Bioconversion of Kraft lignin

Analysis of Kraft lignin treated with Sphingobacterium sp., R. erythropolis and

M. phyllosphaerae was performed using the same techniques as for wheat straw and Organosolv lignin, although all samples were in liquid form since the Kraft lignin was completely dissolved in the media.

Figure 3.23. Number of CFUs per ml in samples of Kraft lignin (2.5%w/v) treated with M. phyllosphaerae, R. erythropolis and Sphingobacterium sp. in the presence of fish meal or CSL (2.0%w/v), taken after 48, 96, 168, 240 and 336hr.

Despite a significant variation in the level of growth of each strain with the two different nitrogen-containing supplements, fish meal and CSL,

Sphingobacterium sp. and R. erythropolis grew much more rapidly in the presence of Kraft lignin than M. phyllosphaerae. In the presence of CSL, 2.10x 109 _{and 1.45x10}9 _CFUsml-1 _{were observed at 240hr for Sphingobacterium sp.}

phyllosphaerae. These observations are consistent with those from the earlier growth experiments in M9 salts supplemented with Kraft lignin and yeast extract (Fig. 3.3), which also show limited growth of M. phyllosphaerae in the presence of Kraft lignin. Another similarity with the observations from the growth experiments in Kraft lignin (Fig. 3.3) is the limited growth of Sphingobacterium sp. and R. erythropolis in the initial 7 days of inoculation, followed by rapid growth between 7 and 14days. It is interesting that Sphingobacterium sp. grew more rapidly than R. erythropolis between 168 and 336hr in the presence of fish meal and CSL since growth of Sphingobacterium sp. was limited in the presence of Kraft lignin and yeast extract, requiring a glucose supplement for good growth (Fig. 3.3).

! !

Figure 3.24. Soluble phenol content of samples of Kraft lignin (2.5% w/v) treated with M. phyllosphaerae, R. erythropolis and Sphingobacterium sp. in the presence of fish meal or CSL (2.0%w/v), taken after 48, 96, 168, 240 and 336hr, and performed in technical triplicate.

Although the soluble phenol content increased in the initial 48hours of treatment with Sphingobacterium sp., only a minor increase was observed following treatment with M. phyllosphaerae and the soluble phenol content decreases following treatment with R. erythropolis supplemented with CSL. These reduced rates of increase in soluble phenol content and decreases could correspond to repolymerization of the phenolic products in the first 48 hours, which was indicated in the gel filtration HPLC analysis of high- and low- molecular weight forms of Kraft lignin following 72hours of treatment with all of these strains (Fig. 3.7–3.9).

The higher content of soluble phenols in Sphingobacterium sp.-treated Kraft lignin fractions compared to Kraft lignin treated with the other two strains is also consistent with gel filtration HPLC data from the size-fractionation experiments, which showed an intense broad peak corresponding to low-molecular weight products following treatment with Sphingobacterium sp. (Fig. 3.7). This peak was of a significantly lower intensity in the analysis of high- and low-molecular weight Kraft lignin treated by M. phyllosphaerae (Fig. 3.8) and R. erythropolis

(Fig. 3.9). The consistency of these observations further suggests that M. phyllosphaerae and R. erythropolis are much more capable of metabolizing low- molecular weight products from lignin degradation than Sphingobacterium sp.

! !

Figure 3.25. pH of samples of Kraft lignin (2.5 %w/v) treated with M. phyllosphaerae, R. erythropolis and Sphingobacterium sp. in the presence of fish meal or CSL (2.0%w/v), taken after 48, 96, 168, 240 and 336hr. Readings were taken in technical triplicate.

The pH analysis of treated and untreated Kraft lignin in the presence of CSL shows an overall decrease of 0.3 following inoculation with Sphingobacterium sp. at 336hr, compared to increases of 0.8 and 0.3 for R. erythropolis and M. phyllosphaerae respectively. It is interesting that the pH changes fluctuated greatly from 168–336hr in the presence of CSL, but not with fish meal. !

! Figure 3.26.!FT–IR (ATR) analysis of fractions of Sphingobacterium sp. (A), M. phyllosphaerae

(B) and R. erythropolis (C) inoculated in M9 salts supplemented with Kraft lignin (2.5%w/v)

and CSL (2%w/v). Samples taken after 96, 168 and 336hr were measured along with untreated

Table 3.8. Tentative assignment of peaks 1!5 from the FT–IR (ATR) analysis of treated and

untreated Kraft lignin (Fig. 3.27), based on literature assignments [191!193]. Numbers in

brackets alongside the frequency values indicate the peak number.

Peak Observed frequency value or range / cm-1

Probable interpretation Literature range / cm-1

1, 2 3400–3352 (1); 2978–2941 (2)

O!H stretch (phenolic and aromatic);

C!H stretch (aromatic !OMe and side

chain !CH2 and !CH3)

3500–2850

3 1657–1597 C=O stretch (conjugated p-substituted aryl ketone)

1650–1600

4 1462–1418 C=C stretch (guaiacyl aromatic ring); C!H bond deformation

1460–1400

5 1130–1090 Asymmetric C!H deformation in !CH2

and !CH3; aromatic skeletal vibration

1150–1100

!

Since the Kraft lignin was completely dissolved in the growth media the FT–IR analysis contains peaks of a greater intensity than for separate solid and liquid analyses for wheat straw and Organosolv lignin. Although the analysis for Kraft lignin is defined by similar peaks to those features in the analyses for wheat straw and Organosolv lignin (Fig. 3.14, 3.15, 3.21, 3.22), peak 1, which

represents phenolics lies from 3400 – 3352 cm-1, which is slightly higher in

frequency than the ranges of 3356–3238cm-1 and 3375–3267cm-1 for wheat

straw and Organosolv lignin respectively. A similar trend is seen for peak 2, which also lies at a higher frequency in the FT–IR analysis of Kraft lignin. Consistent with the FT–IR analysis for treated and untreated wheat straw and

Organosolv lignin, a much greater increase in intensity from 0 – 336 hr is

observed during treatment with Sphingobacterium sp. compared to R.

eryhtropolis and M. phyllosphaerae, which further suggests that

!