Infectious Aerobic Bacteria
Aerobic bacteria are bacteria that can grow and live when oxygen is present. An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. In contrast, an anaerobic organism (anaerobe) is any organism that does not require oxygen for growth. Some anaerobes react negatively or even die if oxygen is present. The ability to exhibit aerobic respiration may yield benefits to the aerobic organism, as aerobic respiration yields more energy than anaerobic respiration.
In July 2020, marine biologists reported that aerobic microorganisms (mainly), in "quasi-suspended animation", were found in organically-poor sediments, up to 101.5 million years old, 250 feet below the seafloor in the South Pacific Gyre (SPG) ("the deadest spot in the ocean"), and could be the longest-living life forms ever found.
Growth of aerobic bacteria
Aerobic bacteria are easily grown at a small scale in tubes and flasks by incubating the media under normal atmospheric conditions. In large-scale operations, the media has to be exposed to air, and sufficient air must be present for respiration of all living microorganisms. The indication of availability of oxygen in the liquid phase is to measure the amount of dissolved oxygen. DO probes are available on the market, and most fermenters are equipped with a DO meter.
For aerobic fermentation, the bioreactor must be equipped with a DO meter. The level of DO in the media is a function of temperature. Higher operating temperatures decrease the level of DO. To have sufficient oxygen, an air sparger is required to purge compressed air or pressured air to be bubbled into the media. The availability of oxygen is a major parameter to be considered for effective microbial cell growth rate.
Many aerobic bacteria are able to thrive in Hg-contaminated environments because they possess the Hg resistance, or mer, operon. The prototypical, broad-spectrum mer operon encodes several proteins and enzymes. In addition to a transcriptional regulator, MerR, Hg-resistant bacteria produce various membrane-bound transporter proteins (MerC, MerT, and others), a periplasmic metallochaperone (MerP), and two key enzymes (MerB and MerA). Our studies have focused specifically on the two enzymes MerB and MerA, and the transcriptional regulator, MerR.
Among aerobic bacteria, aminoglycoside resistance is most commonly due to enzymatic inactivation through aminoglycoside-modifying enzymes. These may be coded by genes on plasmids or chromosomes. Several aminoglycoside-modifying enzymes have been shown to be carried on transposons.
Aminoglycoside-modifying enzymes confer antibiotic resistance through three general reactions: N-acetylation, O-nucleotidylation, and O-phosphorylation. For each of these general reactions, there are several different enzymes that attack a specific amino or hydroxyl group. The nomenclature for these enzymes lists the molecular site where the modification occurs after the type of enzymatic activity. An aminoglycoside acetyltransferase (AAC) that act at the 3′ site is designated AAC. There may be more than one enzyme that catalyzes the same reaction, however, and Roman numerals may be necessary. Enzymatic aminoglycoside resistance is achieved by modification of the antibiotic in the process of transport across the cytoplasmic membrane.
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