Antonio L. Extremera

Differential Regulation of Six Heavy Metal Efflux Systems in the Response of Myxococcus xanthus to Copper

ABSTRACT Myxococcus xanthus has to cope with changes in its environment during growth and development. Among these factors, the concentration of copper is crucial due to the essential toxic effect of this metal, which forces the cells to maintain a tight homeostasis. The M. xanthus copper response is more complex than that in other bacteria, which is reflected by the different copper sensitivities of growing and developing cells. In the present study, the participation in copper homeostasis of six heavy metal efflux systems encoded in the M. xanthus genome has been examined. Three of these pumps exhibit the signature sequences in transmembrane domain 4 of the Cus systems (Cus1, Cus2, and Cus3), while the other three exhibit the motifs of the Czc systems (Czc1, Czc2, and Czc3). The Cus2 and Cus3 systems are inducible by copper and monovalent metals, functioning as the main copper efflux pumps, while the Cus1 system is implicated in Zn2+ homeostasis. The Czc systems are also differentially regulated either by divalent metals but not by copper (Czc1), by copper and divalent metals (Czc2), or by starvation (Czc3). The differential regulation of these six efflux systems ensures the proper completion of the M. xanthus life cycle in an environment with fluctuating concentrations of copper and other metals.

Chemical, enzymatic and microbiological synthesis of 8,12-eudesmanolides: Synthesis of sivasinolide and yomogin analogues

Abstract Conversion of α-santonin into 8,12-eudesmanolides was accomplished by chemical, enzymatic and microbiological means. Catalytic hydrogenation of α-santonin gave a mixture of hexahydro derivatives, which were sequentially isolated by lipase-catalysed selective acylation. Reduction of the 6α-lactone ring, chemical acetylation and enzymatic selective deacetylation gave an eudesmane with a hydroxymethylene group at C-12, which was hydroxylated at C-8 by Rhizopus nigricans . Finally lactonization with TPAP allowed us to obtain 8,12-eudesmanolides.

Expression and physiological role of three Myxococcus xanthus copper-dependent P1B-type ATPases during bacterial growth and development.

ABSTRACT Myxococcus xanthus is a soil-dwelling bacterium that exhibits a complex life cycle comprising social behavior, morphogenesis, and differentiation. In order to successfully complete this life cycle, cells have to cope with changes in their environment, among which the presence of copper is remarkable. Copper is an essential transition metal for life, but an excess of copper provokes cellular damage by oxidative stress. This dual effect forces the cells to maintain a tight homeostasis. M. xanthus encodes a large number of genes with similarities to others reported previously to be involved in copper homeostasis, most of which are redundant. We have identified three genes that encode copper-translocating P1B-ATPases (designated copA, copB, and copC) that exhibit the sequence motifs and modular organizations of those that extrude Cu+. The expression of the ATPase copC has not been detected, but copA and copB are differentially regulated by the addition of external copper. However, while copB expression peaks at 2 h, copA is expressed at higher levels, and the maximum is reached much later. The fact that these expression profiles are nearly identical to those exhibited by the multicopper oxidases cuoA and cuoB suggests that the pairs CuoB-CopB and CuoA-CopA sequentially function to detoxify the cell. The deletion of any ATPase alters the expression profiles of other genes involved in copper homeostasis, such as the remaining ATPases or the Cus systems, yielding cells that are more resistant to the metal.

Glycerol 3-Phosphate Inhibits Swarming and Aggregation of Myxococcus xanthus

We have cloned a gene of Myxococcus xanthus with similarities to the permease for glycerol 3-phosphate (G3P) of other bacteria. Expression of the gene increased significantly during the first hours of starvation. Swarming of the wild-type strain was inhibited and aggregation was delayed by G3P. Conversely, a DeltaglpT strain aggregated even on rich medium. These results indicate that G3P may function to regulate the timing of aggregation in M. xanthus.

Bacteriological study of the feathers and lice of captive common buzzards (Buteo buteo)

We have investigated the external and internal bacterial flora associated with several species of lice parasites of captive common buzzards (Buteo buteo) and studied the bacterial flora on the host feathers. The bacterial flora inside the ectoparasites was significatively different from that of their surface. Bacteria of genus Staphylococcus, especially S. aureus, predominated, being more abundant on lice surface. Bacillus was another Gram-positive bacteria frequently isolated, although it was more abundant as a component of the internal flora. A very low number of enterobacteria and strict anaerobes was obtained. Bacteria isolated from bird feathers reveal some contamination from humans.

mlpB, a gene encoding a new lipoprotein in Myxococcus xanthus

Aims: To search for and study the genes involved in the regulation of phosphate in the soil developmental bacterium Myxococcus xanthus.

phoR1, a gene encoding a new histidine protein kinase in Myxococcus xanthus

A soil bacterium able to undergo multicellular development and a coordinated gliding in swarms, requires an accurate regulatory network of phosphorelay proteins. Inorganic phosphate is a limiting nutrient in soil and its importance in regulation is critical. As a step towards studying phosphate regulation and its influence in the developmental process in this bacterium, we screened a Myxococcus xanthus library for clones with phosphatase activity, and found four different ones. The deduced sequence of one of the cloned inserts is similar to that of the classic transmembrane histidine protein kinase of the sensor family of the two-component signal transduction systems with a high sequence similarity to the sensor kinase in the Pho regulon of Bacillus subtilis PhoR. This gene has been named phoR1 and its deduced amino acid sequence consists of 455 residues with a predicted molecular mass of 48.5 kDa. The M. xanthus PhoR1 deduced sequence contains all the characteristic histidine protein kinase motifs in the same order and with the same spacing. A hydropathy profile indicates two membrane-spanning segments located at the extreme N-terminus, according to the putative sensor role of this domain. A gene-disrupted mutant is unable to produce normal mature fruiting bodies and produces fewer spores.

DNase activity during the life cycle of Myxococcus coralloides and M. xanthus

Abstract DNase activity was measured during various stages of the life cycle of Myxococcus coralloides D. A high level of activity was maintained in vegetative cells, fruiting bodies and after myxospore induction by glycerol. In this microorganism, DNase specific activity increased during both the vegetative and developmental cycles. In contrast, Myxococcus xanthus DK101 exhibited a different DNase activity.