Abstract:
Actinomycete bacteria are often associated with insects that have a mutualistic association with fungi.
These bacteria are believed to be important to this insect–fungus association as they produce antibiotics
that exclude other saprophytic fungi from the immediate environment. The aim of this study was to
investigate the presence of potentially protective actinomycetes associated with Orthotomicus erosus, an
alien invasive pine bark beetle, in South Africa. This bark beetle and its relatives have an association with
Ophiostomatales species which are often the only fungi found in the bark beetle galleries. We hypothesised
that antibiotic-producing actinomycetes could be responsible for the paucity of other fungi in the galleries
by producing compounds to which the Ophiostoma spp. are tolerant. Several actinomycetes in the genus
Streptomyces and one Gordonia sp. were isolated from the beetle. Interestingly, most isolates were from
the same species as actinomycetes associated with other pine-infesting insects from other parts of the
world, including bark beetles and the woodwasp Sirex noctilio. Most actinomycetes isolated had strong
antifungal properties against the selected test fungi, including Ophiostoma ips, which is the most common
fungal symbiont of Orthotomicus erosus. Although the actinomycetes did not benefit Ophiostoma ips and
the hypothesis was not supported, their sporadic association with Orthotomicus erosus suggests that
they could have some impact on the composition of the fungal communities present in the bark beetle
galleries, which is at present poorly understood.
SIGNIFICANCE :
• Discovery of four putative undescribed Streptomyces spp. with antibiotic potential
• First record of the introduction of actinomycete bacteria with pine-infesting insects into South Africa
• Actinomycetes from South Africa group with undescribed Streptomyces spp. from pine-infesting insects
of North America
