Mixed Microbes Research Articles

Characterisation of proteolytic activity of rumen microbes and commercial proteases

Commercial proteases yield more reproducible estimates of extent of rumen protein degradation than either in situ or rumen in vitro methods. Although extents of protein digestion determined using commercial proteases have been positively correlated to extents of in situ protein degradation, these values have not proven reliable predictors of rates of rumen protein degradation. This is because no protease-based assay has yet been developed that successfully mimics the specificities of the organisms involved in protein degradation in the rumen. If the proteolytic activity of rumen microbes and commercial proteases can be correctly characterised, then it would be possible to elaborate protease blends that match the protein degradative activity of mixed rumen microbes. The research reported here is an extension of earlier work as a prelude to preparing enzyme mixes with “protease fingerprints” similar to rumen microbes.

Effects of pH and Electron Donors on Nitrate and Nitrite Reduction in Ruminal Microbiota

Factors affecting nitrate and nitrite reduction in the rumen were examined. Nitrate and nitrite reduction by mixed microbes harvested from the goat rumen was increased by feeding a high-roughage diet, which contained a much higher amount of nitrate than concentrate. The activities of nitrate reductase and nitrite reductase per bacterial mass appeared to be increased by feeding a high-nitrate diet, suggesting that these enzymes are induced by substrates. Nitrate and nitrite reduction was confirmed to be the fastest at neutral pH and affected by electron supply. The supplementation of electron donors, such as formate, H2, and lactate, stimulated nitrate and nitrite reduction, especially nitrite reduction, which decreased nitrite accumulation. As a result, addition of formate or lactate in the presence of nitrate alleviated the inhibitory effect of nitrite on fermentation, and greatly reduced methanogenesis.

Production of a bioflocculant by mixed culture.

Colony groups that form large amounts of slime externally were obtained from activated sludge among phthalate-assimilating microbes. That slime, which R-3 mixed microbes produced externally, had a high level of flocculation activity. R-3 mixed strains, one of such colony groups, efficiently produced a bioflocculant (APR-3) in liquid cultures of production medium, especially that containing starch and glucose (1:1) as carbon sources. Identification of this group of bioflocculant-producing microbes (R-3 mixed strains) showed that it was comprised of four strains belonging to the genera Oerskovia, Acinetobacter, Agrobacterium, and Enterobacter. The bioflocculant (APR-3) was purified electrophoretically to homogeneity by ethanol and CPC precipitation. Its molecular mass is at least 2 x 10(6) Da. APR-3 is an acidic polysaccharide made of glucose, galactose, succinic acid, and pyruvic acid (molar ratio: 5.6:1:0.6:2.5).

Entrapment of Mixed Microbial Cells for Water and Wastewater Treatment

An entrapment of mixed microbial cells process was used to remove the pesticide Ethylene Dibromide (EDB), Trichlopropane (TCP) and nitrate contaminated in the groundwater. The mixed microbes were entrapped into a polymeric cellulose triacetate. The system is able to remove (aerobically) more than 90% of EDB (influent concentration of 300 μg/l) at more than 30 minutes of hydraulic retention time (HRT). TCP (influent concentration of 2.81 μg/l) could not be detected in the effluent at the same HRT. The system is also able to remove (anaerobically) more than 99% of nitrate influent concentration of NO3-N ranging from 50 to 850 mg/l) at an HRT of more than 2 hours. The system has shown very promising results in respect of the removal of trace pesticide and nitrate contaminated groundwater. It can also be considered as an alternative for direct treatment of nitrate-rich water or in a combination with an ion exchange process with an intermittent to eliminate the high nitrate concentration from the spent regenerant. The system could easily develop a package plant for removal of trace organics and inorganics from the groundwater.

Denitrification of Nitrate-Rich Water Using Entrapped-Mixed-Microbial Cells Immobilization Technique

A denitrification process was examined by using Entrapped-Mixed-Microbial Cells Immobilization (EMMCI) process. The mixed microbes were entrapped into a polymeric cellulose triacetate. The reactor was operated over one year with feed concentration ranging from 50 to 850 mg NO3-N/l. The hydraulic retention times (HRT) were also varied from 1.8 to 11.3 hours. Complete denitrification was obtained at an HRT of 2.6 to 11.3 hours. At an HRT of 1.8 hours, the maximum nitrate-N loading rate of 591.6 g/m3 ·h (based on carriers volume) was achieved with an 88.3% denitrification efficiency. Under high range of NaHCO3 concentrations from 10 to 20 g/l, the denitrification efficiency above 96% could be obtained. This EMMCI process has showed very promising results in respect to nitrate removal. It can be considered as an alternative approach tor direct treatment of nitrate-rich water or in a combination with an ion exchange process with an intent to eliminate the high nitrate concentration from the spent regenerant.

The prompt demonstration without culturing of gram-negative bacteria in burn wound infections

Burn wound sepsis is the most important factor in the morbidity and mortality associated with major burns. Blood cultures often give false negative results and wound biopsy is a much more accurate and reliable means of assessing the burn's microbial status. From 1950 to 1965, due to the introduction of antibiotics, gram-negative organisms became predominant among those recovered from burn wound infections. Although few grampositive organisms are now seen in Gram-stained burn wound biopsies, the light pink or red staining of gram-negative organisms can occasionally go unnoticed (Fig. 1). This is not the case when the biopsy sections are stained with the new positive PATS stain developed in our laboratories for gram-negative bacteria. This reaction deposits silver on the lipopolysaccharides of the outer walls of gram-negative, but not gram-positive, bacteria. The assessment of the microbial content of the specimen site as colonized, infected, or having mixed or unmixed gram-negative microbes is facilitated by this stain (Figs. 2-4).