Screening of Local Wild Xanthomonas Species for Xanthan Production on Crude Glycerol-based Medium

Abstract

In this study, the effect of cultivation time on xanthan biosynthesis by different Xanthomonas campestris and Xanthomonas euvesicatoria strains, isolated from crucifers and pepper leaves, respectively, was examined. Xanthan was produced by submerged cultivation on crude glycerol-based medium at a laboratory level under aerobic conditions at 30 °C and 150 rpm for 168 h and 240 h. Bioprocess efficacy was estimated based on the xanthan concentration in media at the end of bioprocess and its average molecular weight. According to the obtained results, Xanthomonas strains have statistically significant effect on xanthan concentration in cultivation media when biosynthesis is performed by X. euvesicatoria strains, and cultivation time has significant effect on this parameter only when bioprocess is performed by X.campestris strains. The combination of Xanthomonas strains and cultivation time has a statistically significant effect on xanthan concentration in medium for both groups of isolates. The obtained results show that all applied Xanthomonas strains and cultivation time as well as their combination have statistically significant effect on average molecular weight of xanthan produced in applied experimental conditions. It is found that X. euvesicatoria strains produce higher amount of xanthan in a shorter period of time (168 h) when compared to the X.campestris strains. Xanthan of higher average molecular weight was produced when cultivation of both groups of isolates was performed for 240 h in applied experimental conditions. Results obtained in this research suggest that X. euvesicatoria strains have the greatest potential for application in biotechnological production of xanthan on crude glycerol-based medium.

XANTHAN PRODUCTION ON CRUDE GLYCEROL BY LAB-SCALE BIOREACTOR CULTIVATION OF LOCAL Xanthomonas ISOLATE

“…This suggests that if there is no carbon source consumption, xanthan biosynthesis does not occur in the stationary phase of producing microorganism growth (Palaniraj & Jayaraman 2011) and bioprocess duration could be shortened by 24 h. Considering the ob-tained results which show that intensive metabolic activity of the Xanthomonas PL 3 strain happened in the first 48 h of cultivation in the 3 L lab-scale bioreactor, it can be concluded that the used producing strain has a great ability to metabolize crude glycerol in the applied experimental conditions. This is also supported by the findings from previous studies when performing the bioprocess by the same producing strain in smaller volumes and less intensive bioprocess conditions (Zahović et al 2022;.…”

“…After the cultivation, xanthan concentration in the medium was 11.10 g/L. This value is higher compared to the values obtained in previous researches, where xanthan was produced by Xanthomonas strains, isolated from pepper leaves and crucifers on a crude glycerol-based medium, but in smaller volumes (300 mL Erlenmeyer flasks and 2.0 L Woulff bottles), and where xanthan concentration in media varied from around 5.00 g/L to 8.00 g/L (Rončević, Zahović, et al 2020;Zahović et al 2022;. Moreover, xanthan concentration obtained in this study is also higher in comparison with the results obtained when reference strain Xanthomonas campestris ATCC 13951 was cultivated on a medium containing crude glycerol (15.00 g/L).…”

“…This result is in agreement with the results obtained in an earlier study, where xanthan biosynthesis was performed on a crude glycerol-based medium in a smaller volume by different Xanthomonas strains, isolated from crucifers and pepper leaves. That study reported the average molecular weight of separated biopolymers in the range from 5 •10 4 g/moL to 3.0 •10 5 g/moL (Zahović et al 2022). By analyzing all the results given in Figure 1 and Table 1, it was determined that xanthan biosynthesis by the cultivation of the Xanthomonas PL 3 strain in a 3 L lab-scale bioreactor on a medium containing crude glycerol from biodiesel production in a domestic factory was successful.…”

“…Commercially, production of xanthan is mainly performed as aerobic submerged batch cultivation of the reference strain X. campestris ATCC 13951 on a medium of appropriate composition and under optimal conditions. The success of xanthan production is largely influenced by the cultivation medium composition, producing strains and bioprocess parameters (Zahović et al 2022). Sucrose and glucose are mostly used as carbon sources in the media for xanthan production (Brandão et al 2013).…”

“…Despite the fact that there are various alternative substrates of lower market value which may be used as a carbon source in the cultivation medium for xanthan production, crude glycerol from the biodiesel industry proved to be one of the most promising (de Jesus Assis et al 2014;Wang et al 2016). Results from several studies have confirmed that besides the reference strain, different wildtype Xanthomonas strains isolated from infected plants possess the ability to biosynthesize xanthan on a medium with glycerol as a sole carbon source (Brandão et al 2013;Trindade, Munhoz, & Burkert 2015;Zahović et al 2022). Moreover, some Xanthomonas isolates are able to metabolize glycerol to a higher degree than glucose .…”