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Essay / An optional aerobic and its characteristics | | is capable of switching to fermentation or anaerobic respiration in the absence of oxygen. In contrast, an obligate aerobe cannot make ATP in the absence of oxygen, and obligate anaerobes die in the presence of oxygen. Some examples of facultative aerobic bacteria are Staphylococcus spp., Streptococcus spp, Escherichia coli, Salmonella, Listeria spp, and Shewanella oneidensis. Some eukaryotes are also facultative aerobes, including fungi such as Saccharomyces cerevisiae and many aquatic invertebrates such as Nereid polychaetes (worms). Examples Streptococcus sanguineous streptococcus aralis Facultative aerobes: can grow with or without oxygen because they can metabolize energy aerobically or anaerobically. They mainly congregate at the top because aerobic respiration generates more ATP than fermentation or anaerobic respiration. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”? Get the original essay Features of facultative aerobic negative sticks Bacteria rely on the liquid phase of a fixed bed anaerobic digester, processing a whey substrate of deproteinized and fermented cheese, were carried out on two different media under aerobic and facultative conditions. Average counts of 16.6 × 10 (6) and 26.5 × 10 (6) ml (-1) were obtained on the two media, with the nutritionally poorer of the two media giving the highest average count. pupil. Seventy-five isolates from the two environments, incubated aerobically as well as in anaerobic jars, were obtained. These isolates as well as 13 reference strains were characterized phenotypically. Similarities between cultures were calculated using the Sokal and Michener similarity coefficient. Organisms were grouped using the unweighted pair group method and the results were presented as a simplified dendrogram. be divided into 3 main groups: Gram-negative fermentative rods, mainly Enterobacter, Klebsiella and Citrobacter, with Klebsiella as the predominant genus; Gram-positive bacteria, mainly enterococci; and non-fermentative Gram-negative rods of the genera Pseudomonas, Alcaligenes and Acinetobacter. All enterobacteria and enterococci were capable of producing acetic acid, an intermediate in methanogenesis. Some facultatively anaerobic Gram-negative rods from the rumen of calves and sheep. SUMMARY: The coliform population in the rumen of twelve calves aged 10 to 105 days never exceeded 106/g and was mainly composed of Escherichia coZi and intermediate types. Only one well-encapsulated strain of Aerobacter aerogenes was isolated, whereas such encapsulated strains could be easily isolated from the rumen of a starch-fed sheep. A small, unidentified catalase-negative Gram-negative rod, which readily produces ammonia from urea, was isolated from the rumen contents of two of the older calves, at a dilution of lo-'. Mann, Masson & Oxford (19544) showed that although the coliform population in the rumen of adult hay-fed sheep was numerically quite small, it was nonetheless composed mainly of intestinal-type Escherichia coli rather than Aerobacter aerogenes or by A. cloacae, the common saprophytes found on However, A. aerogenes in capsule form has since been isolated quite easily from the rumen of a sheep fed starch and concentrates (see below). It therefore seemed interesting to study the distribution of coliform types. in the rumen of the young ruminant, in particular of the calf raised according to the usual method with milk and starter porridge, since the first attemptfrom straw nibbling at the age of 1 to 2 weeks until the establishment of the complete rumen microflora after the cessation of milk in the ration. This has now been achieved in conjunction with aureomycin feeding of calves described by Mann, Masson & Oxford (1954b), which resulted in the isolation of lactobacilli from the rumen of younger calves only (reported by Mann & Oxford, 1954~). A description is now given of some other unidentified non-coliform Gram-negative rods also isolated from the rumen of the calf in the same experiment. These appear to be of possible importance in the functioning of the rumen microflora due to their greater capacity to produce ammonia from urea than that possessed by A. aerogenes or A. cloacae. Calf feeding methods This is described in detail by Mann et al. (1 9 5 4b). The calves (twelve in total) were bucket-fed with starter porridge. Hay and grass were available after the 3rd week, but fresh milk was discontinued after the 6th week. The three youngest calves examined (10–11 days old; group OC in Table 1) were slaughtered in March–May 1954 and were therefore separated from the main May–August aureomycin feeding experiment 1953. Isolation of Gram-negative rods from the rumen in pure culture. The bottle counting technique used for the rumen contents of sheep by Heald, Krogh, Mann, Appleby, Masson & Oxford (1953) and for the isolation of rumen lactobacilli by Mann & Oxford (1954a), although adapted to Gram-positive saccharolytic bacteria Grarn - the negative rods of the rumen cannot be reliable to give a faithful representation of the Gram-negative saccharolytic bacteria of the rumen when these are in the minority. It was therefore replaced by the following method. A sample of rumen contents (10 g) taken from the well-mixed total contents of a rumen as soon as possible after slaughter of the calf (i.e. within 2 hours) was placed in a McCartney bottle sterile, diluted with an equal weight of sterile saline, gassed with sterile CO and mechanically shaken for 20 min. to detach as many bacteria as possible from plant particles. The mixture was then centrifuged very lightly to remove larger plant particles, and serial tenth-fold dilutions were made from the supernatant in sterile saline. One ml. of each dilution was transferred to a sterile Petri dish and embedded at 45" in 15 ml of Wright's nutrient agar containing glucose (0.2%) and crystal violet (0.0005%). This low concentration of crystal Violet did not inhibit all Gram-positive bacteria, but allowed the maximum number of Gram-negative bacteria (coliforms and others) to form distinct colonies within 48 hours when plates were incubated anaerobically at 38 hours. the Gram-negative isolates obtained in this study, however, were found to be facultative anaerobes. They were purified by repeated plating on glucose + peptone + yeast extract + salt agar and maintained until needed in the medium. of cooked meat by Robertson. Examination of Gram-negative rod isolates. Those which fermented lactose in MacConkey's bile salt medium with acid and gas production and were also catalase-positive, were studied in more detail by. standard methods for coliform bacteria. Indole was tested with the KOV~CS reagent, and the O'Meara and Barritt modifications of the Voges-Proskauer test were used. The production of ammonia from urea was tested by the method of Christensen (1946) as well as in the more highly buffered medium of Stuart, van Stratum & Rustigian. ResultsClassification of bacteriacoliforms isolated from the rumen of calves of varying ages from 10 to 105 days; the viable coliform population was generally 10 L106/g. rumen contents; sometimes much less (102/g. in the 3A calf), sometimes apparently zero, for example in the 1 A, 1 Al, 1 C and 2Al calves. The thirty-nine coliform isolates are classified in Table 1 according to the scheme used by Wilson et al. (1935, p. 156) for milk coliform bacteria. It can be seen from the table that Escherichia coli I and I1 and intermediate types, all vp-negative and ME-positive, accounted for 87% of the total isolates, while Aerobacter aerogenes (VP + MR − ) accounted for only 18%. . and A.cloacae was not found. All isolates of A. aerogenes attacked urea weakly and inconsistently. Only one of these isolates (out of five) showed well-marked capsulation and, unlike the other four isolates, fermented adonitol and inositol. Capsulated strains of Aerobacter aerogenes from the rumen of a sheep fed with concentrates : The sheep in question with rumen fistulation received the following daily ration: hay (300 g), concentrates (500 g) and potato starch (200 g). The medium used for isolation of coliforms from rumen contents was MacConkey agar. Capsulated isolates of Aerobacter aerogenes could always be easily obtained from the rumen contents of the above sheep, usually at a dilution of 10. Control experiments with the rumen contents of two hay-fed fistulated sheep confirmed the conclusion of Mann et al. (1954a) that A. aerogenes could not be isolated from this source. Twenty-three encapsulated isolates of A. aerogenes were obtained in total from six separate samples of the rumen contents of starch-fed sheep. All produced distinctly mucoid colonies on agar medium containing a fermentable carbohydrate and were indole and methyl red negative, nitrate reducers, Voges-Proskauer, citrate, catalase, and urease positive. No liquefied gelatin isolates, two only fermented starch, six fermented neither dulcitol nor adonitol, two (starch fermenters) attacked adonitol but not dulcitol, one attacked dulcitol but not l 'adonitol, and the remaining fourteen fermented these two sugar alcohols. Gram-negative positive isolates from calves Among eleven catalase-negative non-coliform isolates, two from the rumen of OCl calves attacked urea only weakly, while the other nine from much older calves (five from the 2C calf and four of calf 3A1) gave the typical reaction in Christensen's medium after 18 h, incubation at 38'. They did not, however, produce the required pH lowering, comparable to an authentic strain of Proteus vutgaris, in the more heavily buffered medium of Stuart et al. (1945); but growth was very low in this case. All of these nine urease-positive non-coliform isolates appeared to be very similar and a brief description is appended. Morphology Films made from growth on Wright's nutrient agar showed: Gram-negative rods from small rods or cocco-bacilli in the rumen, 0.5-1.u . x 0-3-0-5 p., with roughly parallel sides and rounded ends, sometimes in short chains but more often arranged in bundles, difficult to distinguish from aggregations of shells; Gram negative, non-motile, non-sporulating. Growth characteristics. The 24 hours. growth on agar consisted of almost colorless, smooth, transparent, punctate colonies measuring up to 0.8 mm. diameter with full edge and convex elevation. After 7 days, the colonies were still small (2 mm in diameter), pale brown in color and differentiated into a weakly convex central zone and an effuse peripheral zone. There is no hemolysis on the agar plates.
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