In its strictest sense, fermentation (formerly called zymosis) is the anaerobic metabolic breakdown of a nutrient molecule, such as glucose, without net oxidation. Fermentation does not release all the available energy in a molecule; it merely allows glycolysis (a process that yields two ATP per glucose) to continue by replenishing reduced coenzymes. Depending on which organism it is taking place in, fermentation may yield lactate, acetic acid, ethanol, or other reduced metabolites. Yeast produces ethanol and CO2; human muscle (under anaerobic conditions) produces lactic acid.
Fermentation is also used much more broadly to refer to the bulk growth of microorganisms on a growth medium. No distinction is made between aerobic and anaerobic metabolism when the word is used in this sense.
Fermentation usually implies that the action of the microorganisms is desirable. Occasionally wines are enhanced through the process of cofermentation. When fermentation stops prior to complete conversion of sugar to alcohol, a stuck fermentation is said to have occurred." ¶ 2:00 AM 0 comments
"Thiobacillus ferrooxidans is recognized as being responsible for the oxidation of iron and inorganic sulfur compounds in areas such a mine tailings and coal deposits where these compounds are abundant." ¶ 1:36 AM 0 comments
"Thiobacillus ferrooxidans is recognized as being responsible for the oxidation of iron and inorganic sulfur compounds in areas such a mine tailings and coal deposits where these compounds are abundant." ¶ 1:29 AM 0 comments
"Thiobacillus ferrooxidans is recognized as being responsible for the oxidation of iron and inorganic sulfur compounds in areas such a mine tailings and coal deposits where these compounds are abundant." ¶ 1:29 AM 0 comments
"Thiobacillus ferrooxidans is recognized as being responsible for the oxidation of iron and inorganic sulfur compounds in areas such a mine tailings and coal deposits where these compounds are abundant." ¶ 1:28 AM 0 comments
Researchers have found L. monocytogenes in at least 37 mammalian species, both domesticated and feral, as well as in at least 17 species of birds and possibly in some species of fish and shellfish. Laboratories can isolate L. monocytogenes from soil, silage, and other environmental sources. L. monocytogenes is quite hardy and resists the deleterious effects of freezing, drying, and heat remarkably well for a bacterium that does not form spores. Most L. monocytogenes are pathogenic to some degree." ¶ 1:19 AM 0 comments
The left side of this diagram shows how Agrobacterium is used in broad-leafed (dicots) crops such as tomatoes, potatoes, cotton and canola to introduce a new gene into a plant. Agrobacterium tumefaciens is a soil microorganism that acts as a natural genetic engineer. It can insert a piece of its DNA into the chromosome of a plant cell. Monsanto researchers discovered that for some kinds of plants, Agrobacterium was the perfect method for introducing new traits into the plant. When pieces of plant tissue were added to culture with the Agrobacterium containing the new gene, the gene could be transferred into the plant cells. These cells grow into plants with the new trait.
¶ 11:58 PM 0 comments
The left side of this diagram shows how Agrobacterium is used in broad-leafed (dicots) crops such as tomatoes, potatoes, cotton and canola to introduce a new gene into a plant. Agrobacterium tumefaciens is a soil microorganism that acts as a natural genetic engineer. It can insert a piece of its DNA into the chromosome of a plant cell. Monsanto researchers discovered that for some kinds of plants, Agrobacterium was the perfect method for introducing new traits into the plant. When pieces of plant tissue were added to culture with the Agrobacterium containing the new gene, the gene could be transferred into the plant cells. These cells grow into plants with the new trait." ¶ 11:56 PM 0 comments
PCR, as currently practiced, requires several basic components. These components are:
* DNA template, or cDNA which contains the region of the DNA fragment to be amplified
* Two primers, which determine the beginning and end of the region to be amplified (see following section on primers)
* Taq polymerase, which copies the region to be amplified
* Deoxynucleotides-triphosphate, from which the DNA-Polymerase builds the new DNA
* Buffer, which provides a suitable chemical environment for the DNA-Polymerase
The PCR reaction is carried out in a thermal cycler. This is a machine that heats and cools the reaction tubes within it to the precise temperature required for each step of the reaction. To prevent evaporation of the reaction mixture (typically volumes between 15-100µl per tube), a heated lid is placed on top of the reaction tubes or a layer of oil is put on the surface of the reaction mixture. These machines cost more than USD 2,500 in 2004." ¶ 11:53 PM 0 comments
明朝宋應星於「天工開物」，即隱喻了紅麴菌具有抑菌的功效。1977年Wong與Bau學者發現粗萃取的紅麴色素具有抗菌的活性。而後發現此抗菌物質monascidin A和Penicillium citrinum 所產生的citrinin在吸收光譜、NMR、MS等分析具有相同的特性，證實了兩者是同種物質。
Citrinin是一種典型的黴菌毒素，最早是由Penicillium citrinum菌中發現。之後於黴菌Aspergillum 及紅麴菌Monascus 中陸續發現。Citrinin是一種檸檬黃的結晶物，可溶於醇及稀鹼，對小鼠及大鼠LD50 值為35、67mg/kg。Citrinin除了是一種黴菌毒素外，亦具有其他生理活性，例如antimicrobial、phytotoxic、 cytotoxic、hypocholesterolemic及酵素抑制效應。
Citrinin對gram-positive細菌如Bacillus、Streptococcus及Pseudomonas等 食品腐敗菌具有抑制作用。此外；citrinin也是一種肝腎毒素。目前亦有研究指出citrinin具有致畸形毒性，當citrinin注射量越高則致 畸形的比率就越高，Ciegler等人曾指出注射citrinin於雞胚胎中會造成雞胚胎畸形，如腦畸形、腳變形、眼球凸出、形成交叉喙及頭頸扭曲方向不 正常等。
紅麴是我國傳統產品，藥用或作為食品添加劑或用於釀酒等在我國及日本等國家都已有規範。但在西方國家使用卻有些爭議，其中以紅麴中所含有的citrinin意見最多。
1999年荷蘭學者Monica等人從市售的紅麴產品中分析citrinin的含量約在0.2-17.1ppm，並進行Ames Salmonella-microsome assay及Salmonella- hepatocyte assay之微生物誘變試驗，結果並未發現紅麴產品有致變異性。作者同時指出紅麴發酵產物應用於食品已經好幾個世紀，但也從未有危害事件發生，這可歸於食品加工技術或發酵方法已減低citrinin 濃度，但對於紅麴中citrinin之污染仍應盡量避免。
國內對citrinin含量仍未定出最低含量標準，國外目前可查到者，一般以1 ppm（百萬分之一）為允許存在最低標準。
紅麴為中國幾千年來使用歷史悠久之傳統食品，其保健功效不斷被發現，相關研究應是方興未艾，前途看好。筆者以為紅麴既然是中國傳統食用之保健食品，其保健 功效應繼續研究，有害成分亦應研發新產品使其符合安全標準。如此具有多功效、且安全的紅麴保健食品之上市，將指日可待。
¶ 11:13 PM 0 comments
What does E.coli mean?
E. coli is the abbreviated name of the bacterium in the Family Enterobacteriaceae named Escherichia (Genus) coli (Species). Dave Graham in the Department of Microbiology, University of Illinois at Urbana/Champaign, recently pointed me to information gleaned from G.W. Tannock's book, Normal Microflora,1995, Chapman & Hall, which reveals that approximately 0.1% of the total bacteria within an adult's intestines (on a Western diet) is represented by E. coli. Although, in a newborn infant's intestines E. coli, along with lactobacilli and enterococci represent the most abundant bacterial flora.In fact, it is for this reason that the organisms which happily inhabit the intestinal tract as normal flora are named enteric bacteria. The Family to which E. coli belongs (Enterobacteriaceae, is named what it is - because of the Greek word enterikos - which pertains to the intestine. The name Escherichia comes from the name of the person Escherich, who in 1885 first isolated and characterized this bacterium...
¶ 10:56 PM 0 comments
The Axiom of Choice (AC) was formulated about a century ago, and it was controversial for a few of decades after that; it may be considered the last great controversy of mathematics. It is now a basic assumption used in many parts of mathematics. In fact, assuming AC is equivalent to assuming any of these principles (and many others):
- Given any two sets, one set has cardinality less than or equal to that of the other set -- i.e., one set is in one-to-one correspondence with some subset of the other. (Historical remark: It was questions like this that led to Zermelo's formulation of AC.)
- Any vector space over a field F has a basis -- i.e., a maximal linearly independent subset -- over that field. (Remark: If we only consider the case where F is the real line, we obtain a slightly weaker statement; it is not yet known whether this statement is also equivalent to AC.)
- Any product of compact topological spaces is compact. (This is now known as Tychonoff's Theorem, though Tychonoff himself only had in mind a much more specialized result that is not equivalent to the Axiom of Choice.)
We use one more simple data structure, a stack L (represented as a list) which we use to identify the subtree rooted at a vertex. We simply push each new vertex onto L as we visit it; then when we have finished visiting a vertex, its subtree will be everything pushed after it onto L. If v is a head, and we've already deleted the other heads in that subtree, the remaining vertices left on L will be exactly the component [v].
We are now ready to describe the actual algorithm. It simply performs a DFS, keeping track of the low and dfsnum values defined above, using them to identify heads of components, and when finding a head deleting the whole component from the graph, using L to find the vertices of the component.
DFS(G)¶ 12:33 PM 0 comments
{
make a new vertex x with edges x->v for all v
initialize a counter N to zero
initialize list L to empty
build directed tree T, initially a single vertex {x}
visit(x)
}
visit(p)
{
add p to L
dfsnum(p) = N
increment N
low(p) = dfsnum(p)
for each edge p->q
if q is not already in T
{
add p->q to T
visit(q)
low(p) = min(low(p), low(q))
} else low(p) = min(low(p), dfsnum(q))
if low(p)=dfsnum(p)
{
output "component:"
repeat
remove last element v from L
output v
remove v from G
until v=p
}
}
