Gastrointestinal stress as innate defence against microbial attack.

The human gastrointestinal (GI) tract has been bestowed with the most difficult task of protecting the underlying biological compartments from the resident commensal flora and the potential pathogens in transit through the GI tract. It has a unique environment in which several defence tactics are at play while maintaining homeostasis and health. The GI tract shows myriad number of environmental extremes, which includes pH variations, anaerobic conditions, nutrient limitations, elevated osmolarity etc., which puts a check to colonization and growth of nonfriendly microbial strains. The GI tract acts as a highly selective barrier/platform for ingested food and is the primary playground for balance between the resident and uninvited organisms. This review focuses on antimicrobial defense mechanisms of different sections of human GI tract. In addition, the protective mechanisms used by microbes to combat the human GI defence systems are also discussed. The ability to survive this innate defence mechanism determines the capability of probiotic or pathogen strains to confer health benefits or induce clinical events respectively.

Rumen methanogens: a review.

The Methanogens are a diverse group of organisms found in anaerobic environments such as anaerobic sludge digester, wet wood of trees, sewage, rumen, black mud, black sea sediments, etc which utilize carbon dioxide and hydrogen and produce methane. They are nutritionally fastidious anaerobes with the redox potential below -300 mV and usually grow at pH range of 6.0-8.0 [1]. Substrates utilized for growth and methane production include hydrogen, formate, methanol, methylamine, acetate, etc. They metabolize only restricted range of substrates and are poorly characterized with respect to other metabolic, biochemical and molecular properties.

Role of anaerobic fungi in wheat straw degradation and effects of plant feed additives on rumen fermentation parameters in vitro.

In the present study, rumen microbial groups, i.e. total rumen microbes (TRM), total anaerobic fungi (TAF), avicel enriched bacteria (AEB) and neutral detergent fibre enriched bacteria (NEB) were evaluated for wheat straw (WS) degradability and different fermentation parameters in vitro. Highest WS degradation was shown for TRM, followed by TAF, NEB and least by AEB. Similar patterns were observed with total gas production and short chain fatty acid profiles. Overall, TAF emerged as the most potent individual microbial group. In order to enhance the fibrolytic and rumen fermentation potential of TAF, we evaluated 18 plant feed additives in vitro. Among these, six plant additives namely Albizia lebbeck, Alstonia scholaris, Bacopa monnieri, Lawsonia inermis, Psidium guajava and Terminalia arjuna considerably improved WS degradation by TAF. Further evaluation showed A. lebbeck as best feed additive. The study revealed that TAF plays a significant role in WS degradation and their fibrolytic activities can be improved by inclusion of A. lebbeck in fermentation medium. Further studies are warranted to elucidate its active constituents, effect on fungal population and in vivo potential in animal system.

Single cell protein: a promising dietary substitute.

Promises and limitations in exploitation of microorganisms for single cell protein (SCP) production have been reviewed. Various aspects discussed include global protein problem, microbes as potential sources of food and feed with its advantages and disadvantages, salient features in selection of microorganisms for SCP production, production of SCP from petroleum based hydrocarbons, renewable raw materials like agricultural and forestry residues, industrial by-products and wastes, nutritional and safety evaluation of SCP, ways of improving SCP production, economics of SCP production and the present status of SCP in India.

In vitro degradation of cell-wall and digestibility of cereal straws treated with anaerobic ruminal fungi.

Ruminal fungal isolates (Orpinomyces sp.; C-14, Piromyces sp.; C-15, Orpinomyces sp.; B-13 and Anaeromyces sp.; B-6), were evaluated under anoxic conditions for their effect on in vitro dry matter digestibility, neutral detergent fibre, acid detergent fibre and acid detergent lignin using rice and wheat straw as substrate. There was no significant effect of the fungal isolates on the disappearance of the substrates along with rumen liquor when compared to control. The doses of 10(6) cfu/ml of the isolate were found to have maximum degradation of straws in comparison to the doses of 10(3) cfu/ml.

Effect of administration of rumen fungi on production performance of lactating buffaloes.

Anaerobic fungi were orally dosed to lactating buffaloes to study their effect on the digestibility of a diet (composed of 50% wheat straw and 50% concentrate along with six kg maize green/animal/day), rumen fermentation patterns and milk production. Group I (control) was administered with fungus-free anaerobic broth, while group II and III were administered with Orpinomyces sp. C-14 or Piromyces sp. WNG-12 (250 ml; 3-5 days of growth/animal/ week), respectively. Milk production was higher in group II and III (8.42 and 8.48 kg/d) than in the control (8.03 kg/d) with virtually the same feed intake (i.e. 11.50 and 10.62 and 11.79 kg, respectively). There was an increase of 6% fat-corrected milk yield/animal/day in group II and III, respectively compared to the control. The milk fat was higher in the fungal culture administered groups than in the control group. The digestibility of dry matter, crude protein, neutral detergent fibre, acid detergent fibre, cellulose and digestible energy also increased significantly in group II and III. The pH and ammonia nitrogen were lower, whereas total volatile fatty acids, total nitrogen, trichloroacid precipitable nitrogen and number of zoospores/ml of rumen liquor were higher in group II and III when compared to the control. Hence, it can be stated that rumen fungi can be used as a direct-fed microbial in lactating buffaloes, to enhance the digestibility of wheat straw based diets leading to higher production.

Interaction of gut microflora with tannins in feeds.

Tannins (hydrolyzable and condensed) are water-soluble polyphenolic compounds that exert antinutritional effects on ruminants by forming complexes with dietary proteins. They limit nitrogen supply to animals, besides inhibiting the growth and activity of ruminal microflora. However, some gastrointestinal microbes are able to break tannin-protein complexes while preferentially degrading hydrolyzable tannins (HTs). Streptococcus gallolyticus, Lonepinella koalarum and Selenomonas ruminantium are the dominant bacterial species that have the ability to degrade HTs. These tanninolytic microorganisms possess tannin-degrading ability and have developed certain mechanisms to tolerate tannins in feeds. Hence, selection of efficient tanninolytic microbes and transinoculation among animals for long-term benefits become areas of intensive interest. Here, we review the effects of tannins on ruminants, the existence and significance of tannin-degrading microorganisms in diverse groups of animals and the mechanisms that tannin-degrading microorganisms have developed to counter the toxic effects of tannin.