**3. Extremophilic microorganisms: invaluable source of novel metabolites**

Microorganisms surviving in the extreme environments are being looked up to as they could help treat a wide spectrum of human illnesses, from ovarian cancer, migraine, high blood pressure, ovarian cancer and lung cancer to Alzheimer's disease. This doctrine has emerged out of the understanding that extremophilic environments present very hostile conditions that impose serious threat to survival of any organism exposed to them [8, 65]. However, extremophilic microorganisms which thrive under such hostile environment must be doing it by synthesizing unusual, but potentially very useful, secondary metabolites. Probably, the best studied molecules produced by extremophilic microorganisms are (i) biocatalytic proteins that are often referred as extremozymes; and (ii) secondary metabolites that are not directly required growth of the microorganism, yet they often perform many helpful functions, such as enabling defense mechanisms etc. [66–69],

It is suggested that extremophile enzymes would be more suitable and stable for use in industrial biotechnology applications than those obtained from mesophilic microbial species [9, 21, 70]. Also, the unusual secondary metabolites isolated from extremophilic microorganisms are steadily being characterized as drug molecules with unique potential and applications. One of the recently published studies

reported characterization of a secondary metabolite (viz., dihydrogranaticin) from a thermophilic fungus exhibits wide spectrum antibiotic functions. Similarly, secondary metabolites isolated from a psychrophilic bacterium from the Arctic glaciers have been reported to inhibit the growth of human colon cancer cells. Another secondary metabolite (psychrophilin D) isolated from a psychrophilic microorganism, exhibits inhibitory activity against mouse leukemia cell line [71].

#### **Figure 1.**

*Schematic representation of the workflow used for culture independent approaches for characterization of microbial diversity viz., metagenomics (A) and single cell genomics (B).*

**69**

*Harnessing the Genetic Diversity and Metabolic Potential of Extremophilic Microorganisms…*

In accordance to the other extremophilic environments, the secondary metabolites produced by organisms that thrive at acidophilic environments, are a valuable source of novel metabolites. According to a recent survey, more than 20 previously unknown natural products have been isolated from acidophilic microbial diversity. Another valuable type of metabolites that is being proposed to have significant technological application is the 'natural inhibitors' of therapeutic target proteins. A representative example of such natural inhibitors was reported as berkeleyamide A, a secondary metabolite isolated from acidophilic strains *Penicillium rubrum* species [72]. This inhibits the proteases caspase-1 and matrix metalloproteinase 3 (MMP3), both of which are implicated in malignancy of some of the cancer types [72]. Another molecule (i.e. Berkelic acid,) isolated from an extremophilic microorganism, has a very unusual tetracyclic structure and it also inhibits both caspase-1 and MMP-3 [73]. Consequently, it exhibits selective inhibitory activity against an ovarian cancer cell line which has implication of abovementioned genes in cancer progress. Unfortunately, there is significantly less information available relevant to the secondary metabolites produced by extremophilic microorganism thriving at high pH and high salt concentrations. It has been often suggested that the enzymes

from these microorganisms would be quite useful a biological detergents.

**4. Cultivation-independent approaches: tapping extremophilic** 

Cultivation-independent approaches are based on direct isolation of whole metagenomic DNA/environmental DNA. Subsequent downstream treatments of metagenomic DNA are broadly classified into 2 categories, i.e. (i) Metagenomic library generation and its functional screening; and (ii) Direct sequencing of the whole metagenomic DNA content [78–82]. The same technological framework is applicable to metagenomic analyses of samples collected from extremophilic environments. However, the complex nature of extremophilic matrix presents certain unique technical challenges with respect to isolation of metagenomic DNA. The methodologies successfully implemented to mesophilic sites for metagenomic DNA isolation often tend to be non-sufficient for isolation of high quality and high quantity metagenomic DNA from extremophilic samples. Even with non- optimal metagenomic DNA isolation procedures, the cultivation independent approach has enabled identification and characterization of several valuable extremozymes and

studying extremozymes and cryptic metabolites.

**metabolites**

extremophilic metabolites [20, 75].

Considering the well-established potentials of the metabolites of the extremophilic origin, there is a need to develop fundamental understanding with respect to their physiological role in the growth and survival of extremophilic microorganism as well as their adaptation to the hostile environment. Many of the metabolites remain 'cryptic' during the cultivation of the extremophiles under the *in vitro* conditions since recreating the physicochemical conditions observed in the extreme environments within the laboratory is technically challenging, complicated and expensive [74]. Metagenomic Analyses and Single Cell Genomic Analyses., which enable the assessment of genetic and metabolic diversity without the need of cultivating the microorganisms, have helped to circumvent the limitations caused by the cryptic nature of secondary metabolic genes [75–77]. **Figure 1** presents a schematic representation of the workflow used for the metagenomics (**Figure 1A**) and single cell genomics (**Figure 1B**). As of now, a number of studies have already been carried out with metagenomes and single cell genomes from the extreme environments for

*DOI: http://dx.doi.org/10.5772/intechopen.82639*

#### *Harnessing the Genetic Diversity and Metabolic Potential of Extremophilic Microorganisms… DOI: http://dx.doi.org/10.5772/intechopen.82639*

In accordance to the other extremophilic environments, the secondary metabolites produced by organisms that thrive at acidophilic environments, are a valuable source of novel metabolites. According to a recent survey, more than 20 previously unknown natural products have been isolated from acidophilic microbial diversity. Another valuable type of metabolites that is being proposed to have significant technological application is the 'natural inhibitors' of therapeutic target proteins. A representative example of such natural inhibitors was reported as berkeleyamide A, a secondary metabolite isolated from acidophilic strains *Penicillium rubrum* species [72]. This inhibits the proteases caspase-1 and matrix metalloproteinase 3 (MMP3), both of which are implicated in malignancy of some of the cancer types [72]. Another molecule (i.e. Berkelic acid,) isolated from an extremophilic microorganism, has a very unusual tetracyclic structure and it also inhibits both caspase-1 and MMP-3 [73]. Consequently, it exhibits selective inhibitory activity against an ovarian cancer cell line which has implication of abovementioned genes in cancer progress. Unfortunately, there is significantly less information available relevant to the secondary metabolites produced by extremophilic microorganism thriving at high pH and high salt concentrations. It has been often suggested that the enzymes from these microorganisms would be quite useful a biological detergents.

Considering the well-established potentials of the metabolites of the extremophilic origin, there is a need to develop fundamental understanding with respect to their physiological role in the growth and survival of extremophilic microorganism as well as their adaptation to the hostile environment. Many of the metabolites remain 'cryptic' during the cultivation of the extremophiles under the *in vitro* conditions since recreating the physicochemical conditions observed in the extreme environments within the laboratory is technically challenging, complicated and expensive [74]. Metagenomic Analyses and Single Cell Genomic Analyses., which enable the assessment of genetic and metabolic diversity without the need of cultivating the microorganisms, have helped to circumvent the limitations caused by the cryptic nature of secondary metabolic genes [75–77]. **Figure 1** presents a schematic representation of the workflow used for the metagenomics (**Figure 1A**) and single cell genomics (**Figure 1B**). As of now, a number of studies have already been carried out with metagenomes and single cell genomes from the extreme environments for studying extremozymes and cryptic metabolites.
