Effect of endophytic bacteria isolates on growth and oxidative stress injury of transgenic tobacco shoots in vitro

Transgenic plants have a great potential for production of high-value molecules, including peptides, for medical or industrial applications. Cultivation of plant tissues in a contained environment, such as plant tissue culture in vitro, could effectively address safety issues associated with transgenic plants as well as strict manufacturing standards. However, unfavourable in vitro conditions can often lead to elevated stress levels and suppressed growth of in vitro tissues urging the need to improve plant adaptation to in vitro conditions. As the beneficial effect of endophytic bacteria on the growth of in vitro cultures has been described previously, the aim of the present study was to assess the effect of growth-promoting endophytic bacteria isolates of the Bacillus cereus group on the growth of transgenic tobacco shoots in vitro and the accumulation of recombinant protein (RP) construct comprising a green fluorescent protein and a collagen mimicking peptide conjugate. The research revealed that transgenic tobacco shoots had reduced growth and increased oxidative injury levels compared with the non-transgenic parental line. The inoculated bacteria isolates colonised plant tissues and were sustained at densities of 0.6???9.0 ?? 105 CFU g-1 of the shoot fresh weight for at least several passages. Enhanced, 18% to 30% higher, biomass accumulation compared to the uninoculated transgenic tobacco shoots, and 14% to 25% lower levels of the oxidative lipid injury marker malondialdehyde (MDA) were detected for three-week-old shoots co-cultivated with isolates of Bacillus mycoides Nt.10.1, B. toyonensis Nt.18 and B. wiedmannii Nt.3.2. B. wiedmannii isolate Nt.14.2 reduced oxidative stress injury symptoms but had no effect on shoot growth. Co-cultivation with endophytic isolates had no effect on the expression of the recombinant protein. These results suggest that co-cultivation with growth-promoting endophytic bacteria provides a viable solution to improve the growth of transgenic plant tissues used for recombinant protein production in vitro.