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Phosphate Limitation (phosphate + limitation)

Distribution by Scientific Domains

Life Sciences	62%

Selected Abstracts

GROWTH AND PHOSPHORUS UPTAKE BY THE TOXIC DINOFLAGELLATE ALEXANDRIUM CATENELLA (DINOPHYCEAE) IN RESPONSE TO PHOSPHATE LIMITATION,

JOURNAL OF PHYCOLOGY, Issue 5 2010
Cécile Jauzein
Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO43,) concentrations in this environment over the 1970,1995 period. To determine if this dinoflagellate species has a competitive advantage in PO43, -limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO43, uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (QP and QC). Shifts in trends of QP/QC and QP per cell (QP·cell,1) along the DR gradient allowed the definition of successive P-stress thresholds for A. catenella cells. The maximal uptake rate of 33PO43, increased strongly with the decrease in DR and the decrease in QP/QC, displaying physiological acclimations to PO43, limitation. Concerning maximal APA per cell, the observation of an all-or-nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO43, limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO43, threshold between 0.4 and 1 ,M. As lower PO43, concentrations are regularly observed during A. catenella blooms in Thau lagoon, a significant portion of P uptake by A. catenella cells in the field may come from organic compounds. [source]

Genome-wide transcriptomic and proteomic analysis of the primary response to phosphate limitation in Streptomyces coelicolor M145 and in a ,phoP mutant

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 14 2007
Antonio Rodríguez-García
Abstract Phosphate limitation in Streptomyces and in other bacteria triggers expression changes of a large number of genes. This response is mediated by the two-component PhoR,PhoP system. A Streptomyces coelicolor ,phoP mutant (lacking phoP) has been obtained by gene replacement. A genome-wide analysis of the primary response to phosphate limitation using transcriptomic and proteomic studies has been made in the parental S. coelicolor M145 and in the ,phoP mutant strains. Statistical analysis of the contrasts between the four sets of data generated (two strains under two phosphate conditions) allowed the classification of all genes into 12 types of profiles. The primary response to phosphate limitation involves upregulation of genes encoding scavenging enzymes needed to obtain phosphate from different phosphorylated organic compounds and overexpression of the high-affinity phosphate transport system pstSCAB. Clear interactions have been found between phosphate metabolism and expression of nitrogen-regulated genes and between phosphate and nitrate respiration genes. PhoP-dependent repressions of antibiotic biosynthesis and of the morphological differentiation genes correlated with the observed ,phoP mutant phenotype. Bioinformatic analysis of the presence of PHO boxes (PhoP-binding sequences) in the upstream regions of PhoP-controlled genes were validated by binding of PhoP, as shown by electrophoretic mobility shift assays. [source]

New ways to break an old bond: the bacterial carbon,phosphorus hydrolases and their role in biogeochemical phosphorus cycling

ENVIRONMENTAL MICROBIOLOGY, Issue 10 2007
John P. Quinn
Summary Phosphonates are organophosphorus molecules that contain the highly stable C,P bond, rather than the more common, and more labile, C,O,P phosphate ester bond. They have ancient origins but their biosynthesis is widespread among more primitive organisms and their importance in the contemporary biosphere is increasingly recognized; for example phosphonate-P is believed to play a particularly significant role in the productivity of the oceans. The microbial degradation of phosphonates was originally thought to occur only under conditions of phosphate limitation, mediated exclusively by the poorly characterized C,P lyase multienzyme system, under Pho regulon control. However, more recent studies have demonstrated the Pho-independent mineralization by environmental bacteria of three of the most widely distributed biogenic phosphonates: 2-aminoethylphosphonic acid (ciliatine), phosphonoacetic acid, and 2-amino-3-phosphonopropionic acid (phosphonoalanine). The three phosphonohydrolases responsible have unique specificities and are members of separate enzyme superfamilies; their expression is regulated by distinct members of the LysR family of bacterial transcriptional regulators, for each of which the phosphonate substrate of the respective degradative operon serves as coinducer. Previously no organophosphorus compound was known to induce the enzymes required for its own degradation. Whole-genome and metagenome sequence analysis indicates that the genes encoding these newly described C,P hydrolases are distributed widely among prokaryotes. As they are able to function under conditions in which C,P lyases are inactive, the three enzymes may play a hitherto-unrecognized role in phosphonate breakdown in the environment and hence make a significant contribution to global biogeochemical P-cycling. [source]

PRODUCTION OF PARALYTIC SHELLFISH TOXINS BY APHANIZOMENON SP.

JOURNAL OF PHYCOLOGY, Issue 4 2002
LMECYA 31 (CYANOBACTERIA)
We examined intracellular and extracellular paralytic shellfish toxins (PST) in a strain of Aphanizomenon sp. (LMECYA31) isolated from a Portuguese freshwater reservoir throughout the growth cycle and under different conditions affected by temperature and nitrate and phosphate availability. PST concentrations and compositions were greatly influenced by cell density, growth stage, and temperature and nutrients conditions. On a per-cell basis results showed (1) the enhancement of PST cell quota after the end of exponential growth phase in nutrient replete batch cultures, (2) the absence of a PST increment at late growth stages under phosphate limitation, (3) a rise in PST maximum cell quota under nitrate depletion, and (4) the enhancement of toxin production at higher temperatures. The relative proportion of the four toxins detected, neoSTX, dcSTX, STX and GTX5, also changed within and between culture settings. While growing under phosphate rich media cells produced mainly GTX5 and neoSTX, whereas under phosphate limitation the proportion of STX and dcSTX increased substantially with culture age. Large amounts of extracellular toxins were found in the culture medium, increasing during culture time. Extracellular toxin composition in each culture was fairly constant and always similar to the intracellular composition found at late stages of growth. This further supported other research that indicates that PSTs are released to the water through cell lysis, and a significant concentration of PST may be expected to remain in the water upon the collapse of a toxic bloom or after cells removal by water treatment. [source]

FERRIC CHELATE REDUCTASE ACTIVITY AS AFFECTED BY THE IRON-LIMITED GROWTH RATE IN FOUR SPECIES OF UNICELLULAR GREEN ALGAE (CHLOROPHYTA)1

JOURNAL OF PHYCOLOGY, Issue 3 2002
Harold G. Weger
Four species of green algae (Chlorella kessleri Fott et Nováková, Chlorococcum macrostigmatum Starr, Haematococcus lacustris[Girod-Chantrans] Rostaf., Stichococcus bacillaris Näg.) were grown in iron-limited chemostats and under phosphate limitation and iron (nutrient) sufficiency. For all four species, steady-state culture density declined with decreasing degree of iron limitation (increasing iron-limited growth rate), whereas chl per cell or biovolume increased. Plasma membrane ferric chelate reductase activity was enhanced by iron limitation in all species and suppressed by phosphate limitation and iron sufficiency. These results confirm previous work that C. kessleri uses a reductive mechanism of iron acquisition and also suggest that the other three species use the same mechanism. Although imposition of iron limitation led to enhanced activities of ferric chelate reductase in all species, the relationship between ferric chelate reductase activity and degree of iron limitation varied. Ferric chelate reductase activity in C. macrostigmatum and S. bacillaris was an inverse function of the degree of iron limitation, with the most rapidly growing iron-limited cells exhibiting the highest ferric chelate reductase activity. In contrast, ferric chelate reductase activity was only weakly affected by the degree of iron limitation in C. kessleri and H. lacustris. Calculation of ferric reductase activity per unit chl allowed a clear differentiation between iron-limited and iron-sufficient cells. The possible extension of the ferric chelate reductase assay to investigate the absence or presence of iron limitation in natural waters may be feasible, but it is unlikely that the assay could be used to estimate the degree of iron limitation. [source]

Phosphate availability regulates biosynthesis of two antibiotics, prodigiosin and carbapenem, in Serratia via both quorum-sensing-dependent and -independent pathways

MOLECULAR MICROBIOLOGY, Issue 2 2003
Holly Slater
Summary Serratia sp. ATCC 39006 produces two secondary metabolite antibiotics, 1-carbapen-2-em-3-carboxylic acid (Car) and the red pigment, prodigiosin (Pig). We have previously reported that production of Pig and Car is controlled by N -acyl homoserine lactone (N -AHL) quorum sensing, with synthesis of N -AHLs directed by the LuxI homologue SmaI, and is also regulated by Rap, a member of the SlyA family. We now describe further characterization of the SmaI quorum-sensing system and its connection with other regulatory mechanisms. We show that the genes responsible for biosynthesis of Pig, pigA,O, are transcribed as a single polycistronic message in an N -AHL-dependent manner. The smaR gene, transcribed convergently with smaI and predicted to encode the LuxR homologue partner of SmaI, was shown to possess a negative regulatory function, which is uncommon among the LuxR-type transcriptional regulators. SmaR represses transcription of both the pig and car gene clusters in the absence of N -AHLs. Specifically, we show that SmaIR exerts its effect on car gene expression via transcriptional control of carR, encoding a pheromone-independent LuxR homologue. Transcriptional activation of the pig and car gene clusters also requires a functional Rap protein, but Rap dependency can be bypassed by secondary mutations. Transduction of these suppressor mutations into wild-type backgrounds confers a hyper-Pig phenotype. Multiple mutations cluster in a region upstream of the pigA gene, suggesting this region may represent a repressor target site. Two mutations mapped to genes encoding pstS and pstA homologues, which are parts of a high-affinity phosphate transport system (Pst) in Escherichia coli. Disruption of pstS mimicked phosphate limitation and caused concomitant hyper-production of Pig and Car, which was mediated, in part, through increased transcription of the smaI gene. The Pst and SmaIR systems define distinct, yet overlapping, regulatory circuits which form part of a complex regulatory network controlling the production of secondary metabolites in Serratia ATCC 39006. [source]

Genome-wide transcriptomic and proteomic analysis of the primary response to phosphate limitation in Streptomyces coelicolor M145 and in a ,phoP mutant