Structure, function and biosynthesis of carotenoids in the moderately halophilic bacterium Halobacillus halophilus

Abstract

Inhibitor studies and mutant analysis revealed a C(30) pathway via 4,4'-diapophytoene and 4,4'-diaponeurosporene to 4,4'-diaponeursoporene-4-oic acid esters related to staphyloxanthin in Halobacillus halophilus. Six genes may be involved in this biosynthetic pathway and could be found in two adjacent gene clusters. Two genes of this pathway could be functionally assigned by functional pathway complementation as a 4,4'-diapophytoene synthase and a 4,4'-diapophytoene desaturase gene. These genes were organized in two operons together with two putative oxidase genes, a glycosylase and an acyl transferase ortholog. Pigment mutants were obtained by chemical mutagenesis. Carotenoid analysis showed that a white mutant accumulated 4,4'-diapophytoene due to a block in desaturation. In a yellow mutant carotenogenesis was blocked at the stage of 4,4'-diaponeurosporene and in an orange mutant at the stage of 4,4'-diaponeurosporene-4-oic acid. The protective function of these pigments could be demonstrated for H. halophilus after inhibition of carotenoid synthesis by initiation of oxidative stress. A degree of oxidative stress which still allowed 50% growth of carotenogenic cells resulted in the death of the cells devoid of colored carotenoids.

Hydroxy-3,4-dehydro-apo-8′-lycopene and methyl hydroxy-3,4-dehydro-apo-8′-lycopenoate, novel C30 carotenoids produced by a mutant of marine bacterium Halobacillus halophilus

“…10,11 In addition, the identification of intermediate 1 without terminal end-group oxidation excludes the possibility that apo-8¢ products are derived by cleavage of C 40 carotenoids at position 8¢. Therefore, we propose that the C 30 pathway in H. halophilus initially starts with apo-8¢ phytoene by condensation of C 20 geranylgeranyl pyrophosphate (GGPP) with C 10 geranyl pyrophosphate (GPP).…”

“…The parent strain, the carotenoid gene cluster of which was recently elucidated, 10 produces methyl glucosyl-3,4-dehydroapo-8¢-lycopenoate, whereas both 1 and 2 were deglucosylated carotenoids; therefore, OC1 should have a mutation in a gene encoding a glucosylase, which is responsible for the glucosylation of 1. The prominent candidate gene for glucosidation is orf-AT in the carotenogenic gene cluster of H. halophilus.…”

“…10 Due to the ratio of about 5:1 between 1 and 2, it can be assumed that in the parent strain, compound 1 is the preferred substrate for the glucosylase and that terminal oxidation to a carboxylic group typically proceeds with glucosyl-3,4-dehydro-apo-8¢-lycopene as the original substrate for the CrtNb-like enzyme (Figure 3). Both 1 and 2 possessed 1 O 2 suppression (antioxidative) activity (IC 50 79 and 44 mM, respectively), but their activities were not so potent as methyl glucosyl-3,4-dehydro-apo-8¢-lycopenoate (IC 50 5.1 mM).…”

Identification of the Bacteriochlorophylls, Carotenoids, Quinones, Lipids, and Hopanoids of "Candidatus Chloracidobacterium thermophilum"

“…Both echinenone and canthaxanthin are xanthophylls and possess 4-keto group(s) on their rings. Xanthophyll carotenoids have been shown to play roles in photoprotection in other microorganisms (34,40,61,78). In particular, echinenone might be involved in protection against peroxide radicals (36,37,57).…”

Bioenergetics of the Moderately Halophilic Bacterium Halobacillus halophilus: Composition and Regulation of the Respiratory Chain

“…Genome-wide expression analyses in nonhalophilic bacteria, such as Escherichia coli (7) and Bacillus subtilis (8,9), or the methanogenic archaeon Methanosarcina mazei (10), revealed upregulation of many different cellular functions, including protective pathways, such as solute transport and biosynthesis, import of phosphate, export of Na ϩ , and upregulation of pathways for modification of DNA and cell surface architecture. In its natural environment, the salt marshes, exposure to sunlight creates an additional stress for H. halophilus that is combated by carotenoids (11). Exposure to sunlight also leads to evaporation of water, which has two important consequences: first, the salinity increases, and second, since the solubility of gases is dependent on the salinity, the consequence is a reduced availability of oxygen at high salinities.…”