Indigenous microbial community governs the survival of Escherichia coli O157:H7 in constructed wetlands

Keystone bacterial groups dominate Escherichia coli O157:H7 survival in long-term reclaimed water headwater stream

Escherichia coli (E. coli) O157:H7 is a highly pathogenic zoonotic bacterium, with water serving as a key medium for its environmental transmission. However, the survival characteristics of E. coli O157:H7 in reclaimed water environments remain poorly understood, which has, to some extent, hindered the development of water reuse technologies. This study examined the survival dynamics of E. coli O157:H7 in a long-term reclaimed water headwater stream through inoculation experiments and identified its main drivers. The results showed that the survival time of E. coli O157:H7 was the longest in the headwater upstream (up to 62 days), gradually decreased as it flowed downstream. Among physicochemical factors, chloride ion, potential of hydrogen, and electrical conductivity were the main factors affecting the survival of E. coli O157:H7. The microbial diversity shown by the alpha diversity index had no significant impact on the E. coli O157:H7 survival. Meanwhile, certain keystone bacterial groups, such as Polynucleobacter, Roseomonas, and Luteolibacter, which are primarily involved in the decomposition of organic matter, suppressed E. coli O157:H7 survival in this stream, while Nitrospira, Dechloromonas, and Sphingomonas promoted the survival of E. coli O157:H7. Overall, the biotic factors have a more direct impact on the E. coli O157:H7 survival compared to abiotic factors in the reclaimed water-replenished stream and deserve more attention. Our research revealed higher biological risks in the upstream sections of the long-term reclaimed water headwater stream, which helped deepen our understanding of pathogen survival in water environments and enhancing our awareness of the biological safety of reclaimed water in ecological replenishment processes.

Bacterial dispersal enhances the elimination of active fecal coliforms during vermicomposting of fruit and vegetable wastes: The overlooked role of earthworm mucus

Earthworms play a pivotal role in the elimination of fecal coliforms during vermicomposting of fruit and vegetable waste (FVWs). However, the specific mechanisms underlying the action of earthworm mucus remain unclear. This study investigated the mechanisms of fecal coliform reduction related to earthworm mucus during FVWs vermicomposting by comparing treatments with and without earthworms. The results show that the secretion of earthworm mucus decreased by 13.93 % during the startup phase, but significantly (P < 0.001) increased by 57.80 % during the degradation phase. Compared to the control without earthworms, vermicomposting led to a significant (P < 0.05) 1.22 -fold increase in the population of active bacteria, with a strong positive correlation between mucus characteristics and dominant bacterial phyla. As the dominant fecal coliforms, Escherichia coli and Klebsiella pneumoniae significantly (P < 0.05) declined by 86.20 % and 93.38 %, respectively, in the vermi-reactor relative to the control. Bacterial dispersal limitation served as a key factor constraining the elimination of E. coli (r = 0.73, P < 0.01) and K. pneumoniae (r = 0.77, P < 0.001) during vermicomposting. This study suggests that earthworm mucus increases the active bacterial abundance and cooperation by weakening the bacterial dispersal limitation, thus intensifying competition and antagonism between fecal coliforms and other bacteria.