New blue pigment produced by Pantoea agglomerans and its production characteristics at various temperatures

Abstract

A bacterium capable of producing a deep blue pigment was isolated from the environment and identified as Pantoea agglomerans. The pigment production characteristics of the bacterium under various conditions were studied. The optimal agar plate ingredients for pigment production by the bacterium were first studied: the optimal ingredients were 5 g/liter glucose, 10 g/liter tryptic soy broth, and 40 g/liter glycerol at pH 6.4. Bacterial cells grew on the agar plate during the incubation, while the pigment spread into the agar plate, meaning that it is water soluble. Pigment production was affected by the initial cell density. Namely, at higher initial cell densities ranging from 10(6.3) to 10(8.2) CFU/cm(2) on the agar plate, faster pigment production was observed, but no blue pigment was produced at a very high initial density of 10(9.1) CFU/cm(2). Thus, the cell population of 10(8.2) CFU/cm(2) was used for subsequent study. Although the bacterium was capable of growing at temperatures above and below 10°C, it could produce the pigment only at temperatures of ≥10°C. Moreover, the pigment production was faster at higher temperatures in the range of 10 to 20°C. Pigment production at various temperature patterns was well described by a new logistic model. These results suggested that the bacterium could be used in the development of a microbial temperature indicator for the low-temperature-storage management of foods and clinical materials. To our knowledge, there is no other P. agglomerans strain capable of producing a blue pigment and the pigment is a new one of microbial origin.

FIG. 1.

Blue pigment production in agar plates containing various concentrations of glucose and tryptic soy broth. Symbols show means, and error bars show SDs. The asterisk shows the optimal combination of the ingredient concentrations. g/l, grams per liter.

FIG. 2.

Blue pigment production in the agar plates with various pH values. Cells were incubated at 20°C for 14 h. Closed circles show means, and error bars show SDs.

FIG. 3.

The effects on pigment production of glycerol supplementation of the agar plates. Symbols show means, and error bars show SDs.

FIG. 4.

Pigment production (A) and growth (B) of the bacterium at various initial densities (•, 10^6.3 CFU/cm²; ▪, 10^7.2 CFU/cm²; ▴, 10^8.2 CFU/cm²; ⧫,10^9.1 CFU/cm²). Cells were inoculated onto the G plate and stored at 20°C. Bars show SDs. (C) Pigment production and bacterial growth with an initial population of 10^6.3 CFU/cm². Arrows show the corresponding axes. An open circle shows the point at an ΔE* value of 20. Curves are described with the new logistic model.

FIG. 5.

Pigment production of the bacterium at various temperatures. Cells at 10^8.2 CFU/cm² were inoculated onto the G plate. Symbols show means, and bars show SDs.

FIG. 6.

Color changes of the inoculated G plates during incubation at 16°C. Numbers show the hours of incubation. Plate diameter is 34 mm.

FIG. 7.

Pigment production by the bacterium at a dynamic temperature. Closed circles show means, and bars show SDs. The periodic curve is the temperature history of the plate. The sigmoidal curves are curves predicted with the new logistic model. The temperature ranges were 9.0 to 15.4°C (A) and 9.4 to 19.5°C (B). The values of n (see equation 2) are 0.39 (curve 1) and 0.22 (curve 2) in panel A and 0.39 (curve 1) and 0.19 (curve 2) in panel B. Arrows show the corresponding axes.

FIG. 8.

The blue-pigmented region of a G plate on which the bacterium grew. The bacterium was isolated and incubated at 25°C for 3 days. The diameter of the plate is 90 mm. The many gray dots in the photo are shadows of isolated colonies cast on the bottom of the plate.