Azo dyes are widely used in the textile, printing, paper manufacturing, pharmaceutical, and food industries and also in research laboratories. When these compounds either inadvertently or by design enter the body through ingestion, they are metabolized to aromatic amines by intestinal microorganisms. Reductive enzymes in the liver can also catalyze the reductive cleavage of the azo linkage to produce aromatic amines. However, evidence indicates that the intestinal microbial azoreductase may be more important than the liver enzymes in azo reduction. In this article, we examine the significance of the capacity of intestinal bacteria to reduce azo dyes and the conditions of azo reduction. Many azo dyes, such as Acid Yellow, Amaranth, Azodisalicylate, Chicago Sky Blue, Congo Red, Direct Black 38, Direct Blue 6, Direct Blue 15, Direct Brown 95, Fast Yellow, Lithol Red, Methyl Orange, Methyl Red, Methyl Yellow, Naphthalene Fast Orange 2G, Neoprontosil, New Coccine, Orange II, Phenylazo-2-naphthol, Ponceau 3R, Ponceau SX, Red 2G, Red 10B, Salicylazosulphapyridine, Sunset Yellow, Tartrazine, and Trypan Blue, are included in this article. A wide variety of anaerobic bacteria isolated from caecal or fecal contents from experimental animals and humans have the ability to cleave the azo linkage(s) to produce aromatic amines. Azoreductase(s) catalyze these reactions and have been found to be oxygen sensitive and to require flavins for optimal activity. The azoreductase activity in a variety of intestinal preparations was affected by various dietary factors such as cellulose, proteins, fibers, antibiotics, or supplementation with live cultures of lactobacilli.

A DNA-mediated transformation system for the blue-green alga Agmenellum quadruplicatum, strain PR-6, is described and characterized for DNA concentration dependence, dependence on time of exposure to DNA, phenotypic expression, sensitivity to various enzymes, and competence. The stability of the transformants has been investigated, and genetic backcross and selfing experiments have been performed. This system fulfills all of the criteria established for the well-characterized transformation systems in heterotrophic bacteria and demonstrates significant similarities to at least one of these systems for all characteristics examined. The efficiency of transformation is high. This system fills a need for a well-characterized genetic system in an oxygen-evolving photoautotroph. We have used it to transform a strain with a mutational lesion in assimilatory nitrogen metabolism to a wild-type genotype. The blue-green algae (cyanobacteria) provide an excellent model system for the study of photoautotrophic metabolism. They carry out oxygen-evolving photosynthesis and assimilate oxidized nitrogen in a fashion similar to that of higher plants and are amenable to many of the techniques utilized in the study of heterotrophic bacteria. A limiting factor in studying the metabolism of these organisms has been the lack of a system for genetic exchange. Although there have been reports of genetic exchange in blue-green algae (reviewed in ref. 1), only the transformation system in Anacystis nidulans has been reasonably well characterized (2, 3).We have found that the blue-green alga Agmenellum quadruplicatum, strain PR-6, possesses an efficient, naturally occurring mechanism for the uptake and integration of exogenous DNA in a process like transformation in other bacteria (4). Here we characterize this system for sensitivity to DNase, dependence on concentration of DNA, dependence on time of exposure of cells to DNA, competence, and expression of newly incorporated genetic material. The PR-6 transformation system is similar to the standard heterotrophic bacterial transformation systems in all respects thus far tested.We also describe an initial experiment wherein a physiologically well-characterized mutant of PR-6, called AQ-6 (5-8), was transformed with parental DNA. AQ-6 reduces nitrate to nitrite but its reduction of nitrite is impaired, resulting in the accumulation of nitrite in the medium. The mutant grows normally in the presence of ammonia. After transformation at least two colonial phenotypes were recovered. Genetic dissection of inorganic nitrogen assimilation in blue-green algae is now feasible. Growth and cell concentration of PR-6 and AQ-6 were routinely measured turbidimetrically with a Spectronic 20 colorimeter at 550 nm. An average concentration of 4.2 X 107 cells per ml was indicated by an optical density of 0.82 in a 22-mm culture tube. MATERIALS AND METHODSDNA Preparation. DNA from and from a streptomycin-resistant derivative (see below) were purified by the procedure of Marmur (11).Standard Transforma...

Poly- ,-hydroxybutyrate has been identified in the cyanobacterium Spirulina platensis. The addition of reduced carbon compounds to the growth medium was not required for poly-,B-hydroxybutyrate accumulation. Poly-P-hydroxybutyrate accumulated during exponential growth to 6% of the total dry weight and then decreased during the stationary phase.