Haloalkaliphilic Bacillus Species from Solar Salterns: an Ideal Prokaryote for Bioprospecting Studies

Ann Microbiol (2016) 66:1315–1327 DOI 10.1007/s13213-016-1221-7 REVIEW ARTICLE Haloalkaliphilic Bacillus species from solar salterns: an ideal prokaryote for bioprospecting studies Syed Shameer 1 Received: 23 December 2015 /Accepted: 26 May 2016 /Published online: 13 June 2016 # Springer-Verlag Berlin Heidelberg and the University of Milan 2016 Abstract Bioprospecting is an umbrella term describing the optimally under moderate halophilic and alkaline conditions. process of search and discovery of commercially valuable Artificial solar salterns are not evenly established as a habitat new products from biological sources in plants, animals, and because they are created and maintained by humans. Hence, microorganisms. In a way, bioprospecting includes the ex- the present paper makes an attempt to review the potential of ploitative appropriation of indigenous forms of knowledge haloalkaliphilic Bacillus species from manmade solar salterns by commercial actors, as well as the search for previously for bioprospecting studies. unknown compounds in organisms that have never been used in traditional ways. These resources may be used in industrial Keywords Haloalkaliphilic Bacillus species . Artificial Solar applications, environmental, biomedical, and biotechnologi- salterns and Bioprospecting cal aspects. Bacillus species are one of the most studied organisms from different perspectives and diverse environments, namely for industrial and environmental applications Introduction owing to the adaptations and versatile molecules they produce. The ability of different species to ferment in the acid, The seas that cover nearly 70 % of the surface of planet Earth neutral, and alkaline pH ranges, combined with the presence contain about 35 g/L−1 dissolved salt. Hypersaline environ- of thermophiles in the genus, has lead to the development of a ments are easily formed when seawater dries up in coastal variety of new commercial enzyme products with the desired lagoons and salt marshes, as well as in manmade evaporation temperature, pH activity, and stability properties to address a ponds of saltern systems built to produce common salt by variety of specific applications. Unlike other microbial species evaporation of seawater. There are also inland saline lakes in Bacillus species have been isolated from different sources which the salt concentrations can reach close to saturation. both natural and artificial sources some being extreme in na- Well-known examples are the Great Salt Lake, UT, USA, a ture, for bioprospecting studies to exploit them to fabricate lake in which the ionic composition of the salts resembles that novel biomolecules or functions. Solar salterns are among of seawater, and the Dead Sea on the border between Israel the least documented environments as a source of Bacillus and Jordan, a lake dominated by magnesium rather than by species due to their unique nature comprising multiple extrem- sodium as the most abundant cation. Furthermore, there are ities of varying degrees, namely temperature, pH, and minimal extensive underground deposits of rock salt that originated by nutrients along with saturating salinity. Haloalkaliphilic the drying of closed marine basins. All of these environments, Bacillus species are the group specifically adapted to grow as well as others such as saline soils, provide a habitat for salt- adapted microorganisms, obligate halophiles, as well as halotolerant organisms that can adjust to life over a wide range * Syed Shameer of salt concentrations. [email protected] Solar salterns are hypersaline water bodies located along the sea-coast and are the main source of salt generated through 1 Department of Microbiology, Sri Venkateswara University, the evaporation of seawater. They are generally composed of a Tirupati, AP, India 517 502 system of shallow ponds with salinities ranging from of 1316 Ann Microbiol (2016) 66:1315–1327 seawater to supersaturated brines. These elevated saline environments, depending on external salinity (Müller and concentrations represent extreme environmental condi- Köcher 2011) (Fig. 1) (Marco and Erhard 2011). Because tions leading to the growth of only a few specialized water tends to flow from areas of high solute concentration groups of microorganisms: the halophiles. These halophil- to areas of lower concentration, a cell suspended in a very ic microbial communities (Oren 2006; Pedrós-Alió 2006) salty solution will lose water and become dehydrated unless are adapted to life at high salt concentrations and to the its cytoplasm contains a higher concentration of salts than its high osmotic pressure of their environment resulting from environment. Halophiles contend with this problem by pro- the high salinity. In addition, other factors such as tem- ducing large amounts of an internal solute or by recollecting a perature, pH, oxygen, nutrient availability, and solar radi- solute extracted from outside (Garabito et al. 1998). Halophily ation prevailing in these environments also limit the refers to the ionic requirements for life at high salt concentra- growth of microorganisms. Most of the solar salterns tend tions. Although these phenomena are physiologically distinct, to be alkaline in nature due to carbonates, and only a they are environmentally associated with other physiological negligible number are acidic in nature (those are near parameters. Thus, a halophile must cope with osmotic stress acidic or sulphur mines). Artificial solar salterns are (Oren 2006). Halophiles include a range of microbes, but unique polyextremophilic environments characterized by some Archaea, cyanobacteria, and the green alga Dunaliella saturating salinities (15–35 %), moderate alkalinity pH salina can withstand periods in saturated NaCl. For instance, (9.0), and mesophilic temperatures (45–50 °C), which an Archaean known as Halobacterium salinarum concen- are the conditions most prevalent in industrial processes. trates potassium chloride in its interior. As might be expected, Another reason that artificial solar salterns are a source of the enzymes in its cytoplasm will function only if a high con- potential prokaryotes is they are the dominant population centration of potassium chloride is present, but proteins in when compared with eukaryotic groups such as fungi or Halobacterium salinarum cell structures that are in contact algae (Syed et al. 2012). with the environment require a high concentration of NaCl. Apart from Haloarchaea, Bacillus species are prominently found in the less saline zones of solar salterns, particularly in saturation ponds, which have 15–25 % salinity. Bacillus spe- Haloalkaliphiles cies continue to be dominant bacterial workhorses in microbial fermentations. Bacillus subtilis is the key microbial partic- Alkaliphiles consist of two main physiological groups of mi- ipant in the ongoing production of large-scale hydrolytic en- croorganisms, alkaliphiles and haloalkaliphiles. Alkaliphiles zyme production, and some Bacillus species are on the Food require an alkaline pH of 9 or more for their growth and have and Drug Administration's GRAS (generally regarded as safe) an optimal growth pH of around 10, whereas haloalkaliphiles list. The capacity of selected Bacillus strains to produce and require both an alkaline pH (>pH 9) and high salinity (up to secrete large quantities (20–25 g/L) of extracellular enzymes 33 % (w/v) NaCl) (Horikoshi 1996). The environments or has placed them among the most important industrial enzyme sources for this group of microorganisms are both natural producers. The Bacillus strains isolated from solar salterns and artificial in nature (Oren 2002a). have properties such as temperature and alkalinity tolerance of considerable level. Thus, the special natural adaptations of the Bacillus species from solar salterns render them ideal can- Adaptation strategies for haloalkaliphiles didates for multiple application bioprospecting studies. This review attempts to consolidate the recent applications of Haloalkaliphiles possess adaptation mechanisms, which in- haloalkaliphilic Bacillus species to inspire extensive study of clude production of high density lipids with branched chains the same to the fullest. and increased content of cell wall components (glutamic acid, diaminopimelic acid, muramic acid, and glucosamine) along with the presence of poly-γ-L-glutamic acid along with Na+/ Halophiles H+ antiporters as internal pH homeostasis for survival in high- ly saline and alkaline pH (Horikoshi 2011; Krulwich et al. Halophiles are able to survive in salty conditions through cel- 2011). These properties make them interesting not only for lular and molecular adaptations, including adjusting the cell fundamental research, but also for industrial application turgor to different external salinities by controlling the con- (Margesin and Schinner 2001; Purohit et al. 2014). So far, centration of protective molecules such as ectoine, betaine, moderately haloalkaliphilic bacteria have been isolated from and amino acids (glutamine, glutamate, proline, and glycine) the different saline and alkaline environments (Ventosa et al. by producing them intracellularly or taken up from the envi- 1998; Patel et al. 2005;Xuetal.2007). ronment, and by concentration regulation of compatible sol- Extremophiles adopt two distinct approaches to living utes such as chloride and sodium/potassium in intracellular within extreme environments; they adapt to function within Ann Microbiol (2016) 66:1315–1327 1317 Fig 1 The core of osmostress response of Bacilli. Schematic

Load more