A Minimal Threshold of c-di-GMP Is Essential for Fruiting Body Formation and Sporulation in Myxococcus xanthus

Generally, the second messenger bis-(3’-5’)-cyclic dimeric GMP (c-di-GMP) regulates the switch between motile and sessile lifestyles in bacteria. Here, we show that c-di-GMP is an essential regulator of multicellular development in the social bacterium Myxococcus xanthus. In response to starvation, M. xanthus initiates a developmental program that culminates in formation of spore-filled fruiting bodies. We show that c-di-GMP accumulates at elevated levels during development and that this increase is essential for completion of development whereas excess c-di-GMP does not interfere with development. MXAN3735 (renamed DmxB) is identified as a diguanylate cyclase that only functions during development and is responsible for this increased c-di-GMP accumulation. DmxB synthesis is induced in response to starvation, thereby restricting DmxB activity to development. DmxB is essential for development and functions downstream of the Dif chemosensory system to stimulate exopolysaccharide accumulation by inducing transcription of a subset of the genes encoding proteins involved in exopolysaccharide synthesis. The developmental defects in the dmxB mutant are non-cell autonomous and rescued by co-development with a strain proficient in exopolysaccharide synthesis, suggesting reduced exopolysaccharide accumulation as the causative defect in this mutant. The NtrC-like transcriptional regulator EpsI/Nla24, which is required for exopolysaccharide accumulation, is identified as a c-diGMP receptor, and thus a putative target for DmxB generated c-di-GMP. Because DmxB can be—at least partially—functionally replaced by a heterologous diguanylate cyclase, these results altogether suggest a model in which a minimum threshold level of c-di-GMP is essential for the successful completion of multicellular development in M. xanthus

FrzS Regulates Social Motility in Myxococcus xanthus by Controlling Exopolysaccharide Production

Myxococcus xanthus Social (S) motility occurs at high cell densities and is powered by the extension and retraction of Type IV pili which bind ligands normally found in matrix exopolysaccharides (EPS). Previous studies showed that FrzS, a protein required for S-motility, is organized in polar clusters that show pole-to-pole translocation as cells reverse their direction of movement. Since the leading cell pole is the site of both the major FrzS cluster and type IV pilus extension/retraction, it was suggested that FrzS might regulate S-motility by activating pili at the leading cell pole. Here, we show that FrzS regulates EPS production, rather than type IV pilus function. We found that the frzS phenotype is distinct from that of Type IV pilus mutants such as pilA and pilT, but indistinguishable from EPS mutants, such as epsZ. Indeed, frzS mutants can be rescued by the addition of purified EPS, 1% methylcellulose, or co-culturing with wildtype cells. Our data also indicate that the cell density requirement in S-motility is likely a function of the ability of cells to construct functional multicellular clusters surrounding an EPS core

Estudi de l efecte a mitjà termini d un tractament selvícola en una massa forestal de Quercus ilex al mont de la Hunde (Ayora) sota les propietats del sòl

[ES] Una manera adecuada de aumentar la calidad de los bosques y por tanto de los suelos es realizar una gestión sostenible de la masa forestal encaminada a aumentar la riqueza de especies y la resiliencia del bosque. En este sentido, los tratamientos selvícolas de aclareo conllevan el desarrollo de los árboles que permanecen y puede favorecer el desarrollo de la vegetación del sotobosque. Estos tratamientos pueden conllevar cambios en diferentes propiedades del suelo y en las condiciones microclimáticas de éste. Considerando que el suelo juega un papel clave en los ecosistemas forestales, al ser primordial para sostener la productividad biológica y mantener la calidad ambiental, en este trabajo se estudia el efecto de un tratamiento selvícola de aclareo, once años después de realizarse sobre una masa forestal de Quercus ilex sobre diferentes propiedades del horizonte orgánico y del suelo mineral relacionadas con el carbono y el nitrógeno. El efecto del aclareo en una parcela Tratada se compara con una parcela Control. Los resultados obtenidos muestran que en el suelo mineral de la parcela Tratada hay un mayor contenido de carbono orgánico del suelo (COS), de carbono orgánico soluble en agua (WCOS) y de carbono de la biomasa microbiana (CBM). Se obtuvo una alta correlación entre el WCOS y CBM del suelo, y entre estos y el COS. No se encontraron diferencias significativas entre tratamientos para ninguna de las variables estudiadas en distintas capas del horizonte orgánico.[EN] An appropriate way to increase the quality of forests and therefore of soils is to carry out sustainable management of the forest stand aimed at increasing species richness and resilience of the forest. In this respect, silvicultural thinning treatments lead to the development of remaining trees and can favour the development of understorey vegetation. These treatments can lead to changes in different soil properties and soil microclimatic conditions. Considering that soil plays a key role in forest ecosystems, as it is essential to sustain biological productivity and maintain environmental quality, this work studies the effect of a silvicultural thinning treatment, eleven years after it was carried out on a Quercus ilex forest stand, on different properties of the organic horizon and mineral soil related to carbon and nitrogen. The effect of thinning on a treated plot is compared with a control plot. The results obtained show that in the mineral soil of the treated plot there is a higher content of soil organic carbon (COS), water soluble organic carbon (WCOS) and microbial biomass carbon (MBC). A high correlation was obtained between soil WCOS and CBM, and between these and COS. No significant differences were found between treatments for any of the variables studied in different layers of the organic horizon.Ordiñaga Lancero, C. (2023). Estudio del efecto a medio plazo de un tratamiento selvícola en una masa forestal de Quercus ilex en el monte de la Hunde (Ayora) sobre las propiedades del suelo. Universitat Politècnica de València. http://hdl.handle.net/10251/19762

Work satisfaction among nurse case managers: A comparison of two practice models

Case management by professional nurses is a rapidly expanding function within managed care systems. The purposes of this study were to describe the extent of perceived control over nursing practice, job stress, and work satisfaction among 30 Nurse Case Managers (n = 30) practicing in two different models of nursing case management and to describe the impact of control over nursing and job stress on work satisfaction. Three instruments were used: Control Over Nursing Practice Scale, Nurse Case Manager Job Stress Index, and Index of Work Satisfaction for Nurse Case Managers. Work satisfaction was positively correlated with control over nursing practice (r =.65, p =.01) and a negatively correlated with job stress (r = -.43, p =.01). Demographic characteristics were not correlated with the variables under study. Control over nursing practice had a stronger impact (B =.59) on work satisfaction than did job stress (B = -.33); together they explained 53 percent of the variance in work satisfaction

A cascade of coregulating enhancer binding proteins initiates and propagates a multicellular developmental program

The signal transduction networks that initiate multicellular development in bacteria remain largely undefined. Here, we report that Myxococcus xanthus regulates entry into its multicellular developmental program using a novel strategy: a cascade of transcriptional activators known as enhancer binding proteins (EBPs). The EBPs in the cascade function in sequential stages of early development, and several lines of evidence indicate that the cascade is propagated when EBPs that function at one stage of development directly regulate transcription of an EBP gene important for the next developmental stage. We also show that the regulatory cascade is designed in a novel way that extensively expands on the typical use of EBPs: Instead of using only one EBP to regulate a particular gene or group of genes, which is the norm in other bacterial systems, the cascade uses multiple EBPs to regulate EBP genes that are positioned at key transition points in early development. Based on the locations of the putative EBP promoter binding sites, several different mechanisms of EBP coregulation are possible, including the formation of coregulating EBP transcriptional complexes. We propose that M. xanthus uses an EBP coregulation strategy to make expression of EBP genes that modulate stage-stage transitions responsive to multiple signal transduction pathways, which provide information that is important for a coordinated decision to advance the developmental process