BIOLOGICAL CHARACTERISTICS OF SOME FILAMENTOUS FUNGAL STRAINS ISOLATED FROM RUBBER SURFACE AT THE DAM BAY MARINE CLIMATIC TESTING STATION, NHA TRANG

Fungal strains can readily colonize and thrive on the surface of rubber materials, particularly in tropical coastal or monsoon climates where high humidity, temperature, and salinity create favorable growth conditions. This study aimed to isolate and characterize filamentous fungal strains inhabiting the surface of rubber materials exposed to coastal climatic conditions at the Dam Bay Marine climatic testing station, Nha Trang, Vietnam. Three rubber samples were collected and assessed for microbial coverage following ASTM G21-15 (2015). High-resolution images were analyzed using ImageJ software, revealing fungal colonization levels ranging from 48.23 ± 3.7% to 68.23 ± 4.1%. Based on morphological characteristics, five isolates were obtained and classified into four genera: Fusarium, Aspergillus, Penicillium, and Nigrospora. All isolates exhibited optimal growth on PDA medium and demonstrated salt tolerance up to 4% (w/v) NaCl, indicating physiological adaptation to saline environments. Screening for extracellular laccase activity showed that DB.F05 was the only strain producing laccase, with a lysis zone diameter of 6 ± 0.5 mm. The identity of DB.F05 was confirmed by combining morphological observations with ITS region sequencing, showing 100% similarity to Nigrospora lacticolonia CGMCC 3.18123 (GenBank accession PV942108). These findings provide the first record of N. lacticolonia isolated from rubber surfaces in a tropical marine environment and reveal its potential enzymatic capability relevant to polymer modification or degradation. These are the results of a preliminary study to record the presence and biological characteristics of filamentous fungi on rubber surfaces in tropical coastal environments, providing a foundation for future studies on biodegradation mechanisms and antifungal preservation strategies.