Differential responses in EPA and fucoxanthin production by the marine diatom Stauroneis sp. under varying cultivation conditions

There has been an increasing drive toward better valorising raw biological materials in the context of the sustainability of bio-based industries and the circular economy. As such, microalgae hold the ability to biosynthesise valuable metabolites, which are sought after within the bioenergy, pharmaceuticals, cosmetics or nutrition sectors. Owing to their bioactivities, the xanthophyll pigment fucoxanthin and the omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA) have fostered increasing interests in terms of sustainably refining them from natural sources, such as microalgae. Together with the suitability of individual species to industrial cultivation, a key challenge resides in optimizing the yields of these compounds within the microalgal biomass they are retrieved from. The marine diatom Stauroneis sp. LACW24 was batch cultivated into its stationary phase of growth prior to being subjected at high cell density (1 × 10⁶ cells mL⁻¹) to seven different regimes of light exposure in replenished medium and under nutritional limitation (silica and nitrate) for 12 days. The highest EPA proportions and yields were obtained under blue LED in f/2 medium (16.5% and 4.8 mg g⁻¹, respectively), double the values obtained under red LED illumination. The fucoxanthin yield was the highest when cells were subjected to blue LEDs (5.9 mg g⁻¹), a fourfold increase compared to the nitrogen-limited treatment under white LEDs. These results indicate that a two-stage approach to the batch cultivation of this diatom can be used for enhancing the production of the high-value metabolites fucoxanthin and EPA post-stationary phase.     

Methylation of DNA by three N-nitroso compounds: evidence for sequence specific methylation by a common intermediate

Methylation in vitro of calf thymus DNA, a supercoiled plasmid, poly(dG).poly(dC), and poly(dGdC).poly(dGdC) by N-nitroso(acetoxy-methyl)methylamine and N-nitroso(acetoxybenzyl)methylamine in the presence of esterase, and by N-nitrosomethylurea was investigated. Although there were differences in the amounts of 7-methylguanine and O6-methylguanine formed in the various DNA substrates, the methylation pattern was the same for each of these methylating agents. The three compounds reacted identically when methylation of a portion of a 345 bp restriction fragment of the plasmid pBR322 was examined at nucleotide resolution by a sequencing assay. They also showed a tendency to react preferentially with particular guanines. These data suggest that the three N-nitroso compounds methylate DNA via a common intermediate such as the methyl diazonium ion, which exhibits some sequence specificity.     

Photosynthetic regeneration of ATP using bacterial chromatophores

We have demonstrated the use of bacterial chromatophores for the continuous photosynthetic regeneration of ATP from ADP in an ultrafiltration reactor. Biphasic kinetics of the degradation of chromatophore activity are described. Using chromatophores in combination with the enzyme adenylate kinase, we have also demonstrated continuous regeneration of ATP from AMP.     

Molecular biology of spiroplasma plasmids

With one exception, all spiroplasma strains examined contained extrachromosomal DNA, most of which was in the form of covalently closed circular plasmids. One plasmid, pIJ2000, carried by Spiroplasma citri strain ASP-1, was purified and characterized and used to probe for related plasmids in other strains. Unsuccessful attempts were made to clone pIJ2000 into Escherichia coli using the vectors pAT153 and pBR322. However, spiroplasma chromosomal DNA fragments could be cloned without difficulty.     

The isolation of Ant1, a transposable element from Aspergillus niger

A transposable element has been isolated from the industrially important fungus Aspergillus niger (strain N402). The element was identified as an insertion sequence within the coding region of the nitrate reductase gene. It had inserted at a TA site and appeared to have duplicated the target site upon insertion. The isolated element was found to be 4798 by in length and contained 37-bp inverted, imperfect, terminal repeats (ITRs). The sequence of the central region of the element revealed an open reading frame (designated ORF1) which showed similarity, at the amino acid level, to the transposase of the Tc1/mariner class of DNA transposons. Another sequence within the central region of the element showed similarity to the 3′ coding and downstream untranslated region of the amyA gene of A. niger. Sequence homology and structural features indicate that this element, which has been named Ant1 (A. niger transposon 1), is related to the Tc1/mariner group of DNA transposons. Ant1 is apparently present as a single copy in strain N402 of A. niger.     

Gelation of sugarbeet and citrus pectins using enzymes extracted from orange peel

Sugarbeet pectin is shown to form gels in the presence of calcium using an enzyme preparation extracted from orange peel. The gels were transparent and exhibited no syneresis. The mechanism of gelation is chain association arising from both lowered pectin solubility and from formation of a limited network of calcium-linked junction zones. The gelation reaction involves limited pectin demethoxylation, the release of acetate presumably from C-2 or C-3 of galacturonyl residues, and a decrease in pH. The enzymes responsible are pectinesterase (EC 3.1.1.11) and pectin acetylesterase. We suggest that the latter is a novel activity associated with triacetin acetylesterase (EC 3.1.1.6). The gels are compared to citrus pectin gels made in the same way.     

Detection of mycotoxins in foodstuffs by use of chick embryos

A method of extracting fungal cultures with aqueous methanol and hexane is described. The extract from 100 grams of foodstuff, or pure fungal cultures on cereals (maize, wheat and rye), was inoculated into groups of twenty fertile hens eggs, both into the air sac and into the yolk, which were then incubated through to hatch at twenty-two days. The results show good sensitivity to aflatoxin and sporidesmin. The fungal cultures are recorded as toxic (below 50% hatch) non toxic (above 68% hatch) and doubtful. Five isolates ofAspergillus repens isolated from one batch of mouldy hay gave a high (43%) incidence of deformed embryos. This method is suggested as a general biological test for toxicity in foodstuffs.     

Growth of Listeria monocytogenes at refrigeration temperatures

The growth of three strains of Listeria monocytogenes at refrigeration temperatures (-0.5 to 9.3°C) in chicken broth and/or UHT milk was determined using a rocking temperature gradient incubator. Minimum growth temperatures ranged from -0.1 to -0.4°C for the three strains. Lag times of 1–3 d and 3 to >34 d were observed with incubation at 5 and 0°C respectively. Corresponding generation times ranged from 13–24 h at 5°C and 62–131 h at 0°C. The type of culture medium had an influence on both the rate and extent of growth. Incubation of cultures at 4°C before inoculation caused a marked reduction in the lag time when compared with cultures which had been previously incubated at 30°C.