Bacillus subtilis, known as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants and humans. A member of the genus Bacillus, B. subtilis is rod-shaped, can form a tough, protective endospore, allowing it to tolerate extreme environmental conditions. B. subtilis has been classified as an obligate aerobe, though evidence exists that it is a facultative anaerobe. B. subtilis is considered the best studied Gram-positive bacterium and a model organism to study bacterial chromosome replication and cell differentiation. It is one of the bacterial champions in secreted enzyme production and used on an industrial scale by biotechnology companies. Bacillus subtilis is a Gram-positive bacterium, catalase-positive, it was named Vibrio subtilis by Christian Gottfried Ehrenberg, renamed Bacillus subtilis by Ferdinand Cohn in 1872. B. subtilis cells are rod-shaped, are about 4-10 micrometers long and 0.25–1.0 μm in diameter, with a cell volume of about 4.6 fL at stationary phase.
As with other members of the genus Bacillus, it can form an endospore, to survive extreme environmental conditions of temperature and desiccation. B. Subtilis is a facultative anaerobe and had been considered as an obligate aerobe until 1998. B. subtilis is flagellated, which gives it the ability to move in liquids. B. subtilis has proven amenable to genetic manipulation, has become adopted as a model organism for laboratory studies of sporulation, a simplified example of cellular differentiation. In terms of popularity as a laboratory model organism, B. subtilis is considered as the Gram-positive equivalent of Escherichia coli, an extensively studied Gram-negative bacterium. This species is found in the upper layers of the soil and B. subtilis is thought to be a normal gut commensal in humans. A 2009 study compared the density of spores found in soil to that found in human feces; the number of spores found in the human gut was too high to be attributed to consumption through food contamination.
B. subtilis has been linked to grow in higher elevations and act as an identifier for both eco-adaptability and honey bee health. B. subtilis can divide symmetrically to make two daughter cells, or asymmetrically, producing a single endospore that can remain viable for decades and is resistant to unfavourable environmental conditions such as drought, extreme pH, solvents. The endospore is formed at times of nutritional stress and through the use of hydrolysis, allowing the organism to persist in the environment until conditions become favourable. Prior to the process of sporulation the cells might become motile by producing flagella, take up DNA from the environment, or produce antibiotics; these responses are viewed as attempts to seek out nutrients by seeking a more favourable environment, enabling the cell to make use of new beneficial genetic material or by killing off competition. Under stressful conditions, such as nutrient deprivation, B. subtilis undergoes the process of sporulation.
This process has been well studied and has served as a model organism for studying sporulation. B. subtilis is a model organism used to study bacterial chromosome replication. Replication of the single circular chromosome initiates at the origin. Replication proceeds bidirectionally and two replication forks progress in clockwise and counterclockwise directions along the chromosome. Chromosome replication is completed when the forks reach the terminus region, positioned opposite to the origin on the chromosome map; the terminus region contains several short DNA sequences. Specific proteins mediate all the steps in DNA replication. Comparison between the proteins involved in chromosomal DNA replication in B. subtilis and in Escherichia coli reveals similarities and differences. Although the basic components promoting initiation and termination of replication are well-conserved, some important differences can be found; these differences underline the diversity in the mechanisms and strategies that various bacterial species have adopted to carry out the duplication of their genomes.
B. subtilis has about 4,100 genes. Of these, only 192 were shown to be indispensable. A vast majority of essential genes were categorized in few domains of cell metabolism, with about half involved in information processing, one-fifth involved in the synthesis of cell envelope and the determination of cell shape and division, one-tenth related to cell energetics; the complete genome sequence of B. subtilis sub-strain QB928 has 4,146,839 DNA base pairs and 4,292 genes. The QB928 strain is used in genetic studies due to the presence of various markers. Several noncoding RNAs have been characterized in the B. subtilis genome in 2009, including Bsr RNAs. Microarray-based comparative genomic analyses have revealed that B. subtilis members show considerable genomic diversity. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the surrounding medium. In B. subtilis the length of transferred DNA is greater than 1271kb. The transferred DNA is double-stranded DNA and is more than a third of the total chromosome length of 4215 kb.
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Jean Bennett is the F. M. Kirby Professor of Ophthalmology in the Perelman School of Medicine at the University of Pennsylvania, her research focuses on gene therapy for retinal diseases. Her laboratory developed the first gene therapy approved for use in humans, which treats a rare form of blindness. Bennett graduated with honors with her bachelor of science in biology from Yale University in 1976. In 1980, she obtained a Doctorate of Philosophy in Zoology. Bennett continued on to Harvard University to receive her Doctor of Medicine in 1986. Bennett received her PhD in Zoology from the University of California, Berkeley in 1980. Under Dr. Daniel Mazia, her graduate research focused on the early development of sea urchin embryos. She moved on to postdoctoral work at the University of California, San Francisco under the guide of Dr. Roger Pedersen; as a postdoc, she collaborated with Dr. William French Anderson developing molecular techniques for gene editing. In 1982, she left this position to attend medical school at Harvard University.
At Harvard, Bennett studied human genetics with. Leon Rosenberg and Wayne Fenton, she investigated Down's syndrome and Alzheimer's disease with John Gearhart, Mary Lou Oster-Granite, Roger Reeves. From this work, she was awarded a career development grant from the Foundation Fighting Blindness to begin research on gene therapy for retinitis pigmentosa. To develop an effective gene therapy in the retina, Bennett started by investigating adenoviruses and adeno-associated viruses for gene editing in mice and non-human primates at the Institute for Human Gene Therapy at the University of Pennsylvania; the field of gene therapy was stymied after the death of Jesse Gelsinger during 1999 in a clinical trial for gene editing. However, Bennett pushed forward and demonstrated that AAV-mediated delivery of a functional RPE65 gene improved sight in near-blind dogs. Based on their pre-clinical data, Bennett's team pursued clinical trials in children with a defective form of the RPE65 gene, their initial trials showed a stark improvement in light sensitivity and visual function in these children.
Based on this, the therapy, marketed as Luxturna, was approved by the FDA for use in humans. Her laboratory is investigating gene therapy approaches for other retinal diseases. Sanford Lorraine Cross Award, Sanford Health, 2018 António Champalimaud Vision Award, 2018 Marion Spencer Fay Award, 2018 Method of treating or retarding the development of blindness, Methods and computer readable media for testing visual function using virtual mobility tests Trans-viral vector mediated gene transfer to the retina, Modified aav8 capsid for gene transfer for retinal therapies Proviral plasmids and production of recombinant adeno-associated virus Method of treating or retarding the development of blindness Gene therapy for ocular disorders Gene therapy for treating peroxisomal disorders Trans-splicing molecules Gene therapy for ocular disorders Syringe actuator Methods and Compositions for Treatment of Disorders and Diseases Involving RDH12 Gene therapy for ocular disorders, pending Enhanced AAV-mediated gene transfer for retinal therapies Synergistic combination of neuronal viability factors and uses thereof Aav vectors expressing sec10 for treating kidney damage Methods and compositions for treatment of ocular disorders and blinding diseases Apparatus and methods for testing visual function and functional vision at varying luminance levels Compositions and Methods for Correction of Heritable Ocular Disease Vision test for determining retinal disease progression Compositions and methods for self-regulated inducible gene expression Aav7 viral vectors for targeted delivery of rpe cells Method for transducing cells with primary cilia Compositions and methods for treatment of disorders related to CEP290 Rapidly deployable modular shelter system
MC4 connectors are single-contact electrical connectors used for connecting solar panels. The MC in MC4 stands for the 4 for the 4 mm diameter contact pin. MC4s allow strings of panels to be constructed by pushing the connectors from adjacent panels together by hand, but require a tool to disconnect them to ensure they do not accidentally disconnect when the cables are pulled; the MC4 and compatible products are universal in the solar market today, equipping all solar panels produced since about 2011. Rated for 600 V, newer versions are rated at 1500 V, which allows longer strings to be created. While small solar panels used for battery charging and similar tasks may not require special connectors, larger systems connect the panels together in series to form strings. In the past this was accomplished by opening a small electrical box on the back of the panel and connecting user-supplied wires to screw terminals within. However, bare terminals of this sort are limited to 50 V or less by the NEC code, above that only a licensed electrician can make the connections.
Additionally, these sorts of connections were subject to problems caused by water leakage, electrical corrosion and mechanical stress on the wires. Starting in the 2000s, a number of companies introduced products to address these issues. In these systems, the junction box was sealed and two wires were permanently attached using strain reliefs; the cables ended with push-fit connectors that met the definition of a convenience receptacle, meaning they could be connected together by anyone. Two connectors became somewhat common during this period, the Radox connector and MC3 connector, both of which looked like weather sealed phono jacks. In 2008 the US National Electrical Code was updated to require solar panel connectors to offer "positive locking", so that they were able to be plugged together by hand but only separated again using a tool. Radox, a European manufacturer, did not respond to this specification and has since disappeared from the market. Two US-based companies, Tyco Electronics and Multi-Contact, responded by introducing new connectors to meet this requirement.
Tyco's Solarlok became a market leader for a period in the late 2000s, but a number of factors conspired to push it from the market. Among these was the fact that the system had two sets of cables and wires, which led to considerable annoyance in the field when equipment from different vendors could not be plugged together. By 2011, the MC4 was in a strong leadership position, which led to the introduction of compatible products from a variety of major connector vendors. Among these are the Amphenol Helios H4 and SMK PV-03; the MC4 system consists of a socket design. The plugs and sockets are inside plastic shells that appear to be the opposite gender - the plug is inside a cylindrical shell that looks like a female connector but is referred to as male, the socket is inside a square probe that looks male but is electrically female; the female connector has two plastic fingers that have to be pressed toward the central probe to insert into holes in the front of the male connector. When the two are pushed together, the fingers slide down the holes until they reach a notch in the side of the male connector, where they pop outward to lock the two together.
For a proper seal, MC4s must be used with cable of the correct diameter. The cable is double-insulated and UV resistant. Connectors are attached by crimping, though soldering is possible; the MC4 connector is UL rated depending on the conductor size used. Standards efforts in Europe allow 1000 V versions. MC Multilam Technology claims that constant spring pressure provides reliable low contact resistance. However, it is important to never connect or disconnect them under load on low-voltage systems. An electric arc may form which can melt and damage contact materials, resulting in high resistance and subsequent overheating; this is because direct current continues to arc, whereas used alternating current more self-extinguishes at the zero-crossing voltage point. Large arrays of panels are interconnected in series, made of strings of panels generating 17 to 34 V each, with overall voltages up to 600 V per string. Connectors made by other manufacturers may be mated with original Stäubli parts and are sometimes described as "MC compatible", but may not conform to the requirements for a safe electrical connection with long term stability.
Interruption requires a special DC circuit breaker which allows opening the circuit without arc damage. Typical 120/230 V AC switches and circuit breakers are not suited for higher DC voltage applications. Daisy chain DC connector