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Introduction to the Biological System
Published in Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu, Interdisciplinary Engineering Sciences, 2020
Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu
As shown in Figure 8.6, the bacterial cell is enclosed by a lipid membrane, which houses proteins, ribosomes, and other necessary components of the cytosol. As mentioned earlier in this chapter, membrane-bound organelles are absent in bacteria and thus have few intracellular structures. The nucleoid is an area of the bacterial cells, which is composed of chromosomes associated with small amounts of RNA and proteins. Like monkeys have tails, the tail-like structures of bacteria are known as flagella, which help in motility or migration on a material substrate. The flagella are proteinaceous structures of about 20 μm in length and up to 20 nm in diameter. Pili are essentially extracellular structures, which can transfer DNA/RNA from one bacterial cell to the other, in the process of bacterial conjugation.
Microbial Biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2020
Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular chromosome located in the cytoplasm in an irregularly shaped body called the nucleoid. The nucleoid contains the chromosome with associated proteins and RNA. The order Planctomycetes are an exception to the general absence of internal membranes in bacteria because they have a membrane around their nucleoid and contain other membrane-bound cellular structures. Like all living organisms, bacteria contain ribosomes to produce proteins, but the structure of the bacterial ribosome is different from those of eukaryotes and archaea. Some bacteria produce intracellular nutrient storage granules such as glycogen, polyphosphate, or sulfur. These granules enable bacteria to store compounds for later use. Certain bacterial species, such as the photosynthetic Cyanobacteria, produce internal gas vesicles, which they use to regulate their buoyancy, allowing them to move up or down into water layers with different light intensities and nutrient levels.
Microbial biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
Bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular chromosome located in the cytoplasm in an irregularly shaped body called the nucleoid. The nucleoid contains the chromosome with associated proteins and RNA. The order Planctomycetes are an exception to the general absence of internal membranes in bacteria, because they have a membrane around their nucleoid and contain other membrane-bound cellular structures. Like all living organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from those of eukaryotes and Archaea. Some bacteria produce intracellular nutrient storage granules such as glycogen, polyphosphate, or sulfur. These granules enable bacteria to store compounds for later use. Certain bacterial species, such as the photosynthetic Cyanobacteria, produce internal gas vesicles, which they use to regulate their buoyancy, allowing them to move up or down into water layers with different light intensities and nutrient levels.
An invisible workforce in soil: The neglected role of soil biofilms in conjugative transfer of antibiotic resistance genes
Published in Critical Reviews in Environmental Science and Technology, 2022
Shan Wu, Yichao Wu, Bin Cao, Qiaoyun Huang, Peng Cai
The conjugative transfer frequency of plasmids in biofilms largely depend on the genetic traits of the plasmid and host (Król et al., 2013; Røder et al., 2013). Additionally, due to the spatial structure and heterogeneity of biofilms, plasmids, of which the host is outside of the biofilm, can transfer merely to the peripheral cells in the biofilm microcolonies whereas deeper biofilm layers are inaccessible. Specifically, the physical isolation of different genotypes within large populations and the eventual isolation of donor and recipient cells allows individuals to exclusively interact with their nearest neighbors, therefore creating subpopulations that are more or less independent from each other, reducing the chances for conjugative transfer (Hallatschek et al., 2007;; Stalder & Top, 2016). Moreover, the spatial/physical heterogeneity of biofilms profoundly influences how populations share genetic information, thus influencing the conjugation of ARGs. The selection imposed by the biofilm environment on plasmid-encoded traits is also an important factor affecting the conjugative transfer of ARGs. By entirely determining the persistence of the plasmid in its new hosts, as well as the host’s local competitiveness, biofilms can influence the resulting transconjugants formed during HGT events to further promote ARGs spread through vertical gene transfer (Jose et al., 2011; Li, Qiu, et al., 2019). Previous studies have also shown that several regulatory mechanisms could impact the conjugative transfer of some plasmids in biofilms. For example, the SOS response, extracytoplasmic stress, quorum sensing, and histone-like nucleoid structuring protein (H-NS) induced gene silencing, which can respond to environmental and physiological cues. As cells grow slowly in the deeper layers of thick biofilms, conjugation could also be limited by a multitude of regulators that are at work within these layers (Stalder & Top, 2016). Thus, factors such as the spatial structure of the biofilm, the component(s) of EPS, and population interactions play a key role in changing the frequency of conjugative transfer.