Increased sensitivity of the microbiological assay for biotin by Lactobacillus plantarum

Transfer of the high-GC cyclohexane carboxylate degradation pathway from Rhodopseudomonas palustris to Escherichia coli for production of biotin

This work demonstrates the transfer of the five-gene cyclohexane carboxylate (CHC) degradation pathway from the high-GC alphaproteobacterium Rhodopseudomonas palustris to Escherichia coli, a gammaproteobacterium. The degradation product of this pathway is pimeloyl-CoA, a key metabolite in E. coli's biotin biosynthetic pathway. This pathway is useful for biotin overproduction in E. coli; however, the expression of GC-rich genes is troublesome in this host. When the native R. palustris CHC degradation pathway is transferred to a DeltabioH pimeloyl-CoA auxotroph of E. coli, it is unable to complement growth in the presence of CHC. To overcome this expression problem we redesigned the operon with decreased GC content and removed stretches of high-GC intergenic DNA which comprise the 5' untranslated region of each gene, replacing these features with shorter low-GC sequences. We show this synthetic construct enables growth of the DeltabioH strain in the presence of CHC. When the synthetic degradation pathway is overexpressed in conjunction with the downstream genes for biotin biosynthesis, we measured significant accumulation of biotin in the growth medium, showing that the pathway transfer is successfully integrated with the host metabolism.

Enterotoxigenic intestinal bacteria in tropical sprue. IV. Effect of linoleic acid on growth interrelationships of Lactobacillus acidophilus and Klebsiella pneumoniae

The factors responsible for colonization of the small intestine by enterotoxigenic coliform bacteria in Puerto Ricans with tropical sprue are unknown, but epidemiological observations have suggested that they may be related to an increased dietary intake of long-chain unsaturated fatty acids, particularly linoleic acid, which is known to exert an inhibitory effect on the growth of gram-positive organisms that normally comprise the flora of the small intestine. We have examined, by using a glucose-limited continuous-culture system, what effect this fatty acid exerts on the growth relationships of enteric gram-positive and coliform bacteria. In this system, colonization by an invading strain of Klebsiella pneumoniae was prevented by the presence of an established culture of Lactobacillus acidophilus, principally by virtue of a lowered pH of the medium that was incompatible with Klebsiella growth. However, when the population density of L. acidophilus was reduced by the presence of a sufficient concentration of linoleic acid, the invading K. pneumoniae successfully colonized the system and, once established, suppressed the growth of L. acidophilus. These observations indicate that, under the conditions of our chemostat, gram-positive enteric bacteria suppress coliform growth and that this effect is reversible by the presence of linoleic acid. It remains to be established, however, what pertinence these in vitro observations have to conditions within the intestinal tract of persons living in the tropics.

Biotin production and utilization in a sewage treatment lagoon

Biotin, in a sewage oxidation lagoon also receiving potato processing wastes, was observed to increase two logs during the summer period of waste stabilization and then to decline to near earlier concentrations. Three organisms, Aerobacter aerogenes, Chlorella vulgaris, and Thiocapsa floridana, were at least partially responsible for these fluctuations; the latter two organisms were associated with biotin utilization and the former with biotin production. Since copious quantities of biotin are produced in these waste treatment facilities, the vitamin may act as a useful indicator of microbial action on certain organic molecules, especially in domestic and industrial wastes such as those from municipalities and potato and sugar beet processing plants. Furthermore, the presence of biotin in rivers and streams may be indicative of the discharge of incompletely stabilized wastes from these sources.