Abstract
BackgroundA rice associated bacterium Burkholderia gladioli strain NGJ1 demonstrates mycophagy, a phenomenon wherein bacteria feed on fungi. Previously, we have reported that NGJ1 utilizes type III secretion system (T3SS) to deliver a prophage tail-like protein (Bg_9562) into fungal cells to establish mycophagy.ResultsIn this study, we report that calcium ion concentration influences the mycophagous ability of NGJ1 on Rhizoctonia solani, an important fungal pathogen. The calcium limiting condition promotes mycophagy while high calcium environment prevents it. The expression of various T3SS apparatus encoding genes of NGJ1 was induced and secretion of several potential T3SS effector proteins (including Bg_9562) into extracellular milieu was triggered under calcium limiting condition. Using LC-MS/MS proteome analysis, we identified several calcium regulated T3SS effector proteins of NGJ1. The expression of genes encoding some of these effector proteins was upregulated during mycophagous interaction of NGJ1 with R. solani. Further, mutation of one of these genes (endo-β-1, 3- glucanase) rendered the mutant NGJ1 bacterium defective in mycophagy while complementation with full length copy of the gene restored its mycophagous activity.ConclusionOur study provides evidence that low calcium environment triggers secretion of various T3SS effectors proteins into the extracellular milieu and suggests the importance of cocktail of these proteins in promoting mycophagy.
Highlights
A rice associated bacterium Burkholderia gladioli strain NGJ1 demonstrates mycophagy, a phenomenon wherein bacteria feed on fungi
Calcium regulates the expression of Type III secretion system (T3SS) apparatus encoding genes We have previously reported that a T3SS mutant strain (NGJ12) of NGJ1 is defective in mycophagy [14]
We have demonstrated that a rice associated bacterium Burkholderia gladioli strain NGJ1 utilizes T3SS to feed on fungi [14]
Summary
A rice associated bacterium Burkholderia gladioli strain NGJ1 demonstrates mycophagy, a phenomenon wherein bacteria feed on fungi. We have reported that NGJ1 utilizes type III secretion system (T3SS) to deliver a prophage tail-like protein (Bg_9562) into fungal cells to establish mycophagy. Single-celled, microorganisms and are omnipresent in diverse natural habitats like soil, water, air, etc. They are found in association with or inhabiting within multicellular organisms and demonstrate diverse interactions such as mutualism, commensalism, antagonism or parasitism with other cohabiting organisms [1, 2]. Burkholderia terrae can feed on a soil fungus There are many reports of mycophagous bacteria, the mechanistic insight about bacterial mycophagy remains largely unknown
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