Version 3: The Relationship between microbial population adenosine triphosphate and quantitative polymerase chain reaction bioburdens in diesel fuel microcosms

Historically, fuel microbiology studies have relied on culture data.  Potentially relevant but unculturable were not detected.  Although adenosine triphosphate (ATP) can quantify total microbial bioburdens in fuels, it cannot differentiate among the taxa present.  Quantitative polymerase chain reaction (qPCR) testing promises to fill this gap by quantifying targeted amplicon sequences and thereby detecting both culturable and non-culturable taxa and quantifying specifically targeted taxa.  In this study, fluid samples drawn from the fuel, interface, and water phases of fuel over water microcosms were tested for cellular ATP concentration ([cATP]), and qPCR bioburdens.  Additionally, surface swab samples from steel corrosion coupon surfaces exposed to each of these three phases were collected and tested for total ATP concentration ([tATP]) and qPCR bioburdens.  Statistical relationships between ATP and qPCR bioburdens were examined.  Correlation coefficients between the two variables were matrix dependent and ranged from negligible (|r| = 0.2) to strong (|r| = 0.7).  When results were categorized into negligible, moderate, and heavy bioburdens, parameter agreement was again matrix dependent.  Percent agreement between [ATP] and qPCR gene copies ranged from 11 % to 89 % – with qPCR-bioburden ratings typically being greater than ATP-bioburden ratings.