House fly larval grazing alters the structure and diversity of the bacterial community in dairy cattle manure

Authors: NEUPANE, SARASWOTI - Kansas State University; SASKI, CHRISTOPHER - Clemson University; Nayduch, Dana

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/13/2019
Publication Date: 6/13/2019
Citation: Neupane, S., Saski, C., Nayduch, D. 2019. House Fly Larval Grazing Alters the Structure and Diversity of the Bacterial Community in Dairy Cattle Manure . Meeting Abstract. 1: 1.

Interpretive Summary: Being microbe-rich, cattle manure serves as a developmental substrate for house fly larvae. The larvae feed on microbes in the substrate, but little is known about the influence that larval grazing has on manure bacterial communities over time. Our study investigated changes in the manure bacterial community including composition, structure and bacterial diversity in manure that had larvae developing within it compared to age-matched manure without larvae. To determine the bacteria present in the manure, the V4 region of bacterial 16S rRNA gene was sequenced using the Illumina MiSeq sequencing platform. These sequences, which represent all the bacteria in the sample, were examined and bacteria species were deduced as well as other taxonomic levels such as Phyla. Statistical analyses revealed that the composition (e.g. species present) of the bacterial community in manure that supported larval development (which lasted 10 days) was significantly different from the control manure (day 0 of the experiment) and the age-matched (day 10) manure without larvae. Bacterial species richness (e.g. the number of species in a community) and diversity of these species were both significantly lower in manure that contained larvae at day 10 compared to both control groups of manure. Furthermore, relative abundances of the phyla Bacteroidetes and Proteobacteria significantly increased after larval feeding, whereas relative abundance of the phylum Firmicutes decreased, when larval treatment day 10 was compared to both control day 0 and control day 10. At lower taxonomic levels, relative abundances of the bacteria Ruminococcus, unclassified Ruminococcaceae, and Bacteroides significantly decreased while relative abundance significantly increased for the bacteria Pseudomonas, Anaerocella, Azoarcus, unclassified Comamonadaceae and Flavobacterium in manure larval treatment day 10 compared to control day 0 and control day 10. These results demonstrate that house fly larval feeding substantially alters bacterial community composition and diversity in cattle manure. Further studies are aimed at determining how larval grazing may influence the presence of pathogenic bacteria in cattle manure, in order to understand whether house flies presence increases or decreases risk of manure-associated pathogen transmission to humans.

Technical Abstract: Being microbe-rich, cattle manure serves as a developmental substrate for house fly larvae. Larvae feed on microbes in the substrate, but little is known about the influence that larval grazing has on manure bacterial communities. We investigated changes in manure bacterial community structure and diversity in response to house fly larval feeding through complete larval development by comparing three treatments: control, day 0 (fresh dairy cattle manure, day 0); control, day 10 (dairy cattle manure only, incubated for 10 days which was matching duration with larval treatment day 10); and larval treatment, day 10 (larval grazed manure, i.e. manure treated with house fly eggs and incubated until the end of the larval developmental period, i.e. 10 days). Each treatment consisted of 4 replicates except control day 0 which consisted of 8 replicates. The V4 region of bacterial 16S rRNA gene was sequenced to characterize bacterial communities in manure using the Illumina MiSeq sequencing platform. Principal coordinates analysis revealed that the bacterial community composition in manure that contained larvae (larval treatment, day 10) was significantly different from both control day 0 and control day 10 manure. Furthermore, bacterial species richness and Shannon diversity index were significantly lower in manure treatment day 10 compared to both control groups. Furthermore, relative abundances of the phyla Bacteroidetes and Proteobacteria significantly increased after larval feeding, whereas relative abundance of Firmicutes decreased, when larval treatment day 10 was compared to both control day 0 and control day 10. At lower taxonomic levels, relative abundances of Ruminococcus, unclassified Ruminococcaceae, and Bacteroides significantly decreased while relative abundance significantly increased for Pseudomonas, Anaerocella, Azoarcus, unclassified Comamonadaceae and Flavobacterium in manure larval treatment day 10 compared to control day 0 and control day 10. These results demonstrate that house fly larval feeding substantially alters bacterial community composition and diversity in cattle manure.