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. 2016 Jan;54(1):23-30.
doi: 10.1007/s12275-016-5461-9. Epub 2016 Jan 5.

Synergistic growth in bacteria depends on substrate complexity

Yi-Jie Deng  1 , Shiao Y Wang  2
Affiliations

Synergistic growth in bacteria depends on substrate complexity

Yi-Jie Deng et al. J Microbiol. 2016 Jan.

Abstract

Both positive and negative interactions among bacteria take place in the environment. We hypothesize that the complexity of the substrate affects the way bacteria interact with greater cooperation in the presence of recalcitrant substrate. We isolated lignocellulolytic bacteria from salt marsh detritus and compared the growth, metabolic activity and enzyme production of pure cultures to those of three-species mixed cultures in lignocellulose and glucose media. Synergistic growth was common in lignocellulose medium containing carboxyl methyl cellulose, xylan and lignin but absent in glucose medium. Bacterial synergism promoted metabolic activity in synergistic mixed cultures but not the maximal growth rate (μ). Bacterial synergism also promoted the production of β-1,4-glucosidase but not the production of cellobiohydrolase or β-1,4-xylosidase. Our results suggest that the chemical complexity of the substrate affects the way bacteria interact. While a complex substrate such as lignocellulose promotes positive interactions and synergistic growth, a labile substrate such as glucose promotes negative interactions and competition. Synergistic interactions among indigenous bacteria are suggested to be important in promoting lignocellulose degradation in the environment.

Keywords: bacterial activity; bacterial synergism; enzyme production; lignocellulose degradation; microbial interaction.

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Figures

Fig. 1
Fig. 1. Phylogenetic relationship of nine bacterial isolates used in study
Bold text with black diamond indicates the nine bacteria isolates used. The letter and number following the name of the bacterium denote the substrate used in isolating each bacterium, C for cellulose, L for lignin and X for xylan. Bootstrap values are shown as the percentage of 1,000 replicates when greater than 50%. The horizontal bar represents nucleotide substitutions per sequence position. GenBank accession numbers are in parentheses.
Fig. 2
Fig. 2. Growth of mixed cultures compared to pure cultures in lignocellulose medium
Growth of 27 mixed cultures (black bars) in relationship to the growth of their three corresponding pure cultures (gray bars). N = 12. Error bar is one standard deviation. Asterisks indicate significantly greater growth compared to pure cultures. One-way ANOVA (F35, 396 = 151.77, P < 0.001) followed by Tukey HSD test (P < 0.05).
Fig. 3
Fig. 3. Comparison of mixed culture growth in lignocellulose and glucose medium
Each data point is the OD595 of one mixed culture (mean ± SD, n =12) plotted against the OD595 of its reference culture (the pure culture with the greatest growth among the three that made up the mixed culture). The isometric line represents equal growth between mixed cultures and their reference cultures.
Fig. 4
Fig. 4. Effect of synergy on bacterial growth, specific growth rate and metabolic activity
Gray bar is the mean value of each group. Error bars represent 95% confidence interval. Different letters indicate significant difference (P < 0.05). NC = non-synergistic mixed cultures, n = 12; PC = pure cultures, n = 9; SC = synergistic mixed cultures, n = 15.
Fig. 5
Fig. 5. Effect of synergy on bacterial production of lignocellulolytic enzymes
BG, β-1,4-glucosidase; CBH, cellobiohydrolase; BX, β-1,4-xylosidase. Gray bar is the mean enzyme activity of each group. Error bars represent 95% confidence interval. Different letters indicate significant difference (P < 0.05). NC = non-synergistic mixed cultures, n = 12; PC = pure cultures, n = 9; SC = synergistic mixed cultures, n = 15.
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