Lawrence Livermore National Laboratory



Yongqin Jiao

Overview

We conducted data synthesis and knowledge integration to explore the relationship between growth rate and microbial persistence, identifying specific key physiological factors that influence microbial persistence. This effort integrates genomic science with the physiological investigation of microbial survival and persistence. Questions addressed in this study relate to the ecological effect of antimicrobial compounds and microbial processes that could have many environmental and biotechnological impacts.

Background and Research Objectives

Our goal was to explore the relationship between growth rate and pathogenicity in human pathogens. Although a great deal of knowledge has been obtained in the past decades on empirical observations of maximum growth rate, pathogen virulence, and host motility (Leggett et al. 2017), there is a limited understanding of mechanisms that underlie and unify these factors, which has caused an apparent disconnect between the predicted influence of growth rate on virulence and the observed cross-species patterns in virulence. A great deal of controversy exists in fundamental assumptions of current theoretical models developed that explain the trade-off between growth rate and pathogenicity. In an effort to help clarify some of the disparity and variability of the relationships observed among different pathogenic species, we conducted data synthesis and knowledge integration concerning the relationship between maximum growth rate and virulence across species. We explored potential underlying factors that control the regulation between growth rate and virulence on individual cell and community levels. This study identified a knowledge gap and developed testable hypotheses with specific pathogens (and hosts) with regard to principles that govern pathogen growth rate, persistence, and pathogenicity.

Impact on Mission

In this feasibility study, we examined bacterial physiology and its unique features under slow-growing conditions. We explored the relationship between growth rate and microbial persistence, with specific key physiological factors identified that influence microbial persistence. Studying the slow growing state of microorganisms is important for many environmental and biotechnological applications. The potential underlying factors that control the regulation between growth rate and cellular fitness were identified, including knowledge gaps and testable hypotheses. Questions addressed in this study relate to a basic understanding of the ecological effect of antimicrobial compounds and microbial processes that could have many environmental and biotechnological impacts. Our research supports the NNSA goal of applying our science and technology capabilities to deal with broad national security challenges. Our research also enhances Lawrence Livermore National Laboratory's core competency in bioscience and bioengineering.

Conclusion

This effort integrated genomic science with a physiological investigation to identify specific key physiological factors that influence microbial persistence. Questions addressed in this study relate to a basic understanding of the ecological effect of antimicrobial compounds resulting from a protective mechanism that microbes exert under stress (Harms et al. 2016). The ability of microbes to cope with environmental changes depends upon both growth rate (when conditions are favorable) and persistence (when conditions are not favorable). The phenomenon of persistence is caused by the formation of specialized persister cells that evade antibiotic mortality and other stresses and enter a physiologically dormant state, irrespective of whether they possess genes enabling antibiotic resistance or not (Miyaue et al. 2018). In an effort to understand the physiological and genetic influence on bacterial persistence during stress, recent studies on antibiotic resistance suggest that adaptation and persistence is not necessarily due to a genetic change of the genome sequences; rather, it is due to transient changes of gene expression programs (Harms et al. 2016, Maisonneuve and Gerdes 2014). Reduced growth or growth arrest significantly diminishes the potency of most antibiotics as a result of the presence of persisters that neither grow nor die in the presence of antibiotics (Hong et al. 2012) Regulation and signaling pathways that govern persister formation is not fully understood (Mechold et al. 2013). A few of the known common physiological factors that could explain the switch from non-virulence to virulence when cells enter a persister-state include ppGpp guanosine tetraphosphate-dependent stringent response (Hauryliuk et al. 2015, Gaca et al. 2015), RpoS-dependent general stress response, and SOS-dependent DNA-damaging response. A deeper understanding of persister formation and its genetic regulation could lead to novel therapeutic strategies that effectively target bacterial persisters.

References

Gaca, A. O., et al. 2015. "Many Means to a Common End: the Intricacies of (p)ppGpp Metabolism and its Control of Bacterial Homeostasis." Journal of Bacteriology 197(7): 1146–1156.

Harms, A., et al. 2016. "Mechanisms of Bacterial Persistence During Stress and Antibiotic Exposure." Science 2016, 354(6318).

Hauryliuk, V., et al. 2015. "Recent Functional Insights Into the Role of (p)ppGpp in Bacterial Physiology." National Review of Microbiology 13(5): 298–309.

Hong, S. H., et al. 2012. "Bacterial Persistence Increases as Environmental Fitness Decreases." Microbial Biotechnology 5(4): 509–522.

Leggett, H. C., et al. 2017. "Growth Rate, Transmission Mode and Virulence in Human Pathogens." Philosophical Transactions of The Royal Society B - Biological Sciences 372(1719).

Maisonneuve, E. and K. Gerdes. "Molecular Mechanisms Underlying Bacterial Persisters." Cell 157(3): 539–548.

Mechold U., et al. 2013. "Differential Regulation by ppGpp Versus pppGpp in Escherichia coli." Nucleic Acids Research 41(12): 6175–6189.

Miyaue, S., et al. 2018. "Bacterial Memory of Persisters: Bacterial Persister Cells Can Retain Their Phenotype for Days or Weeks After Withdrawal From Colony-Biofilm Culture." Frontiers in Microbiology 9:1396.