Abstract
Two unrecognizable strains of the same bacterial species form a distinct colony boundary. During growth as colonies, Myxococcus xanthus uses multiple factors to establish cooperation between recognized strains and prevent interactions with unrecognized strains of the same species. Here, ΔMXAN_0049 is a mutant strain deficient in immunity for the paired nuclease gene, MXAN_0050, that has a function in the colony-merger incompatibility of Myxococcus xanthus DK1622. With the aim to investigate the factors involved in boundary formation, a proteome and metabolome study was employed. Visualization of the boundary between DK1622 and ΔMXAN_0049 was done scanning electron microscope (SEM), which displayed the presence of many damaged cells in the boundary. Proteome analysis of the DK1622- boundary disclosed many possible proteins, such as cold shock proteins, cell shape-determining protein MreC, along with a few pathways, such as RNA degradation, phenylalanine, tyrosine and tryptophan biosynthesis, and Type VI secretion system (T6SS), which may play major roles in the boundary formation. Metabolomics studies revealed various secondary metabolites that were significantly produced during boundary formation. Overall, the results concluded that multiple factors participated in the boundary formation in M. xanthus, leading to cellular damage that is helpful in solving the mystery of the boundary formation mechanism.
Highlights
Close relatives of some bacterial species, such as Proteus mirabilis, Bacillus subtilis, and Myxococcus xanthus, are able to form visible boundaries to separate the swarming colonies of different strains that are unrecognizable from each other [1,2,3,4,5]
A mechanism for the colony-merger incompatibility is that a donor cell transports effector proteins to a recipient cell in close proximity through the type VI secretion system (T6SS) apparatus in a contact-dependent process, and myxobacteria use the contact-dependent mechanism for outer membrane exchange (OME) [6,7,8,9,10,11,12]
We investigated the morphologies of the colony boundaries between M. xanthus DK1622 and the incompatible mutant, ∆MXAN_0049, to gain more insight into the cell status within the boundary by staining technique, light, and scanning electron microscope (SEM)
Summary
Close relatives of some bacterial species, such as Proteus mirabilis, Bacillus subtilis, and Myxococcus xanthus, are able to form visible boundaries to separate the swarming colonies of different strains that are unrecognizable from each other [1,2,3,4,5]. A mechanism for the colony-merger incompatibility is that a donor cell transports effector proteins to a recipient cell in close proximity through the type VI secretion system (T6SS) apparatus in a contact-dependent process, and myxobacteria use the contact-dependent mechanism for outer membrane exchange (OME) [6,7,8,9,10,11,12]. It was reported that formation of the boundary is due to the delivery of toxins by OME [13]. What happens in the boundary and how the boundaries form between the incompatible cells remains unclear.
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