Let’s know about Xanthomonas Campestris: Xanthomonas campestris is a genus of Proteobacteria (Class: Gamma Proteobacteria, Order: Xanthomonadales, Family: Xanthomonadaceae) phytopathogenic that affects important crops.
X. campestris It presents an epiphytic stage on the plant in which it does not harm it. This stage is preceded by infection, resulting from the spread of bacteria due to favorable environmental variations. Infection by this species or the infected plant Cassiona causes a variety of symptoms that can eventually result in its death.
X. Campistris It is also known for the production of the biopolymer xanthan or xanthan gum , a polysaccharide that exfoliates the medium (exopolysaccharide) and increases the viscosity of aqueous solutions.
Xanthan exopolysaccharide was the first bioproduct of commercial importance generated by the fermentation processes of corn starch. It is currently produced in large quantities and has many applications as a thickener and emulsifier due to its characteristics. Xanthan is used in the food industry, pharmaceutical, cosmetic, agriculture, oil, among others.
Now we will know about the description of Xanthomonas Campestris. Xanthomonas campestris It is a Gram-negative bacillus, which is an aerobic and facultative saprophyte purulent. It is mobile, 0.2 to 0.6 µm wide, and between 0.8 and 2.9 µm long. It may appear as a solitary individual or filaments, surrounded by xanthones, that they produce.
The formation of biofilms of Xanthan is favored by X. campestris and also exerts a protective action of the communities established in this structure, when there are abrupt changes in temperature, pH, ultraviolet radiation, marked osmotic changes and / or a decrease in humidity.
interact with the plant
This species has several mechanisms to evade the defense responses of the plants it infects. The plant’s first barrier to bacterial infection is the cell wall and surface substances with antimicrobial activity.
X. Campistris can infect the plant through its foliar stomata (pores where gases exchange with the environment), its hydrates (a type of stomata through which excess water is released), or wounds present.
Plants usually close their stomata when attacked by microorganisms. But, X. Campistris produces a virulence factor that prevents stomata from closing, thus favoring the entry of more bacteria from the external environment.
When bacteria are found inside the plant, they inhibit the transport of water, inhibiting the vascular tissues. The result is leaf necrosis and deformity of the infected parts.
Also, X. campestris produces a compound called neutral cyclic glucan 1-(1,2) which inhibits the expression of defense genes in the plant. These compounds may be associated with the bacterial periplasmic space or may be excreted through the extracellular medium, favoring the motility of the bacteria, its virulence and the formation of biofilms.
Produced by Xanthomonas It acts as a virulence factor, suppressing the immune response of the infected plant and enhancing the infection capacity of the bacterium.
Xanthan is a polysaccharide consisting of 5 sugar units that are repeated (2 glucose, 2 mannose and 1 glucuronic acid) and polymerize.
Synthesis of xanthan depends on an operon called cluster gamma (a set of genes that form a functional unit), which represents 12 genes that are under the control of a single promoter region.
The separation of X. campestris from plant tissue
X. Campistris PV. campestris It can be distinguished from the foliar tissue that presents spots in the form of a “V” or damaged vascular tissue, or the neck of the plant, which is said of the injured areas of the plant.
To obtain strains of X. campestris , it is selected because it shows the injured area (leaf spots or fruit or cankers). If the lesion is not observed in the plant, tissue susceptible to damage is taken as a sample and analyzed by culture media and by the polymerase chain reaction (PCR) technique.
Among the culture media used are the following:
Milk Tikki (MT)
For the initial isolation of microorganisms from plant tissue samples, the medium can be applied to milk powder (MT):
10 ml of Skim Milk, 0.25 g of CaCl 2 , 10 g of Protease Peptone No. 3, 15 g of Bacto Agar, 0.5 g of Tyrosine, 80 ml of Tween 80, 80 ml of Cephalexin (in 2 ml of 4% NaOH) , 200 g cycloheximide (2 ml of methanol 75%), 100 mg vancomycin (in 1 ml of distilled water).
A solution of skim milk, cephalexin, cycloheximide and vancomycin should be filtered and sterilized and added to the medium at 50 °C.
After allowing bacterial colonies to grow in the TM, the most similar ones can be passed on to X. Campistris (colonies of yellow pigmentation at 72 and 120 h in culture) King B :
20 g of protease peptone No. 3, 20 g agar, K 2 HPO 4 1.5 g, MgSO 4 X / H 2 O 1.5 g, 10 ml glycerol, 700 distilled water.
The medium should be heated to 80 °C by stirring, 1 L with distilled water and homogenizing, and the pH adjusted to 7.2. Sterile at 121 °C for 15 min.
Enriched culture medium has also been used in the cultivation of PYM or YMM X. Campistris .
To prepare PYM , for every 1000 ml of total volume, you will need to add: 10 grams of glucose, 5 grams of peptone extract, 3 grams of malt extract and 3 grams of yeast.
If it is desired to cultivate it in solid medium in Petri dishes, 15 g of agar should also be added to the mixture.
To prepare the medium YMM , you need per 1000 ml of total volume: 10 g glucose, 1 ml MgSO solution 4 : 7 H 2 O (10 g / l), 1 ml of CaCl solution 2 (22 g / l ), 1 ml of a K solution 2 HPO 4 (22 g / L), 1 ml of a FeCl solution 3 0.1 M HCl (2 g / L), Casamino acid 0.3% m / v (amino acid from hydrolysis of casein) and 11% v/v sodium glutamate solution.
Incubation conditions of bacterial strains of X. campestris should be 27 or 28 °C, and in the case of liquid culture media, continuous agitation should be maintained at 200 revolutions per minute (rpm).
production of xanthan
If production of xanthan in the fermentation process is desired, glucose, sucrose or corn syrup (between 20 and 40 g/L), among other nutrients that provide nitrogen, must be supplied as a carbon source. .
metabolic activity detection
To detect the presence of X. campestris viable in plant tissue, some researchers recommend measuring metabolic activity, rather than microbial growth, in laboratory culture.
Metabolic activity has been measured using the viability indicator via the electron transport system. This compound is called tetrazolium and its salts accept electrons from hydrogen, yielding formazan, which is insoluble in water. Thus, the presence of formazan in between is an indicator of cellular metabolic activity.
is a means of cultivation of X. campestris To perform this feasibility test, it contains tetrazolium chloride (TTC), tetrazolium triphenyl chloride and other additives such as sodium chloride and sugars. This is a medium with the following substances for a total volume of 500 ml: 5 g of peptone, 0.5 g of hydrolyzed casein, 2.5 g of glucose and 8.5 g of agar.
Now we will know about the physiopathologies of Xanthomonas Campestris. bacterium X. Campistris It is the cause of several diseases that affect the leaves of ornamental plants (such as Anthurium and Araneum ) and the common bean ( Phaseolus vulgaris L.). They also affect the fruits of stone fruits, such as almonds, nectarines, cherries, peaches, apricot, plum, etc.
X. Campistris is known to affect the family Brassicaceae or crucifers, being among the 10 most threatened phytopathogenic species for agricultural activity in the tropics.
For example, X. Campestris causes black rot disease in cauliflower ( Brassica oleracea ), broccoli ( B. napus ), Chinese cabbage ( B. pekinensis ), turnip ( B. rapa ), mustard ( Bnai ), radish ( Raphanus sativus ) and cabbage ( B. fruticulosa ).
Its symptoms are X. campestris They appear initially in leaves and then may appear on fruits and branches. They are limited by ribs to irregular and angular yellow leaf spots (1 to 5 mm in diameter) that eventually become necrotic.
Leaf burns are also present; spots on fruits; Vascular wilt and the presence of chlorotic or necrotic lesions in the form of a “V”.
Leaves are visible on the edges and around the central nerve. There may be loss of leaves in the plant. The fruits show green spots which are necrotic, also capable of cracking them. Cankers may also be present.