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Other types of lipids can also be degraded by certain microbes. For example, the ability of certain pathogens, like Mycobacterium tuberculosis , to degrade cholesterol contributes to their virulence. The side chains of cholesterol can be easily removed enzymatically, but degradation of the remaining fused rings is more problematic. The four fused rings are sequentially broken in a multistep process facilitated by specific enzymes, and the resulting products, including pyruvate, can be further catabolized in the Krebs cycle.
Proteins are degraded through the concerted action of a variety of microbial protease enzymes. Extracellular proteases cut proteins internally at specific amino acid sequences, breaking them down into smaller peptides that can then be taken up by cells. Some clinically important pathogens can be identified by their ability to produce a specific type of extracellular protease. For example, the production of the extracellular protease gelatinase by members of the genera Proteus and Serratia can be used to distinguish them from other gram-negative enteric bacteria. Following inoculation and growth of microbes in gelatin broth, degradation of the gelatin protein due to gelatinase production prevents solidification of gelatin when refrigerated. Other pathogens can be distinguished by their ability to degrade casein, the main protein found in milk. When grown on skim milk agar, production of the extracellular protease caseinase causes degradation of casein, which appears as a zone of clearing around the microbial growth. Caseinase production by the opportunist pathogen Pseudomonas aeruginosa can be used to distinguish it from other related gram-negative bacteria.
After extracellular protease degradation and uptake of peptides in the cell, the peptides can then be broken down further into individual amino acids by additional intracellular proteases, and each amino acid can be enzymatically deaminated to remove the amino group. The remaining molecules can then enter the transition reaction or the Krebs cycle.
Because bacterial meningitis progresses so rapidly, Hannah’s doctors had decided to treat her aggressively with antibiotics, based on empirical observation of her symptoms. However, laboratory testing to confirm the cause of Hannah’s meningitis was still important for several reasons. N. meningitidis is an infectious pathogen that can be spread from person to person through close contact; therefore, if tests confirm N. meningitidis as the cause of Hannah’s symptoms, Hannah’s parents and others who came into close contact with her might need to be vaccinated or receive prophylactic antibiotics to lower their risk of contracting the disease. On the other hand, if it turns out that N. meningitidis is not the cause, Hannah’s doctors might need to change her treatment.
The clinical laboratory performed a Gram stain on Hannah’s blood and CSF samples. The Gram stain showed the presence of a bean-shaped gram-negative diplococcus. The technician in the hospital lab cultured Hannah’s blood sample on both blood agar and chocolate agar, and the bacterium that grew on both media formed gray, nonhemolytic colonies. Next, he performed an oxidase test on this bacterium and determined that it was oxidase positive. Last, he examined the repertoire of sugars that the bacterium could use as a carbon source and found that the bacterium was positive for glucose and maltose use but negative for lactose and sucrose use. All of these test results are consistent with characteristics of N. meningitidis .
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The process by which two-carbon units are sequentially removed from fatty acids, producing acetyl-CoA, FADH 2 , and NADH is called ________.
β-oxidation
The NADH and FADH 2 produced during β-oxidation are used to make ________.
ATP by oxidative phosphorylation
________ is a type of medium used to detect the production of an extracellular protease called caseinase.
Skim milk agar
How are the products of lipid and protein degradation connected to glucose metabolism pathways?
What is the general strategy used by microbes for the degradation of macromolecules?
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