Ultraviolet radiation (UVR) sensitivity analysis and UVR survival strategies of a bacterial community from the phyllosphere of field-grown peanut (Arachis hypogeae L.)
Gw. Sundin et Jl. Jacobs, Ultraviolet radiation (UVR) sensitivity analysis and UVR survival strategies of a bacterial community from the phyllosphere of field-grown peanut (Arachis hypogeae L.), MICROB ECOL, 38(1), 1999, pp. 27-38
The short-term population dynamics of the culturable bacterial community fr
om field-grown peanut (Arachis hypogeae L.) was analyzed over three 2-day p
eriods. As in other phyllosphere studies, significant numbers of pigmented
organisms were detected, suggesting the importance of pigmentation in the c
olonization of this habitat. Isolates were grouped according to pigmentatio
n (orange, pink, yellow, nonpigmented), and the sensitivity of each isolate
in the collection (n = 617) to ultraviolet radiation (UVR) was determined
as the minimal inhibitory dose (MIDC) of UVR that resulted in an inhibition
of growth compared to an unirradiated control. The majority of isolates re
covered (56.1%) had an MIDC equal to or exceeding that of Pseudomonas syrin
gae 8B48, a known UV-tolerant strain. Among pigmentation groups, the mean M
IDC of pink- and orange-pigmented isolates was significantly greater than t
hat of yellow- or nonpigmented isolates at each sampling time of day. Ident
ification of 213 of the isolates using fatty acid methyl ester analysis ind
icated that a large proportion of the isolates were gram-positive, with Bac
illus spp. alone accounting for 35.7% of the total. The genus Curtobacteriu
m contained the largest percentage of highly WR-tolerant strains. Nonpigmen
ted mutants of four Curtobacterium strains were selected following ethyl me
thane sulfonate mutagenesis; these nonpigmented mutants were significantly
altered in survival following irradiation with UV-A wavelengths. The strate
gy of avoidance of WR through colonization of the abaxial leaf surface was
evaluated on three separate occasions by leaf imprint sampling. Only 3 of 1
20 leaves (2.5%) contained larger bacterial populations on the adaxial surf
ace, indicating that colonization of the abaxial leaf surface is important
to phyllosphere survival. Our results indicate that tolerance to UVR is a c
ommon phenotype among phyllosphere bacteria, suggesting that solar radiatio
n has a strong influence on the microbial ecology of the phyllosphere.