Seasonal and daily dynamics of the population of the pathogenic bacterium Burkholderia pseudomallei in the natural environment largely depends on bacteriophages

Bacteriophages are important natural regulators of bacterial populations. Researchers from the UK and Russia found further evidence of this when they developed a mathematical model describing the spread of melioidosis in South Asia.

Melioidosis (false glanders, Whitmore's disease) is an infectious disease caused by the bacterium Burkholderia pseudomallei . The infection typically affects the lungs and manifests as sepsis with the formation of abscesses of varying severity in the internal organs. B. pseudomallei lives in soil and groundwater and is transmitted to humans and animals through direct contact with the infecting organism. Strains that cause melioidosis are found in Southeast Asia, northern Australia, and some other tropical regions.

B. pseudomallei naturally coexists with viruses specific to this bacterium—bacteriophages (phages). While studying the factors influencing the spread of melioidosis, scientists decided to investigate the relationship between the abundance of phages and bacteria and their exposure to various environmental factors, particularly ultraviolet radiation and temperature*. They chose rice fields in Thailand as their experimental site.

Scientists have found that the risk of B. pseudomallei infection is highest between March and September due to a decrease in phage numbers, which, in turn, is caused by high levels of solar UV radiation. Thus, in spring and summer, from 8 a.m. to 9 p.m., the active sun reduces phage numbers and, consequently, increases bacteria numbers.

With regard to the ambient temperature, the following dependence is observed: at more than 35°C, phages enter the lytic phase and begin to actively destroy bacteria, reducing their population.

Bacterial abundance also depends on the use of fertilizers. For example, iron-containing fertilizers promote the death of phages. Given the potential risk of increasing the population of pathogenic B. pseudomallei bacteria, the authors believe it is important to further study the effects of various fertilizers on the balance of bacteriophages and bacteria in the natural environment.

Scientists continue to refine a mathematical model of the spread of melioidosis, which could potentially help predict periods of increased risk of infection and, consequently, prevent outbreaks among rice field workers. This model could also improve occupational safety by adjusting work schedules according to the season. The model will also help assess how global warming will affect the spread of the disease.

* Egilmez HI, Morozov AY, Clokie MRJ, et al. Temperature-dependent virus lifecycle choices may reveal and predict faces of the biology of opportunistic pathogenic bacteria // Scientific Reports, 2018, 8, Article number: 9642. DOI: 10.1038/s41598-018-27716-3