Table 2.

Comparison of Proposed Molecular Methods for Bioburden Assessment of Spacecraft Surfaces

Methods	Analysis targets	Microbial diversity	Quantification	Previous NASA work	Turnaround time for data and analysis	Cost	Background contamination risk
Molecular methods for bioburden measurements
Real-time quantitative PCR	Variable, depending on primers	Noa	Absolute or relative	Yes	<24 h	$	Variable, depending on assay specificity
Digital quantitative PCR	Variable, depending on primers	Noa	Absolute	No	<24 h	$$	Variable, depending on assay specificity
Molecular methods for microbial diversity assessments
NGS Amplicon sequencing	Variable, depending on primers	Yes	Relative, with possibility of absolute	Yes	∼1 week	$$	High
NGS metagenome sequencing	All dsDNAsb	Yes	Relative, with possibility of absolute	Yes	∼1 week	$$$	High

^a Assay specificity can provide evidence of specific taxa.

^b Most metagenome library synthesis is performed using protocols targeting double-stranded DNA; however, assays targeting single- and double-stranded DNA are available.

dsDNA; NGS.