Table 1.

Comparison of the screening methods for metagenomeic libraries

	Function-based screening	Sequence-based screening	SIGEX
Screening principle	• Detecting changes by enzymatic reactions (e.g. halo formation around the colonies)	• PCR or Southern hybridization based on the DNA sequence consensus	• Trapping the operon induced by a substrate and sorting using FACS
Advantages	• Secures a complete form of gene or gene cluster required for desired traits • Potentially obtains completely novel genes.	• Overcomes the limitations of the heterologous expression	• Fast and economical • Any substrates that can be introduced into cytoplasm can be used in its native forms.
Disadvantages	• Must satisfy the expression conditions (transcription, translation, folding, secretion) in heterologous hosts	• Requires a database and analyses of the DNA sequence consensus. • Does not guarantee the acquisition of complete forms of genes or gene clusters.	• Sensitive to the orientation of the genes with desired traits • Cannot use substrates that do not migrate to cytoplasm • Sensitive to the initial FACS setting
Examples	antibiotics [9, 19-22], genes involved antibiotic resistance [9, 23, 24], agarases [15], amidases [13], amylases [15, 21, 25, 26], esterase/lipases [8, 15, 21, 27, 28], xylanases [29], 4-hydoxybutyrate dehydrogenase [30] alcohol oxidoreductases [14], pectate lyases [31]	amylases [26], polyketide synthases [32, 33]	Benzoate-degratative or catechol degradative operon, P450 enzyme [16]