Effect of Chemical Factors on Natural Biocontrol of the Melioidosis Agent by AMP1-Like Bacteriophages in Agricultural Ecosystems

The causative agent of melioidosis, Burkholderia pseudomallei, as well as closely related nonpathogenic bacteria of the B. pseudomallei/thailandensis complex of species, are found in soils and water bodies in melioidosis-endemic areas which results in significant biological risks to agricultural workers in these regions. Bacteriophages related to the phiBp-AMP1 phage are the most common known group of B. pseudomallei/thailandensis viruses. The interaction of these bacteriophages with their hosts may be a key factor in the natural control of the B. pseudomallei population, which determines the dynamics of melioidosis infection in humans. In this study, we showed that frequently used herbicides (paraquat, atrazine, 2,4-D, ametrine, and copper dichloride) did not significantly affect the stability and infectivity of the AMP1 phage, while iron(II) salts, which are used as fertilizers, inactivated the phage even at concentrations of about 0.1 mM or lower. Moreover, the concentration of sodium chloride was critical for the infectivity of the AMP1 phage, both against B. thailandensis and against the pathogen B. pseudomallei. When the concentration of this salt in solution was less than 3 g/L, the phages ceased infecting the host cells. Therefore, soil salinity may thus be responsible for the mosaic pattern of B. pseudomallei population dynamics within a number of endemic regions, such as northeastern Thailand.