Process for Preparing Xanthomonas Heteropolysaccharides

1. Field of the Invention

The present invention relates to a process for preparing Xanthomonas heteropolysaccharides by fermenting a certain Xanthomonas species.

2. Description of the Prior Art

From U.S. Pat. No. 3,485,719 it is known that heteropolysaccharides can be prepared by subjecting a carbohydrate source to fermentation by the organisms Xanthomonas campestris NRRL B-1459. In this patent specification it is stated that the heteropolysaccharide produced from Xanthomonas campestris NRRL B-1459 has been shown to be an exceptionally effective agent when used in secondary oil recovery operations as well as exhibiting utility as a thickening agent for foodstuffs, cosmetics, etc., and also as an edible film-forming agent, and as an emulsifying agent, for example, in printing ink and as thickening agent in textile print pastes.

Applicant has now isolated a novel substrain of Xanthomonas campestris species which has been deposited at the National Collection of Industrial Bacteria, Torry Research Station, Aberdeen, under accession No. 11854. Compared with the microorganism Xanthomonas campestris NRRL B-1459, the present microorganism, NCIB 11854 appears to exhibit a much higher specific growth rate in a defined medium coupled with a remarkably higher specific rate of polymer production.

Furthermore, the filterability of the heteropolysaccharide produced by the NCIB 11854 microorganism is as good as or is even better than that of the heteropolysaccharide produced by the Xanthomonas campestris NRRL B-1459, especially at higher salinities. The present invention therefore provides a process for preparing Xanthomonas heteropolysaccharide which comprises growing the organism Xanthomonas campestris NCIB 11854 in an aqueous nutrient medium by aerobic fermentation of an assimilable carbohydrate and nitrogen source and recovering the heteropolysaccharide. The process may suitably be carried out as a batch-process or a fed-batch process with or without fill-and-draw or as a continuous process.

From productivity considerations a continuous process or a fill-and-draw process is preferred. Preferably, the organism is grown in the absence of yeast extract in a nutrient medium. The use of a chemically defined nutrient medium is advantageous since for a given productivity or for a given final cell concentration it appears easier to handle a nitrogen source such as sodium glutamate, ammonium or nitrate salts than complex nitrogen sources such as yeast extract or distillers dried solubles. Sodium glutamate is preferably used as a nitrogen source. The present invention further relates to the heteropolysaccharide as prepared by the process as hereinbefore described and to the use of the heteropolysaccharide as viscosity modifier in an aqueous solution for various conventional utilities.

A drilling fluid comprising water and 0.06-1.5% by weight of the above heteropolysaccharide is a further aspect of the present invention. The present invention also encompasses a method of treating a well comprising the introduction into the well of an aqueous medium comprising water and 0.05-1.5% by weight of the above heteropolysaccharide as well as a method for displacing a fluid through a well and/or a permeable subsurface formation communicating with the well by injecting into the well an aqueous solution comprising the above heteropolysaccharide. The present invention further relates to a biologically pure culture of Xanthomonas campestris NCIB 11854.

The present invention will now be further illustrated by the following Example.

Xanthomonas campestris NCIB 11854 was grown on three different chemically defined salt media (as shown in Table 1) in a Chemap GF 7 liter fermentation vessel under batch conditions as summarized in Table 2.

In the first experiment the sole source of nitrogen for microbial growth was ammonium ion (24 mM), allowing exponential growth of cells to a maximum concentration of 3 gl.sup.-1. In the second and third experiments the ammonium was substituted with nitrate (24 mM) and glutamate (24 mM) respectively. The results are shown in FIGS. 1-3.

As is clear from a comparison of these figures, glutamate as a nitrogen source is preferred since it gives a .mu.max, i.e. maximum cell growth rate of 0.12 h.sup.-1, a qp value, i.e. specific rate of polymer production of 0.36 g.(g.sup.-1)h.sup.-1 and a final polymer yield YP of 0.59 g.g.sup.-1. This combination of high .mu.max and high qp resulted in a final polymer productivity of 0.49 g.(l.sup.-1)h.sup.-1, which is more than double the normal productivity of a heteropolysaccharide fermentation using Xanthomonas campestris NRRL B-1459.

Table 3 indicates under A the values of .mu.max, qp, qg, i.e. the specific glucose utilization rate, Yp, i.e. yield of polymer on glucose and p, i.e. polymer productivity for Xanthomonas campestris NCIB 11854 on the above defined salts growth medium and under B the respective values for Xanthomonas campestris NRRL B-1459.

This table clearly shows the better performance of Xanthomonas campestris NCIB 11854 compared with Xanthomonas campestris NRRL B-1459.

In Table 4 the filterability of Xanthomonas campestris NCIB 11854 broth is compared with that of Xanthomonas campestris NRRL B-1459 broth for different salinities of the medium before and after enzyme treatment.

For the actual filtration, Millipore (trade mark) filters having a diameter of 47 mm have been used. 5.mu. and 1.2.mu. are sizes of the pores of these filters. As is clear from the above table, the filterability of Xanthomonas campestris NCIB 11854 broth before and after enzyme treatment is remarkably better than that of Xanthomonas campestris NRRL B-1459.

The results were similar to NCIB 11803 and NCIB 11854 except where stated.

A. Oxoid CMI Nutrient Broth+0.75% Difco Agar plates were inoculated with `young` growth and incubated for 71/2 hours at 25.degree. C. Cells from the margins of c. 0.2 mm patches of growth were examined and photographed in situ under coverslips by phase-contrast. Mobility and the other features were determined in pools surrounding 0.1 mm glass beads scattered on other patches. Cells at the margins of growth occurred singly and in pairs, with cell dimensions of 0.4-0.5 .mu.m width.times.1.2-2.5 .mu.m length for NCIB 11803 and 0.5-0.6 .mu.m.times.1.2-2.5 .mu.m for NCIB 11854. In from the growth margin in pools, aggregates (symplasmata? See Graham & Hodgkiss, 1967) of a hundred to several thousand cells were commonly seen with NCIB 11803 but much less frequently with NCIB 11854. Mobility was positive.

B. Using conditions as in A above but with 0.5% glucose added to the medium and 7 hours incubation result were similar except that cells were 0.1 .mu.m wider and aggregates were not seen with NCIB 11854.

A. After 48 hours growth at 30.degree. C. on Oxoid CM3 Nutrient Agar plates growth was good, and isolated colonies were yellow in colour, circular, entire, mucoid, smooth, string and convex. Colony diameter was 1-1.5 mm for 11803 and 1.5 mm for NCIB 11854.

B. After 72 hours growth at 30.degree. C. on medium as in A above but with 1% glucose growth was good and isolated colonies were pale cream in colour, circular, entire, very mucoid, smooth and convex, while confluent growth was pale cream-yellow. Colony diameter was 2 mm for NCIB 11803 and 2-2.5 mm for 11854.

Mineral Base Palleroni 6 Doudoroff 1972 Modified (PD) (A. Rev. Phytophethol. 10, 73)

PD Mineral Base+0.1% Filter-Sterilized Glucose (PDG)

Biochemical Characteristics: at 30.degree. C. except as stated

Growth in Presence of Salt

Basal media containing NaCl at concentrations of 2, 3, 4 and 5% were prepared according to the method of Hayward & Hodgkiss (1961). Cultures were incubated for 3 days. NCIB 11854 was less salt tolerant than NCIB 11803 as follows

Hydrolysis of Gelatin and Casein

Cultures were incubated for 7 days. Gelatin stabs were at 20.degree. C. NCIB 11854 showed a lesser degree of proteolytic activity than NCIB 11803 as follows

Growth Factor Requirement Tests

Subcultures were made by straight wire three times in PDG medium made with glass distilled water. Satisfactory growth was obtained in about 4 days indicating there was no absolute requirement for growth factors.

Methionine Stimulation Test

One drop each of a faintly turbid young growing culture in PDG medium made with glass distilled water was inoculated into PDG with and without 10 .mu.g/ml L-methionine in 1 ml amounts in 16 mm tubes. There was no stimulation of the growth rate by L-methionine.

Carbon Source Utilization

PD medium with 0.1% filter-sterilized sole carbon sources shown in Table 5 were inoculated and incubated for 14 days. Three apparently minor differences in growth between the strains were found.

Acid Production from Carbohydrates

The oxidation-fermentation medium of Hayward and Hodgkiss (1961) was supplemented with 1% filter-sterilized carbon sources shown in Table 5. The tubes were inoculated and incubated for 14 days. Acid was produced from galactose and melibiose by NCIB 11854 but not by NCIB 11803. The significance of this is doubtful particularly because both compounds were utilized as sole carbon sources by both NCIB 11854 and NCIB 11803.

These tests indicate limited differences so the main differences are that T.1188 exhibits better kinetics of polymer production in a defined medium, better growth with inorganic nitrogen, especially NH.sub.4 + and stability in continuous culture in a defined medium.

1. Bergey's Manual of Determinative Bacteriology, 8th edn (1974). (R. E. Buchanan & N. E. Gibbons, eds). Baltimore: Williams & Wilkins.

2. Cowan, S. T. & Steel, K. J. (1974). Manual for the Identification of Medical Bacteria. Cambridge University Press.