Effect of spineless-cactus mucilage on the in vitro rumen fermentation of cellulose, starch, and protein

SUMMARY The aim of this study was to evaluate the effect of the levels of spineless-cactus mucilage on the in vitro rumen fermentation of cellulose, starch, and protein. A completely randomized experimental design was adopted with a 5 × 3 factorial arrangement consisting of five levels of spineless-cactus mucilage (0, 5, 10, 20, and 40%) and three substrates (carboxymethylcellulose, starch, and trypticase). Treatments were evaluated in a ruminal environment simulated by in vitro incubation at different times of assessment: 0, 3, 6, 12, 24, and 48 h. The incubation procedure was repeated three times, totaling three evaluations per incubation time for each treatment. There was an interaction (P<0.05) between the mucilage levels and substrate for all evaluated ruminal parameters, except for the concentration of microbial protein after 48 h of fermentation and for the proportions of acetate and butyrate fermentation at time 0 h. There was a quadratic increase (P<0.05) in the concentration of ammoniacal nitrogen after 48 h of incubation in the media containing carboxymethylcellulose and trypticase. pH values decreased quadratically (P<0.05) as a function of the mucilage levels in the media containing carboxymethylcellulose and trypticase. Overall, no expressive alterations were observed between the individual molar proportions of acetate, propionate, and butyrate with the addition of spineless-cactus mucilage levels to the different substrates. Spineless- cactus mucilage affects the pattern of fermentation of starch, cellulase, and protein performed by rumen microorganisms.

Efficient Metabolic Exchange and Electron Transfer within a Syntrophic Trichloroethene-Degrading Coculture of Dehalococcoides mccartyi 195 and Syntrophomonas wolfei

ABSTRACTDehalococcoides mccartyi195 (strain 195) andSyntrophomonas wolfeiwere grown in a sustainable syntrophic coculture using butyrate as an electron donor and carbon source and trichloroethene (TCE) as an electron acceptor. The maximum dechlorination rate (9.9 ± 0.1 μmol day−1) and cell yield [(1.1 ± 0.3) × 108cells μmol−1Cl−] of strain 195 maintained in coculture were, respectively, 2.6 and 1.6 times higher than those measured in the pure culture. The strain 195 cell concentration was about 16 times higher than that ofS. wolfeiin the coculture. Aqueous H2concentrations ranged from 24 to 180 nM during dechlorination and increased to 350 ± 20 nM when TCE was depleted, resulting in cessation of butyrate fermentation byS. wolfeiwith a theoretical Gibbs free energy of −13.7 ± 0.2 kJ mol−1. Carbon monoxide in the coculture was around 0.06 μmol per bottle, which was lower than that observed for strain 195 in isolation. The minimum H2threshold value for TCE dechlorination by strain 195 in the coculture was 0.6 ± 0.1 nM. Cell aggregates during syntrophic growth were observed by scanning electron microscopy. The interspecies distances to achieve H2fluxes required to support the measured dechlorination rates were predicted using Fick's law and demonstrated the need for aggregation. Filamentous appendages and extracellular polymeric substance (EPS)-like structures were present in the intercellular spaces. The transcriptome of strain 195 during exponential growth in the coculture indicated increased ATP-binding cassette transporter activities compared to the pure culture, while the membrane-bound energy metabolism related genes were expressed at stable levels.

Significance of acetogenic H2 consumption in dark fermentation and effectiveness of pH

Two identical thermophilic H2 fermenters (R1 and R2) were operated at different pH levels between 4.7 and 5.7. In R1, several unexpected and severe drops in H2 yield inversely proportional to increase in acetate production were experienced at pH 5.5 and 5.7. In contrast, R2 operated at pH 5and 4.7 performed more stable H2 production mainly through butyrate fermentation. Although the H2 partial pressure (&gt;50 kPa) was far above the favorable values, acetate was produced as well as butyrate in all pH levels tested. To determine whether some portion of the acetate is produced through another pathway such as autotrophic synthesis via H2 dependent reduction of CO2 or not, batch dissolved H2 consumption rate tests were performed at pH 5.0, 5.5 and 6. The specific H2 consumption rate was 488(±49) μmol/gVSS.hr at pH 6 and slightly higher than at pH 5and 5.5. The results of continuous and batch experiments revealed that acetogenic H2 consumption is more favorable at pH levels above 5.5 and is one of the reasons of instabilities in dark fermentative H2 production.

Trophic interaction of the aerotolerant anaerobe Clostridium intestinale and the acetogen Sporomusa rhizae sp. nov. isolated from roots of the black needlerush Juncus roemerianus

Acetogens were enumerated from root homogenates of the black needlerush Juncus roemerianus obtained from a nearly pristine salt marsh. An isolated colony, ST1, yielded acetogenic activity and was initially thought to be a pure culture; however, ST1 was subsequently found to be composed of an aerotolerant fermentative anaerobe (RC) and an acetogen (RST) (T indicates type strain). The two spore-forming mesophiles were separated by selective cultivation under conditions favouring the growth of either RC or RST. The 16S rRNA gene sequence of RC was 99 % similar to that of Clostridium intestinale, indicating that RC was a new isolate of this clostridial species. The rRNA gene sequence most similar to that of RST was only 96 % similar to that of RST and was from a species of the acetogenic genus Sporomusa, indicating that RST was a new sporomusal species; the name Sporomusa rhizae sp. nov. is proposed. RC grew at the expense of saccharides. H2-forming butyrate fermentation was the primary catabolism utilized by RC under anoxic conditions, while homolactate fermentation was the primary catabolism under oxic conditions. RC consumed O2 and tolerated 20 % O2 in the headspace of shaken broth cultures. In contrast, RST was acetogenic, utilized H2, lactate and formate, did not utilize saccharides, and could not tolerate high concentrations of O2. RST grew by trophic interaction with RC on saccharides via the uptake of H2, and, to a lesser extent, lactate and formate produced by RC. Co-cultures of the two organisms yielded high amounts of acetate. These results indicate that (i) previously uncharacterized species of Sporomusa are associated with Juncus roots and (ii) trophic links to O2-consuming aerotolerant anaerobes might contribute to the in situ activities and survival strategies of acetogens in salt marsh rhizospheres, a habitat subject to gradients of plant-derived O2.