Mixed fungal populations and lignocellulosic tissue degradation in the bovine rumen

Abstract

Anaerobic fungi in ruminal fluid from cows eating Bermuda grass hay plus a grain and minerals supplement were evaluated for diversity in sporangial morphotypes and colony growth patterns and for the degradation of various lignocelluloses. In selective cultures containing streptomycin and penicillin, an active population of ruminal fungi colonized leaf blades and degraded fiber at rates and extents almost equal to that of the total ruminal population. Three major sporangial morphotypes were consistently observed on leaf blades: oval, globose, and fusiform. Fungal colonies representing three distinct growth types consistently developed in anaerobic roll tubes inoculated with strained ruminal fluid. Sporangial morphotypes could not be matched to colony types due to multiple sporangial forms within a colony. Under identical growth conditions, one type exhibited a monocentric growth pattern, while two types exhibited polycentric growth patterns previously unreported in ruminal fungi. Mixed ruminal fungi in selective cultures or in digesta taken directly from the rumen produced a massive clearing of the sclerenchyma. Quantitation of tissue areas in cross sections by light microscopic techniques showed that fungal incubations resulted in significant (P = 0.05) increases in sclerenchyma degradation compared to whole ruminal fluid incubations. The mestome cell wall was at times penetrated and partially degraded by fungi; the colonization was less frequent and to a lesser degree than with the sclerenchyma. Conversely, ruminal bacteria were not observed to degrade the mestome sheath. Phenolic monomers at 1 mM concentrations did not stimulate to a significant (P = 0.05) extent the dry weight loss or fungal colonization of leaf blades; at 10 mM concentrations cinnamic and benzoic acids were toxic to ruminal fungi.

Effect of forage cell wall phenolic acids and derivatives on rumen microflora

“…Under similar conditions the photodimer was non-toxic ( Table 2 ) . The data confirm the extremely toxic nature of p-coumaric acid to rumen microorganisms noted in earlier work (Jung and Sahlu 1986;Akin and Rigsby 1987), and establish the highly toxic nature of the esters. It is also of interest to note that, as indicated in earlier studies (Akin and Rigsby 1987), the activity of the fungi was enhanced when bacteria were removed ( Table 2).…”

“…The data confirm the extremely toxic nature of p-coumaric acid to rumen microorganisms noted in earlier work (Jung and Sahlu 1986;Akin and Rigsby 1987), and establish the highly toxic nature of the esters. It is also of interest to note that, as indicated in earlier studies (Akin and Rigsby 1987), the activity of the fungi was enhanced when bacteria were removed ( Table 2). The addition of the photodimer did not lead to a significant difference ( P < 0.05) from the control in any test (Tables 1 and 2), suggesting that the compound was non-toxic or the level of toxicity was too low to be detected.…”

“…A further test for inhibition of digestibility by the phenolics was the same as above, but streptomycin and penicillin were added to the rumen fluid to inhibit bacteria and to select for rumen fungi as described earlier (Akin and Rigsby 1987).…”

Effect of phenolic monomers on biomass and hydrolytic enzyme activities of an anaerobic fungus isolated from wild nil gai (Baselophus tragocamelus)

“…The earlier reports in literature indicate that rumen fungi are more resistant to phenolic monomers as compared with other rumen microbes (Akin and Rigsby 1987). Borneman et al (1986) observed varied effects of phenolic monomers on bacteria (inhibitory or stimulatory), depending on the compound and the microbial species.…”

Pectinolytic enzymes of anaerobic fungi

“…Rumen fungi produce all enzymes necessary both for depolymerization of cellulose and hemicellulose and hydrolysis of free oligosaccharides (Akin and Rigsby 1987;Mountfort 1987). Up to now no described isolate was able to grow on pectin alone (Orpin and Joblin 1987).…”