Global analysis of phase variation in Myxococcus xanthus

Abstract

SUMMARY Myxococcus xanthus can vary its phenotype or “phase” to produce colonies that contain predominantly yellow or tan cells that differ greatly in their abilities to swarm, survive, and develop. Yellow variants are proficient at swarming (++) and tend to lyse in liquid during stationary phase. In contrast, tan variants are deficient in swarming (+) and persist beyond stationary phase. The phenotypes and transcriptomes of yellow and tan variants were compared with mutants affected in phase variation. Thirty-seven genes were upregulated specifically in yellow variants including those for production of the yellow pigment, DKxanthene. A mutant in DKxanthene synthesis produced nonpigmented (tan) colonies but still phase varied for swarming suggesting that pigmentation is not the cause of phase variation. Disruption of a gene encoding a HTH-Xre-like regulator, highly expressed in yellow variants, abolished pigment production and blocked the ability of cells to switch from a swarm ++ to a swarm (+) phenotype, showing that HTH-Xre regulates phase variation. Among the four genes whose expression was increased in tan variants was pkn14, which encodes a serine-threonine kinase that regulates programmed cell death in Myxococcus via the MrpC-MazF toxin-antitoxin complex. High levels of phosphorylated Pkn14 may explain why tan cells enjoy enhanced survival.

Genetic Redundancy, Proximity, and Functionality of lspA , the Target of Antibiotic TA, in the Myxococcus xanthus Producer Strain

“…The above-mentioned result is consistent with prior findings that the ta biosynthetic gene cluster is transcriptionally repressed in tan variants and that expression of DKxanthene (yellow pigment) and that of TA are transcriptionally coupled (36,41,42). From these findings, we hypothesized that the tan phase bias of the ⌬lspA3 mutant may explain why it produced a smaller ZOI (Fig.…”

“…When performing the ZOI assays, we found that when the DK1622 colony that was used for liquid inoculation was older (e.g., 10 to 14 days old), the resulting culture predominantly produced tan colonies when aliquots were transferred to CTT agar plates (Fig. 6B, top), a finding that is consistent with tan variants being more fit or enriched in stationary phase (36). Thus, we directly compared yellow and tan colonies for TA production by overlaying them with E. coli (2).…”

“…5B shows that the ⌬lspA3 and ⌬lspA4 mutant colonies were smooth and tan, whereas DK1622, ⌬lspA1, and ⌬lspA2 colonies were rough and yellow. Therefore, the described development and motility phenotypes of ⌬lspA3 and ⌬lspA4 mutants could be an indirect result of a bias toward the tan phase (36,39,40). Based on a number of indirect observations, it appeared to us that tan variants produced less TA than did yellow variants.…”

“…A noted property of M. xanthus is the ability to vary phases between tan and yellow colonies, which differ in their abilities to produce the yellow pigment DKxanthene, to swarm, and to develop; in colony texture; and in other phenotypes (36)(37)(38). Under standard laboratory conditions, DK1622 is generally biased toward the yellow phase; however, importantly, when lspA3 or lspA4 was deleted, these mutants produced predominantly tan colonies (Fig.…”

Calcium is required for ixotrophy of Aureispira sp. CCB-QB1

“…A protocol to compare relative levels of EPS (Furusawa et al, 2011) was modified as follows. Aureispira QB1 cells were suspended to a density of about 1|10 8 ml 21 in SH and CNH (7 mM CaCl 2 in NH) containing 10 mg toluidine blue O (TBO) ml 21 .…”