Experimental Bacteriophage Addition to Soil Depresses Bacterial Respiration and Alters Nitrogen Transformations

Soil heterogeneity and complex host-phage relationships impede understanding phage influence on terrestrial nutrient cycles. We performed laboratory experiments quantifying phage effects on bacterial respiration and inorganic soil nitrogen and phosphorus changes. Soil microcosms under reducing conditions were inoculated with a single bacterial host ( Gordonia rubripertincta ) or with the host + phage (φApollonia6). Respiration declined immediately following phage introduction and was lower in the presence of phage through time. Phage additions increased variance in N transforms. NH 4 + decline did not match <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mtext>NO</mml:mtext> </mml:mrow> <mml:mn>3</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> gain, suggesting microbial immobilization in +phage microcosms. Net <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mtext>NO</mml:mtext> </mml:mrow> <mml:mn>3</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> accumulation was observed with phage, suggesting viral interruption of bacterial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mtext>NO</mml:mtext> </mml:mrow> <mml:mn>3</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> reduction. Phosphate pools declined in both treatments, likely due to cell uptake and incorporation into phage. This single host-phage system highlights phage depression of bacterial respiration and altered nutrient transformation and can be the basis for further investigations into phage-bacteria soil interactions and their impacts on terrestrial nutrient cycling.