Microbial colonisation and degradation of chitin in aquatic environments
The occurrence of chitinolytic microbes and the colonisation and degradation of a native chitin substrate (squid pen) was studied in riverine, estuarine and marine aquatic environments m the Aberdeen area. Chitinolytic microbes were prevalent at all the sites (means: aerobic water 616ml-1, 2% of heterotrophs; anaerobic sediment 11560ml-1 0.8% of anaerobic heterotrophs). It was proposed that the chitinolytic numbers were directly influenced by the presence of chitinous material and indirectly influenced due to a heterotrophic response by organic/suspended matter levels. Hence chitinolytic numbers in the river and were largely influenced by allochthonous inputs while numbers in the sea were influenced by autochthonous production of organic and chitinous matter. From the results of a chitin assay of seawater it was extrapolated that 6.65x1013 metric tons of particulate chitin exist in the world's oceans. Chitin was found to degrade in all the sites studied. The annual rate ranged between 0.905% (river) to 0.074% (marine) squid pen day-1(approx 50mg seeded). The maximum rate recorded was 1.39% day at the river. At most of the sites the rate was positively correlated (P 0.05) with temperature. It was proposed that the marine annual rate would not cope with the annual chitin production and that degradation in the sea is mediated by the synergistic action of the chitinolytic microflora and fauna. The colonisation studies indicated that chitin was rapidly colonised at all the sites studied. The microbial numbers and biomass increased up to about 14 days after exposure, then levelled off and remained relatively constant for the remainder of each exposure period. It was proposed that the numbers of chitinolytic microbial colonisers remained relatively constant at each site studied throughout the year (i.e. changes in the degradation rate were due to variation in activity and not numbers), but the numbers and biomass of chitinolytic microbial colonisers was different between sites and this accounted for some of the variation in degradation rate recorded between sites. Samples with dense colonising biofilms and extensive filamentous growth were also characteristic of sites of relatively high chitin degradation.