Opportunities for applying whole‐cell bioreporters towards parasite detection

In nature, living cells and organisms have evolved, over billions of years, an astonishing suite of mechanisms that are used to detect and respond to diverse, transient and long-term external stimuli (Khalil and Collins, 2010). Whole-cell bioreporters (WCBs; sometimes referred to colloquially as whole-cell biosensors) are characterized as cells (termed chassis) that have been deliberately modified to make use of re-engineered versions of these biosensing systems, such that biological detection is coupled with a measurable response. Whilst WCBs have been successfully employed to detect a wide range of environmental pollutants (Tauriainen et al., 1997, 1998; Ivask et al., 2009; Joshi et al., 2009; de Mora et al., 2011; Roda et al., 2011), metabolites (Sticher et al., 1997; Sevilla et al., 2015) and other molecules (Hansen and Sørensen, 2000; Urban et al., 2007; Chappell et al., 2013)(Wu et al., 2000), there are clear opportunities for applying WCBs within global health contexts. In parallel, the field of synthetic biology, which uses engineering design principles for constructing novel biological systems and cells, is poised to enable a rapid increase in next-generation WCBs, which can be applied to global health challenges (Rooke, 2013; Slomovic et al., 2015). Notable examples of microbial WCBs that are currently being integrated into global health initiatives include two arsenic bioreporters, both of which are currently undergoing field trials to determine their utility for detecting arsenic-contaminated freshwater. One of these is based upon lyophilized Escherichia coli (Siegfried et al., 2012) cells. The other arsenic bioreporter is based upon engineered Bacillus subtilis cells – the researchers are currently seeking regulatory approval as a contained genetically engineered microorganism (European Union directive 2009/41/EC) before moving to widespread field trials of the WCB (see http://www.arse nicbiosensor.org). The decision to seek regulatory approval before use is a direct consequence of applying responsible research and innovation approaches in synthetic biology (Anderson et al., 2012), where societal implications and consequences are considered before implementation. Using this process, the B. subtilis project identified complex social, cultural and data protection issues that interrelated with the technological development and implementation of the arsenic WCB. One example was the need to respond to the concerns of Nepalese villagers, during initial field trials, by changing the colour output of the bioreporter test, so that green signified that the water was OK, and shades of indigo were set to a numerical scale for progressively higher levels of arsenic contamination. However, beyond such concerns, critics of WCBs often raise concerns relating to the risks associated with accidental or even deliberate release of engineered WCB organisms. The decision to use B. subtilis as a WCB in the arsenic biosensor project was partly influenced by the United States Food and Drug Administration (U.S. FDA) classification of B. subtilis as a generally regarded as safe (GRAS) organism (Cutting, 2011). Whilst GRAS is a term that specifically relates to food applications, it is arguable whether the use of GRAS organisms has any bearing on whether engineered forms of GRAS organisms (e.g. WCBs) pose fewer safety risks than nonGRAS organisms. Risks associated with WCBs may also be mitigated through the continual development of novel physical containment (e.g. sealing the WCBs within a capsule) and genetic containment (e.g. genetic kill switches, synthetic auxotrophy (Wright et al., 2015; Mandell et al., 2015)) strategies – such approaches make the safe use of WCBs more practical. Therefore, Received 24 October, 2016; revised 12 December, 2016; accepted 2 January, 2017. *For correspondence. E-mail [email protected]; Tel. +44 (0) 207 594 5327; Fax +44 (0) 207 594 3057. Joint first authors. Microbial Biotechnology (2017) 10(2), 244–249 doi:10.1111/1751-7915.12604 Funding Information Engineering and Physical Sciences Research Council, (Grant / Award Number: ‘EP/J02175X/1’,‘EP/K034359/1’).