Estimation in vitro à l'aide du phosphore radioactif des besoins en phosphore des microorganismes du rumen

Abstract

Summary. In vitro estimate of rumen microbial requirements for phosphorus using 32 P label%d phosphate.Microbial requirements for P were assumed to be a function of the amount of microbial protein synthesis (microbial growth) and of the quantity of organic matter (OM) fermented in the rumen. The relationships among P incorporation into microbial matter and protein synthesis, ammonia utilization, volatile fatty acid (VFA) production and organic matter fermented (OMF) were studied in short-term incubations (3 h) using 32 P-labelled phosphate. The amount of P incorporated was calculated from extracellular phosphate pool specific activity and the radioactivity incorporated into the microbial sediment during incubation (table 11. The inocula came from sheep fed a protein-free purified diet. In order to vary the intensity of fermentation, carbohydrates with a wide range of degrees of enzymatic susceptibility were used as substrates and the medium was either provided or was deficient in S and trace elements (table 4). Nitrogen was supplied as ammonium salts.Linear regression analyses showed that P incorporation was positively correlated with the criteria of protein synthesis and OM fermentation (figs. 1, 2, 3, 4). However, there was significant phosphorus incorporation when the value for nitrogen incorporation was zero (equation A : (Pi (mg) = 0.162 NH 3 -N + 0.376 ; r = 0.9). This was assumed to result either from energetic uncoupling (fermentation without concomitant bacterial growth) or from the lysis of cold microbial cells only. Equation A would reflect total P incorporation and equation A' Pi (mg) = 0.16! NH 3 -N (mg), net P incorporation.It was assumed that in vitro microbial requirements for P were in the range of 30-70 mg of P/liter of medium for 3-hour incubation, depending on the intensity of fermentation. Form a mean value of microbial N yield of 30 g/kg of DOMR (organic matter apparently digested in the rumen), it was calculated that the total and net P requirements in vivo were 6 and 4.9 g/kg of DOMR, respectively, corresponding to 3.9 and 3.z g/kg of DOM (digestible organic matter). From equation D, relating Pi to OMF, the P requirements were about 4.4 g/kg of DOM. It is suggested that microbial requirements for P varied from 3 to 5 g of P/kg of DOM, depending on the efficiency of microbial synthesis and the extent of carbohydrate fermentation. These results, considered as indicative, should be checked in in vivo experiments.Introduction.

Effect of different levels of phosphorus on rumen microbial fermentation and synthesis determined using a continuous culture technique

“…This change in fermentative activity was confirmed by significant reductions in cellulose and hemicellulose digestion with no apparent depression of starch digestion, indicating perhaps a change in the balance of the bacterial population (Latham et al 1974;Leedle & Hespell, 1984). Bryant et al (1959) have suggested a minimum requirement of 20 mg Pi/l for the maximum cellulolytic activity of pure cultures of cellulolytic bacteria, and extreme sensitivity of cellulolytic bacteria to P deficiency has been reported by Durand et al (1986). It has also been shown that cellulases isolated from mixed rumen bacteria associated with fibre have specific P requirements and that the enzymes show different affinities for different fibre fractions (Francis et af.…”

“…Other adaptive mechanisms contributing to P salvage in order to maintain nucleic acid synthesis have also been reported (Barsdate et al 1974). Reduced microbial-N flow at the duodenum of lambs and sheep receiving P-depleted diets has been reported (Breves et al 1985;Durand et al 19833) but the effect of P depletion on growth yield is uncertain, having been variously reported as having no or a reducing effect (Durand et al 1983b;Durand et al 1986). In the present work, although there was a reduction in microbial growth at low e concentrations, no evidence of reduced efficiency of microbial protein synthesis was observed at any level of 5.…”

Response of lactating goats to low phosphorus intake 2. Nitrogen transfer from rumen ammonia to rumen microbes and proportion of milk protein derived from microbial amino acids

“…Increased pH of rumen fluid during P deficiency has been reported in vitro (Milton & Ternouth, 1984;Komisarczuk et al 1984) and in vivo (Holler, Breves & Martens, 1983). This may be explained by reduced VFA production as shown in vitro (Durand, Beaumatin & Dumay, 1983;Komisarczuk etal. 1984).…”

Valorization of various sources of rabbit manure in agro-piscicultural system in Benin (West Africa): dynamics and effect of mineralization upon quality of fresh water

“…Phosphorus content was important in T 4 and explains that the degradation of organic matter continues under its influence. In fact, phosphorus allows microorganism's longer life time than nitrogen (Durand et al 1983). The orthophosphate content from T 4 was higher than those obtained by Bokossa et al (2014a), whose maximum value was 2.80 mg/L.…”