or carR mutants it expresses -galac se in dark-as well as light-grown cells. We conclude that carotenogenesis in M. xanthus is activated at the level of transcription by a light-induced mechanism in which the carA and the carR loci (or their gene products) take part. The potential usefulness ofM. xanthus as a simple and sensitive tool for studies in photobiology is discussed.OD K1910 tcarR2) aoK2836(carB1)

A Repressor-Antirepressor Pair Links Two Loci Controlling Light-induced Carotenogenesis in Myxococcus xanthus

“…pMAR191 and pMAR192 were introduced into M. xanthus by electroporation, and integration of the plasmid was selected for on CTT plates containing 40 g/ml kanamycin. Expression of the reporter lacZ gene under the control of the 130-bp fragment was qualitatively monitored on CTT plates containing 40 g/ml 5-bromo-4-chloro-3-indolyl ␤-D-galactopyranoside (X-gal) and assessed quantitatively by measurements of ␤-galactosidase activity as described previously (27).…”

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

“…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).…”

A genetic link between light response and multicellular development in the bacterium Myxococcus xanthus.

“…xanthus strains, which carry gene lacZ fused transcriptionally to the promoter of carQRS, carB, or carC, have been obtained (Balsalobre et al 1987;Fontes et al 1993;Hodgson 1993). To understand better the function of carD, mutation carD1 was transferred to each of these strains.…”