Polyphasic Characterization of a Thermotolerant Siderophilic Filamentous Cyanobacterium That Produces Intracellular Iron Deposits

Despite the high potential for oxidative stress stimulated by reduced iron, contemporary iron-depositing hot springs with circum-neutral pH are intensively populated with cyanobacteria. Therefore, studies of the physiology, diversity, and phylogeny of cyanobacteria inhabiting iron-depositing hot springs may provide insights into the contribution of cyanobacteria to iron redox cycling in these environments and new mechanisms of oxidative stress mitigation. In this study the morphology, ultrastructure, physiology, and phylogeny of a novel cyanobacterial taxon, JSC-1, isolated from an iron-depositing hot spring, were determined. The JSC-1 strain has been deposited in ATCC under the name Marsacia ferruginose, accession number BAA-2121. Strain JSC-1 represents a new operational taxonomical unit (OTU) within Leptolyngbya sensu lato. Strain JSC-1 exhibited an unusually high ratio between photosystem (PS) I and PS II, was capable of complementary chromatic adaptation, and is apparently capable of nitrogen fixation. Furthermore, it synthesized a unique set of carotenoids, but only chlorophyll a. Strain JSC-1 not only required high levels of Fe for growth (≥40 μM), but it also accumulated large amounts of extracellular iron in the form of ferrihydrite and intracellular iron in the form of ferric phosphates. Collectively, these observations provide insights into the physiological strategies that might have allowed cyanobacteria to develop and proliferate in Fe-rich, circum-neutral environments.Cyanobacteria inhabiting ferrous iron-rich hot springs with circum-neutral pH represent unique models for examining the mechanisms by which early organisms evolved to cope with such habitats common on early Earth. Such organisms have previously been shown to be resistant to Fe²⁺ (37) or Fe³⁺ (6, 7) at concentrations in the micromolar to millimolar range. Moreover, high Fe concentrations (apparent optimum of ∼0.5 mM) stimulated the growth of these cyanobacteria, which were described as siderophilic (having an affinity for iron) cyanobacteria (7).The cyanobacteria inhabiting the Chocolate Pots hot springs in Yellowstone National Park, Wyoming, were shown to have played at least a passive role in contributing to iron deposition by serving as nucleation sites for the accumulation of iron minerals and associated silica deposits (36, 38). The precipitation of external iron that encrusts the cyanobacterial cells inhabiting this hot spring appears to be dependent on the species composition and chemistry of the mat (36, 38); however, multiple anoxygenic phototrophs found in the Chocolate Pots hot springs (8) could also contribute to the formation of Fe oxides (21, 49). Therefore, only iron mineralization experiments with model cyanobacterial strains can demonstrate the role of siderophilic cyanobacteria in the formation of specific, iron-bearing minerals.An additional common feature of circum-neutral iron-depositing hot springs is elevated concentrations of hydrogen peroxide (50). Shcolnick and coauthors (41) showed that a wild type of Synechococcus sp. PCC 6803 was resistant to 8 mM H₂O₂ if grown with 0.3 μM Fe³⁺, while the same concentration of hydrogen peroxide completely inhibited the growth of this cyanobacterium if it was grown with 10 μM Fe³⁺. If a similar correlation between iron concentration and the magnitude of an externally applied oxidative stress were the case for siderophilic cyanobacteria, iron-depositing hot springs should be free of cyanobacteria. However, such springs are very rich with cyanobacteria (38, 7, 36), which suggests that siderophilic cyanobacteria may possess unusual mechanisms of iron homeostasis maintenance and oxidative stress mitigation. Additionally, understanding iron tolerance and phenomena associated with siderophily in oxygenic prokaryotes is also important because such siderophilic organisms might help us find applications for bioremediation of waters polluted with iron.The current work describes the morphology, ultrastructure, physiology, and phylogeny of a previously undescribed, siderophilic cyanobacterium. The results of this polyphasic characterization led to the conclusion that strain JSC-1 represents a new operational taxonomic unit (OTU). (The epithet for JSC-1, Marsacia ferruginose, was chosen in honor of Nicole Tandeau de Marsac.) Additionally, biomineralization of intracellular iron by a cyanobacterium is demonstrated for the first time.     

Mycogenic metal nanoparticles: progress and applications

Nanotechnology is relevant to diverse fields of science and technology. Due to the many advantages over non-biological systems, several research groups have exploited the use of biological systems for the synthesis of nanoparticles. Among the different microbes used for the synthesis of nanoparticles, fungi are efficient candidates for fabrication of metal nanoparticles both intra- and extracellulary. The nanoparticles synthesized using fungi present good polydispersity, dimensions and stability. The potential applications of nanotechnology and nanoparticles in different fields have revolutionized the health care, textile and agricultural industries and they are reviewed here.     

Characterization of a novel riboswitch-regulated lysine transporter in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is an opportunistic pathogen that resides primarily in the mammalian oral cavity. In this environment, A. actinomycetemcomitans faces numerous host- and microbe-derived stresses, including intense competition for nutrients and exposure to the host immune system. While it is clear that A. actinomycetemcomitans responds to precise cues that allow it to adapt and proliferate in the presence of these stresses, little is currently known about the regulatory mechanisms that underlie these responses. Many bacteria use noncoding regulatory RNAs (ncRNAs) to rapidly alter gene expression in response to environmental stresses. Although no ncRNAs have been reported in A. actinomycetemcomitans, we propose that they are likely important for colonization and persistence in the oral cavity. Using a bioinformatic and experimental approach, we identified three putative metabolite-sensing riboswitches and nine small regulatory RNAs (sRNAs) in A. actinomycetemcomitans during planktonic and biofilm growth. Molecular characterization of one of the riboswitches revealed that it is a lysine riboswitch and that its target gene, lysT, encodes a novel lysine-specific transporter. Finally, we demonstrated that lysT and the lysT lysine riboswitch are conserved in over 40 bacterial species, including the phylogenetically related pathogen Haemophilus influenzae.     

Mutations of CDKL5 cause a severe neurodevelopmental disorder with infantile spasms and mental retardation

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused, in most classic cases, by mutations in the X-linked methyl-CpG-binding protein 2 gene (MECP2). A large degree of phenotypic variation has been observed in patients with RTT, both those with and without MECP2 mutations. We describe a family consisting of a proband with a phenotype that showed considerable overlap with that of RTT, her identical twin sister with autistic disorder and mild-to-moderate intellectual disability, and a brother with profound intellectual disability and seizures. No pathogenic MECP2 mutations were found in this family, and the Xq28 region that contains the MECP2 gene was not shared by the affected siblings. Three other candidate regions were identified by microsatellite mapping, including 10.3 Mb at Xp22.31-pter between Xpter and DXS1135, 19.7 Mb at Xp22.12-p22.11 between DXS1135 and DXS1214, and 16.4 Mb at Xq21.33 between DXS1196 and DXS1191. The ARX and CDKL5 genes, both of which are located within the Xp22 region, were sequenced in the affected family members, and a deletion of nucleotide 183 of the coding sequence (c.183delT) was identified in CDKL5 in the affected family members. In a screen of 44 RTT cases, a single splice-site mutation, IVS13-1G-->A, was identified in a girl with a severe phenotype overlapping RTT. In the mouse brain, Cdkl5 expression overlaps--but is not identical to--that of Mecp2, and its expression is unaffected by the loss of Mecp2. These findings confirm CDKL5 as another locus associated with epilepsy and X-linked mental retardation. These results also suggest that mutations in CDKL5 can lead to a clinical phenotype that overlaps RTT. However, it remains to be determined whether CDKL5 mutations are more prevalent in specific clinical subgroups of RTT or in other clinical presentations.     

Activation of proteases in an anaerobic sulphidogenic bioreactor

Activities of proteases were stimulated by specific sulphur metabolites during the enhanced hydrolysis of complex polymeric organic carbon in an anaerobic sulphidogenic environment. While sulphate at 1000 mg l(-1) inhibited proteases by 50%, there was a 2.5-fold increase in activity of proteases by added sulphite and a 3.6-fold increase from added sulphide. Two hypothetical models are proposed. First the sulphur species, sulphite (HSO3-) and sulphide (HS-), liberated at different times during the sulphate reduction process, directly activate the proteases, which are associated with the organic particulate matter, leading to a subsequent enhancement of hydrolysis of polymeric material. Second, they indirectly activate the proteases by neutralising the cations on the floc surface disrupting the integrity of the organic particulate floc therebye releasing further entrapped enzymes from the organic particulate matter.     

Bioaugmentation strategies for remediating mixed chemical effluents

Operationally exhausted metal working fluids are chemically mixed, produced in large quantities (400 000 tonnes year in the U.K.), and potentially environmentally toxic. It is essential to develop more reliable and economical approaches for their disposal. We investigated the effectiveness of a defined bacterial consortium, constructed specifically for treating metal-working fluid (MWF), and contrasted its performance to that of undefined inocula from activated sludge. Construction of the consortium was based on knowledge of the diversity of bacterial communities that naturally colonize MWF and determination of their catabolic abilities and tolerance to the chemical constituents. Chemical analysis of the inoculated MWF bioreactor revealed that, after 100 h at 28 degrees C, the defined inoculum reduced the pollution load by over 80% from an initial chemical oxygen demand of approximately 48 000 mg L(-)(1). The inocula performance was approximately 50% more effective than that of the undefined microbial community from the activated sludge. Furthermore, the performance of the constructed consortium was more reproducible than that of an undefined community, an essential feature for bioaugmentation treatment of industrial wastes.