I find B.subtilis to be a particularly interesting bacterium because it is a dominant bacterial workhorse in microbial fermentation and is used in foods, feeds, and industrial applications. A few examples include:

• Animal feeds as a probiotic
• Production of the soy-based traditional natto fermentation for human consumption
• As a probiotic for human consumption
• Large scale manufacturing of enzymes that are used in food, feed, leather, laundry, etc.
• Production of antibiotics, nucleotides, the vitamin riboflavin, the flavor agent ribose, and the supplement poly-γ-glutamic acid
• The genetics of B. subtilis has been widely studied and utilized that knowledge to manipulate the organism to make value added products.

I will limit my discussion to B.subtilis's application in animal feeds. B.subtilis is quite different from other microbial agents as it is a ubiquitous aerobic, or facultative aerobic, bacterium commonly recovered from water, soil, air, and decomposing plant residues. It produces endospores that are protected by a thick spore coat which enables them to withstand the high temperatures and acidic pH of the gut. This protective layer is not found in bifidobacterium, lactobacillus, etc., making them more vulnerable. These unique properties are extremely useful when applying B.subtilus in animal feeds.

The spores are typically formed when environmental conditions are not favorable (perhaps they learned how to survive during difficult times) and once favorable conditions return, the spores are germinated into vegetative cells. The spores are actually quite similar to plant seeds in that they are healthy but dormant until they are put into the right environmental conditions, when they start to germinate.

Major differences between the vegetative cells and spores:

Several studies have been conducted to understand the process of transforming spores to vegetative cells. Some studies clearly showed that the spores are germinating into vegetative cells within the host and providing beneficial effects.

Very recently the Lawrence Livermore National Laboratory have conducted a very interesting study and tracked as how spores break out of dormant state. This study was published in the June 2007 issue of the Proceedings of the National Academy of Sciences. For a quick look at the pictures please follow this link

Now let us examine as what are the most important attributes of a microorganism that can be potentially used as a probiotic in animal feeds.

• Microorganisms must be host specific
• Microorganisms must be viable (live) or in case of spores they should survive the gut environment and turn into vegetative cells
• Preferably shelf stable at room temperatures
• Microorganisms must have the ability to colonize within the intestinal tract of the animal of interest
• Safe to humans, animals and environment, Generally Recognized As Safe (GRAS)
• Ease of handling, long time storage and distribution
• Withstand higher temperatures during pelletization

The question is which one is better Spores or Live vegetative cells?

Unlike brewers and bakers yeast, torula yeast made its entry into foods and feeds very late: during World Wars I and II. The best explanation for this is that torula yeast is not used to make breads or beer and wines; it made its debut when there was a shortage of protein and to utilize the by-product containing larger amounts of pentoses.

The name "torula" is derived from its original name: Torulopsis utilis. Later it was re-classified as Candid utilis. There is lot of confusion about torula yeast, some think it is a nutritional yeast; others think that it is used only in animal feeds; few think it is grown to reduce the biological oxygen and chemical oxygen demand of the by-product that is obtained from the paper mills; yet some others think that it is used to replace MSG and as a flavor enhancer. However, not many are aware that it is also used for honey production, aquaculture, as a media additive in industrial fermentation and insect cell culture, or as an attractant for the management of the olive fruit fly. All of these applications are accurate, but it is important to have a clear understanding about the differences of torula yeast that is grown on a by-product and primary grown torula yeast that is grown on a refined sugar feed stocks such as corn syrup, glucose, or alcohol.

The quality of torula yeast is very much dependent on the substrates and production methods employed. For example, sometimes it may have fungus Pichia jadinti, which may be grown on wood sugars from paper mill wastes. The quality and concentration of protein and vitamins is superior when torula yeast is grown on the wood hydrolysate containing pure sugars as a substrate compared to by-products such as spent sulfite liquor and molasses.See the table below for composition of torula yeast that is grown on various substrates:

It is interesting to note that the first commercial production of torula yeast was started in Germany during WWI from the by-product spent sulfite liquor (SSL; for more information see the NF Wiki). Prof. Fink in Germany first reported that torula yeast could be grown on SSL, which has significant amounts of pentoses that are not easily metabolized by S.cerevisiae. The process for commercial manufacturing of torula yeast is known as Waldhof process (using Waldhof fermentor) and has been used in United States also. Several scientists all over the world including the Forest Products Laboratory, later modified this process. If you would like more information about the process or references for the applications listed below, please contact the Site Administrator.

As the applications of torula yeast have gone beyond the feed industry, modern manufacturers in US and other countries are producing primary grown torula yeast utilizing refined sugar feed stocks or alcohol ensuring pure yeast and consistency batch after batch, unlike that of torula yeast made using by-products.

Why is torula yeast so much in use when brewers and bakers yeast are available?

• Torula yeast is relatively easy to maintain, grow quickly, has the ability to utilize pentose sugars, excellent nutritional properties, and has been accepted all over the world as a safe and wholesome food and feed.
• Torula Yeast contains relatively higher amounts of nucleotides, especially RNA, that help to enhance flavors. Some companies have isolated torula yeast strains to make extracts with exceptionally high amounts of 20% IMP+GMP (Inositol Mono Phosphate and Guanosine Mono Phosphate). Since it is all naturally occurring, it can be labeled as yeast extract while still providing the powerful flavoring effect of nucleotides.
• Torula yeast has a very clean flavor profile and does not come with bitter/strange taste like regular yeast extract. It can be used without tainting your overall flavor as it reaches the threshold of flavor enhancement.
• Because of its high nucleotide content, torula is a good source for pet foods, especially for cats.
• Torula yeast was found to be the most palatable feed when fed individually into one beehive at a time.
• Torula yeast was superior to the soybean meal or brewers' yeast for chick growth when fed on a ten percent level in the feed.
• One study observed that when torula yeast is supplemented with methionine the results were almost comparable to that of casein when fed to the adult rats:

  Net protein digestibility and growth promoting values of Bakers, Brewers and Torula Yeast
  
  Adapted from J. Nutrition, 517-526, 1949

• In another study the results suggest that it is possible to replace up to 65% of animal protein with a mixture of plant proteins, including 30% from torula yeast, in tilapia fry diets without adverse effects on fish performance and culture profit.
• The two most important factors to be considered in animal feeds are: the protein hydrolysis (degradability) and their digestion in the intestine. One study found that the protein hydrolysis into peptides and amino acids of torula yeast is much higher (70%) compared to that of soybean meal (59%) bone & meat meal (50%) and fish meal (50%). However, the intestinal digestibility is relatively lower for torula yeast (87%) compared to that of soybean meal (98%) bone & meat meal (70%) and fish meal (94%):

  

• Torula yeast provides nutritional benefits, enhances flavor as well as improves palatability and is economical to use.
• Torula Yeast is used in dry and canned pet foods, moist pet treats and animal feeds.
• Torula yeast is used Foods: Gravies, soups, sauces,
• The most important aspect one should consider in manufacturing torula yeast is the strain and media as they greatly influence the flavor profile and palatability.

To learn more about yeast extract flavors in the food industry follow this link

In closing, I must say that based on the scientific studies the digestibility of torula yeast is relatively higher compared to soybean, fish meal, bone and meat meal. Absorption of the digested proteins (peptides and amino acids) is closer to that of the fish meal and higher than bone and meat meal products. Further, the unique characteristics of torula yeast (by itself neutral in flavor) give it the potential to enhance flavors in any applications, unlike brewers yeast which is bitter and astringent. Torula yeast is highly palatable and not thoroughly exploited in the feed industry.

As we just enjoyed the holidays, good food, music, movies and alcoholic and non-alcoholic drinks I thought it would be appropriate to look at yeast, yeast varieties used for foods and drinks, and their use in animal feeds.

History and Types of Yeast
In Egypt as early as 4000 B.C. yeast has been used in the preparation of food and drink but it was only in the 19th century that the role of yeast in fermentation was clearly established by Pasteur, and only in the past few decades that yeast has been genetically modified to make value added chemicals, pharmaceutical drugs, etc.

There are several types of yeast available in the market, such as brewers yeast, sake yeast (Japanese alcoholic beverage made from rice sometimes referred to as "rice wine"), wine yeast, bakers yeast, and distillers yeast (obtained after ethanol by wet mill process). All of these are S.cerevisiae, Torula yeast (Candida utilis) and Lactic yeast (Kluyveromyces lactis). There are several other yeasts (for example methylotrophic yeast) that do not need glucose feedstock but can be easily grown on methane or methanol. However, methylotrophic yeast is typically used to modify the yeast cells to produce chemicals, drugs and enzymes. An interesting development with yeast is that they can be grown with chromium and selenium (antioxidant) so that these minerals are delivered biologically more effectively through yeast.

Yet another category of yeast called "osmophilic yeast" such as Zygosaccharomyces rouxii, Pichia farinos can tolerate higher concentrations of salt and sugars and can survive in low water activity environments such as jelly and jams. There are also some pathogenic yeasts which bring the bad press and commonly referred to as "yeast infection".

Yeast Uses
There are countless uses for yeast, however, the majority of the yeast and yeast extracts are used in a variety of foods such as baking, brewing, or used as flavor enhancers (an essential ingredient in replacing MSG), bioremediation, production of biochemicals, drugs, as probiotics, or as nutritional supplements. In other words we are dependent on yeast for our delicious food, drinks, and good nutrition for human beings and animals.

Manufacturing of Yeast
I am not detailing the manufacturing process of yeast here but would like to highlight the sources of yeast and their effect on consistency. Most yeast products are made from the by-products with the exception of some bakers and torula yeast. The yeast that are grown on glucose feedstock are known as the "primary grown" in other words the yeast is primarily grown for food/feed applications. The whole process starting from the raw materials are well controlled therefore, the yeast is expected to be more consistent unlike brewers yeast.

Brewers yeast is a by-product of alcohol fermentation and may not be consistent (not all brewers yeast are same, varies from brewery to brewery or sometimes within the same brewery depending on the type), and so is the yeast and yeast extracts made from them.

The feedstock for yeast varies and it is important because some of the constituents are carried along with the yeast and to the yeast extracts. For example:

• Brazil pretty much uses sugarcane molasses.
• Brewers yeast carries with it some of the metabolites from hops.
• Distillers yeast carries some of the metabolites from corn steep (wet milling process).
• Kluyveromyces carries soluble constituents from whey.
• Torula yeast is manufactured from the by-product of paper companies brings along some sulfites. However, a very few companies grow torula yeast on a glucose feedstock as "Primary Grown".

I will be discussing in detail about the yeast autolyzates, yeast extracts and yeast cell walls and their applications in the near future.

• Follow this link for one of the earlier reports of yeast feeding to lactating cows. Not a positive one but it is interesting to see scientific papers on yeast in animal feeds from 1924. http://jds.fass.org/cgi/reprint/8/2/89.pdf
• Follow this link as how yeast is contributing to the modern medicine. http://nobelprize.org/nobel_prizes/chemistry/laureates/2006/illpres/2_yeast.html
• Follow this link as how a Nobel Laureate used yeast cells http://nobelprize.org/nobel_prizes/medicine/laureates/2001/press.html

Pretty much all the enzymes are proteins, except ribozymes that act as biocatalysts and artificial enzymes which are developed by synthetic organic chemists to imitate enzymes.

Enzymes are present in all the living cells and carry out the essential functions of the living organisms. All enzymes are proteins, with couple of exceptions mentioned above. However, not all proteins are enzymes: for example, casein, soy protein, gelatin, etc., are broken down to smaller peptides and amino acids before they are consumed. Enzymes, by their mere presence, and without being consumed, speed up the hydrolysis of proteins.

In other words, enzymes are biocatalysts that can be used over and over. Like any other protein, enzymes are made up of long chains of amino acids that are held together by peptide bonds. There are several enzymes, such as those commonly found in digestive tract: Pepsin and Trypsin that break down proteins to peptides and amino acids, lipases that break down fats into fatty acids and glycerol, and amylases that break down starch to simple sugars. Unlike inorganic catalysts, enzymes are highly specific and pharmaceutical and biotechnology companies exploit this unique feature to potentially make drugs and drug intermediates.

Most of the enzymes are manufactured by submerged and solid-state fermentation process; some are extracted from plants and animal glands. Enzymes are used in a wide variety of industrial applications ranging from animal feeds, meat, leather, food, bio ethanol, biotechnology, biomedical, and many more industrial segments. One of the earlier uses of enzymes was the manufacture of cheese using the stomach extracts of young calves. Today this is significantly replaced by the enzyme chymosin, produced by recombinant cultures.

Over the years research work on enzymes led to several Nobel prizes and revolutionized recombinant technology. More than 30 years ago, the introduction of recombinant DNA technology as a tool for the biological sciences transformed the study of life. Some of the enzymes that revolutionized this field are Restriction enzymes, DNA Ligases, and Polymerase Chain Reactions (PCR), which enabled the production of large quantities of a specific DNA from a complex DNA template in a simple enzymatic reaction. Without these enzymes we would not have seen such rapid progress in biotechnology.

In biotechnology and many other scientific fields there is enormous amount of potential for the discovery of new enzymes and applications of existing enzymes to improve the quality of food and feed.

The following link is the text from Nobel Prize winning speech on enzymes, must read for people who are interested in enzymes: nobelprize.org/nobel_prizes/chemistry/laureates/1972/presentation-speech.html 

 Enzymes  | Comments (1)
Vijai Pasupuleti,   December 3rd, 2007 08:15:29 AM

MRSA Infections- Impact on the Feed Industries:

With the media coverage on MRSA (Methicillin-resistant Staphylococcus aureus) infections in US schools, awareness of this so-called superbug, 'super staph', is increasing. Perhaps people are getting scared thinking that it will become an epidemic. In reality, MRSA has been in existence for a very long time and it can still be treated with antibiotics like Vancomycin.

MRSA connection with animals especially pigs:

A major concern is that the MRSA bacteria are already transferring from animals to humans. Farmers and their families, farm workers, vets and abattoir workers are at highest risk because of their direct contact with animals.

A recent study by Khanna et al 2007 published in Veterinary Microbiology, identified MRSA on 45% of 20 Ontario farms in nearly one in four pigs and one in five farmers.

In the Netherlands, contact with pigs is now recognized as a risk factor for MRSA carriage:

Despite a strict control program for methicillin-resistant Staphylococcus aureus (MRSA) in human medicine in the Netherlands, MRSA was cultured from exudative epidermitis lesions of 4 piglets on a breeding farm, 20 pigs on a supplier farm, and 2 workers on these farms. The MRSA strains were indistinguishable, suggesting direct transmission.

Further details on this study can be found here.

Until recently, MRSA infections have remained rare both inside and outside the hospitals in Netherlands. However, this landscape is changing with a high proportion of cases of MRSA being detected. Now it is not just in Netherlands, Canada, Belgium but many countries have detected and reported MRSA infections in humans and pigs. Because of these latest findings that pig farms may be a source of MRSA, the FDA and other agencies may potentially start sampling the pig farms.

MRSA infections are not just limited to human beings or pigs and other livestock animals, but have also been spreading to companion animals. Fortunately enough some antibiotics still work against MRSA and it can be treated, but the daunting question is how long these antibiotics can remain effective. According to Dr. John Jernigan at CDC, "We can always expect antibiotic resistance to follow antibiotic use, as surely as night follows day," It is only a matter of time.

According to some estimates, 70% of antibiotics and related drugs produced in USA are used on livestock. To prevent and control common harmful bacteria and promote growth low doses of antibiotics are included in feed. This practice, over a period of time, may lead to the emergence of antibiotic resistant bacteria such as MRSA. For this reason Europe has banned the use of antibiotics in the feeds for routine use. This has led to the emergence of 'probiotics' and as the pro name suggests these promote healthy bacteria in the gut unlike anti (against) biotics.

According to the currently adopted definition by FAO/WHO, probiotics are: 'Live microorganisms which when administered in adequate amounts confer a health benefit on the host'.

The simplest amino acid Glycine, HO₂CCH₂NH₂