native to Eurasia, Pirttiläet al. ( 2000 ) isolated bacterial endophytes from buds of
mature, healthy Scots pine trees growing on a natural stand in northern Finland.
One of the bacterial endophytic strains (isolate F) was identified as
Methylobacterium extorquens(DSM 13060). In a subsequent study, it was reported
that this bacterial endophyte produced adenine derivatives like adenine ribosides,
which could be used as precursors in cytokinin biosynthesis (Pirttiläet al. 2004 ). In
an effort to detect the endophytic colonization sites ofM. extorquensDSM 13060 in
Scots pine, Pohjanen et al. ( 2014 ) tagged DSM 13060 with GFP and viewed
endophytic colonies by using CLSM. GFP-tagged DSM 13060 was observed in
root epidermis and root parenchymatic and xylem tissues. Also,M. extorquens
DSM 13060 significantly increased shoot and root dry weight of Scots pine
seedlings. In addition, this bacterial endophyte in association with ectomycorrhizal
(ECM) fungi (Suillus variegatusand/orPisolithus tinctorius) was able to enhance
the growth of Scots pine seedlings even more than the only ECM fungi inoculation.
In a recent study with limber pine (Pinusflexilis), Moyes et al. ( 2016 ) found
evidence of diazotrophic bacterial endophytes in foliar parts of the plant. These
bacteria can provide 6.8–13.6lg of N per square meters to limber pine stands per
day or approximately 1–2 mg of N per square meters in one year (Moyes et al.
2016 ). In another study, Carrell and Frank ( 2014 ) found that limber pine and
another conifer tree species, Engelmann spruce (Picea engelmannii), growing in a
sub-alpine, N-limited environment are colonized by bacterial endophytes of the
same phylotype. This phylotype was related toGluconacetobacter diazotrophicus
and other N-fixing acetic acid bacterial endophytes.
Fig. 6.3 Intracellular colonization of a 4-week-old lodgepole pine stem cortex cell by
P. polymyxaP2b-2Rgfp.Arrowspoint to P2b-2Rgfpnear thered-orangechloroplasts (Anand
and Chanway2013a)
120 A. Puri et al.