Ecophysiological Profiling of Ignatzschineria larvae Isolated from an Aquatic Insect: pH, Salinity, Thermal, Radiation, and Antibiotic Tolerance

Ignatzschineria larvae are a recently characterized bacterium with limited ecophysiological data and are proposed as a potential microbial biomarker for insect colonization. We isolated I. larvae (strain MW602513) from the gut of an aquatic insect and assessed their tolerance and antibiotic susceptibility (Kirby-Bauer, CLSI/EUCAST) to pH (3-11), NaCl salinity (0.5-10 %), temperature (4-55°C) and ultraviolet radiation. Inhibition zones were interpreted according to current breakpoints. The isolate exhibited robust growth at pH 6-7, low salinity (≤ 2%) and moderate temperatures (30-37°C); there was no growth at 10°C or 50-55°C, and a significant growth reduction was observed at ≥ 5% NaCl. Bacteria were observed to not grow under UV radiation applied for 5 minutes. Resistance to various antibiotic groups tested was observed. The results demonstrate that the bacteria can adapt to mesophilic environments with low salinity and neutral to alkaline pH, highlighting their ecological resilience and potential impact on ecosystems.