Novel avermectins produced by mutational biosynthesis.

Avermectins with a wide range of novel C-25 substituents have been prepared by feeding carboxylic acids or their biosynthetic precursors to a Streptomyces avermitilis mutant strain ATCC 53568. This organism lacks the ability to form isobutyric and S-2-methylbutyric acids from their 2-oxo acid precursors and thus is unable to produce natural avermectins unless supplied with these acids. The novel avermectins produced by mutational biosynthesis possess broad-spectrum antiparasitic activity.

Automatic on-line fermentation headspace gas analysis using a computer-controlled gas chromatograph.

A computer-controlled headspace gas chromatograph was used to monitor the progress of ethanol production from both aerobic batch and anaerobic continuous fermentations. Using an automatic, electropneumatic sampling system, aliquots of fermentation headspace gas were injected directly onto the column for quantitative ethanol determinations every six minutes. A sample volume of 1 mL permitted liquid ethanol concentrations from 2 to 100 g/L to be measured with better than 3% standard deviation on five repeated injections. Provided fermenter liquid temperature and ionic strength were maintained constant, the signal-tohyphen;concentration ratio remained linear to 80 g/L ethanol. This quantitative gas chromatographic (GC) method is suitable for accurate, precise analysis of multiple solvent fermentations, and is limited only by the elution rate and separating capacity of the GC column.

A rational approach to the fixation of peptidergic nerve cell bodies in the gut using parabenzoquinone.

Study of the possible chemical mechanisms by which parabenzoquinone acts as a fixative in the localisation of neuronal peptides by immunohistochemistry suggested several possible improvements to standard techniques. In particular, by using favourable conditions for regenerative oxidation reactions, i.e. fixing at 37 degrees C in well oxygenated, slightly alkaline buffer, it was possible to improve the localisation of substance P-, vasoactive intestinal polypeptide-, enkephalin- and somatostatin-like immunoreactive peptides such that nerve cell bodies were routinely visualised without the use of drugs to block axonal transport. Application of the improved fixation method is likely to facilitate study of the organisation of peptidergic systems.

Extremely thermophilic acidophilic bacteria convergent with Sulfolobus acidocaldarius.

A series of extremely thermophilic acidophilic bacteria has been characterized as closely resembling the species Sulfolobus acidocaldarius except for a totally different guanosine-cytosine content in the DNA; some conceptual consequences of this situation are discussed. Both organisms also share special features, including a very characteristic type of ether lipid, with other extreme acidophilic thermophiles.

Ultrastructure of an extremely thermophilic acidophilic micro-organism.

A thermoacidophilic micro-organism, isolated from volcanic hot springs near Naples, was cultivated in vitro, and examined by electron microscopy in sections and after negative staining. The cells were almost spherical, with a diameter of about 0.7 to 1.0 mum. Their morphology was very primitive: the protoplasm was composed only of ground cytoplasm, ribosomes, and randomly distributed DNA strands. They were surrounded by a plasma membrane and by an extracellular coat about 20 nm thick which displayed a regular hexagonal pattern. Cell replication occurred by binary fission with median constriction during which a bipolar localization of nuclear material was observable. The morphology is compared with that of other known micro-organisms living in similar habitats.

Effects of pH and temperature on the fatty acid composition of bacillus acidocaldarius.

The fatty acid composition of lipid extracts from cells of Bacillus acidocaldarius grown at temperatures of 50 to 70 C and pH values of 2 to 5 was determined by gas chromatography of the methyl esters. The most abundant fatty acids are 11-cyclohexylundecanoic and 13-cyclohexyltridecanoic, followed by anteiso- and iso-heptadecanoic; unsaturated acids are absent. Highly aerated cultures produce more of the iso and anteiso acids and less of the cyclohexyl acids. The effects of temperature and pH are interdependent; at lower pH, increasing temperature raises the proportion of the iso and anteiso acids, but at higher pH the effect of increasing temperature is reversed and the proportion of the cyclohexyl acids is increased.

The formation of -cyclohexyl-fatty acids from shikimate in an acidophilic thermophilic bacillus. A new biosynthetic pathway.

Labelled acetate, phenylalanine and shikimic acid were fed to Bacillus acidocaldarius. A high proportion of the (14)C incorporated from acetate and shikimate was recovered in methyl esters from the cell lipids, but such recovery of (14)C from phenylalanine was low. Only the (14)C from shikimate was selectively incorporated into 11-cyclohexylundecanoate and 13-cyclohexyltridecanoate. Degradation of these cyclohexyl-fatty acids showed that shikimate was incorporated as an intact C(7) unit.