Synthesis by bacteria

West and Wilson (409) showed that riboflavin was synthesized by Rhizo-bia, but there were indications that initiation of growth with a washed inoculum was difficult or impossible unless some riboflavin was present in the medium. This is a situation similar to the need for CO2 in the initiation of growth by various organisms which produce ample COj when once active metabolism has ) egun (106). West and Wilson observed that the concentration range of riboflavin and of thiamin which was effective in initiating 

The specificity of riboflavin in bacterial growth has been examined by Snell and Strong (362) using Lactobacillus casei and B. lactis acidi (both of which require riboflavin) and using a number of synthetic flavins, including — 

7-Dimethyl-9-(d-l -arabityl)-isoalloxazine VL 6,7-Dimethyl-9- (Z- T-arabityl) -isoalloxazine 

Snell and Strong compared the activity of these riboflavin analogs with their reported activities as vitamin B2 by rat assay and in Kuhn and Rudy s enzyme tests (174). The correlation was close, analogs inactive for the 

Snell and Strong (363, 364) developed the growth response of Lactobacillus casei to riboflavin as an assay method, and it was soon used, for example by Fraser, Topping, and Isbell (102) to assay riboflavin in the urine and tissues of normal and riboflavin-deficient dogs. The microbiological riboflavin assay has since been widely used e.g., 394). 

Some of the most recent work which has been recorded in this review has thrown new light upon the problem of the biosynthesis of ascorbic acid. Until recently the pathway whereby ascorbic acid is formed from sugars was one of almost complete speculation. Now, with knowledge of some of the possible intermediates and with the demonstration of the i thesis of ascorbic acid by enzymes in vitro, it would seem that new 

This review was prepared as part of the program of the Food Investigation Organization of the Department of Scientific and Industrial Research, Cambridge, England. 

Bernhauer, K. 1940. In Handbuchder Enzymologie, Vol. 2,1662. Akad. Verlagi es., Liepzig. 

McCarrison, R. 1919. Sutnmarized in Studies of Deficiency Disease. Oxford Medical Publication, Oxford, 1921. 

Polytech. Osaka City Univ. 2, 1-7. 

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Enzyme Formation and Polysaccharide Synthesis by Bacteria. III. Polysaccharides Produced by Nitrogen-fixing Organisms, W. A. Cooper, W. D. Daker, and M. Stacey, Biochem. J., 32 (1938) 1752-1758. 

Both sulfonamides and trimethoprim (not a sulfonamide) sequentially interfere with folic acid synthesis by bacteria. Folic acid functions as a coenzyme in the transfer of one-carbon units required for the synthesis of thymidine, purines, and some amino acids and consists of three components a pteridine moiety, PABA, and glutamate (Fig. 44.1). The sulfonamides, as structural analogues, competitively block PABA incorporation sulfonamides inhibit the enzyme dihydropteroate synthase, which is necessary for PABA to be incorporated into dihydropteroic acid, an intermediate compound in the formation of folinic acid. Since the sulfonamides reversibly block the synthesis of folic acid, they are bacteriostatic drugs. Humans cannot synthesize folic acid and must acquire it in the diet thus, the sulfonamides selectively inhibit microbial growth. 

Kirchman, D.L., K Nees, E., and Hodson, R. (1985) Leucine incorporation and its potential as a measure of protein synthesis by bacteria in natural aquatic systems. Appl. Environ. Microbiol. 49, 599-607. 

The term PHA (Figure 9.1) is applied to a family of polyesters accumulated by various bacteria, deposited in the cells in the form of highly refractive granules of carbon reserve, energy and reducing equivalents. " In general, PHA synthesis by bacteria in a nutrient medium occurs when there is an excess of carbon source and a lack of one necessary nutrient at least (N, P, Mg, Fe etc.) for cell multiplication. ... 

There is no published evidence that biotin can be synthesized by mammals thus, the higher animals must derive biotin from other sources. The ultimate source of biotin appears to be de novo synthesis by bacteria, primitive eukaryotic organisms such as yeast, moulds, and algae, and some plant species. 

The phenomenon of vitamin synthesis by bacteria presents important considerations in the nutrition of man. Its full significance, however, should await a more complete knowledge of the human need for the B vitamins than we now possess. At the present time, we are certain that at least part of our requirements are furnished by bacterial action in the intestines. It is, therefore, comforting to know that we can at least rely to some extent on this mechanism to supplement the average American diet should the ever persistent vitamin vendor fail in his benevolent task. 

It has been known for some time that tetracyclines are accumulated by bacteria and prevent bacterial protein synthesis (Fig. 4). Furthermore, inhibition of protein synthesis is responsible for the bacteriostatic effect (85). Inhibition of protein synthesis results primarily from dismption of codon-anticodon interaction between tRNA and mRNA so that binding of aminoacyl-tRNA to the ribosomal acceptor (A) site is prevented (85). The precise mechanism is not understood. However, inhibition is likely to result from interaction of the tetracyclines with the 30S ribosomal subunit because these antibiotics are known to bind strongly to a single site on the 30S subunit (85). 

The fluoroquinolones exert their bactericidal (bacteria-destroying) effect by interfering with an enzyme (DNA gyrase) needed by bacteria for the synthesis of DNA. 

Finally, the synthesis of biodegradable poly(hydroxyalkanoic acids) (PHA) by bacteria or genetically modified plants should be mentioned. The microbiology, biochemistry, and genetics of PHA biosynthesis have been reviewed by several authors52,105,405 407 and are beyond the scope of this chapter. 

The process of RNA synthesis in bacteria—depicted in Figure 37-3—involves first the binding of the RNA holopolymerase molecule to the template at the promoter site to form a PIC. Binding is followed by a conformational change of the RNAP, and the first nucleotide (almost always a purine) then associates with the initiation site on the 3 subunit of the enzyme. In the presence of the appropriate nucleotide, the RNAP catalyzes the formation of a phosphodiester bond, and the nascent chain is now attached to the polymerization site on the P subunit of RNAP. (The analogy to the A and P sites on the ribosome should be noted see Figure... 

Feedback inhibition of amino acid transporters by amino acids synthesized by the cells might be responsible for the well known fact that blocking protein synthesis by cycloheximide in Saccharomyces cerevisiae inhibits the uptake of most amino acids [56]. Indeed, under these conditions, endogenous amino acids continue to accumulate. This situation, which precludes studying amino acid transport in yeast in the presence of inhibitors of protein synthesis, is very different from that observed in bacteria, where amino acid uptake is commonly measured in the presence of chloramphenicol in order to isolate the uptake process from further metabolism of accumulated substances. In yeast, when nitrogen starvation rather than cycloheximide is used to block protein synthesis, this leads to very high uptake activity. This fact supports the feedback inhibition interpretation of the observed cycloheximide effect. 

Mode of action Interferes with bacterial cell wall synthesis during active multiplication, causing cell wall death and resultant bactericidal activity Inhibits bacterial cell wall synthesis by binding to one or more of the penicillin-binding proteins, which in turn inhibit the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls bacteria usually lyse from ongoing autolytic enzyme activity... 

The answer is b. (Hardman, p 1159.) Rifampin inhibits RNA synthesis in bacteria, mycobacteria, and chlamydiae by binding to the DNA-de pen dent RNA polymerase it also inhibits assembly of poxvirus particles. Rifampin is used as a single prophylactic agent for contacts of people with meningococcal or H. influenzae type b infections. Otherwise, it is not used alone because 1 in 10 organisms in a population exposed to rifampin will become resistant, possibly because of mutation or a barrier against rifampin s entry into cells. 

The answer is b. (Hardman, p 1061.) Sulfasalazine consists of sul-fapyridine with 5-aminosalicylic acid linked by an azo- bond. This bond is broken by bacteria that release the salicylic acid, which is believed to be the active agent. Sulfa drugs or salicylic acid used alone is not as effective. The mechanism of action is unknown, but it is believed to be protective action on the mucosa by inhibition of the synthesis of prostaglandins and leukotrienes. 

I. F. Nes V. G. H. Eijsink, Regulation of Group II Peptide Bacteriocin Synthesis by Quorum-Sensing Mechanisms. In Cell-Cell Signaling In Bacteria] G. M. Dunny, S. C. Winans, Eds. ASM Press Washington, DC, 1999 pp 175-192. 

Donald Woods discovered that sulphonamides exerted their action by inhibiting an enzyme used by bacteria to synthesise folic acid. The compound 4-aminobenzoic acid is the precursor for folic acid, and is structurally similar to sulphonamide. Bacteria that were unable to synthesise folic acid were unable to achieve de novo synthesis of purines for their DNA and RNA synthesis and hence could not proliferate. Such competitive inhibitors, which mimicked normal metabolites, became known as antimetabolites (many are used in cancer chemotherapy. Chapter 21). 

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