**Acknowledgements**

*Human Microbiome*

field of synthetic biology.

**5.2 Genome editing/synthetic biology of microbial community**

Genome sequencing data of thousands of bacteria are now available in various databases. Currently, many types of genome editing tools are available to manipulate the genome of animals and plants including microbial genomes. Many scientists have exploited these tools in the manipulation of gut microbiota so that desirable genetic changes can be brought into the metagenomes. The most widely used genome editing tool CRISPR-Cas systems also called clustered regularly interspaced short palindromic repeats (CRISPRs) and CRISPR-associated (Cas) proteins are present in the microbes which are mainly responsible for adaptive immunity for prokaryote cells. CRISPR-Cas systems comprise combinations of short DNA sequences called spacers that guide Cas proteins to cleave foreign DNA. So far, CRISPR-Cas systems are the most widely studied and applied method used for genetic manipulation. There are several types of a spacer or genome editing CRISPR-Cas systems, for example, Cas9, CasX, and CRISPR-CasY, that can be used to manipulate genomic content of gut microorganisms. Class 2 CRISPR-Cas systems are streamlined versions, in which a single RNA-bound Cas protein recognizes and cleaves target sequences. Actually, components of Class 2 CRISPR-Cas systems are studied, and assembly from its components in vitro system has revolutionized the

The gut microbiota also comprises a microorganism, for example, single-cell eukaryotes, bacteria, fungus, and bacteriophages. They live in the gut in a very harmonious manner with trillions of bacteria in a natural environment, hence, well adapted to the local environment. Therefore, researchers are embarking on the idea that gut symbionts can be potential agents or vectors for genetic manipulation of gut microbial communities. The new genome editing tools are used to genetically reprogram gut communities under synthetic biology [65]. CRISPR-Cas systems have been exploited to modification of gene expression, change of the production of metabolites, biocatalyst, and protein production that can act as better microbiome modulators. Moreover, genome editing tools will prove extremely helpful in the functional characterization of gut microbiota. Current genome editing tools have offered opportunities in the investigation of intricate relationships between members of the microbiome and host and have opened new avenues for the development of pharmaceutical agents that target the microbiome. But still many demerits are also linked with genome editing tools including their off-targets and inability to introduce exogenous DNA into the metagenome [66]. Moreover, many bacteria particularly unculturable are naturally ill-adapted to transformation methods such

as electroporation, conjugation, or transduction in lab conditions.

The gut microbiome is an unexploited huge wealth of microbes that synthesized

the valuable and unique metabolites to be used for pharmaceutical industries and the preparation of functional foods. Additionally, metabolites produced by the gut microbiome also contribute in maintaining the health and immunity of the host. In order to exploit microbiome's wealth, we need to apply appropriate and suitable analytical techniques in a highly systematic manner to dig out unique biomolecules. The gut microbial community contains trillions of microbes that make it highly complex. It carried out thousands of metabolic and biochemical reactions in the natural environment. Hence, investigating gut microbiota requires new culturomics methods because of a large number of microbes not able to grow in an artificial environment. Currently, data generated by high-throughput sequencing

**6. Summary and future prospectus**

**18**

I would like to thank to the Department of Biochemistry, GGDSD College (Panjab University), India, for providing me all the facilities and support for preparation of this manuscript.
