Some Effects of Phosphate and Volatile Fatty Acid Salts on the Growth of Rumen Bacteria

Abstract

Bacterial cultures in media with a low (0.38 %, w/v) initial glucose concentration showed much smaller pH changes during growth than cultures grown in media with excess (1.25 %, w/v) glucose. Increasing the concentration of the phosphate or volatile fatty acid salt (VFA salt, i.e. acetate, propionate or butyrate) in the media had no beneficial effect on cultures of Streptococcus bovis or Lactobacillus plantarum which had only minor falls in pH during growth (final pH 3 6.0), but increased the dry weight yield (but not the molar growth yield) of cultures which had major pH falls (final pH < 4-6) during growth. The improvements in dry weight yield could be correlated with increases in the pH buffering capacity of media caused by the increased phosphate or VFA salt concentration.The response of Bacteroides ruminicola to increases in the phosphate concentration of media was qualitatively similar to that of S. bovis. However, VFA salts (particularly acetate) always decreased both dry weight and molar growth yield. The effects of VFA salts on three other rumen bacteria, Butyrivibrio jibrisolvens, Megasphaera elsdenii and Veillonella akalescens, were varied. The possible mechanisms and ecological implications of the effects of these compounds are discussed. I N T R O D U C T I O NThe complex nature of the nutrient requirements of rumen bacteria makes the formulation of fully defined media laborious and costly. A number of workers, therefore, have developed semi-defined media, containing protein hydrolysates and yeast extract but lacking centrifuged rumen fluid, for the study of the metabolism of rumen bacteria (Hobson, 1969).Although an accurate comparison of the composition of media and of rumen fluid is hindered by the variable nature of rumen fluid, some semi-defined media contain only small amounts of the phosphates and volatile fatty acid (VFA) salts which are important in determining the pH buffering capacity of rumen fluid (Turner & Hodgetts, 1955). The effect of pH control in increasing the yields of bacteria has been described (see, for example, Kempe, Halvorson &Piret, 1950 andSargeant, 1968), but apart from effects on pH, both classes of compound have other effects on micro-organisms. Phosphates are essential in small quantities, but may be toxic in high concentration (Good et al. 1966 The aim of the present study was to investigate the response of some rumen bacteria, grown in batch culture on semi-defined media, to increases in the phosphate and VFA salt concentrations of the media to levels within the rumen range. A preliminary study (Stewart, 1972) showed that only small effects were involved, but the results seemed likely to be relevant to a number of areas of current microbiological interest. For instance, the isolates used in the present study have been inoculated into the rumens of gnotobiotic lambs (Lysons et al. 1971 ;Mann & Stewart, 1974) as part of a continuing investigation into factors affecting the growth of rumen bacteria in vivo. It was therefore possible to compare the growth of these b...

Biohydrogen production with mixed anaerobic cultures in the presence of high-concentration acetate

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Effect of pH and Oxygen on Growth and Viability of Acetivibrio cellulolyticus

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

“…Hungate (1966) estime qu'elle est comprise entre 2 et 6 % de la matière sèche (MS) et Stewart (1975), pour des bactéries en culture pure, entre 2 et 2,8 %. Sur des prélèvements effectués in vivo, les valeurs se situent en général entre 1 et 2 % (Durand, non publié ;Martinez, 1972 ;Czerkawski, 1976 ;Van Nevel et Demeyer, 1977 …”