Upstream gene of the mgl operon controls the level of MglA protein in Myxococcus xanthus

Abstract

The mgl operon contains two open reading frames (ORFs) which are transcribed together. A collection of nonmotile mutants helped to define the downstream ORF as the mglA gene. Single mutations at the mglA locus completely abolish motility. A series of deletion mutations was constructed to determine the role of the upstream ORF (now called mglB). A strain carrying a deletion in mglB and with an intact mglA produces small colonies. The cells are motile, but their rate of swarm spreading is reduced. Measurements of cell movement showed that mglB mutant cells advanced, on average, less than 0.1 cell length in 5 min. The mglB+ cells advanced an average of 1.3 cell lengths in the same time. Extracts of AmglB cells contain 15 to 20% as much of the 22-kDa MglA protein as do mglB+ cells, as measured in Western immunoblots and enzyme-linked immunosorbent assays. However, the amount of mgl transcript is the same in the AmglB mutants as in the mglB+ strain. Heterozygous partial diploids mglBImglA with the wild-type alleles in trans have normal motility, demonstrating that the largest of the mglB deletions is not polar on mglA. Like other motility defects, a AmglB mutation alters fruiting body development and sporulation. The mglB mutants delayed aggregation, produced small immature fruiting bodies, and sporulated at 45 to 50% wild-type levels. All aspects of the mglB mutant phenotype are explained by the reduced levels of mglA protein and the assumption that it limits the amount of gliding.Gliding motility is defined as translocation over a solid surface and involves movement in the direction of the long axis of the cell (8). In all known gliding organisms, movement is correlated with the production of slime. There is occasional reversal of direction, but motion is smooth, with no rotation apparent. No appendages, which would suggest a mechanism for gliding, have been identified. Gliding is employed by a diverse group of organisms, including Cytophaga and Flexibacter spp., the myxobacteria, and the filamentous cyanobacteria, all of which belong to evolutionarily different groups (33). These organisms range in length from 5 to 50 ,um and glide at rates of 1 to 300 pum/min. While different explanations for gliding have been proposed for different organisms (directional extrusion of slime [24], polar release of surfactant [12], and movement by contraction [8,26], for example), the molecular mechanism of gliding remains unsettled.Genes that regulate the pattern of gliding motility have been found. Two genetically independent sets of genes, called the adventurous (A) and social (S) motility systems, have been identified in Myxococcus xanthus (18,19

Alignment enhances the cell-to-cell transfer of pilus phenotype

“…Null mutations in mglA block both Aand S-motility (16). Although mgl mutant cells have been observed to oscillate back and forth there is no net translocation; the oscillations are at high frequency and have small ) was mixed with a ⌬mgl recipient (⌬tgl pilA ϩ ⌬mglBA) there was stimulation, but only after a delay of several hours (Fig.…”

“…xanthus Strains and Media. Strains DK1217 (aglB1), DK6204 (⌬mglBA), DK10405 (⌬tgl::Tc r ; tetracycline resistance), DK10407 (⌬pilA::Tc r ), and DK10410 (⌬pilA) have been described previously (1,11,16,17). The following strains were constructed by generalized transduction with the bacteriophages Mx4 or Mx8 as indicated (13 ) transcriptional fusion was constructed by E. Licking (Stanford University) and will be described elsewhere.…”

Frozen motion of gliding bacteria outlines inherent features of the motility apparatus

“…For ' in vivo ' studies of actively gliding cells, four different bacterial strains were used : the fruiting bacteria M. xanthus [strain DK1622, a non-gliding mgl mutant of M. xanthus ; strain DK6204 (genotype ∆mglAB ; Hartzell & Kaiser, 1991) ; and mutant strains DK10407 (A + S − ; genotype pilA : :Tc R ), DK11303 (A − S + ; genotype aglB1) and DK11316 (A − S − ; genotype pilA : :Tc R , ∆cglB) ; M. xanthus mutant genotypes according to D. Kaiser, personal communication] and S. aurantiaca (strain DW4\3-1 ; Qualls et al, 1978), and the non-fruiting bacteria F. filiformis (strain Fxe1 ; DSMZ, Braunschweig, Germany) and F. johnsoniae (formerly C. johnsonae) (strain Cyj3 ; DSMZ, Braunschweig, Germany). Cells were grown as liquid cultures (50 ml) in appropriate media at 320 r.p.m.…”

Regulation of cohesion-dependent cell interactions in Myxococcus xanthus

“…There are several taxonomically unrelated groups of gliding bacteria, including the myxobacteria, Cytophaga and Flexibacter spp., and because of the very distant relationship between these groups, there may be more than one mechanism for gliding motility. In Myxococcus xanthus, the most well-studied myxobacterium, gliding motility appears to be controlled by two nearly independent multigene systems, the adventurous (A) motility system, which controls the movement of individual cells, and the social (S) motility system, which controls the movement of groups of cells (17)(18)(19)(20)(21). Also involved in gliding in M. xanthus are the fiz genes, which show striking homology to the chemotaxis genes of Salmonella typhimurium and control the frequency of direction reversal (5,6,31).…”