Life Cycle Plasticity of Colpoda aspera Fed With Petroleum Tolerant Gram-Positive and Gram-Negative Bacteria.

Abstract

Soil recovery after contamination relies on the surviving microbiota to reconstruct microbial food webs. The ciliate Colpoda aspera and Brevundimonas sp., Rhizobium sp1, Rhizobium sp2 (gram-negative), Bacillus sp1, Bacillus sp2, and Microbacterium sp.(gram-positive) remain active after pulses of light petroleum contamination. We used phase contrast microscopy to assess excystation time and cyst production by C. aspera after placing 65 cysts in petri dishes with 0.5% LNA medium and adding 100 μL of a 5.2 × 10⁸ cell bacterial inoculum from contaminated soil. C. aspera excystation was monitored by triplicate every hour for 72 h. Excystation occurred faster and resulted in a higher number of cysts when fed with gram-negative bacteria, particularly Rhizobium sp2 and Brevundimonas sp. In contrast, C. aspera cysts formed only two daughter cells when fed with Microbacterium sp., reducing the quantity and speed of reproduction. This reproductive behavior may allow other predatory ciliates to coexist when Microbacterium sp. becomes prevalent in a soil hotspot. Ciliates' feeding preferences and nutritional value are required to understand resource partitioning and understanding these interactions can inform strategies to promote resilient microbial communities and accelerate recovery after contamination.