J. Field Ornithol. 76(3):264±270, 2005 Prevalence and genetic diversity of Bacillus licheniformis in avian plumage Justine M. Whitaker,1 Daniel A. Cristol and Mark H. Forsyth Institute for Integrative Bird Behavior Studies, Department of Biology, College of William and Mary, Williamsburg, Virginia 23187-8795 USA Received 28 May 2004; accepted 30 November 2004 ABSTRACT. Bacillus licheniformis, a soil bacterium capable of degrading the b-keratin in feathers, is present in the plumage of some wild-caught birds, but the published carriage rate is quite low. Microbial degradation could be a selective agent leading to the evolution of molt and plumage pigmentation, but we hypothesized that for B. licheniformis to have played an important role in avian evolution, it is likely to occur more widely in bird populations than previously reported. We sampled the plumage of 461 wild-caught birds of eight species. We designed a selective and differential culture method to isolate bacteria with the potential to degrade feathers. Putative feather-degrading bacteria were isolated from 21±59% of the individuals of each of the species tested, for an average carriage rate of 39%. 16S rRNA (rrnA) sequencing of 98 of these bacterial isolates indicated that 69% were Bacillus lichenformis, suggesting that the prevalence of this feather-degrading bacterium is 4 3 higher than previously reported. We also hypothesized that interspeci®c variation in avian plumage, behavior, and habitat may have led to the evolution of host-speci®c B. licheniformis strains. Fingerprinting of B. licheniformis isolated from Northern Saw-whet Owls (Aegolius acadicus) and Gray Catbirds (Dumetella carolinensis) using REP-PCR demonstrated that for nine owls, one individual carried four different strains and eight individuals carried only one strain. Of 20 catbirds, there was a single strain found on nine birds, but four carried two different strains each. SINOPSIS. Prevalencia y diversidad geneÂtica de Bacillus licheniformis en el plumaje de aves Bacillus licheniformis, es una bacteria que se encuentra en los suelos que es capaz de degradar la keratina-b en la pluma de las aves. La misma esta presente en algunas aves silvestres, pero son pocas las publicaciones sobre este tema. La degradacioÂn microbiana pudiera ser un agente de seleccioÂn natural dando origen a la muda y la pigmen- tacioÂn del plumaje en las aves. Planteamos la hipoÂtesis de que esta bacteria ha tenido un rol importante en la evolucioÂn de las aves y que debe estar presente en un gran nuÂmero de especies que lo previamente informado. Examinamos a 461 aves silvestres, perteneciente a ocho especies. DisenÄamos un cultivo selectivo y diferencial para aislar la bacteria que tenõÂa el potencial de degradar las plumas. La bacteria fue aislada de 21±59% (xÅ 5 39%) de las especies de aves muestreadas. El estudio secuencial de 16srRNA (rrnA) de 98 de los cultivos aislados dio positivo para B. licheniformis, lo que sugiere que la presencia de esta bacteria en las plumas de las aves es cuatro veces mayor que lo previamente informado. Proponemos otra hipoÂtesis en referencia a que dado que hay variaciones en el plumaje de las aves, conducta y seleccioÂn de haÂbitat, esto puede haber dado origen a sepas especi®cas de estas bacterias en aves. La huella genetica de sepas aisladas del bacilo antes mencionado, de aves como Aegolius acadicus y Dumetella carolinensis, utilizando REP-PCR ha demostrado que para nueve individuos del Aegolus, uno de estos cargaba cuatro sepas de la bacteria y los otros ocho tan solo una. De los 20 individuos de Dumetella, en nueve individuos tan solo se encontro una sepa y en otros cuatro dos sepas diferentes. Key words: Bacillus licheniformis, b-keratin, feather-degrading microbes, keratinolytic, REP-PCR By digesting the b-keratin in avian plumage, sortium of keratin-digesting microbes that have feather-degrading microbial symbionts poten- contributed to the evolution of feather shed- tially decrease host ®tness. In response, birds ding through molt, plumage strengthening may have evolved mechanisms to reduce dam- through increase in melanin content, and be- age to their plumage, such as preening, anting, havior that might increase ®tness in the face of dusting or molt (Hart 1997). Burtt (1999; microbial assault on the plumage. Yet Burtt and Burtt and Ichida 1999) proposed that B. lichen- Ichida (1999) reported that keratinolytic bacilli iformis may be an important member of a con- were detected within the plumage of only 7.4% (range across species; 0±23%) of individuals among 870 wild birds of seven species with ad- 1 Corresponding author. Current address: P.O.Box 38, One Solomons Way, Chesapeake Biological Lab- equate sample sizes. Such a carriage rate may oratory, Solomons, Maryland 20688 USA. Email: be too low to be a powerful force of natural [email protected] selection since plumage is not the moist, warm 264 Vol. 76, No. 3 Feather-degrading Bacteria 265 environment in which B. licheniformis thrives, avian hosts. Understanding the diversity of B. and there is no evidence of their ability to dam- licheniformis strains on wild birds is an initial age feathers on living birds (Cristol et al. 2005). step to understanding if B. licheniformis has B. licheniformis does not require a host for sur- evolved to degrade feathers while on a living vival, as it thrives in the soil. Feather-degrading bird. We carried out a preliminary investigation bacilli may only degrade feathers when they are of the diversity of bacterial strains within in- in contact with the soil (after molt or death of dividuals of a host species and across host spe- the bird) and may have no impact on avian cies. evolution. Before the importance of feather-de- grading microbes can be evaluated, we need to METHODS determine if they occur on a high enough pro- portion of individuals to be ecologically impor- Study species. Until 1990, B. lichenifor- tant. Our main objective in this study was to mis was considered a typical soil bacterium, but estimate the frequency of occurrence of B. li- Williams et al. (1990) isolated this bacterium cheniformis on a large sample of free-living birds from a poultry waste digester and characterized to determine if carriage rates were as low as its feather-degrading capabilities. B. lichenifor- previously reported. mis is a gram positive, facultatively aerobic bac- If our hypothesis is correct and B. lichenifor- terium most closely related to the well-studied mis is found commonly on birds, it is worth- bacterium, Bacillus subtilis. At least three species while to ask whether B. licheniformis might of Bacillus are known to degrade b-keratin in- have played an important role in avian evolu- cluding B. licheniformis, B. subtilis (Evans et al. tion. A secondary objective was to learn more 2000), and B. pumilis (Burtt and Ichida 1999). about possible routes of transmission for feath- Optimal growth of B. licheniformis in nutrient er-degrading microbes. To achieve this we ex- broth occurs at 508C and pH 7.5 (Williams et amined whether the B. licheniformis present on al. 1990; Cheng et al. 1995). an individual bird were of one or many genetic To determine the carriage rate of Bacillus spe- strains. If one strain or a consistent consortium cies within the plumage of wild-caught birds, of strains is present on a host species, that 40 or more individuals of eight bird species would suggest clonal spread after infection. Un- were mist netted during routine banding op- derstanding if birds randomly acquire feather- erations of the Coastal Virginia Wildlife Ob- degrading bacterial strains from the environ- servatory in Kiptopeke State Park, Virginia (all ment (i.e., contamination) or if the bacteria are species), and on the campus of the College of passed on by infection from conspeci®cs, is crit- William and Mary in Williamsburg, Virginia ical to determining the potential for coevolu- (sparrows only), between 5 September 2001 tion between these microbes and their hosts. In and 18 March 2002 (Table 1). the case of transmission by contamination, a Sampling. Bacteria were sampled by rub- variety of strains are acquired by a variety of bing a sterile cotton-tipped applicator through avian species. Those B. licheniformis strains each bird's feathers starting with the right side would likely remain generalized to degrade any of the head and continuing over the top and feather under appropriate conditions (moist, left side. The applicator was then rubbed down warm environment) and may therefore remain the ventral side of the body, through the tail genetically indistinct. However, if a particular and across the rump. Applicators had been sat- strain or group of strains become associated urated with isotonic saline and sterilized by au- with one species of bird because it is passed toclaving. Two replicate samples were taken from parent to offspring each generation, those from the same individual bird with separate ap- strains may become specialized to degrade plicators. The applicator was continually rotat- feathers of a particular type, such as high mel- ed during sampling to ensure optimal contact anin content. The behavior of the bird (e.g., with feathers. After sampling applicators were higher af®nity for sunning), may also select for frozen at 2808C until culturing. Ethanol one strain or a group of strains. As B. licheni- (70%) was used to decrease the risk of contam- formis strains become more adapted to living on ination during sampling. The senior author car- a speci®c host, they may become genetically ried out all of the plumage sampling and care- distinct from other strains living on different fully washed her hands between samples; how- J. Field Ornithol. 266 J. M. Whitaker et al. Summer 2005 Table 1. Birds sampled and found positive for putative feather-degrading bacteria.