Why were the advent of metagenomics, and the application of molecular techniques such as single-cell and next-generation sequencing, important for defining a microbial relationship

Based on novel approaches, it has been seen that symbiotic associations prevails between a host and one to thousands of more microbes, which challenges the previous meaning of symbiotic association as one that takes place between the host and a single microbe. It was considered previously that symbiotic association’s takes place only between the pair of single microbe and host.  

However, newer approaches has revealed that such kind of association can take place between one microbe and many other hosts. A symbiotic association can take place between microbe-microbe, plants-plants, microbe-plants, and others. However, symbiotic association has never been found to take place between a bacteria and animal host. The symbiotic associations are always not parasitic.  

allowed for the prediction of the properties of missing elements.