Bacteria are tiny microorganism species that are biologically important. They were initially considered solitary organisms capable of independent function. However, research has shown that bacteria communication, also called Quorum sensing, is real, and bacteria do this using numerous cell-signalling mechanisms 1.
The goal of bacterial communication is to enable coordination among their communities regarding behaviour, specific attacks, and adaptation to the microenvironment. This article explores the different microbial interaction mechanisms and their implications for human health.
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Introduction To Bacterial Communication Mechanisms
Bacterial communication or Quorum sensing is a complex chemical signalling process that enables these microorganisms to perform coordinated functions. The process begins with the release of specific chemical substances into their surroundings. The substance differs depending on the type of bacteria. Gram-positive ones release peptides, while gram-negative ones release Acyl-homoserine Lactones (AHLs) 2.
These signalling molecules increase as the bacterial population rises till it clinches a certain threshold. Once the ideal population of bacteria is reached, they detect the substance's threshold and read it as a quorum. Eventually, the goal sets in to form unity among individual cell types and trigger an organized and collective behaviour or function.
However, another bacterial communication mechanism exists. Conjugation, unlike quorum sensing, is an interactive process involving sharing genetic material directly from one bacterial cell to another to create a coordinated function. This mechanism involves the donating bacterium forming a thin cell-traversing component that binds to a receptor on the receiving bacterium.
Eventually, the donor bacterium replicates its DNA sequence (plasmid) into the recipient's cytoplasm. Ultimately, the bacteria will have unified characteristics (e.g. metabolic function, drug resistance, and virulence factors) and functions as new traits are replicated from the donor to the recipient cell.
The contact-dependent signalling mechanism does not use chemical transmitters or genetic sharing; instead, it uses direct cell-to-cell contact. The cells, on closure, develop unique surface proteins that bind to the receptors, which appear in the form of proteins and peptides. Consequentially, the recipient understands the signal, which can translate to protein activity, microbial behaviour, or a generalized function.
Understanding Quorum Sensing: The Language of Bacteria
Chemical molecules form the basis of quorum sensing, a complex but essential bacterial communication mechanism. Individual microbial cells continuously secrete substances like peptides and acyl-homoserine lactones (AHLs) until they reach a sufficient point where they form a quorum. Eventually, the bacterial cells understand the information through the molecules and act uniformly with the set behaviour and function.
Role of Chemical Signals in Bacterial Interaction
Bacteria perform numerous biologically essential functions which rely on chemical signals. Research on Vibrio cholera shows that the microorganism relies on specific substances to achieve quorum sensing and attack the human intestine 3.
Virulence factors and controls are a primary function of bacteria that depend on chemical signals. Before the pathogenic bacteria perform a unified attack, they continue to grow in population and secrete signal molecules sufficiently until they reach a quorum. This initiates the release of virulence factors, increasing their infective ability to the highest and causing a coordinated attack on host cells.
Chemical signals also perform protective microbial functions as they form the structures by which bacteria unite on surfaces to develop biofilms. These protective structures help the microorganism become resistant to pharmacological therapies like antibiotics and disinfectants. The biofilm also causes chronic infections and food spoilage.
Environmental sensitivity highlights the essential role of chemical signals in bacterial function. These microorganisms employ such signal molecules to understand fluctuations in their environment to adapt and survive better. Examples of environmental variables include nutrient availability, temperature, PH. Bacteria rely on chemical signalling to identify nutrient deficiencies in individual cells. Once the intention of nutrient acquisition is shared with all cells in the community, the bacteria degrade high molecules, thereby ensuring nutrient accessibility to the entire microbial territory.
Bacterial Communication in Biofilm and Virulence
Biofilm is a bacterial virulence factor that makes it resistant to antibiotics, disinfectants, and other pharmacological treatments. They're a collection of bacteria unified in a matrix that cause numerous infective attacks 4.
Research on Staphylococcus aureus, Vibrio cholerae, and Pseudomonas aeruginosa reveals that inhibiting quorum-sensing molecules greatly downgrades biofilm formation 5. Studies have also shown that these biofilm-producing microorganisms, like Pseudomonas aeruginosa, secretes exopolysaccharides that have unique genes activated by quorum sensing 6.
Bacterial virulence depends on microbial communication among the community of cells to attain its maximum infective potential. During the pathogenic process of Staphylococcus aureus, microbial communication forms the basis for controlling the release and function of toxins and enzymes responsible for its virulence.
Pseudomonas aeruginosa, a major cause of Pneumonia, Urinary Tract Infections (UTIs), Cystic fibrosis, bronchiectasis and several other diseases, has been revealed to use quorum sensing before it releases its toxins (virulence factor). Eventually, bacterial communication ensures the coordinated attack and is highly responsible for their virulence.
Quorum sensing | Cell communication | Bacteteria | virulence | AHL | Ligand | Basic Science Series
Implications of Bacterial Communication for Human Health
Understanding quorum sensing and other bacterial communication mechanisms has created revolutionary opportunities in microbiology and pharmacology. The knowledge of such mechanisms is important to create innovation and impact human health.
Firstly, the positives. Pharmacological therapies stand high as an essential implication of bacterial communication on human health. Research reveals that some substances containing Furanone are capable of interrupting quorum sensing in Pseudomonas aeruginosa 7. Newer advances are in place for human T-cells to destroy quorum-sensing molecules, creating potential treatments for chronic bacterial infections.
Knowledge of bacterial communication plays a massive role in biofilm control in water treatment. Research has shown that inhibiting quorum sensing mechanisms are hugely beneficial in water treatment plants due to their ability to stop the growth of dangerous biofilms 8. Studies have also proved that microorganisms engineered with improved communication mechanisms downgrade polycyclic aromatic hydrocarbons and other environmental hazards 9.
However, the communication between bacterial colonies has negative implications for human health. Research reveals that Staphylococcus aureus employs quorum sensing to develop genes capable of inducing methicillin resistance 10.
Bacteria like Pseudomonas aeruginosa produce biofilm serving as a protective structure, preventing the penetrative ability of antibiotics. Therefore, their communication provides room for dangerous infections due to current pharmacological therapy proving worthless.
Conclusion
In summary, yes, bacteria do communicate, and they do this through several mechanisms like quorum sensing, conjugation and contact-dependent signalling. The goal is for the bacterial colony to be in alignment with the necessary characteristics, behaviour, and function essential for its survival. Eventually, this interaction plays a role in virulence factor control, biofilm formation and other microbial functions.
The knowledge of such communication allows innovation on new drug therapies, water treatment plants, pollutant removal and other important aspects of human health. However, it's essential not to neglect the negative implications as new strategies arise to combat dangerous diseases.
References
- N A Whitehead, A M Barnard, H Slater, N J Simpson, G P Salmond. (2012). Quorum sensing in Gram-negative bacteria.
- J W Costerton, P S Stewart, E P Greenberg (1999). Bacterial biofilms: a common cause of persistent infections.
- Ana A. Weil,a,b,* Rachel L. Becker,a and Jason B. Harris. Vibrio cholerae at the Intersection of Immunity and the Microbiome. doi: 10.1128/mSphere.00597-19
- Davies, D. G. (2003). Understanding biofilm resistance to antibiotics and other biocides.
- Kuldeep Gupta, Salam Pradeep Singh, Ajay Kumar Manhar, Devabrata Saikia, Nima D. Namsa, Bolin Kumar Konwar, and Manabendra Mandal. Inhibition of Staphylococcus aureus and Pseudomonas aeruginosa Biofilm and Virulence by Active Fraction of Syzygium cumini (L.) Skeels Leaf Extract: In-Vitro and In Silico Studies.
- Minh Tam Tran Thi, David Wibowo, and Bernd H.A. Rehm. Pseudomonas aeruginosa Biofilms. doi: 10.3390/ijms21228671.
- T. de Kievit. Comprehensive Biotechnology (Third Edition), 2011.
- Jingming Zhao, Wei Cheng, Xigang He, Yanli Liu, Ji Li, Jiaxing Sun, Jinfeng Li, Fangfang Wang, and Yufang Gao. Association of furanone C-30 with biofilm formation & antibiotic resistance in Pseudomonas aeruginosa.
- Sonam Tripathi, Ram Chandra, Diane Purchase, Muhammad Bilal, Raja Mythili, Sangeeta Yadav. Quorum sensing - a promising tool for the degradation of industrial waste containing persistent organic pollutants.
- Richard P Novick & Edward Geisinger (2008). Quorum sensing in staphylococci. doi:10.1146/annurev.micro.54.1.549
Further Reading