GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

6. MICROBIAL GROWTH

6.2. ADAPTIVE RESPONSES OF MICROORGANISMS TO STRESS

6.2.4. The role of intercellular chemical communication in microbial stress adaptation

When studying the Mechanisms of microbial adaptation to stress, researchers have traditionally focused on "individual" defense mechanisms occurring at the intracellular level. Alongside metabolic shifts and Changes in the microbial Cell composition, The regulatory mechanisms, genetics, and molecular aspects of various stress responses have been thoroughly investigated. However, Intercellular Contacts and cellular "mutual aid" under stress conditions have largely remained overlooked. In some studies, bacterial colonies and cultures are viewed as a unified whole that responds in a coordinated and appropriate manner to environmental fluctuations, or even as Multicellular Organisms.

One of the potential and most thoroughly studied channels of Intercellular Communication is the "chemical language," which involves the transmission and reception of information via chemical compounds. Such compounds can be categorized into autoregulators (for communication within the same species), attractants and repellents (for navigating the environment through active movement), as well as Antibiotics and other antibacterial compounds synthesized by living organisms to suppress microbial activity.

It is well established that chemical autoregulators play a crucial role in microbial life. Autoregulators can influence microbial GROWTH AND DEVELOPMENT, Cell Differentiation, reproductive behavior, and physiological state. The ability of microorganisms to synthesize extracellular autoregulatory metabolites during their development was first described in the late 1970s and early 1980s.

Under conditions of low salinity that induce lysis, halobacteria release osmotic alarm signals into the environment, which enhance cell stability under these adverse conditions.

Under stress conditions, bacterial Cells can employ another mechanism of collective defense: the secretion of protective exometabolites. If co-cultivation of two different microorganisms is considered a stressful situation for them, it can be observed that under such stress, certain Bacillus cells begin synthesizing a specific antibiotic against co-cultivated micromycetes. Yeast cells secrete a range of protective exometabolites when grown in the presence of phenol. The production of various exometabolites that bind heavy toxic metals in response to their presence in the growth medium can also be regarded as a manifestation of microbial chemical communication under stress. The co-presence of certain microorganisms belonging to different genera and families can trigger the production of exopolysaccharides. For instance, EPS accumulation during the growth of mixed cultures can be 3–4 times higher than that of monocultures. E. coli cells treated with tetracycline, and consequently unable to grow, produce a yet-unidentified exometabolite(s) that accelerates the growth of a tetracycline-resistant strain of this bacterium in the presence of a bacteriostatic concentration of the antibiotic. This exometabolite also exerts a protective effect on E. coli cells growing under heat, cold, oxidative, and osmotic stress conditions. This protective effect manifests as an increased growth rate in the presence of tetracycline and during heat stress, or as a reduced lag phase during Other types of stress.

It should be noted that currently there are only a few studies at the intersection of two fields—stress adaptation and microbial chemical language—focusing specifically on The Role of intercellular chemical communication in bacterial stress adaptation.