Alkaliphiles: Some Applications of Their Products for Biotechnology

Abstract

SUMMARY The term “alkaliphile” is used for microorganisms that grow optimally or very well at pH values above 9 but cannot grow or grow only slowly at the near-neutral pH value of 6.5. Alkaliphiles include prokaryotes, eukaryotes, and archaea. Many different taxa are represented among the alkaliphiles, and some of these have been proposed as new taxa. Alkaliphiles can be isolated from normal environments such as garden soil, although viable counts of alkaliphiles are higher in samples from alkaline environments. The cell surface may play a key role in keeping the intracellular pH value in the range between 7 and 8.5, allowing alkaliphiles to thrive in alkaline environments, although adaptation mechanisms have not yet been clarified. Alkaliphiles have made a great impact in industrial applications. Biological detergents contain alkaline enzymes, such as alkaline cellulases and/or alkaline proteases, that have been produced from alkaliphiles. The current proportion of total world enzyme production destined for the laundry detergent market exceeds 60%. Another important application is the industrial production of cyclodextrin by alkaline cyclomaltodextrin glucanotransferase. This enzyme has reduced the production cost and paved the way for cyclodextrin use in large quantities in foodstuffs, chemicals, and pharmaceuticals. It has also been reported that alkali-treated wood pulp could be biologically bleached by xylanases produced by alkaliphiles. Other applications of various aspects of alkaliphiles are also discussed.

Membrane-derived oligosaccharides (MDOs) are essential for sodium dodecyl sulfate resistance inEscherichia coli

“…In this regard, Delcour et al [17] showed that MDOs can modulate outer-membrane permeability by closing E. coli porin channels. This theme of protection by electrostatic repulsion is the same as that suggested for alkaliphilic bacilli where the plasma membrane is very unstable at alkaline pH values (pH 8.5^9.0) much below the pH optimum for growth [18]. For those alkaliphilic bacilli strains, the cell wall may play a key role in protecting the cell from alkaline environments in that they contain certain acidic polymers.…”

“…For those alkaliphilic bacilli strains, the cell wall may play a key role in protecting the cell from alkaline environments in that they contain certain acidic polymers. The negative charges on these acidic, non-peptidoglycan polymers would repulse hydroxide ions, and, as a consequence, assist cells to grow in alkaline environments [18]. In both cases, a negatively charged polymer participates in the repulsion of low-molecular-mass, noxious anions.…”

Nonheterocytous cyanobacteria from Brazilian saline‐alkaline lakes

“…Although morphological evaluation is still needed due to the traditional morphological classification of Cyanobacteria, it is not always in agreement with molecular phylogeny. Therefore, the systematics of Cyanobacteria has been repeatedly reviewed to arrive at a consensus (Kom arek and Anagnostidis 1986, 1999, Hoffmann et al 2005, Kom arek 2010.…”

“…This approach can be valuable for solving selected taxonomic questions and also for providing biological material useful for applied and physiological studies (Ward et al 1998, L opez-Cort es et al 2001, Taton et al 2006. Several studies have shown that strains from extreme environments are sources of interesting metabolites with biotechnological applications (Grant 1992, Horikoshi 1999, Silva-Stenico et al 2012, Taton et al 2012.…”

Identification of thermostabilizing residues in a Bacillus alkaline cellulase by construction of chimeras from mesophilic and thermostable enzymes and site-directed mutagenesis

“…Alkaliphilic Bacillus spp. are known to produce a variety of alkaline hydrolytic enzymes of industrial importance, including amylases, cellulases, pectinases, and proteases [1,2]. Alkaline endo-1,4-L-glucanase (Egl; EC 3.2.1.4), a cellulase produced by various alkaliphilic Bacillus spp., has been studied extensively for use as an e¡ective detergent additive [2^4].…”