The Identification Of Soil Bacteria Biology

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The dirt ecosystem includes species with alone life histories that make up a complex nutrient web. The ecosystem ‘s energy pyramid is founded on organic residues and consists of primary, secondary and third consumers. This study focuses on bacteriums found within compost dirt in Prince George, British Columbia. The bacterium belong to the primary consumers which besides includes a assortment of Fungis and simple invertebrates. The primary consumers support the ecosystem from the underside up by feeding on debris and organic residue and supplying nutrition for beings at higher trophic degrees ( Trautmann ) .

Bacteria, along with Fungi, are paramount in the decomposition and recycling of cardinal foods found in supermolecules. Most fungi bacteriums are chemoheterotrophs and, hence, usage bing organic stuff as a C and energy beginning ( Campbell and Reece, 2002, page 533 ) . As such, they are improbably of import in the decomposition of debris. Soil bug besides play an built-in function in sulfur recycling. Some are capable of catabolising sulfur-containing amino acids or cut downing inorganic sulfur-containing compounds into H sulphide ( Wind & A ; Conrad, 1995 ) . Many bugs, including mycorrhizal Fungis and nitrogen-fixing bacteriums, fix N in order to do it available for uptake by workss ( Jasper, 2007 ) . They are capable of biologically change overing inert atmospheric N ( N2 ) into N compounds ( such as ammonium hydroxide, nitrite and nitrate ) which are so used by other beings ( Scott et al. , 2008 ) . Ammonium ion ( NH4+ ) and nitrate ions ( NO3 ) are so available in the dirt for the workss to absorb through their root hairs. Additionally when a works dies or an carnal excretes, bacteriums, or in some instances, Fungis, convert the organic N in the debris back into ammonium hydroxide ; this procedure is called ammonification ( Hayatsu et al. , 2008 ) . In short, bacteriums are built-in to the recycling of many foods.

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The end of this experiment was to first insulate a bacterial civilization from a sample of nutrient-rich compost dirt and so place the isolate. Several features were tested in order to decently place a bacterial isolate. Microbiologists frequently foremost gram-stain an unknown isolate to find whether it is gram positive, holding simpler walls with big sum of peptidoglycan, or gm negative, walls structurally more complex with less peptidoglycan ( Campbell and Reece, 2002, page $ $ $ ) . Further designation is based on an isolates peculiar morphology, metamorphosis and optimum turning environment.


Water was added to one gm of compost dirt and a 10-7 dilution was prepared. One millilitre of the dilution was placed onto the underside of an empty Petri home base and was filled and swirled with liquid TSA ( Trypticase soy agar ) to do a pour home base. The home base was so cultured in an brooder for a hebdomad ( ~48hours at 25A°C and ~120 hours at 4A°C ) . A bacterium settlement was chosen randomly from the Petri dish and described quantitatively and qualitatively.

In order to place the bacterial isolate, several trials were conducted to better understand its morphology, metamorphosis and optimum turning environment. First, a run home base was prepared by sub-culturing a part of the settlement ; this farther propagated and purified the settlement. Another part was gram-stained and viewed under the microscope. The undermentioned hebdomad, the metamorphosis of the bacterial isolate was so evaluated. The bacterial isolate was run through the undermentioned trials: Starch Hydrolysis, H2S and Motility, Ammonification, Nitrification, Denitrification and Catalase. Each trial followed the processs outlined in the research lab manual ( Egger, 2008 ) .

In order to find the optimum turning environment, the bacterial civilization was cultured at assorted temperatures, pH degrees and osmotic force per unit areas. Bacterial isolates were streaked and cultured for 36 hours on 4 TSA home bases at assorted temperatures: 4A°C, 10-15A°C, 22A°C and 50A°C. Bacterial isolates were besides cultured for 36 hours in 4 TSB tubings at assorted pH degrees: 3, 5, 7 and 9. Finally, bacterial isolates were streaked and cultured for 36 hours on TSA home bases at different salt concentrations: 0 % , 0.5 % , 2 % and 5 % NaCl.


The stray settlement from the pour home base of the 10-7 dilution proved to be round and pulmonate in signifier and lift with full borders. It is dull, opaque and bright yellow in coloring material. The settlement measures 1.5mm in diameter and is smooth in texture. The single cells are bacillar, step ~1.2I?m in diameter and are arranged in irregular ironss ( streptobacillus ) . The cells dye pink during gram-staining proposing that they are gram negative.

Table 1.0: Starch Hydrolysis, H2S production, Motility and Ammonification Trials


Starch Hydrolysis

H2S and Motility



Dark red/ purple

No coloring material alteration

Cloudy white media around bacteriums

Pale yellow peptone stock with Nessler ‘s reagent

Positive or negative consequence



Negative H2S production

Positive motility


As noted in table 1.0, the bacterial civilization turns dark ruddy to purple during the amylum hydrolysis trial proposing that the bacteriums are capable of hydrolysing amylum. This implies that the bacterium is chemoheterotrophic and uses bing organic compounds as a beginning of C and energy. The bacterial civilization turns nebulose white and growing deviated from the stab line during the H2S and motility trial proposing the bacteriums are motile ( flagellated ) but can non degrade proteins and other S incorporating compounds to H2S.

Table 1.1: Nitrification Trials

Nitrification Trial

Ammonium sulphate stock with Nessler ‘s reagent

Ammonium sulphate stock with Trommsdorf ‘s reagent and H2SO4

Nitrite stock with Trommsdorf ‘s reagent and H2SO4

Nitrite stock with diphenylamine reagent and H2SO4


Bright Orange

Light Purple

Dark purple

Baby blue

“ + ” or “ – ” consequence





Table 1.1 reveals that the civilization turns pale xanthous when added to Nessler ‘s reagent during the ammonification trial bespeaking the bacteriums are capable of catabolising a little sum of proteins to amino acids, which are enzymatically deaminated which, in bend, releases ammonium hydroxide. When the ammonium sulphate stock is inoculated with the bacteriums, it expresses positive consequences with the Nessler ‘s and Trommsdorf ‘s reagent. This suggests the bacteriums are capable of oxidising ammonium hydroxide to nitrite nevertheless the procedure is non immediate and non all the ammonium hydroxide is converted. When the nitrite stock is inoculated with the bacteriums, it expresses little positive consequences. This suggests either merely some nitrite is oxidized to nitrate or all nitrite is oxidized to nitrate but some nitrate is reduced back to nitrite. Both scenarios would explicate why nitrite and nitrate are present.

Table 1.2: Denitrification and Catalase Test





Blood red broth after add-on of sulfanilic acid and N, N-dimehtyl-1-1-naphthylamine

( Zinc pulverization was non added )

Bubbles when H2O2 was added

Positive or negative consequence



As noted in table 1.2, the civilization turns ruddy after the add-on of sulfanilic acid and N, N-dimehtyl-1-1-naphthylamine. This suggests the bacteriums are able to cut down nitrate back to nitrite utilizing the enzyme nitrate reductase but unable to farther cut down nitrite to ammonium ion. Furthermore, when H peroxide is added to the civilization, O is released proposing the bacteriums are catalase positive and can interrupt down H peroxide into H2O and free O.

Table 1.3: Optimum Temperature, pH and Osmotic Pressure



Osmotic force per unit area ( % NaCl )




0 %





Table 1.3 shows at which temperature, pH degrees and osmotic force per unit area the bacterial isolate grows optimally. The bacterial isolate grows best at 22A°C at a impersonal pH on 0 % NaCl medium. This suggests the bacteriums can be classified as mesophiles, neutrophiles and nonhalophiles.


The bacterial isolate was able to be identified after measuring several morphological and metabolic traits. The bacteriums are gram negative, rod shaped, nomadic and form xanthous settlements. Additionally, the bacteriums possess catalase which breakdowns H peroxide. These indices would propose, harmonizing to Bergey ‘s Manual of Systematic Bacteriology, that the bacteriums belong to the household Azotobacteraceae ( Krieg & A ; Holt, 1986, p. 224 ) . Furthermore, the bacteriums fix nitrogen under normal atmospheric force per unit area and are less than 2I?m proposing that they belong to the genus Azotobacter ( Krieg & A ; Holt, 1986, p. 226 ) .

This peculiar bacterial isolate surely fills a really of import niche in the compost dirt ecosystem. Compost dirt is highly alimentary rich and relies on the work of bugs to catabolise supermolecules and fix assorted elements. This chemoheterotrophic bacteriums absorbs foods from dead organic affair and, in bend, decomposes the debris and returns foods back to the ecosystem. Furthermore, like many other bacteriums and Fungis, one of the most important functions of this Azotobacter is to oxidise ammonium into nitrite and nitrate. The latter are signifiers that are more easy absorbed by workss and, in bend, allows for N recycling ( Campbell and Reece, 2002 ) . Several surveies have investigated the ecological function of several Azotobacter and the bulk highlight the bacterium ‘s function in nitrogen arrested development ( Garg et al. , 2001 ; MunozCenteno et al. , 1996 ; Bakulin et al. , 2007 ) . Some Azotobacter are so efficient at repairing N that they can be used as biofertilizer for heightening N input and phosphate solubilization in fish pools ( Garg et al. , 2001 ) . Azotobacter are besides known to organize interactive or linear interactions with arbuscular mycorrhizal fungi to organize symbiotic relationships with works roots ( Bagyaraj & A ; Menge, 1978 ) . It is of no surprise to happen this nitrogen-fixing chemoheterotroph in compost dirt.

There are several other trials that may hold aided in the designation of the bacterial isolate. Bacterias are normally distinguished based on the presence or absence of nitrogenase, a bacterial enzyme which converts atmospheric N to ammonia ( Lubambo et al. , 2007 ) . Additionally, disagreements in growing within lighted versus dark incubation Chamberss would uncover any photosynthetic activity of the bacteriums. Alongside the amylum hydrolysis trial, this would farther confirm the favoritism between heterotrophism and autotrophism. Additionally, one could measure the degree of metamorphosis under assorted anaerobic/aerobic conditions to find whether the bacteriums are rigorous, tolerant or facultative aerobes or anaerobes.

There be several beginnings of mistake and restrictions to the trials that were performed. Designation was carried out by associating our observations to a dichotomous key found in Bergey ‘s manual. The observations, nevertheless, were non purely dichotomous but more ranked. It was hard to distinguish between a really positive and a decrepit positive consequence when using the observations to the key. Besides, it was hard to know apart between a bacteria non capable of wholly oxidising nitrite to nitrate and one that could to the full oxidise nitrite to nitrate who besides reduced some nitrate back to nitrite. Another combative issue is one of pureness. More than one bacterial strain may hold been cultured or incorporated into the trials due to improper sterile technique. This may hold produced deceptive consequences doing a misidentification of the bacteriums.

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