Publisher Summary This chapter presents the chemistry and antimicrobial activity of the saturated straight-chain monocarboxylic acids, and reference is made, where appropriate, to derivatives of this group— for example, unsaturated (cinnamic, sorbic), hydroxylic (citric. lactic), phenolic (benzoic, cinnamic, salicylic) and multicarboxylic (azelaic, citric, succinic) acids. Organic acids are distinguished from other acids by the functional group COOH to which an organic group or a hydrogen atom may be attached. Common names used to describe this group of organic compounds include fatty, volatile fatty, lipophilic, weak, or carboxylic acids. There is no standard protocol for studying the antimicrobial activity of organic acids and many reports give only the pH value of the solution under test without indicating the concentration of the acid, thus making evaluation of the results difficult or impossible. In addition, it is difficult to compare the activity of different acids because it is influenced by the physical chemistry of the microbial species, the growth conditions, and the phase of growth. The chapter discusses two aspects of the use of organic acids: in animal husbandry as animal feed additives and in abattoirs and food-processing plants where they may be used in controlling microbial contamination of carcass meat.

Organic acids: chemistry, antibacterial activity and practical applications.

Growth of bacteria and fungi on fatty acid substrates requires the catabolic beta-oxidation cycle and the anaplerotic glyoxylate cycle. Propionyl-CoA generated by beta-oxidation of odd-chain fatty acids is metabolized via the methylcitrate cycle. Mycobacterium tuberculosis possesses homologues of methylcitrate synthase (MCS) and methylcitrate dehydratase (MCD) but not 2-methylisocitrate lyase (MCL). Although MCLs share limited homology with isocitrate lyases (ICLs) of the glyoxylate cycle, these enzymes are thought to be functionally non-overlapping. Previously we reported that the M. tuberculosis ICL isoforms 1 and 2 are jointly required for growth on fatty acids, in macrophages, and in mice. ICL-deficient bacteria could not grow on propionate, suggesting that in M. tuberculosis ICL1 and ICL2 might function as ICLs in the glyoxylate cycle and as MCLs in the methylcitrate cycle. Here we provide biochemical and genetic evidence supporting this interpretation. The role of the methylcitrate cycle in M. tuberculosis metabolism was further evaluated by constructing a mutant strain in which prpC (encoding MCS) and prpD (encoding MCD) were deleted. The DeltaprpDC strain could not grow on propionate media in vitro or in murine bone marrow-derived macrophages infected ex vivo; growth under these conditions was restored by complementation with a plasmid containing prpDC. Paradoxically, bacterial growth and persistence, and tissue pathology, were indistinguishable in mice infected with wild-type or DeltaprpDC bacteria.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2958.2006.05155.x

Role of the methylcitrate cycle in Mycobacterium tuberculosis metabolism, intracellular growth, and virulence

Even though significant advances have been made in understanding microbial diversity, most microorganisms are still only characterized by 'molecular fingerprints' and have resisted cultivation. Many different approaches have been developed to overcome the problems associated with cultivation of microorganisms because one obvious benefit would be the opportunity to investigate the previously inaccessible resources that these microorganisms potentially harbour.

Tapping into microbial diversity

There are many factors that affect denitrification and these have been reviewed by Delwiche and Bryan (1976), Payne (1981), and Knowles (1982). None of these authors have provided an in-depth review of the critical role of organic carbon in the denitrification process. Organic carbon availability is one of the most important factors that affects denitrifying activity in soil, yet the chemistry of soil organic matter is only partially understood and its complexity has probably inhibited studies. A readily available C substrate is often added to denitrifying systems in the laboratory to ensure an electron supply when other variables are studied.

Carbon Sources for Bacterial Denitrification

Sporulation of the baker's yeast Saccharomyces cerevisiae is a response to nutrient depletion that allows a single diploid cell to give rise to four stress-resistant haploid spores. The formation of these spores requires a coordinated reorganization of cellular architecture. The construction of the spores can be broadly divided into two phases. The first is the generation of new membrane compartments within the cell cytoplasm that ultimately give rise to the spore plasma membranes. Proper assembly and growth of these membranes require modification of aspects of the constitutive secretory pathway and cytoskeleton by sporulation-specific functions. In the second phase, each immature spore becomes surrounded by a multilaminar spore wall that provides resistance to environmental stresses. This review focuses on our current understanding of the cellular rearrangements and the genes required in each of these phases to give rise to a wild-type spore.

Ascospore formation in the yeast Saccharomyces cerevisiae

https://mmbr.asm.org/content/mmbr/32/1/1.full.pdf

Alternate pathways of metabolism of short-chain fatty acids.

Publisher Summary This chapter discusses the assays of enzymes of the tricarboxylic acid and glyoxylate cycles. The photometric and spectrophotometric assay methods combine the most desirable advantages: simplicity, rapidity, sensitivity, specificity, and the fact that they can be used to assay relatively crude preparations of each enzyme. The aerobic oxidation of acetate to carbon dioxide is catalyzed by a series of discrete enzymatic reactions collectively referred to as the “tricarboxylic acid cycle.” The purified enzyme is conveniently assayed by determining the formation of citrate from oxaloacetate and acetyl-S-CoA either colorimetrically or enzymatically.

Chapter X Assays of Enzymes of the Tricarboxylic Acid and Glyoxylate Cycles

https://science.sciencemag.org/content/sci/150/3703/1548.full.pdf

Glyoxylate in Fatty-Acid Metabolism

Propionate oxidation in Escherichia coli

Propionate metabolism: III. Studies on the significance of the α-hydroxyglutarate pathway☆

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