You can certainly try to express any open reading frame in a standard expression system such as E.coli. However, I would start with a thorough bioinformatics analysis to formulate at least some hypotheses on what to look for in respect to function, and then use the recombinant protein to specifically test these hypotheses

You would need to get hold of the gene. (Which I would do by amplifying the gene with PCR and primer, using the organism.) Then you need put it into your vector of interest and into the system you want.

However I would do some proper analysis of the gene before doing so, since there could be some hindrances. (Codon usage, maybe there are some posttranslational modifications needed your system is not capable of making, ...)

You may use fosmid libraries (in two words, fosmids - are plasmids carrying large inserts) to screen large amount of metagenome DNA for activity that You need. Then You should sequence the fosmid showed activity and acquire gene sequence to amplify and clone it.

This method is time-consumptive and labor-intensive, but if You don't know the sequence of gene to amplify and clone - it's the only solution.

You could find more information on the protocol here: http://www.epibio.com/docs/default-source/protocols/copycontrol-fosmid-library-production-kit-with-pcc1fos-vector.pdf?sfvrsn=6

Regards!

thank you all