Journal of Microbiology

Research Support, Non-U.S. Gov'ts

Effects of Exopolysaccharide Production on Liquid Vegetative Growth, Stress Survival, and Stationary Phase Recovery in Myxococcus xanthus: Wei Hu , Jing Wang , Ian McHardy , Renate Lux , Zhe Yang , Yuezhong Li , Wenyuan Shi; J. Microbiol. 2012;50(2):241-248. Published online April 27, 2012; DOI: https://doi.org/10.1007/s12275-012-1349-5

Abstract: Exopolysaccharide (EPS) of Myxococcus xanthus is a wellregulated cell surface component. In addition to its known functions for social motility and fruiting body formation on solid surfaces, EPS has also been proposed to play a role in multi-cellular clumping in liquid medium, though this phenomenon has not been well studied. In this report, we confirmed that M. xanthus clumps formed in liquid were correlated with EPS levels and demonstrated that the EPS encased cell clumps exhibited biofilm-like structures. The clumps protected the cells at physiologically relevant EPS concentrations, while cells lacking EPS exhibited significant reduction in long-term viability and resistance to stressful conditions. However, excess EPS production was counterproductive to vegetative growth and viable cell recovery declined in extended late stationary phase as cells became trapped in the matrix of clumps. Therefore, optimal EPS production by M. xanthus is important for normal physiological functions in liquid.

ppGpp-Mediated Stationary Phase Induction of the Genes Encoded by Horizontally Acquired Pathogenicity Islands and cob/pdu Locus in Salmonella enterica serovar Typhimurium: Miryoung Song , Hyun-Ju Kim , Sangryeol Ryu , Hyunjin Yoon , Jiae Yun , Hyon E. Choy; J. Microbiol. 2010;48(1):89-95. Published online March 11, 2010; DOI: https://doi.org/10.1007/s12275-009-0179-6

Abstract: Salmonella enterica is highly diverse in terms of genome structure, which is at least partly due to the horizontal transfer of genetic elements from various sources. In this study, we examined the expression profiles of such genes in Salmonella Pathogenicity Islands (SPIs) and the cob/pdu locus, horizontally acquired large DNA segments, during growth under standard growth conditions. Transcripts from exponentially growing and early stationary phase Salmonellae were compared using various methods including cDNA microarray analysis. Nearly all genes encoded by SPIs and the cob/pdu locus were induced at the onset of the stationary phase in a stringent molecule ppGpp-dependent but stationary phase σ, σ38-independent manner. Although, it has been suggested that ppGpp acts in concert with DksA, we found the stationary phase induction of those SPI genes was not DksA dependent. It is suggested that ppGpp stimulates the expression of these stress-inducible genes encoded by horizontally acquired DNA, by itself or in concert with DksA.

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