New Insights into Microbial Degradation of Cyanobacterial Organic Matter Using a Fractionation Procedure

Abstract

Cyanobacterial blooms caused by phytoplankton Microcystis have occurred successively since 1980 in Lake Taihu, China, which has led to difficulty collecting clean drinking water. The effects of cyanobacterial scum-derived dissolved organic matter (DOM) on microbial population variations and of algal-derived filtrate and algal residual exudative organic matter caused by the fraction procedure on nutrient mineralization are unclear. This study revealed the microbial-regulated transformation of DOM from a high-molecular-weight labile to a low-molecular-weight recalcitrant, which was characterized by three obvious stages. The bioavailability of DOM derived from cyanobacterial scum by lake microbes was investigated during 80-d dark degradation. Carbon substrates provided distinct growth strategy links to the free-living bacteria abundance variation, and this process was coupled with the regeneration of different forms of inorganic nutrients. The carryover effects of Microcystis cyanobacteria blooms can exist for a long time. We also found the transformation of different biological availability of DOM derived from two different cyanobacterial DOM fractions, which all coupled with the regeneration of different forms of inorganic nutrients. Our study provides new insights into the microbial degradation of cyanobacterial organic matter using a fractionation procedure, which suggests that the exudate and lysate from degradation products of cyanobacteria biomass have heterogeneous impacts on DOM cycling in aquatic environments.

Regulation of the Nutrient Cycle Pathway and the Microbial Loop Structure by Different Types of Dissolved Organic Matter Decomposition in Lakes

“…During the summer and autumn with Microcystis bloom, high labile DON (Figure ), LAP (Figure ), NH 4 + –N (Figure ), bacterial respiration (Figure ), and organic N decomposition gene abundance, as well as nitrification and DNRA genes (Figure ), facilitated N regeneration and retention to support the bloom. However, the abundance of organic C decomposition genes was not high (Figure A), probably due to the easy degradability of algal-derived organic C. Different algal-derived DOM drove different biological availability, which coupled with the regeneration of different forms of inorganic nutrients . Thus, in Lake Tangxun, N 2 -fixing Dolichospermum drove bacteria to hydrolyze organic P, and when Dolichospermum decayed, the accumulated DON was further remineralized by bacteria co-occurring with Microcystis.…”

“…However, the abundance of organic C decomposition genes was not high (Figure 6A), probably due to the easy degradability of algalderived organic C. Different algal-derived DOM drove different biological availability, which coupled with the regeneration of different forms of inorganic nutrients. 68 Thus, in Lake Tangxun, N 2 -fixing Dolichospermum drove bacteria to hydrolyze organic P, and when Dolichospermum decayed, the accumulated DON was further remineralized by bacteria co-occurring with Microcystis. A similar phenomenon was recorded in Lake Zhiyin, where DON accumulation due to bait input provided the precondition for the N acquisition of Microcystis.…”