Bipolaris
The genus Bipolaris contains about 45 species, which are mostly subtropical and tropical plant parasites.
Recent molecular studies have recognised Bipolaris cynodontis, B. micropus, and B. setariae as species isolated from clinical samples (da Cunha et al. 2014). However recent phylogenetic studies have transferred several well-documented human pathogens, notably B. australiensis, B. hawaiiensis and B. spicifera to the genus Curvularia (Manamgoda et al. 2012).
RG-1 organisms.
Morphological description:
Colonies are moderately fast growing, effuse, grey to blackish brown, suede-like to floccose with a black reverse. Microscopic morphology shows sympodial development of hyaline to deep olivaceous pigmented, pseudoseptate conidia on a geniculate or zig-zag rachis. Conidia mostly curved, canoe-shaped, fusoid or obclavate, rarely straight, 2–14 pseudoseptate (usually more than 6), germinating only from the ends (bipolar).
Key features:
Dematiaceous hyphomycete producing sympodial, pseudoseptate, pale brown, straight, fusiform to ellipsoidal conidia, which are rounded at both ends.
Comment:
The genera Drechslera, Bipolaris, Curvularia and Exserohilum are all closely related. In the past, morphological differentiation of the genera relied upon a combination of characters including conidial shape, the presence or absence of a protruding hilum, the contour of the basal portion of the conidium and its hilum, the point at which the germ tube originates from the basal cell and, to a lesser degree, the sequence and location of the first three conidial septa.
However, Manamgoda et al. (2012) have found that there is no clear morphological boundary between genera Bipolaris and Curvularia and some species show intermediate morphology. These authors recommend using a combined ITS and GPDH gene analysis for definitive identification of species (Manamgoda et al. 2012).
Molecular identification:
ITS sequencing may be used to identify clinical species (da Cunha et al. 2012a). GPDH has been determined to be the best single phylogenetic marker of Bipolaris species (Manamgoda et al. 2012, 2014).
References:
Ellis (1971, 1976), Luttrell (1978), Domsch et al. (2007), Alcorn (1983), McGinnis et al. (1986b), Sivanesan (1987), Rippon (1988), de Hoog et al. (2000, 2015), Manamgoda et al. (2012, 2014), da Cunha et al. (2012a).