Strong alone, weak together: biofilm tensile strength in kangaroo rat burrows

Desert kangaroo rats (Dipodomys deserti) construct burrows that create protected micro-niches favorable to increased microbial activity and biofilm formation. Biofilms within these burrows bind sand particles together, increase the tensile strength of the burrow sand and burrow stability. Our previous work 1) demonstrated that kangaroo rat burrow sand exhibits higher tensile strength than surrounding surface sand due to the cementation by biofilms, and 2) characterized the microbial biofilm communities within kangaroo rat burrow sand and isolated abundant microorganisms. In this study, isolated species are used to quantify tensile strength of pure and mixed biofilms using the microcantilever technique. Mono-species biofilms of Aspergillus tamarii (59.30 ± 4.36 kPa) exhibited the highest tensile strength, while Neobacillus niacini (9.45 ± 1.98 kPa) showed the lowest. Dual-species biofilms displayed synergistic or antagonistic effects, depending on species combinations. Mixing N. niacini with Peribacillus frigoritolerans increased tensile strength to 55.11 ± 2.51 kPa, whereas combining A. tamarii with N. niacini reduced the tensile strength to 18.98 ± 2.54 kPa. Mixing up to five species reduced tensile strength to a minimum value of 2.16 kPa. We conclude that biofilms formed by microbial isolates from burrow sand individually had higher tensile strength, but when all were mixed, the tensile strength decreased, making them weaker.