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- All Subjects: Cyanobacteria
- Creators: Vermaas, Willem Fj
- Status: Published
Description
The unicellular cyanobacterium Synechocystis sp. PCC 6803 contains a NiFe-type bidirectional hydrogenase that is capable of using reducing equivalents to reduce protons and generate H¬2. In order to achieve sustained H2 production using this cyanobacterium many challenges need to be overcome. Reported H2 production from Synechocystis is of low rate and often transient. Results described in this dissertation show that the hydrogenase activity in Synechocystis is quite different during periods of darkness and light. In darkness, the hydrogenase enzyme acts in a truly bidirectional way and a particular H2 concentration is reached that depends upon the amount of biomass involved in H2 production. On the other hand, in the presence of light the enzyme shows only transient H2 production followed by a rapid and constitutive H2 oxidation. H2 oxidation and production were measured from a variety of Synechocystis strains in which components of the photosynthetic or respiratory electron transport chain were either deleted or inhibited. It was shown that the light-induced H2 oxidation is dependent on the activity of cytochrome b6f and photosystem I but not on the activity of photosystem II, indicating a channeling of electrons through cytochrome b6f and photosystem I. Because of the sequence similarities between subunits of NADH dehydrogenase I in E. coli and subunits of hydrogenase in Synechocystis, NADH dehydrogenase I was considered as the most likely candidate to mediate the electron transfer from hydrogenase to the membrane electron carrier plastoquinone, and a three-dimensional homology model with the associated subunits shows that structurally it is possible for the subunits of the two complexes to assemble. Finally, with the aim of improving the rate of H2 production in Synechocystis by using a powerful hydrogenase enzyme, a mutant strain of Synechocystis was created in which the native hydrogenase was replaced with the hydrogenase from Lyngbya aestuarii BL J, a strain with higher capacity for H2 production. H2 production was detected in this Synechocystis mutant strain, but only in the presence of external reductants. Overall, this study emphasizes the importance of redox partners in determining the direction of H2 flux in Synechocystis.
ContributorsDatta, Īpsitā (Author) / Vermaas, Willem Fj (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Rittmann, Bruce (Committee member) / Jones, Anne K (Committee member) / Arizona State University (Publisher)
Created2015
Description
Sexually transmitted diseases like gonorrhea and chlamydia, standardly treated with antibiotics, produce over 1.2 million cases annually in the emergency department (Jenkins et al., 2013). To determine a need for antibiotics, hospital labs utilize bacterial cultures to isolate and identify possible pathogens. Unfortunately, this technique can take up to 72 hours, leading to several physicians presumptively treating patients based solely on history and physical presentation. With vague standards for diagnosis and a high percentage of asymptomatic carriers, several patients undergo two scenarios; over- or under-treatment. These two scenarios can lead to consequences like unnecessary exposure to antibiotics and development of secondary conditions (for example: pelvic inflammatory disease, infertility, etc.). This presents a need for a laboratory technique that can provide reliable results in an efficient matter. The viability of DNA-based chip targeted for C. trachomatis, N. gonorrhoeae, and other pathogens of interest were evaluated. The DNA-based chip presented several advantages as it can be easily integrated as a routine test given the process is already well-known, is customizable and able to target multiple pathogens within a single test and has the potential to return results within a few hours as opposed to days. As such, implementation of a DNA-based chip as a diagnostic tool is a timely and potentially impactful investigation.
ContributorsCharoenmins, Patherica (Author) / Penton, Christopher (Thesis director) / Moore, Marianne (Committee member) / College of Integrative Sciences and Arts (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
Creating sustainable alternatives to fossil fuel resources is one of the greatest
challenges facing mankind. Solar energy provides an excellent option to alleviate modern dependence on fossil fuels. However, efficient methods to harness solar energy are still largely lacking. Biomass from photosynthetic organisms can be used as feedstock to produce traditional fuels, but must be produced in great quantities in order to meet the demands of growing populations. Cyanobacteria are prokaryotic photosynthetic microorganisms that can produce biomass on large scales using only sunlight, carbon dioxide, water, and small amounts of nutrients. Thus, Cyanobacteria are a viable option for sustainable production of biofuel feedstock material. Photobioreactors (PBRs) offer a high degree of control over the temperature, aeration, and mixing of cyanobacterial cultures, but cannot be kept sterile due to the scales necessary to meet domestic and global energy demands, meaning that heterotrophic bacteria can grow in PBRs by oxidizing the organic material produced and excreted by the Cyanobacteria. These heterotrophic bacteria can positively or negatively impact the performance of the PBR through their interactions with the Cyanobacteria. This work explores the microbial ecology in PBR cultures of the model cyanobacterium Synechocystis sp. PCC6803 (Synechocystis) using microbiological, molecular, chemical, and engineering techniques. I first show that diverse phylotypes of heterotrophic bacteria can associate with Synechocystis-based PBRs and that excluding them may be impossible under typical PBR operating conditions. Then, I demonstrate that high-throughput sequencing can reliably elucidate the structure of PBR microbial communities without the need for pretreatment to remove Synechocystis 16S rRNA genes, despite the high degree of polyploidy found in Synechocystis. Next, I establish that the structure of PBR microbial communities is strongly influenced by the microbial community of the inoculum culture. Finally, I show that maintaining available phosphorus in the culture medium promotes the production and enrichment of Synechocystis biomass in PBRs by reducing the amount of soluble substrates available to heterotrophic bacteria. This work presents the first analysis of the structure and function of microbial communities associated with Synechocystis-based PBRs.
challenges facing mankind. Solar energy provides an excellent option to alleviate modern dependence on fossil fuels. However, efficient methods to harness solar energy are still largely lacking. Biomass from photosynthetic organisms can be used as feedstock to produce traditional fuels, but must be produced in great quantities in order to meet the demands of growing populations. Cyanobacteria are prokaryotic photosynthetic microorganisms that can produce biomass on large scales using only sunlight, carbon dioxide, water, and small amounts of nutrients. Thus, Cyanobacteria are a viable option for sustainable production of biofuel feedstock material. Photobioreactors (PBRs) offer a high degree of control over the temperature, aeration, and mixing of cyanobacterial cultures, but cannot be kept sterile due to the scales necessary to meet domestic and global energy demands, meaning that heterotrophic bacteria can grow in PBRs by oxidizing the organic material produced and excreted by the Cyanobacteria. These heterotrophic bacteria can positively or negatively impact the performance of the PBR through their interactions with the Cyanobacteria. This work explores the microbial ecology in PBR cultures of the model cyanobacterium Synechocystis sp. PCC6803 (Synechocystis) using microbiological, molecular, chemical, and engineering techniques. I first show that diverse phylotypes of heterotrophic bacteria can associate with Synechocystis-based PBRs and that excluding them may be impossible under typical PBR operating conditions. Then, I demonstrate that high-throughput sequencing can reliably elucidate the structure of PBR microbial communities without the need for pretreatment to remove Synechocystis 16S rRNA genes, despite the high degree of polyploidy found in Synechocystis. Next, I establish that the structure of PBR microbial communities is strongly influenced by the microbial community of the inoculum culture. Finally, I show that maintaining available phosphorus in the culture medium promotes the production and enrichment of Synechocystis biomass in PBRs by reducing the amount of soluble substrates available to heterotrophic bacteria. This work presents the first analysis of the structure and function of microbial communities associated with Synechocystis-based PBRs.
ContributorsZevin, Alexander Simon (Author) / Rittmann, Bruce E. (Thesis advisor) / Krajmalnik-Brown, Rosa (Thesis advisor) / Vermaas, Willem Fj (Committee member) / Arizona State University (Publisher)
Created2015
Description
Like most other phototrophic organisms the cyanobacterium Synechocystis sp. PCC 6803 produces carotenoids. These pigments often bind to proteins and assume various functions in light harvesting, protection from reactive oxygen species (ROS) and protein stabilization. One hypothesis was that carotenoids bind to the surface (S-)layer protein. In this work the Synechocystis S-layer protein was identified as Sll1951 and the effect on the carotenoid composition of this prokaryote by disruption of sll1951 was studied. Loss of the S-layer, which was demonstrated by electron microscopy, did not result in loss of carotenoids or changes in the carotenoid profile of the mutant, which was shown by HPLC and protein analysis. Although Δsll1951 was more susceptible to osmotic stress than the wild type, the general viability of the mutant remained unaffected. In a different study a combination of mutants having single or multiple deletions of putative carotenoid cleavage dioxygenase (CCD) genes was created. CCDs are presumed to play a role in the breakdown of carotenoids or apo-carotenoids. The carotenoid profiles of the mutants that were grown under conditions of increased reactive oxygen species were analyzed by HPLC. Pigment lifetimes of all strains were estimated by 13C-labeling. Carotenoid composition and metabolism were similar in all strains leading to the conclusion that the deleted CCDs do not affect carotenoid turnover in Synechocystis. The putative CCDs either do not fulfill this function in cyanobacteria or alternative pathways for carotenoid degradation exist. Finally, slr0941, a gene of unknown function but a conserved genome position in many cyanobacteria downstream of the δ-carotene desaturase, was disrupted. Initially, the mutant strain was impaired in growth but displayed a rather normal carotenoid content and composition, but an apparent second-site mutation occurred infrequently that restored growth rates and caused an accumulation of carotenoid isomers not found in the wild type. Based on the obtained data a role of the slr0941 gene in carotenoid binding/positioning for isomerization and further conversion to mature carotenoids is suggested.
ContributorsTrautner, Christoph (Author) / Vermaas, Willem Fj (Thesis advisor) / Chandler, Douglas E. (Committee member) / Misra, Rajeev (Committee member) / Bingham, Scott E (Committee member) / Arizona State University (Publisher)
Created2011
Description
Desert organisms lead harsh lives owing to the extreme, often unpredictable environmental conditions they endure. Climate change will likely make their existence even harsher. Predicting the ecological consequences of future climate scenarios thus requires understanding how the biota will be affected by climatic shifts. Biological soil crusts (biocrusts) are an important ecosystem component in arid lands, one that covers large portions of the landscape, improving soil stability and fertility. Because cyanobacteria are biocrust’s preeminent primary producers, eking out an existence during short pulses of precipitation, they represent a relevant global change object of study. I assessed how climate scenarios predicted for the Southwestern United States (US) will affect biocrusts using long-term, rainfall-modifying experimental set-ups that imposed either more intense drought, a seasonally delayed monsoon season, or a shift to smaller but more frequent precipitation events. I expected drought to be detrimental, but not a delay in the monsoon season. Surprisingly, both treatments showed similar effects on cyanobacterial community composition and population size after four years. While successionally incipient biocrusts were unaffected, mature biocrusts lost biomass and diversity with treatment, especially among nitrogen-fixing cyanobacteria. In separate experiments, I assessed the effect of rainfall with modified event size and frequency after a decade of treatment. Small, frequent rainfall events surprisingly enhanced the diversity and biomass of bacteria and cyanobacteria, with clear winners and losers: nitrogen-fixing Scytonema sp. benefited, while Microcoleus vaginatus lost its dominance. As an additional finding, I could also show that water addition is not always beneficial to biocrusts, calling into question the notion that these are strictly water-limited systems.
Finally, results interpretation was severely hampered by a lack of appropriate systematic treatment for an important group of biocrust cyanobacteria, the “Microcoleus steenstrupii complex”. I characterized the complex using a polyphasic approach, leading to the formal description of a new family (Porphyrosiphonaceae) of desiccation resistant cyanobacteria that includes 11 genera, of which 5 had to be newly described. Under the new framework, the distribution and abundance of biocrust cyanobacteria with respect to environmental conditions can now be understood. This body of work contributes significantly to explain current distributional patterns of biocrust cyanobacteria and to predict their fate in the face of climate change.
Finally, results interpretation was severely hampered by a lack of appropriate systematic treatment for an important group of biocrust cyanobacteria, the “Microcoleus steenstrupii complex”. I characterized the complex using a polyphasic approach, leading to the formal description of a new family (Porphyrosiphonaceae) of desiccation resistant cyanobacteria that includes 11 genera, of which 5 had to be newly described. Under the new framework, the distribution and abundance of biocrust cyanobacteria with respect to environmental conditions can now be understood. This body of work contributes significantly to explain current distributional patterns of biocrust cyanobacteria and to predict their fate in the face of climate change.
ContributorsMoreira Camara Fernandes, Vanessa (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Rudgers, Jennifer (Committee member) / Sala, Osvaldo (Committee member) / Penton, Christopher (Committee member) / Arizona State University (Publisher)
Created2020